Showing papers in "Philosophical Transactions of the Royal Society B in 1978"

Carotenoids in photosynthesis

Abstract: Carotenoids are usually considered to perform two major functions in photosynthesis. They serve as accessory light harvesting pigments, extending the range of wavelengths over which light can drive photosynthesis, and they act to protect the chlorophyllous pigments from the harmful photodestructive reaction which occurs in the presence of oxygen. Drawing upon recent work with photosynthetic bacteria, evidence is presented as to how the carotenoids are organized within both portions of the photosynthetic unit (the light harvesting antenna and the reaction centre) and how they discharge both their functions. The accessory pigment role is a singlet-singlet energy transfer from the carotenoid to the bacteriochlorophyll, while the protective role is a triplet-triplet energy transfer from the bacteriochlorophyll to the carotenoid.

The separation of visual axes in apposition compound eyes

Abstract: Measurements of the interommatidial angle (Δ ϕ ) and facet diameter ( D ) of the same ommatidia in a number of insects and crustaceans with large eyes have been related to the effective intensity at which the eye functions by the following theory. The highest spatial frequency which the eye is able to reconstruct as a pattern is limited by the interommatidial angle Δ ϕ , Which is the sampling angle, because two ommatidia are required to cover each cycle of the pattern. At the same time, the absolute modutlation of light in the receptors caused by the pattern depends on three interdependent factors. ( a ) The theoretical minimum angular sensitivity function, which has a width of θ/ D at the 50% level. The wavelength θ is taken as 0.5 μm. This component is not only the limiting angular resolving power of the lens: it reduces modulation caused by all patterns, with greater loss at higher spatial frequencies. Larger lenses increase resolution and sensitivity. ( b ) The effective light catching area of the rhabdom. This is the angular subtense of the rhabdom area (the receptor) as seen in the outside world (i.e. subtended through the posterior nodal point of the lens), and is the equivalent of the grain size in a film. Large receptors favour sensitivity at the expense of resolution. ( c ) The F value or focal ratio f/D , as in the camera, where F is the distance from the focal plane to the posterior nodal point. Larger F values increase sensitivity. The modulation resulting from these three factors is then set so that it exceeds the noise caused by the random arrival of photons at each ambient intensity. From this, the optimum value of the product D Δ ϕ (known as the eye parameter) can be calculated for eyes adapted to any ambient intensity. The same result is reached by a recent theory of Snyder, Stavenga & Laughlin (1977) who calculate the value of D Δ ϕ which allows the eye to reconstruct the maximum number of pictures despite photon noise. The eye parameter (divided by half the wavelength) is the ratio of the highest spatiai frequency passing the lens to the highest spatial frequency reconstructed by the eye. Compound eyes should have larger facets and interommatidial angles than predicted by diffraction theory alone because photon noise must be exceeded at all intensities. Theoretically, D Δ ϕ lies in the range 0.3 to 0.5 for bright light insects and is increased to 2.0 or more for those active in dim light. As well as depending on intensity, D Δ ϕ should depend on factors such as the typical angular velocity and level of intensity discrimination at which the eye is used. As D Δ ϕ can be measured from the outside of the eye, the theoretical predictions can be compared with measured values. Most of this paper consists of maps of the values of D Δ ϕ for eyes of a variety of arthropods from different habitats. The maps are made by a new convention in which the minimum theoretical field of each ommatidium is placed in angular coordinates as a circle of diameter θ/ D with centre on the axis at the place where it lies on the eye. To do this, a value of θ must be assumed. Every fifth facet is taken on most maps with the fields magnified five times. The overlap or separation of these circles of diameter θ/ D shows the local value of D Δ ϕ for any direction for each part of the eye. The method is independent of horizontal and vertical axes, of directions of facet rows, of regularity of facets and of eye radius. The problem of mapping a surface with double curvature upon a flat sheet was solved approximately by working with strips taken along the eye surface. Equal distances on the map then represent equal angles in any direction; with this projection there are no poles, and axes are arbitrary. Maps of D Δ ϕ reveal that compound eyes differ according to the intensity of light they normally encounter; eyes of animals which are active in bright light have smaller values of D Δ ϕ . The smallest value of about 0.3 is found in the forward facing acute zone of the sand wasp Bembix , which hovers while hunting in bright sunshine. The absolute limit set by diffraction of 0.25 (for square facets) is approached but never reached. Values of D Δ ϕ up to about 2.0 or even 4.0 are found in crepuscular animals which have apposition eyes. The interpretation is that the values of D and Δ ϕ are the result of a compromise between contrast sensitivity and resolution. An increase in aperture provides increased modulation and therefore increased sensitivity, but the additional angular resolving power which comes with the increased aperture is not used because sensitivity is also enhanced by an increase in the receptor size. The ommatidium then detects only the lower spatial frequencies (wider stripes) from the range which passes the lens. In an ommatidium optimized for any but the highest known intensities, both Δ ϕ and D (and therefore D Δ ϕ ) are larger than they would have to be if set at the diffraction limit. The maps also reveal that many apposition compound eyes have one or more regions of smaller Δ ϕ , called acute zones. None of the eyes are spherically symmetrical; all have gradients of both D and Δ ϕ , and all have regions where Δ ϕ varies in different directions on the eye surface. The acute zone is usually forward looking, but is upward looking in some insects which catch prey or mate in flight. In addition, some dragonflies have a lateral acute zone. In the acute zone the facet pattern is always more regular than elsewhere. Some acute zones, as in the locust ( Locusta ), the mantid Orthodera and the ghost crab Ocypode , are formed by reduction in Δ ϕ with little compensatory increase in D . Others such as the native bee Amegila , the dragonfly Austrogomphus , and the mantid shrimp Odontodactylus have larger values of D which match the decreasing Δ ϕ towards the centre of the acute zone, so that D Δ ϕ remains constant. Others again, particularly the wasp Bembix , the dragonflies Hemicordulia, Orthetrum and several mantids, show an increase in D which is insufficient to compensate for the large decrease in Δ ϕ , so that D Δ ϕ is smaller in the acute zone. A reduced D Δ ϕ in the acute zone may imply that it requires brighter light or more time than the rest of the eye in order to make full use of its increased sampling density. Mapping the regional differences of the theoretical resolving power of the ommatidia, and of the potential spatial resolution of different parts of the eye is only the first step towards understanding the functions of the different eye regions. The anatomical basis of the optics, the actual field sizes of receptors as measured physiologically, the part played by binocular overlap, the regional differences in the mechanisms of integration behind the eye, and the patterns of behaviour that are dependent on each eye region, remain to be elucidated.

Observations on the recent history of lough neagh and its drainage basin.

Abstract: The present study traces the recent development of Lough Neagh from the microfossil record of the lake sediment. The history of vegetational change in the catchment area is discussed on the basis of pollen analytical information and by reference to primary and secondary documentary historical sources. Changes in the history of the lake itself are inferred from changes in the relative composition of diatom assemblages in the sediment and from changes in the calculated influx of diatoms to the sediment. The accumulation of sediment in the lake basin is discussed and radiometric data ( 14 C, 137 Cs, 210 Pb) are used to construct a sediment chronology from which accumulation rates are calculated. It is shown that the rate has increased from about 0.08 cm a-1 (where a is the symbol for year) in A.D. 1700 to about 0.8 cm a -1 today. Four major stages in the recent development of the lake are indicated: a pre-disturbance stage ( > 2000 B.C. to ca . a.d. 1700), a stage of accelerated mineral inwash (from ca . A.D. 1700); and two stages of cultural eutrophication (from ca . 1915 and from ca . 1960 respectively). The eutrophication stages are characterized by increased sediment accumulation rates, increased diatom influx rates, and the emergence of Stephanodiscus as the most important diatom genus.

