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Showing papers in "Philosophical Transactions of the Royal Society B in 1968"


Journal ArticleDOI
TL;DR: The permeability of the perinephric membrane has been re-investigated and it is shown that the membrane is more permeable to water and solutes at the anterior end, as might be expected if the inner sheath were the main barrier.
Abstract: An electron microscopical study has been made of the rectal complex. The perinephric membrane is a complicated structure which, in the posterior region, comprises an inner and an outer sheath separated by a space containing tracheolar end cells. The outer sheath is formed of a single layer of cells covered by an external basement membrane. The inner sheath is a multi-laminate structure made up of many thin, cellular layers which in places are reduced to closely apposed plasma membranes. Anteriorly the cellular layers are reduced in number, but each layer is of greater thickness; they finally terminate where the perinephric membrane is applied to the intestine. Posteriorly the inner sheath makes contact with the rectal epithelium. An earlier description identified three spaces within the rectal complex: the perirectal, subepithelial and peritubular spaces. The first two are true intercellular spaces, bounded by basement membranes, but the so-called peritubular space is occupied by necrotic cells. The inner sheath of the perinephric membrane is interrupted by the leptophragmata. Each leptophragma is bounded by a prominent electron-dense ring into which the laminae of the inner sheath are inserted. The outer sheath forms a blister over the leptophragma and is completely noncellular in this region. At the base of the blister a basement membrane covers the leptophragma itself, and the body of the leptophragma cell projects into the lumen of the tubule, with a thin layer of cytoplasm lying beneath the basement membrane. Both this layer and the cell body itself bear microvilli. The cell has a normal complement of mitochondria, but these do not invade the microvilli. In this last respect the ordinary tubule cells differ from the leptophragma cells in that most of their microvilli contain mitochondria, with connexions between the outer mitochondrial membrane and the plasma membrane. The tubule cells have a poorly developed endoplasmic reticulum but are filled with numerous small granules; basal infoldings are restricted to those parts of the cell which face the perirectal space. The permeability of the perinephric membrane has been re-investigated and it is shown that the membrane is more permeable to water and solutes at the anterior end, as might be expected if the inner sheath were the main barrier. Using preparations isolated in small volumes of haemolymph or other external media it has been shown that the rectal complex takes up potassium against a gradient of concentration. The lumen of the perirectal tubule is some 50 mV positive with respect to the external medium, so the uptake of potassium must be active. The leptophragma is freely permeable to chloride and this ion appears to enter the tubule passively. A model of the mechanism of the rectal complex is proposed, whose main feature is that the high osmolarity of the fluids within the rectal complex is brought about by the inward secretion of potassium chloride, unaccompanied by water, at the leptophragmata. This should result in a fall in the osmolarity of the external medium. A substantial fall has been observed on occasion, but in most experiments a fall is barely detectable. It is believed that the impermeability of the leptophragmata to water is rapidly lost in a deteriorating preparation.