Morphology, morphoclines and a new classification of the Pteriomorphia (Mollusca: Bivalvia)

Abstract: Two morphological paradigms have long been used in comparative anatomical studies of bivalves: (1) the primary ligament is three-layered, with the layers corresponding to three shell layers; and (2) the primary mantle edge is composed of three folds with clearly defined functions. The results of studies of larval development indicate, on the contrary, that the primary ligament is completely organic. Calcified, fibrous ligamental material develops from lamellar material near areas of contact between ligament and shell, and development of the fibrous portions then proceeds toward the midline, finally achieving in many lineages a continuous fibrous bridge between valves. Furthermore, these results suggest that the mantle edge in the Bivalvia is primarily twofold and that the only clearly homologous structure between major groups is the periostracal groove itself. These morphological concepts, with other new and previously published data on shell ultrastructure, ligaments, mantle edges, ctenidia, palps, lips, stomachs, muscles, and photoreceptors, lead to a new picture of the evolution of primitive and derived character states in groups previously included in a subclass Pteriomorphia. Furthermore, a cladistic analysis of these data allows predictions of the morphology of ancestors which can be tested by reference to the preserved morphology and sequence of fossils. A new phylogenetic classification separates these groups into three superorders within the subclass Autobranchia: Isofilibranchia (mytiloids), Prionodonta (arcoids), and Pteriomorphia. The most complex radiation has been in the Pteriomorphia. Three orders originated in the early Palaeozoic: Pterioida, Limoida, and Ostreoida. The Pterioida and Ostreoida developed monomyarian, pleurothetic states independently, and each order developed its own mode of shell secretion. Further differentiation in the order Ostreoida occurred in the mid-Palaeozoic, producing two suborders, the Ostreina and Pectinina, both of which had already developed foliated calcitic ultrastructure from simple prismatic structure. By the early Mesozoic, the Ostreina had given rise to three extant superfamilies - the Ostreacea (true oysters), Dimyacea, and Plicatulacea - through atrophy of the foot, the assumption of a pleurothetic state on either the left or right side, and early obligate cementation. The Pectinina, through retention of the foot and the assumption of a pleurothetic mode of life, had evolved before the late Palaeozoic to the Anomiacea and Pectinacea. Within the superfamily Pectinacea, four extant families have origins ranging from early Carboniferous to Cretaceous in age: Propeamussiidae, Pectinidae, Syncyclonemidae, and Spondylidae. The new family Syncyclonemidae, which contains a genus long assumed to have become extinct at the end of the Cretaceous, is here recognized in the Recent and late Pleistocene on opposite sides of the Earth. With regard to extinct groups, many genera previously assigned to the Pteriacean family Malleidae belong in the Ostreacea on the basis of shared derived character states. Incorporation of these taxa as well as the Dimyacea in the Ostreina suggests that oysters have a dimyarian, possibly non-pleurothetic, origin and cannot have evolved from forms like the Pseudomonotids, which retained their foot and became pleurothetic. The new name Buchiacea is introduced for a set of extinct taxa within the suborder Pectinina including the Buchiidae, Monotidae, Oxytomidae, and Pseudomonotidae of previous authors. Derivation of this group is from the common ancestry of the Anomiacea and Pectinacea. The extinct Palaeozoic Aviculopectinidae, Pterinopectinidae, Deltopectinidae, and Leiopectinidae are grouped in a superfamily Aviculopectinacea, which also appears to have branched from the early ancestry of the Pectinina.

The Nature and Significance of Microatolls

Abstract: Microatolls, those coral colonies with dead, flat tops and living perimeters, result from a restriction of upward growth by the air/water interface. The principal growth direction is horizontal and is recorded in the internal structure, though fluctuations in water depth can influence the surface morphology producing a terraced effect. The morphology of the basal surface of the colony is controlled by the sand/water interface such that the thickness of the coral records the depth of water in which it lived. In open water at the margin of reefs in the Northern Province of the Great Barrier Reef, tall-sided uneven-topped microatolls live, whereas, on the reef flats in rampart-bounded moats and ponds, thin flat-topped and terraced microatolls are abundant. Because water in moats can be ponded to levels as high as high water neaps (1.6 m above datum at Cairns) and still have daily water replenishment, microatolls on reef flats can grow to levels 1.1 m higher than open-water microatolls (which grow up to a maximum elevation of low water springs, i.e. 0.5 m above datum). This imposes a major constraint on the use of microatolls in establishing sea level history. The two factors controlling pond height during one sea stand (relative to the reef) are tidal range (which governs the height of high water neaps) and wave energy (which governs the height of ramparts which enclose moats). Dating and levelling fossil microatolls exposed on the reefs show that 4000 years (a) B.P., high water neaps was at least 0.7 m higher than it is at present.

On the evolution of myoglobin.

Abstract: In previous studies, particularly of primates, a high degree of concordance was obtained between an evolutionary pattern based on comparative anatomy and another based on a reconstruction of the possible pathway of evolution of the myoglobin molecule. Accordingly, in extending our studies, we included species of uncertain evolutionary kinship, such as the tree shrew, and also increased the representation of species within the mammalian orders already studied, in the hope that it would be possible to resolve some contended issues and to establish the sequence of branching and pattern of relationship between those orders. As a first step, the phylogenetic pattern within each of the mammalian orders was constrained on zoological grounds according to generally accepted kinship based on the evidence of comparative anatomy and the fossil record. Eight phylogenetic patterns reflecting different possible kinship between the orders were chosen for detailed investigation and for each of these the most economical (parsimonious) pathway which could be obtained for the evolution of myoglobin was reconstructed. The uncertainties which are inherent in such reconstruction were increased by a high incidence of parallel substitutions. Although the eight phylogenetic patterns were widely different from one another it was found that none of the solutions had a An amino acid difference matrix is of special interest because it carries information which is more comparable with that obtained by immunological methods, where access to sequence information has not usually been available. Several different clustering procedures were applied to the amino acid difference matrix for myoglobin. As would be expected from the different assumptions on which each is based, the procedures resulted in different branching patterns which varied in their degree of zoological acceptability. Clustering of the harbour seal with the Cetacea suggested that there might be functional reasons, perhaps associated with diving, for several substitutions acquired in parallel by the myoglobins of these mammals. Repeated clustering of the horse with the sportive lemur, and a tendency for the opossum to join the primates, is associated with a high proportion of parallel substitutions. This tends to undermine confidence in phylogenetic inferences which might be drawn from the repeated clustering of the tree shrew (and often the hedgehog) among the primates. If we assume that there is an overall resemblance of the three-dimensional structure of all myoglobins, and use the crystallographic model of sperm whale myoglobin as a basis, the availability of over 30 vertebrate myoglobin sequences (and that of the mollusc Aplysia ) has provided an opportunity to consider the functional relevance of certain positions at which the nature of the amino acid residue appears to have remained unchanged, or to have changed only conservatively, during several hundred million years of evolution. Part of this conservation is attributable to the maintenance of the monomeric nature of the molecule, and it seems likely that much of the conservatism can be attributed to functional needs in initiating the folding of the molecule and in the maintenance of its tertiary structure. Concomitantly, consideration is given to the likely functional consequence of some of the substitutions which have been accepted. Atassi and his co-workers have carried out extensive immunological studies on myoglobin using antisera prepared in rabbit and goat. The availability of the amino acid sequences of rabbit and sheep (in lieu of goat) has made it possible to investigate the relation between amino acid sequence difference and the distance as measured by immunological criteria. It has not been possible to confirm Reichlin’s hypothesis that the myoglobin antigenic reactive regions of Atassi are particularly variable compared with the rest of the molecule; on the contrary it appears that differences in the immunological reactive regions occur approximately in proportion to those occurring in the molecule as a whole. Estimates of the rate of molecular evolution are of interest because its supposed constancy has been a major argument in favour of the hypothesis that a high proportion of fixed mutations are neutral, or nearly so, as far as selection is concerned. F urthermore, a near constant rate of molecular evolution holds promise for a molecular clock which might be used for dating evolutionary events. However, there is considerable variation in the rate of molecular evolution as evidenced by differences in the number of nucleotide substitutions (‘hits’) in lineages arising from the same phylogenetic branching point or by the examination of the changes at the amino acid level. In order to investigate absolute rates of evolution we sought to establish the best estimate of the date of divergence between the ancestors of the living species included in this study. These dates are based on direct fossil evidence and must be regarded as minimum dates because we have not indulged in open-ended speculations about fossils which have not yet been found. The combination of these dates with the evidence of our cladograms leads us to reaffirm our earlier finding that there are considerable differences in the amount of change in different lineages. For example, whereas one lineage (to gibbon) appears to have accepted no mutations during the past 20 Ma, another lineage (to ox) seems to have fixed seven mutations during the last 18 Ma. Goodman and others have drawn attention to the apparently low rate of molecular evolution among higher primates; a similar observation applies to the myoglobin of the Old World monkeys so far studied, but neither the myoglobins of New World monkeys nor the prosimian myoglobins share this feature. After their divergence from one another the two bird lineages included in this study appear to have fixed mutations at rates comparable with those found among mammals during the past 79 Ma. However, the number of differences between the bird and mammal ancestral stems appears to be remarkably low bearing in mind the date of divergence of their ancestors, about 293 Ma ago. Recognizing that this could be an artefact resulting from multiple changes at the same site, from undetectable back mutations and from isosemantic mutations accumulating during a long period of evolution, various procedures were adopted to transform the data in order to estimate the number of such events. None of these procedures, however, eliminated the phenomenon that during the first 214 Ma since their separation the ancestral stems leading eventually to birds and mammals seem to have fixed mutations in their myoglobin at a lower rate than the average rate prevailing during the past 79 Ma, the latter being approximately one mutation in 4 Ma. It is to be expected that sampling error will produce some fluctuations in rate, but even over the relatively long period of 79 Ma the fastest rate of fixation of mutations is about three times the slowest rate and so we are inclined to discard the molecular clock as unreliable for dating divergences, at least within this span of time. On integrating the various sections of this study we see that the changes in myoglobin have not been at random throughout the molecule. Given the constraints demanded by the functional morphology of the molecule itself and the constraints of the genetic code, it is to be expected that both will contribute to parallel change in different lineages. In the reconstructed pathways of evolution of myoglobin about 50 % of the changes were found in parallel in other lineages. There is an indication, provided by the larger number of arginine residues present in aquatic forms, that some of these parallel changes may be correlated with mode of life. The adaptive significance of the several parallel changes between the cetaceans and the pinnipeds certainly deserves physiological investigation. Regardless of the causes of parallel evolution at the molecular level this phenomenon has contributed to unexpected similarities between myoglobins and has led to difficulties in phylogenetic reconstruction of a nature already familiar to comparative anatomists.

Fossil Giraffes from the Miocene of Africa and a Revision of the Phylogeny of the Giraffoidea

Abstract: Specimens of Climacoceras africanus are described from Maboko, Kenya. The new species Climacoceras gentryi is established on the basis of ossicones, mandibles, and upper and lower dentitions from Fort Ternan and Baringo, Kenya. By interpretation of its lower canines Climacoceras is identified as a giraffoid and is placed in the new family Climacoceridae. Canthumeryx sirtensis is identified from Muruarot and Rusinga, Kenya. A dentition and associated partial skeleton of this species are described. The teeth agree closely with specimens of the same species from Gebel Zelten, Libya. Zarafa zelteni from Gebel Zelten is synonymized with Canthumeryx sirtensis. Again on the basis of its lower canines Canthumeryx is identified as a giraffoid and is placed in the new family Canthumerycidae. Specimens of Palaeotragus primaevus are described from Baringo, Kenya. This material includes a cranium with the ossicones, skull roof, occipital and basicranial regions preserved. Palaeotragus primaevus specimens from Fort Ternan are used in this description and some of these are redescribed. The relations of the giraffoids are assessed by methods of phylogenetic systematics. Palaeomeryx, Prolibytherium and Propalaeoryx are excluded from the Giraffoidea as their lower canines are not known. The Palaeotraginae is shown to be an invalid polyphyletic grouping and the genus Palaeotragus is also shown to be polyphyletic. Palaeotragus microdon is probably synonymous with Palaeotragus rouenii and the three species Palaeotragus rouenii (P. microdon), Palaeotragus coelophrys and Palaeotragus quadricornis are retained in the genus Palaeotragus. It is suggested that 'Palaeotragus' expectans and 'Palaeotragus' decipiens are closely related to Samotherium. Palaeotragus primaevus is probably synonymous with Palaeotragus tungurensis and this species is closely related to the giraffines. With slight changes the subfamilies Sivatheriinae and Giraffinae are valid monophyletic groups. Hydaspitherium is synonymized with Bramatherium and the Sivatheriinae includes the genera Giraffokeryx, Birgerbohlinia, Bramatherium and Sivatherium while the Giraffinae includes the genera Honanotherium, Bohlinia and Giraffa and the species 'Palaeotragus' tungurensis (P. primaevus). Okapia is identified as the sister-group of the other giraffids. Triceromeryx is the sister-group of the Giraffidae. Canthumeryx is the sister-group of Triceromeryx plus the Giraffidae while Climacoceras is the sister-group of the other giraffoids.

The morphology, mode of life, and affinities of Canadaspis perfecta (Crustacea: Phyllocarida), Middle Cambrian, Burgess Shale, British Columbia

Abstract: A detailed description and reconstruction of Canadaspis perfecta demonstrates its status as the earliest well-preserved crustacean. The cephalon consisted of five somites (in addition to the eyes), the thorax eight, and the abdomen seven, excluding the telson. Two pairs of apparently uniramous antennae flanked a median cephalic spine. The mandible bore a massive incisor process posterior of a molar area made up of finer spines, and apparently lacked a palp. The first and second maxillae were essentially similar to the eight pairs of thoracopods, with a multisegmented inner ramus, and foliaceous outer ramus made up of wide filaments attached to a proximal lobe. A bivalved carapace covered the thorax; no rostral plate was present. The abdomen lacked appendages, apart from a pair of spinose ventral projections of the pre-telson somite. There was no caudal furca. The evidence suggests that C. perfecta fed on coarse particles, possibly with the aid of currents set up by the biramous appendages. The erection of a new order Canadaspidida and family Canadaspididae Novozhilov (in Orlov 1960) to include Canadaspis is vindicated, and they are re-defined and the subclass Phyllocarida amended to include them.