137 citations


Journal ArticleDOI
John D. Taylor1
TL;DR: The Seychelles Bank is an area of approximately 31 000 km $2$ of shoal water with an average depth between 44 and 65 m as discussed by the authors, it is located centrally on the Bank, it is 27 km long, 6 to 8 km wide and rises to a height of 900 m above sea level.
Abstract: The Seychelles Bank is an area of approximately 31 000 km $^2$ of shoal water with an average depth between 44 and 65 m. The granitic island of Mahe is situated centrally on the Bank, it is 27 km long, 6 to 8 km wide and rises to a height of 900 m above sea level. The climate is oceanic with two distinct seasons; from April until October the strong South-East Trades blow with an average speed of 8 to 10 knots and from November until March the area is under the influence of the northwest monsoon, when calms are frequent and the average wind speed is 4.5 knots. The average temperature is 26.8 $^\circ$ C and the average rainfall at sea level is 2500 mm. The near-shore sea-water temperature varies between 27.5 and 32 $^\circ$ C but in tidal pools values up to 40.7 $^\circ$ C were recorded, with a daily range of about 8 $^\circ$ C. Salinities in water with open circulation were close to that of normal sea-water but on reef flats after heavy rain values as low as 5.6% were recorded. Tides are mixed semidiurnal, with a maximum range of 1.8 m. Sites exposed to the dominant S. E. Trades experience the highest degree of wave action. Fringing coral reefs are developed around the island, on the eastern side they are generally wide and more or less continuous, but on the western side they are confined to narrow bay reefs. Submarine topography, wind direction and strength have influenced the development and resultant shape of the reefs. The most obvious feature of the flora and fauna occurring on and in the fringing reef is that there is a zonation parallel to the shore. This zonation may be related to that occurring upon rocky intertidal shores throughout the world: most of the reef lies in the sublittoral zone but with projections upwards into the eulittoral and littoral fringe zones. The upper limit of abundant coral corresponds with the appearance of Laminaria in temperate regions. A number of distinct communities of organisms can be recognized forming and inhabiting these zones. The area above highwater mark but with maritime influence is the supralittoral zone and around Mahe is colonized by salt-resistant plants such as Ipomoea, Scaevola, Cocos and Calophyllum. In creeks and sheltered areas mangrove patches occur, commonly Rhizophora and Avicennia and inhabited by many crabs such as Uca, Cardisoma and Scylla, and the gastropod Terebralia. Where the shores are rocky, either granite or beachrock they are colonized by a typical rocky shore biota; in the littoral fringe blue green algae and Littorina are common, below in the eulittoral zone green algae, barnacles, limpets, several species of Nerita, Isognomon and oysters occur. The area between the tide marks on sandy beaches is inhabited by the crabs Ocypode and Coenobita and the burrowing bivalves Donax and Atactodea. On the reef flat proper, communities are almost completely sublittoral and only partly emersed at lowest spring tides. In sheltered areas around Port Victoria, where the once extensive mangrove swamps have now been cleared, the remaining sediment is blackened, has a high organic content and smells of hydrogen sulphide; the overlying water is turbid with generally reduced salinities. The area is inhabited by a large population of 'fiddler' crabs (Uca), green algae and the burrowing bivalves Gafrarium, Quidnipagus and Psammotea. On reef flats which are wide enough beds of marine angiosperms are developed which extend up to 300 m seawards from the base of the beach. They are mainly formed by the genera Thalassia, Cymodocea and Syringodium which by means of rhizome and root systems accumulate and fix sediment. These 'grass' beds support a large population of holothurians and burrowing bivalves, principally Codakia, Quidnipagus, Tellinella and Gafrarium. On windward reefs immediately seawards of the grass beds are open sandy areas which interdigitate with lower ridges of loosely bound calcareous algal cobbles and coral fragments arranged at right angles to the algal ridge with which they are in continuity. Brown algae such as Sargassum and Turbinaria are abundant and attached to hard substrates; Halimeda is common in the sandy areas. A great number of species of burrowing gastropods and bivalves inhabit the sandy areas, the fauna on the cobble ridges is very similar to that occurring on the algal ridge. The algal ridge is well developed only on windward reefs, it consists of a low ridge at the seaward edge of the reef flat made up of a cavernous growth of calcareous red algae such as Lithophyllum and Porolithon. This substrate is clothed in Sargassum, Turbinaria and many other algae. The associated fauna shows an extraordinary diversity with many species of gastropods, particularly Cypraea, Conus, Triphora, Turbo and Trochus. Many crabs, echinoids, ascidians, sponges and cemented foraminifera are present. The extreme seaward edges of the reef flat, the reef front and the reef edge are the only environments where corals are the dominant organism in the community. The reef edge marks the seaward extent of the reef flat and slopes shallowly seawards from the algal ridge to the change in slope at the reef front and is the area where the waves break. The reef front is generally steep but around Mahe is only about 20 m high, descending to the shallow base platform outside the reefs. Two distinct reef edge and front communities can be recognized, the Acropora-Millepora-Stylophora community characteristic of windward edges with good water circulation and dominated by branching corals, and the Porites-Favia-Leptoria community is characteristic of reef edges in sheltered areas with massive, rounded, growth forms. An abundant molluscan fauna has been dredged from areas outside the reefs, but sufficient information is not yet available to warrant a division into communities.