The Lobopod Animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia

Abstract: Fifteen specimens of A.pedunculata have been prepared, photographed, and drawn to show how each specimen is interpreted and how portions preserved only in part or counterpart are related to the whole. The body was elongate, sub-cylindrical, bearing one pair of conical, branched anterior appendages inserted in the lateral wall, and ten pairs of short, uniramous limbs; anteriorly no distinct head region, posteriorly the body merged into the bases of the last pair of limbs. The cuticle was unmineralized, flexible, the body wall, anterior appendage and limbs, annulated. On the trunk the evenly spaced annulations were high, sharp-crested dorsally, changing to low and rounded laterally and faint or absent ventrally; dorsally the annulations appear to have borne a row of seven tubercles, each tubercle sharp and possibly spinose apically. One annulation opposite midline of anterior appendage and limbs 1-9, three in the space intervening between these limbs, five between anterior appendage and first limb; posteriorly annulations of trunk formed a continuous series with those of last pair of limbs. This arrangement implies that the body consisted of at least 12 somites. Annulations of the anterior appendage were sharp-crested, uniform in height; branches of the appendage were long, slim, pointed, three at the tip and three along the anterior side, each branch slightly flexible and movable about its base. About ten annulations on each limb, uniform in height, the cross-section varied from low, rounded, to high, sharp-crested, as the limb was extended, contracted or flexed. The tip of the limb was bluntly rounded, on the posterior wall of limbs 1-8, and the anterior wall of limbs 9, 10, was a group of seven curved claws. On limbs 2-8 a forwardly directed spine on the seventh annulation and a shorter spine on the distal annulation, on limbs 9 and 10 a prominent, backwardly directed spine. In front of the anterior appendage the one or two annulations were faint, the anterior end of the body bluntly rounded, the mouth, surrounded by a ring of six or so slim papillae, situated medially on the anterior wall. The alimentary canal is not preserved as a sediment fill, but as a reflective strip, widest adjacent to the mouth, extending back to end between the bases of the last pair of limbs. Sagittal length 1 to 6 cm, smallest similar to largest specimen. Aysheaia pedunculata is one of the rarer animals in the Burgess Shale, occurring in association with arthropods and worms, and to an exceptional extent with sponge fragments. It was not a burrowing, mud-ingesting animal, and the soft body would seemingly make it vulnerable to predatory arthropods. It may have been protected by living amid sponge colonies, the claws having facilitated clinging to the sponge, the anterior appendage holding the suctorial mouth in position to feed on the soft parts. While it shows resemblances to both Onychophora and Tardigrada, it is not placed in either group, nor in any taxon of higher rank than Family Aysheaiidae. It may be regarded as the sole known example of the types of lobopod animals from which the arthropod phylum Uniramia, and the Tardigrada, may have been derived.

Skull asymmetry, ear structure and function, and auditory localization in Tengmalm’s owl, Aegolius funereus (Linné)

Abstract: The ear apertures in the skin of Tengmalm’s owl, Aegolius funereus (Linne) (Strigiformes), are slit-like and ca . 24 mm long. This equals the height of the skull. The ear opening in the skin is bounded by a continuous fold of skin that is developed into a preaural and a postaural flap. The preaural flap carries the facial disk feathers that are structurally specialized to be sound transparent. They form a multi-layered, but sparse and delicate web over the ear opening. The postaural flap carries very densely packed feathers that form an anteriorly concave facial ruff. The ear folds (flaps) and the ear slit in the skin of one ear exhibit bilateral symmetry relative to those of the other ear, but because of asymmetry of underlying skull bones the postaural folds come to be oriented in somewhat different ways in the left and right ear. The skull bones, their constellation, and their role in the bilateral skull asymmetry are described in skulls at various stages of development (12-25 days post-hatching). Inside the ear aperture in the skin lies the smaller ear aperture in the skull. This is ca . 11 mm high. The ear and skull asymmetry reaches its maximum at the ear apertures of the skull. Hence the right ear aperture of the skull lies, ca 6.5 mm higher than the left one. Viewed from in front, a line connecting the centres of the ear apertures deviates 12° from the horizontal. The asymmetry then decreases towards the posterior parts of the external auditory meatuses, and the flattened meatus parts extended over the eardrum exhibit complete bilateral symmetry. As projected on the vertical median plane of the head, an axis through the centre of the eardrum and the centre of the ear aperture of one ear gives an angle of vertical divergence of ca. 40° with the corresponding, projected, axis of the other ear. The tympanic ring, the eardrum, the middle ear, the stapedial complex, and the bony cochlea and semicircular canals exhibit complete bilateral symmetry. However, one pair of the three pairs of air spaces communicating with the middle ear, namely the superior air space, is of different shape on the two sides. The skull bones participating in the asymmetry are: the orbitosphenoid, squamosal, parietal, frontal, and the squamosooccipital wing. Of the jaw muscles the M. depressor mandibulae and the aponeurosis 1 portion of M. adductor mandibulae externus exhibit pronounced bilateral asymmetry. Both muscles are related to the highly asymmetrical squamoso-occipital wings. The combined volume of the middle ear cavity and the air spaces communicating with it is ca . 730 mm 3 in one ear. This is almost as much as the volume of the external auditory meatus, which is about 830 mm 3 . The large volume of air inside the eardrum should result in (1) a lowering of the resonant frequency of the middle ear, and (2) a lowering of impedance in the stiffness controlled frequency region below the resonance frequency, with a corresponding increase in transmission of these frequencies to the cochlea. An ecological consequence to the owl of lowered middle ear impedance, and hence threshold of hearing at low frequencies, is an improvement of the owl’s ability in far range detection of sounds containing low frequencies, such as rustling sounds made by prey moving about in vegetation. While high frequencies are potentially more useful for sound localization than low ones, low frequencies are less attenuated by air and less diffracted and reflected by vegetation, and therefore travel farther and are more useful for detection of sound at some distance. The area ratio between the eardrum and the footplate of stapes is 35.3, which is a high value for a bird. The stapedial complex consists of two functional units that perform two different, but interrelated, movement patterns. One unit is formed by the extracolumella and the Ligamentum ascendens. This unit is rigid and rotates about its axis of rotation at the rim of the tympanic ring. It is the functional equivalent to the mammalian ear ossicles malleus and incus. The other unit is the bony stapes. It performs a pistonlike motion and corresponds to the mammalian stapes. Because of the oblique orientation of the stapedial complex relative to the plane of the tympanic ring, the force lever arm becomes longer than the resistance arm. The maximum transformer ratio attainable by the stapedial complex amounts to 1.6. The combined transformer action, due to the area ratio and the transformer action of the stapedial complex, thus becomes 56 (the possible curved-membrane effect not included). The middle ear transformer ratio thus seems to be close to the optimal one ( ca . 65), i.e. that resulting in maximum pressure transfer to the inner ear. The external ears are bilaterally asymmetrical in the vertical plane. This strongly suggests that the asymmetry is linked to vertical directional hearing . The mere fact that there is a bilateral asymmetry of the external ears strongly suggests that vertical directional hearing is based on binaural comparison of signals from the two ears. Indeed, the entire asymmetry would seem meaningless as to auditory localization, if the information processing at the neural level were not based on binaural comparison. It is suggested that the remarkably large height of the symmetrical ear slits in the skin serves the purpose of extending the effect of ear asymmetry to lower frequency domains. Data from acoustical measurements show that the vertical sensitivity pattern is different between the left and right ear for frequencies above 6000 Hz. This demonstrates that the ear asymmetry in Aegolius is capable of producing excellent physical cues to vertical localization of sound. A hypothesis on localization of complex noise is given; it suggests that the owl performs a binaural comparison of spectral pattern. Low frequencies (below 6000 Hz) provide intensity cues to azimuth, high frequencies intensity cues to elevation angle. In theory, the median plane ambiguity, inherent to symmetrical ears, is removed by the bilateral asymmetry. This is because the asymmetry, at some frequencies, causes interaural intensity differences at most elevation angles in the median plane. The use of interaural differences in spectral pattern in auditory localization, would remove also the problem of distinguishing ‘what’ from ‘where’, i.e. the uncertainty as to whether a specific spectral pattern should be attributed to the sound source or to a directiondependent spectral transformation imposed by head and ear. The ear asymmetry provides the cue in the vertical plane. The hypothesis on auditory localization is summarized in a simple mathematical expression.

The English Silurian fossil Placocystites forbesianus and the ancestry of the vertebrates

Abstract: Placocystites forbesianus de Koninck, from the Silurian Dudley Limestone, near Dudley, West Midlands, is here interpreted as a primitive chordate with a calcite skeleton of echinoderm type. This agrees with earlier papers by the senior author and disagrees with the work of Ubaghs (1968 etc.). Applying Hennig’s terminology, Placocystites probably belongs to the stem group of the vertebrates and therefore throws light on primitive vertebrate anatomy. It also belongs to the group Calcichordata, set up by one of us as a subphylum (Jefferies 1967). The Calcichordata, however, are not comparable in phylogenetic position with the living chordate subphyla, so the word calcichordate will henceforth be used only informally, for any chordate with a skeleton of echinoderm type. Ubaghs, who has developed a totally different interpretation, assigns Placocystites to the subphylum Homalozoa of the phylum Echinodermata. In assigning it to that phylum, Ubaghs’s work is more traditional than ours. Within the calcichordates, Placocystites forbesianus belongs to the more advanced group known as mitrates. These are distinguished from more primitive calcichordates (cornutes) by having right gill slits in addition to left ones. Within the mitrates it is possible to suggest the stem groups, in the Hennigian sense, of acraniates, tunicates and vertebrates. The term standard vertebrate is proposed to denote vertebrates in the usual sense, as contrasted with those stem vertebrates included in the mitrates. The two obvious parts of a calcichordate, formerly called theca and stem, or body and tail, are best called head and tail by homology with standard vertebrates. Mitrates correspond to the tunicate-tadpole-like protovertebrate of ‘antisegmentationist’ morphologists such as Froriep, Starck and Romer. The uniformly segmented protovertebrate of 9segmentationist’ morphologists such as Goodrich would represent a real but later stage in the ancestry of standard vertebrates, descended from a mitrate. The somites of standard vertebrates and acraniates can be plausibly identified inside calcichordates. The premandibular and mandibular somites would be located in the head, along with the buccal cavity, pharynx, gill slits and viscera. The left and right mandibular somites were probably represented in mitrates by the left and right anterior coeloms. The paired premandibular somites would be represented by a crescentic body situated in the posterior part of the head just in front of the brain. The hyoidean somites would be the most anterior pair of somites of the tail, totally separated from gill slits and gill bars. More posterior somites would also be in the tail, behind the hyoidean somites. The homologues of the paired eyes of standard vertebrates can also be recognized as having existed in mitrates (cispharyngeal eyes). The presumed premandibular, mandibular and hyoidean somites were grouped round them in an arrangement which could give rise to the extrinsic eye muscles of standard vertebrates. The ears of mitrates were lateral to the hyoidean somites as they are in living vertebrate embryos. The nervous system of Placocystites and its relatives is comparable with that of a fish. The brain was divided into two parts broadly corresponding to the prosencephalon and rhombencephalon of an early standard vertebrate (though the rhombencephalon of vertebrates also includes derivatives of the mitrate tail). The cranial nerves are deduced to have included olfactory, perhaps terminalis, optic, trigeminal and acusticolateralis complexes. The trigeminal complex included opthalmicus superficialis and ophthalmicus profundus branches and a single pair of ganglia. Contrary to classical theory, it was not divided into profundus and ‘true’ trigeminal subcomplexes. The pharynx of Placocystites and related mitrates was like that of a tunicate, particularly in certain asymmetries. Details of the skeleton strongly indicate that the pharynx in life would have contained an endostylar mucous trap of tunicate or ammocoete type, as classical theory would predict. The neural gland (‘hypophysis’) seems to have had the same relations as in a fully formed tunicate tadpole, but was probably endodermal in origin, homologous with Seessel’s pouch of a vertebrate. The anatomy of the head of the primitive calcichordate Cothurnocystis , which was a cornute, and like other cornutes and larval amphioxus had left gill slits only, is reconstructed by working backwards from mitrates and by direct evidence from its skeleton. The hypothetical latest common ancestor of lampreys and gnathostomes is deduced. The parts derived from the mitrate head can be distinguished from those derived from the mitrate tail. The animal probably possessed a notochordal head region and a trunk. These would have formed when gill slits and viscera migrated backwards ventral to the anterior part of the mitrate tail. The pericardium would have arisen by ventral growth of mitrate tail somites down the gill bars and their fusion ventrally to form a cavity. The visceral coelom arose by the ventral growth of mitrate tail somites round the viscera, accompanied by the development and fusion of cavities in the ventral parts of these somites. The branchial nerves of standard vertebrates are a mixture of placodal elements, probably derived from the mitrate head, and neural crest elements, probably derived from the mitrate tail. This hypothetical animal probably evolved from the mitrates when one of them took to habitual forwards swimming. Placocystites probably crept backwards through the sediment just below the sea bottom, pulled by the tail. A pair of spines near the mouth would serve to cut into the sediment, probably assisted by water squirted along them from the buccal cavity.

Non-Photosynthetic Functions of Carotenoids

Abstract: In addition to their important role as accessory pigments in photosynthesis, carotenoids also participate as agents which protect cells and tissues against the potentially harmful effects of visible radiation. They seem to play a unique role in this regard, for there are at least three separate mechanisms which can be invoked to explain the protective aspects of carotenoid function. These involve interrupting the potentially destructive photochemical reactions by quenching the triplet state of chlorophyll, physically inactivating the highly reactive singlet state of oxygen ( $^1\Delta_g$ ) which can be formed photochemically, and finally serving as an oxidizable substrate to protect other molecules and processes from photodestruction. These protective effects, which were first elucidated in mutant strains of photosynthetic organisms, have been shown to have an even wider role in nature, for many non-photosynthetic systems utilize carotenoid pigments for similar protective purposes.

The origin and early taxonomic diversification of pelecypods

Abstract: A series of Cambrian morphologically intermediate forms show that the bivalved shell of pelecypods is probably derived from the pseudobivalved shell of rostroconchs, which in turn is probably derived from the univalved shell of helcionellacean monoplacophorans. In Ordovician time, pelecypods underwent their first major radiation, which produced seven major groups herein called subclasses. The subclasses Orthonotia and Lucinata are newly named herein; the subclass Actinodontia is elevated to this rank from the rank of order. The group Heterodonta may be polyphyletic, as the taxa included within it seem to be derived from various Ordovician groups, herein regarded as subclasses. It seems likely that the solemyids are descendants of Ordovician palaeotaxodonts. The duplivincular ligament may have had a polyphyletic origin, having evolved independently in the Arcacea, Myalinidae, and Pteriacea.

The rôle of abscisic acid and farnesol in the alleviation of water stress

Abstract: The complex responses of stomata which provide protection for land plants against excessive water loss are best understood if we consider them as occupying two lines of defence. The first line of defence consists of immediate responses to factors of the aerial environment, especially carbon dioxide concentration and water vapour pressure deficit, which ensure that the rate of transpiration is regulated to a level which can be supported by water uptake through the roots in moist soil. When the soil becomes dry, further controls become necessary, and the second line of defence comes into operation. A ceiling is imposed on the extent to which stomata can open, and an increase in the efficiency of water use is achieved, though at the expense of some reduction in the rate of photosynthesis. A sesquiterpenoid, abscisic acid (ABA) plays a major part in the second line of defence. It is contained in the mesophyll chloroplasts in leaves of well watered plants and is released when the water potential falls; the synthesis of new ABA is also induced by water stress. Movement of ABA from the mesophyll to the guard cells is assumed to take place, because the chloroplasts of guard cells appear to be unable to form ABA in response to water stress. We suggest that farnesol, another sesquiterpenoid hitherto considered to have a separate role as a regulator of transpiration, is the agent responsible for altering the permeability of chloroplast envelope membranes, allowing the release of ABA into the cytoplasm. The closure of stomata induced by ABA appears to be part of a series of integrated responses throughout the plant which helps to maintain turgor and growth when water is in short supply.