109 citations


Journal ArticleDOI
TL;DR: In P. memnon the dominance relationships of the monomorphic tailed and tailless condition indicate that dominance can be evolved even when the characters concerned are not polymorphic, which contrasts with the genetic control of Mullerian mimicry as evidenced in the Heliconids.
Abstract: Papilio memnon is a swallowtail butterfly widely distributed in south-east Asia. The females are highly polymorphic and many of them are mimetic. The mode of inheritance of seventeen of the female forms is reported. In contradistinction to earlier work it has been shown that they are controlled by what appears to be a series of at least eleven autosomal alleles at one locus, sexcontrolled to the female in effect. There is evidence, however, that the locus is complex, comprising at least three closely linked loci with occasional occurrence of crossing over between them. Two characters which are not polymorphic and one which may be polymorphic are controlled by genes unlinked to the complex locus (the super-gene). In general, dominance is complete between sympatric forms but absent when they are allopatric. The resemblance between the mimetic forms of P. memnon and their models is greater in the genecomplex of a race in which the allelomorph occurs than in hybrids with a race in which it does not. Thus in no case is the resemblance better in the race cross, in ten cases there is no change and in thirty-five the mimicry is less good. The genetic control of the polymorphism in P. memnon shows remarkable parallels with that in P. dardanus and provides further supporting evidence for Fisher’s and Ford’s view that mimicry evolved gradually by adjustment of the gene-complex as a result of natural selection favouring those wing patterns which most closely resembled the models. Furthermore, as in P. dardanus, the mimicry is controlled by what appears to be a super-gene, adding weight to the conclusion that the genetic control of the polymorphic Batesian mimicry has evolved gradually by the accumulation of closely linked allelomorphs in advantageous combinations. This contrasts with the genetic control of Mullerian mimicry as evidenced in the Heliconids. In P. memnon the dominance relationships of the monomorphic tailed and tailless condition (excluding the form achates ) indicate that dominance can be evolved even when the characters concerned are not polymorphic. In addition, the lower frequency of dominance between allopatric forms than between sympatric ones is strongly in favour of the view that dominance has evolved. Similar evidence has been found from breeding work in the Heliconids and in P. dardanus ; however, the phenomenon is not confined to mimetic situations since there is also evidence for the evolution of dominance in other polymorphisms including industrial melanism.

85 citations


Journal ArticleDOI
TL;DR: An interpretation of the climatic regime based on the northern requirements of the species in this fauna, suggests that conditions were more severe than for any other entomologically investigated site.
Abstract: An insect fauna of 172 taxa, chiefly of coleoptera, is described from Mid-Weichselian deposits at Brandon, Warwickshire. This fauna includes two species that are now believed to be extinct and thirty-three that are no longer found living in Britain. All but one of these species live today in Arctic or sub-Arctic regions of north-east Europe and northern Sibera-the single exception being an insect of decidedly steppe environments. The fauna as a whole indicates an open treeless habitat closely analogous to the northern tundras of the present day to which several of the recorded species are exclusively confined. Details of the local environment of the times are inferred from the fossil insect fauna. An interpretation of the climatic regime based on the northern requirements of the species in this fauna, suggests that conditions were more severe than for any other entomologically investigated site. A moderate degree of continentality is inferred and an attempt is made to give a range of average monthly temperatures through the year. A comparison of this fauna with other known fossil insect assemblages suggests that these may be of value in correlation of Quaternary deposits.