The size, structure and distribution of the giant tortoise population of aldabra

Abstract: The results of a two year field study of the endemic giant tortoise population (Geochelone gigantea) on the western Indian Ocean atoll of Aldabra are described. The work entailed an extensive sample census from which the size of the population was estimated to be 150 000 individuals. A large scale marking programme was also carried out. 6882 tortoises (4.6% of the total population) have now been individually marked and measured. Tortoises are unevenly distributed over the atoll with local densities ranging from 0 to 217 per hectare. Various environmental factors are considered in relation to their distribution. A method of age estimation, based on growth ring counts, is described and the characteristics of populations in high and low density areas are compared. Analysis of preliminary recapture information shows that the majority of tortoises are relatively sedentary in their habits, although some are capable of long distance movements; and that individual growth rate is density dependent. The remains of 643 natural tortoise mortalities were examined. Life tables of survivorship and mortality were calculated for the tortoise population in the southeast of the atoll. Crude estimates of mortality and recruitment indicate that the tortoise population in that area is on the decline. Tortoise biomass estimates are far in excess of those for other natural tropical ecosystems with similar rainfall. The vegetation in the southeast is being greatly modified by tortoise activity and there is every indication that the tortoise population there exceeds 'the stable carrying capacity'.

The Rhabdomere organization of some nocturnal pisaurid spiders in light and darkness

Abstract: The retinae of the posterior eyes of pisaurid spiders in the genus Dolomedes are described.They resemble those of Lycosidae, but the receptors are much larger, and proximal to the strips of tapetum upon which they rest the receptor axons are grossly dilated. Each receptive segment contains two rhabdomeres, and pairs of rhabdomeres belonging to adjacent receptors are contiguous. Prolonged (6 h) illumination at physiological levels causes the rhabdomeres to diminish in volume by loss of membrane which is restored on return to darkness. W hen spiders are kept in darkness for 4-5 d, the rhabdomeres grow by the orderly addition of membrane to the microvilli until they completely fill the receptive segments, and such novel membrane is subsequently disassembled when the retina is illuminated. It is proposed that under normal conditions there is a balance maintained between the growth and destruction of rhabdomere membrane. The paired rhabdomeres are flanked by the processes of supportive cells which exhibit much membrane amplification, and the supportive cell system extends below the tapetum completely to ensheath the swollen receptor axons, which are some 70-80 pm long. In dark-adapted retinae the supportive processes are shrunken; illumination causes them to swell, and the extracellular space between the interdigitations fills with electron-dense material derived from the breakdown of rhabdom ere membrane. The material is passed basally and reintroduced into the receptor axons via an extensive system of endocytotic pleats. The tips of pleats often enclose pigment granules from the supporting system, and identical granules in various states of lysis are found within the axoplasm after exposure to light, thus implying that the pleats burst rather than merely transport material across their membranes. There is evidence that pleats may become detached. Exposure of retinae to infrared radiation also evokes breakdown of rhabdomere membrane, but the extracellular route is not employed. The swollen axons are filled with whorls of rough endoplasmic reticulum, abundant Golgi bodies, and mitochondria. After long periods of darkness, all these systems are depleted, and the space they occupied becomes highly vacuolated. Light adaptation from dim light on a normal diurnal cycle evokes dilation of the cisternae of the endoplasmic reticulum, which pinch off smooth vesicles, and the Golgi bodies become highly active and produce coated vesicles in abundance. The relations between smooth vesicles and microvilli are ambiguous; precedents exist for supposing that smooth vesicles in the inter-rhabdom eral cytoplasm are pinocytotic and have been pinched off from the bases of the microvilli, but in Dolomedes there is some evidence to suggest that they may be identical with those manufactured by the endoplasmic reticulum and are also fusing with rhabdomere membrane. Multivesicular and multilamellar bodies are the product of membrane fragments which have broken off from the rhabdomeres during light adaptation, and of coated vesicles produced by pinocytosis; they are transported within the receptors to the swollen axons where they undergo lysis. It is proposed that in Dolomedes the role of the endoplasmic reticulum is to synthesize materials for the repair of rhabdomere membrane, and that the bulk of precursors to sustain this process is obtained by recycling the products of rhabdom ere breakdown via the supportive cell system. The hypothesis is discussed in terms of current information about invertebrate retinae, and analogous processes which are well established for those of vertebrates. Dolomedes do not move retinal pigment granules to modulate the shielding of their receptors, and it is likely that manipulation of the properties of photoreceptor membrane is the only strategy of adaptation available to them.

The Evolution of Functional Design in Rudists (Hippuritacea) and Its Taxonomic Implications

Abstract: Poor understanding of rudist growth geometry and anatomy has hampered systematic studies of the superfamily. A flexible model that simulates the growth of rudist shells is therefore presented so that evolutionary trends in the group may be consistently analysed; this model is constructed by rotational or irrotational stacking of inclined gnomons around a contained axis. Functional analysis of shell geometry and reconstructed anatomy provides a more solid foundation for rudist systematics. The first rudists (Diceratidae) employed one or other of the spirogyrate umbones, inherited from megalodontid ancestors, as a facultatively elevating encrustation stem. Invagination of the ligament in the Caprotinidae permitted uncoiling of the shell, though this also entailed reduced gaping and therefore externalization of food entrapment, with increasing involvement of the mantle margins. Caprotinid functional design was preadapted to several new adaptive zones, which were exploited by various advanced descendant groups. Some of these groups show homeomorphic evolution and have often been assembled by earlier workers into polyphyletic 'families' (e.g. Caprinidae). An attempt is therefore made to establish a skeletal classification of rudists on the basis of true clades, as distinguished by careful functional analysis.

Heat Shock of Drosophila melanogaster Induces the Synthesis of New Messenger RNAs and Proteins

Abstract: The heat shock proteins, labelled in vivo with [35S]methionine, were separated by sodium dodecylsulphate-polyacrylamide gel electrophoresis and fingerprinted after tryptic digestion. Eight distinct heat shock polypeptides are characterized in this way. Heat shock messenger RNAs were isolated and partially purified. Assayed in vitro for protein synthesis, they were found to code for heat shock polypeptides. Some parameters of the kinetics of in vivo synthesis of the heat shock proteins are presented.

Evolution of the deep sea protobranch bivalves

Abstract: The number of protobranch species of the continental shelves of the world comprise between 10 and 15 % of the total number of bivalve species present. This is in contrast to the bivalve fauna of the deep sea which, distant from the lower continental slopes, is dominated by the protobranchs. The protobranchs may comprise more than 70 % of the bivalve species in a sample and more than 95 % of the total number of bivalve specimens present. The Subclass Protobranchia has one of the longest recorded geological histories and its continuing success, particularly in the deep sea, is probably due to a suite of physiological characters that enable it to utilize a low and refractory food supply at considerable depths and pressures. Probably as a result of the lack of competition from bivalves of more recent origin as well as the long stability of their environment, the deep sea bivalves show a radiation of form and habit that is analogous to that shown by the more recently evolved lamellibranchs of the continental shelf. The study of the bivalve fauna of the deep sea helps in the understanding of the evolution and ecology of the Mollusca of late Cambrian and early Ordovician periods.