79 citations


Journal ArticleDOI
TL;DR: In this paper, a stratigraphical study of the Triassic System of the southern North Sea basin has been undertaken by lithological and palynological analysis, and the type Germanic Triassic and the dated Alpine Triassic are briefly reviewed.
Abstract: Intensive drilling activity, particularly in the United Kingdom part of the North Sea, has greatly increased our knowledge of the subsurface geology of north-west Europe. The Triassic, perhaps more than any other system, has provided results of a special interest. In this paper a stratigraphical study of the Triassic System of the southern North Sea basin has been undertaken by lithological and palynological analysis. The type Germanic Triassic and the dated Alpine Triassic are briefly reviewed. The facies development of the Germanic Triassic is traced by means of subsurface data from north-west Germany and the northern Netherlands into the North Sea. Further studies of the onshore Triassic of England from subsurface well data and surface outcrop sections are discussed. The results, particularly those from wells in the North Sea, provide a lead to the understanding of the position of the English Triassic of Keuper and Bunter within the framework of the Germanic Triassic.

76 citations


Journal ArticleDOI
TL;DR: It is likely, therefore, that the snails are extremely localized in their wanderings, the more so as the authors had to collect from each division, take the samples away to be marked, and scatter them on release, each at random in its own division.
Abstract: On the discovery of area effects in morph frequency variation in the snail Cepaea nemoralis on the Marlborough Downs (Cain & Currey 1963 a) an intensive study with mark-release-recapture methods of a population subject to these effects was begun. The area investigated was divided into four quarters (downland grass) and two nettlepatches; the snail population is continuous through the area. Frequent visits were made during the snails' active season in 1962, 1963 and 1964; in 1965 and 1966 a single large sample was collected, marked and released in the spring. Five-banded shells are absent. The scoring of mid-bandeds with reduced bands being difficult, attention was concentrated on the principal colour morphs, yellow, pink and brown. Thrushes were predating the snails heavily in 1962, but the hard winter of 1962/3 removed them, and they have not yet returned in any numbers; the snail population does not seem to have been affected by this hard season. Throughout the period of investigation, the density of snails in the nettlepatches has been about ten times that in quarters 2, 3 and 4. Quarter 1 has less than half the density in the other quarters, and differs markedly from them and the nettlepatches in morph frequency, although it resembles quarter 2 strongly in vegetation. It is likely, therefore, that the snails are extremely localized in their wanderings, the more so as we had to collect from each division, take the samples away to be marked, and scatter them on release, each at random in its own division. Our estimates of migration from one division to another also suggest strong localization and perhaps homing. The total population in the area is about 3000 adults. Subpopulations have decreased in all divisions from 1963 to 1965. Adult survival rates are high, about 0.65 per year; no differential survival of the colour classes has been found, but much more data are needed. Predation by thrushes in 1962 was heavy in the summer, but not in proportion to snail density; the nettlepatches were proportionately much less predated, probably because of their dense growth of herbage. Winter predation, by contrast, was almost entirely in the nettlepatches, then showing expanses of bare earth. A check on our own efficiency of collecting shows that we are taking non-random samples in the quarters (downland grass) but not in the nettlepatches. We find pinks rather more conspicuous than yellows, but dark browns much less conspicuous than either. As the snails' bodies in this area are very dark, yellows appear green, pinks dirty straw-colour. It seems unlikely that browns are really more cryptic visually than yellows. Possibly their behaviour is different. The samples of predated shells taken by the thrushes agree very closely with our samples, and it appears that they also are predating with a bias (missing browns) in the quarters but not in the nettlepatches. Morph frequencies show no sign of alteration in the period of investigation, except that in 1963 and 1964 there was a drop in percentages of browns in quarters 2, 3 and 4, apparently not continuing in 1965 and 1966. (The compensatory increase is shared equally between pinks and yellows.) This could well be due to the sudden cessation of selection by thrushes, but the rate seems excessive if there was selection only on adults. There is no obvious relation between morph frequencies and population density. The growth in size of the juveniles in our samples has been studied through the snails' active season. It is clear that they take two years to reach maturity (i.e. to form the lip terminating the adult shell). This finding and the survival rates give a minimum generation interval of four years, and the actual period may be close to five in this area.

70 citations


Journal ArticleDOI
TL;DR: Murray’s finding that the hyalozonate gene when homozygous pales shell colour as well as removing the lip and banding pigment is confirmed; faint pink or yellow-white shells homozygotes for hyalozoneate may be genetically faint pinkor pale pink; the strong linkage between it and shell colour previously suggested is confirmed, but crossovers are recorded.
Abstract: The following segregants of shell colour are described: pale brown, faint brown, faint pink, yellow-white. Faint pink is dominant to dark and pale yellow and recessive to pale pink. Murray’s finding that the hyalozonate gene when homozygous pales shell colour as well as removing the lip and banding pigment is confirmed; faint pink or yellow-white shells homozygous for hyalozonate may be genetically faint pink or pale pink. Deep pink hyalozonates exist and transmit their phenotype to their offspring; in these the paling effect is not noticeable. Shells with no bands but a strip of fascialbate opaque material in the position for bordering the middle band are genetically mid-banded. The condition is due to a multifactorial suppression of the pigmented band. Spread-banded is described in the five-banded form as well as the m id-banded; the strong linkage between it and shell colour previously suggested is confirmed, but crossovers are recorded. White lip (with normally pigmented bands) is recessive to normal lip, linked to the locus for shell-colour, and allelic to hyalozonate. The normal lip/white lip heterozygote appears to be palelipped, but the degree of pallor is modified by the presence of yellow or pink shell colour. White lip, when homozygous, may reduce the intensity of shell colour in some cases, as does hyalozonate. Hyalozonate is shown to be linked to the banding locus, which itself is strongly linked to that for shell colour. Orange-banded is complementary to hyalozonate, not allelic to it as is the very similar form lurida described by Murray in Cepaea hortensis . A form of the var. punctata producing only traces of bands and occasionally a definite punctate band is described, which is linked to the shell colour locus and dominant to normal bands. This and the form figured by Lang and by Taylor with well-developed punctate bands (the segregation of which from normal bands is confirmed) may well be alleles. A segregation of medium grey to very pale body is described, with medium grey dominant to pale. It appears to be unlinked to shell colour, banding and mid-banded.