Polymorphisms for Melanism

Abstract: Northwest England is one of the oldest industrial regions in the world and has suffered intense air pollution since early in the nineteenth century. Soot has blackened trees and walls in the area and sulphur dioxide has killed most of the lichens that were originally present. Night-flying moths, in particular the Peppered Moth Biston betularia , rest on such surfaces by day and are sought by birds as food. In 1848 a black, industrial melanic form of B.betularia was discovered near Manchester and by 1900 had almost completely replaced the light-coloured typical form. Kettlewell showed that this was because the carbonaria melanic was better camouflaged than typical when it rested on trees and walls affected by air pollution. In the last 25 years clean air policies have markedly reduced smoke and sulphur dioxide pollution in the region. A polymorphism with visually distinct forms of B. betularia exists in northwest England and adjacent areas of Wales. These forms are determined by a series of multiple alleles, with the darkest phenotypes ( carbonaria ) dominant to the lighter ( insularia )while typical is recessive. Carbonaria is by far the commonest melanic in the northwest and is most abundant in the populations of B. betularia in Greater Manchester and Merseyside and is relatively rare in northern Wales. Data for the frequency of carbonaria, insularia and typical from 158 sites, between Leeds in the east to beyond Bangor in the west, are tabulated. The date of collection and the map reference of the sampling site are given to facilitate prospective sampling as the environment continues to improve. Some evidence suggests that the increase in the frequency of typical moths at Caldy, Merseyside and in Central Manchester may be due to reductions in air pollution. Gonodontis bidentata is another geometrid moth with a melanic ( nigra ) dominant to the non-melanic. The intensity of pigmentation of the non-melanic varies and specimens from northwest England are darker than those from the south of the country. The species is secretive and in the study area does not rest on exposed surfaces. Nevertheless nigra shows much local variation in frequency; it is most common in urban districts and least in the intervening rural areas. (In this way it is unlike B. betularia where carbonaria remains at over 85 % frequency throughout.) Superimposed on this pattern of local differentiation is a tendency of nigra to increase in frequency from west to east. In Liverpool the highest frequency attained is 45 % whereas in Manchester it reaches 80 %. Data from 112 sites are also tabulated. There is no evidence of a fall in the frequency of nigra associated with a decline in air pollution. Some results are given which suggest that adults emerge at different times in different parts of the survey area. The two spot ladybird Adalia bipunctata also shows increases in the proportion of melanics in populations that inhabit the inner urban areas. The advantage conferred by melanism is not completely understood since the species is warningly coloured and distasteful. Melanics may be at an advantage in the presence of certain pollutants or they may be favoured by the lower amounts of sunshine received by areas suffering air pollution. In the ladybird there has been a spectacular decline in the frequency of melanics in Merseyside between the late 1960s and 1976. (Data from 40 samples are given.) This rapid response would be expected if the environment is acting directly on the species rather than through changes in the background on which the species rests as is the case in B. betularia . The maintenance of the polymorphism for melanism in B. betularia is discussed. Three possibilities are examined in relation to the evidence available from the study area as well as from the rest of the United Kingdom: (1) heterozygous advantage is important irrespective of selective predation by birds, (2) there is a balance between the disadvantage of the melanic homozygote and the forces of selective predation, and (3) predation is the sole important selective agent while migration of animals from different environments occurs to produce polymorphism. At present the available evidence is insufficient to distinguish between these possibilities, the existence of heterozygous advantage, assumed to be of primary importance by other authors, has yet to be established.

Classification and the bivalve gill

Abstract: The proposal by Atkins (1938), that the Bivalvia can, on the basis of the composition of the latero-frontal ciliated tracts, be divided into two groups, the Macrociliobranchia and the Microciliobranchia, is examined. It is concluded that the Ostreidae, in which the latero-frontal tracts consist of compound cirri together with subsidiary simple cilia, should not be grouped with the Microciliobranchia. The remaining families in this group are characterized by the possession of latero-frontal tracts consisting of simple cilia only; the Pinnidae show some modifications of the latero-frontal tracts, the precise details of which are still to be determined. The form of the gill in the Anomiidae, Pectinidae, Limidae and Pinnidae is reviewed. It is suggested that in these families, possibly correlated with latero-frontal tracts consisting of simple cilia only, the collection and transport of particles by the gill for possible ingestion is primarily dependent upon the flow of water currents rather than direct ciliary action as in those bivalves which possess compound eu-latero-frontal cirri. The families possessing latero-frontal tracts consisting of simple cilia only are all included in the subclass Pteriomorphia, together with two families, the Mytilidae and Ostreidae, which possess compound latero-frontal cirri. Some workers already exclude the Mytilidae from the Pteriomorphia. It is suggested that before discounting the value of the laterofrontal tracts in indicating relations there should be a reappraisal of the position of the Ostreidae.

Evolutionary Rates and Patterns Among Cretaceous Bivalvia

Abstract: Analyses of over 100 lineages of Cretaceous Mollusca, primarily Bivalvia, representing diverse levels of morphological complexity, habitats, and adaptive strategies, clearly show that evolutionary rates (new taxa/unit time; or average taxa duration) vary widely within lineages subjected to changing environmental stresses, and between lineages and/or adaptive strategies subjected to broadly similar sets of environmental parameters through time. Modes of evolution range from gradualistic to punctuated, dependent upon rates and intensity of change in stress, or on levels of ecological opportunity (available ecospace). Extremely rapid rates of species evolution (one sp./0.08 Ma) and abrupt appearance of higher taxa occur during rapid radiations into unoccupied ecospace, and/or during high stress situations affecting whole biotas during short time intervals (e.g. rapid marine regression). Classification and reconstruction of molluscan phylogeny is most difficult over these intervals of geological time. Ecological factors far outweigh purely genetic factors in determining evolutionary rates and patterns among Mollusca, as determined by tests applied to Cretaceous lineages.

Geomorphology of reef islands, northern Great Barrier Reef

Abstract: During the 1973 Great Barrier Reef Expedition, 67 reef islands were mapped between latitudes 11° 309 S and 17° S on the Great Barrier Reef. During the mapping, the major topographic, lithological, sedimentological and vegetational features of the islands were distinguished, and their elevations relative to a sea level datum established. The islands themselves were categorized in terms of topographic and vegetational complexity. Previous classifications by Steers, Spender, Fairbridge and others are reviewed in the light of these findings. Some of the islands had been previously mapped by Steers in 1928-29 or 1936; on others, changes could be identified from the evidence of shoreline advance or retreat and from vegetation patterns. The floristics and vegetation units of the islands are briefly described, on the basis of the field mapping and a large collection of flowering plants. Vegetation is influenced by stage in island development, latitudinal variation in rainfall, effects of ground-nesting seabirds, and probably also by disturbance by aboriginal man. Development of mangroves on reef flats is related to stage of reef flat and island development, and relation to tidal levels. This study of the geomorphology of the islands raises questions over the nature, origin and history of specific features (ramparts, beach ridges, boulder tracts, exposed limestones) which the Expedition attempted both to define and to answer.

The infaunal descendants of the Cycloconchidae: an outline of the evolutionary history and taxonomy of the Heteroconchia, superfamilies Cycloconchacea to Chamacea

Abstract: The history of the Heteroconchia is traced from the earliest Ordovician, where they occur in shallow, marine sand and silt and inshore mud facies throughout the Palaeozoic, where in contrast to Mesozoic and more recent times they are numerically less important than the Anomalodesmata in the number of species present in the infauna. Evidence for the relationship of the heteroconch superfamilies from Cycloconchacea to Chamacea is discussed and a number of modifications to their existing classification made.

Origin and evolution of the Class Rostroconchia

Abstract: The pseudobivalved Rostroconchia, first recognized as a separate class of molluscs in 1972, may be the only extinct molluscan class. Until recently, primitive rostroconchs (ribeirioids) were generally thought to be the carapace of crustacean arthropods and advanced rostroconchs (conocardioids) were considered to be unusual pelecypods. In fact, rostroconchs were a diverse class of molluscs (2 orders, 8 families, 31 genera, 400+ species known) that grew a bivalved adult shell from a univalved larval and juvenile shell. They were bilaterally symmetrical animals that probably had an anterior mouth, posterior anus, a pair of lateral gills, and a pelecypod-like foot. Most are believed to have been deposit feeders that used enlarged anterior mantle tissue to collect food, but some were clearly suspension feeders. They lived on top of the sea floor (rarely) or partly buried within it (commonly). Rostroconchs are known only from Palaeozoic rocks and range in age from earliest Cambrian to latest Permian (approximately 575-245 Ma ago). They evolved from untorted univalved molluscs (helcionellacean monoplacophorans) in the late Precambrian, remained an inconspicuous component of the biota through the Cambrian, and then radiated rapidly in the palaeotropical seas of the Early Ordovician. Relatively few genera survived the Ordovician, possibly because of competition by the Pelecypoda, but many species of these are found in younger Palaeozoic rocks. The last refuge of the class seems to have been the cool-temperature regions of the Permian Earth. By the middle Early Cambrian, the first pelecypod Fordilla had evolved from a primitive rostroconch. Rostroconchs were preadapted to exploit the pelecypod form, and the appearance of Fordilla may have been a relatively insignificant step. Somewhat later, probably in the Late Cambrian or Early Ordovician, the Scaphopoda were also derived from the Rostroconchia. This evolutionary event seems to have required the ventral fusion of an elongate rostroconch shell at the post-larval stage of development. Animals resembling primitive rostroconchs were required as theoretical links between monoplacophorans and pelecypods before the Class Rostroconchia was well studied. These hypothetical intermediates differ from the real thing in only one important respect; it was predicted that such forms would have many pedal muscle insertions on each valve, which they do not. The single anterior and posterior pedal muscle insertions of primitive rostroconchs therefore indicate a secondary simplification of the molluscan stock; this probably occurred after the anatomy of Neopilina was attained, but before the main radiation of the phylum.

Function of sterols

Abstract: In plants, neither sterol synthesis nor sterol balance is static. While all plant tissues have the ability to synthesize sterols, generally the younger tissue has a higher rate of synthesis. Additionally, the synthesis of the various individual sterols changes with tissue age and environmental factors. For example, the plant apex has a higher level of sitosterol than stigmasterol and as the tissue becomes older the ratio of sitosterol changes in favour of stigmasterol. The level of campesterol is also quite high in the plant apex, especially in the region of cell division. The change in sterols of the various tissues is apparently not due to intercellular sterol transport. With regard to light, both its intensity and photoperiod are important factors in controlling sterol synthesis, especially the sitosterol to stigmasterol balance. The change in sterol metabolism induced by light does not appear to be due to activation of the 22,23-dehydrogenase enzyme. The change in sterols and their possible relation to the development and physiology of the plant are discussed.

Evolution of Reefs and Islands, Northern Great Barrier Reef: Synthesis and Interpretation

Abstract: This paper brings together the evidence from shallow coring, surface geomorphology, lithology of exposed rocks, superficial sediment accumulations, vegetation patterns, and the historical record derived from radiometric dating to suggest a sequence of reef and island development on the northern Great Barrier Reef in Holocene time. Reefs initially grew vertically as the sea rose rapidly from glacial low levels. This continued until vertical growth was limited by the air/sea interface as the rate of sea level rise slowed. Vertical growth was then replaced by reef flat formation at low intertidal levels, and by the lateral extension of reefs, especially to leeward. Superficial sediment accumulations on the reef flat define a series of changing habitats for further organic growth, and also record the sequence of Holocene events. Controls of the transition from vertical to horizontal reef growth will be discussed and some comments offered on latitudinal variation in reef form along the Great Barrier Reef.

Relative Fitness of Morphs and Population Size

Abstract: The melanic forms of Biston betularia and Gonodontis bidentata are common in northwest England. Kettlewell suggested that such morphs are better camouflaged from birds that seek them as food while they rest by day on exposed surfaces blackened by air pollution. He demonstrated that in an urban area the carbonaria melanic of B. betularia survived longer than the relatively conspicuous non-melanic typical form, and that this situation was reversed in an unpolluted area. Capture-recapture methods can be used to estimate daily survival rates and size of natural populations. These techniques were applied to Biston betularia at two localities and Gonodontis bidentata at five localities in northwest England and north Wales. The methods of Fisher & Ford (1947), Jolly (1965), Manly (1973) and Seber (1973) were used to analyse field data. Daily survival rates of the morphs, their expectations of life and their relative fitnesses were estimated. The rate of loss (1-survival rate) is a complex parameter including death and permanent emigration. There was no evidence for differential rates of movement of the morphs of a species, so differences in loss are due to selective death of morphs, probably arising as a result of predation by birds. In the study area the data for Biston betularia, together with the results of Bishop (1972) for seven other localities, present an unequivocal picture. There is a significant regression of the estimated fitness of typical relative to carbonaria at a locality and the frequency of typical in samples from that locality. Previous work has shown a strong correlation between the frequency of typical and the number of lichen taxa present on oak trees. There is no similar regression of fitness on frequency for Gonodontis bidentata although at Rusholme, central Manchester the evidence suggests that the non-melanic morph is at a disadvantage to the nigra form. The selective forces maintaining the polymorphism for nigra in G. bidentata are poorly understood. The density of populations of Gonodontis bidentata ranged from about 4:00 000 moths/ km $^2$ per flying season in south Liverpool to about 8000 moths/km $^2$ per season in central Manchester. Corresponding figures for B. betularia are probably less than 1000 moths/km $^2$ per season. That species appears to be highly mobile, a substantial fraction of adult males leaving the area where they developed. The evidence available for G. bidentata suggests that it is very much less mobile. The differences in density and movement affect the relative rates of gene flow in the two species.

Abscisic acid as a natural growth regulator

Abstract: Abscisic acid (ABA) is accepted as one of the five major classes of natural plant growth regulators. In many tests ABA inhibits growth and metabolism, and enhances degradative changes, as in ripening and senescence. Its sites of biosynthesis appear not to be strictly localized and it is transported within the plant both within the phloem and by cell-to-cell transport. The best authenticated example of its function as a growth regulator is in the geotropic responses of roots in which growth curvature is apparently brought about by the asymmetric distribution of ABA produced in the root cap. The evidence for a role of ABA in the dormancy of seeds and buds, and in the ripening and abscission of fruits, is suggestive but at present incomplete. Experiments involving both exogenous and endogenous ABA suggest that ABA may play a significant role in tuberization in potato and other species. ABA inhibits hormone-induced nucleic acid and protein synthesis and there is evidence for its action both at the transcription and at the translation levels. On the other hand, ABA induces very rapid inhibition of growth which appears to be mediated via its effects on cell membrane properties. Its effects on potassium uptake may be mediated through inhibition of proton excretion by the cell. ABA counteracts the effects of other growth promoting hormones in various tests but the nature of this interaction is unknown. It seems likely that ABA plays a general role in the regulation of growth and certain aspects of metabolism, through its interaction with other growth substances.

Forty-five years of change on low wooded islands, Great Barrier Reef

Abstract: During the 1928-29 Expedition, centred at Low Isles, Spender mapped the ‘low wooded islands’ or ‘island-reefs’ of Low Isles and Three Isles in detail, and additional information was published by Steers, T. A. Stephenson and others. From this work, two different models of the evolution of low wooded islands were proposed, Spender holding that the islands were in a state of equilibrium resulting from their location on the reef, Steers that they could be placed in an evolutionary sequence. Moorhouse described the results of cyclones at Low Isles in 1931 and 1934, and Fairbridge & Teichert reconsidered the general issues following aerial reconnaissance and a brief visit to Low Isles in 1945. Subsequently, aspects of change since 1928-29 have been studied at Low Isles by W. Stephenson, Endean & Bennett in 1954 and by W. Macnae in 1965. Maps produced since 1929, however, have all been based on Spender’s surveys. In 1973, Low Isles and Three Isles were remapped in detail, and a direct comparison can now be made over an interval of 45 years. This shows changes in island topography, and substantial alteration in the size and location of shingle ramparts which has affected conditions for coral growth on reef flats. Mangroves have extended greatly at Low Isles, but not at all at Three Isles. The implications of these findings for the general models of Steers and Spender will be discussed and related to the Holocene history of the Great Barrier Reefs.