63 citations


Journal ArticleDOI
TL;DR: In this article, the effects of climate on the shell color and banding polymorphism of Cepaea nemoralis were investigated in two extensive valley complexes in the Pyrenees; populations were sampled over a wide altitudinal range, such that considerable differences in the climatic environment were apparent.
Abstract: In order to investigate the effects of climate on the shell colour and banding polymorphism of Cepaea nemoralis, surveys were carried out, in 1962 and 1963, in two extensive valley complexes in the Pyrenees; populations were sampled over a wide altitudinal range, such that considerable differences in the climatic environment were apparent, both within and between the valley complexes. The valleys selected for study were that of the Garonne in the central Pyrenees and on the north side of the watershed, and that of the Segre and its major tributary, the Valira, nearer the Mediterranean and on the southern side. The unbanded phenotype exhibits a parallel frequency distribution in colonies sampled near the rivers in both regions. It is at higher frequencies at high altitudes, and also in the lower parts of the valleys sampled, intermediate altitudes having populations which are predominantly fivebanded. There is, however, a marked difference between the two regions in the extent of the changes between the intermediate-altitude banding zones and the lower and upper zones; unbanded reaches much higher frequencies regularly in the upper zones of the Garonne compared with those in the Segre-Valira, whereas it is the latter region which exhibits really high frequencies in the lower zone. The distribution of frequencies of the yellow morph in the Garonne resembles that of unbanded; only intermediate-altitude populations have appreciable frequencies of pink, other populations having high or very high frequencies of yellow. In the Segre-Valira, there are some parallels in frequency distribution, but yellow is at a high overall frequency almost everywhere. The species is polymorphic for lip colour in the Pyrenees, and the results agree with Lamotte's for other Pyrenean valleys; the white-lipped morph is rare or infrequent in the foothills, and reaches high frequencies in the higher parts of the mountains. The relative constancy of morph frequencies over considerable distances, and their regular distribution between valleys and between the two regions (for example) show that selection is operating. It is argued that the colour and banding zones are area effects as there is no evidence for variation with habitat in districts where this can be tested by comparing open habitat samples with samples taken from woods, despite the occurrence of visual predation; and certain morph frequencies characterize quite clearly geographical areas rather than habitats. The broad correlation between morph frequencies--particularly banding morph frequencies-and altitude in the upper parts of the valleys suggested that some climatic aspects might be acting selectively. Comparison of samples made from hill slopes with those made by the rivers shows that the former tend to have less extreme morph frequencies; thus, at similar altitudes, hillside populations have lower frequencies of unbanded and of white-lip, and tend to have lower frequencies of yellow. This indicates that the factors favouring these morphs at higher altitudes do not act at the same strength on the hill slopes as in the valleys. It seems likely, from the accepted generalization that hill slopes are usually more temperate than valley bottoms, that cold air and concomitant low temperatures favour unbanded, yellow, and white-lip. Consideration of aspect of the valleys, and of certain colonies exceptional for banding frequencies concur with this: north-facing valleys and occluded situations tend to have populations with higher frequencies of unbanded than south-facing ones and sunny open localities. A comparison of morph frequencies in the Garonne and Segre-Valira regions with their climates also supports this interpretation for colour and banding. Similarly, the increase in frequencies of unbanded and of yellow at lower altitudes in the Garonne, and the very marked rise in frequency of unbanded in the Segre-Valira suggests that these two morphs are also favoured in conditions which tend to be warm and dry. The extent of the changes agrees, for the lower Segre-Valira, unlike the lower surveyed reaches of the Garonne, is essentially mediterranean in climate, and the frequency of unbanded is overall much higher there. Other field evidence, both from the Pyrenees and elsewhere, is in broad agreement with yellow and unbanded being favoured in more extreme climatic conditions, and most of the artificial resistance experiments performed with Cepaea accord in that these two morphs survive better when subjected to severe temperatures. The results are discussed with relevance to morph frequency distributions elsewhere; it is suggested that area effects in unbanded and yellow may occur when climate becomes sufficiently extreme, and some evidence is presented that this may be so on high country in the English counties Of Staffordshire and Cumberland. It is also suggested that if the strength of visual selection is relaxed in open country, as recent work indicates, then area effects in pink and fivebanded may occur in mild conditions; some evidence is produced in support of this idea. The clines in banding in the lower valleys are stepped; banding morph frequencies change apparently suddenly from one relatively stable frequency to another in both regions, without relation tO topographical features which might cause climatic disjunction in the vicinity of the step. It is tentatively suggested that co-adaptive selection may interact with climatic selection in the intermediate and lower zones, to produce sharp steps in frequency with stability despite change in altitude and climate on either side.

55 citations


Journal ArticleDOI
TL;DR: Two new and twelve little known species of Phyllobothrium or of allied genera, mainly from elasmobranchs and teleosts caught off the British Isles, have been investigated and the genus is revised for the first time.
Abstract: Two new and twelve little known species of Phyllobothrium or of allied genera, mainly from elasmobranchs and teleosts caught off the British Isles, have been investigated. As some of these could not be identified to species and the others presented difficulties, material from various other sources was obtained and examined for comparison. In addition, the literature on about 100 species allocated to Phyllobothrium was consulted and brought together. A critical appraisal of this literature is given and the genus is revised for the first time. Information on most of the species was found to be inadequate to provide a key and, therefore, a host-parasite list was compiled. As only about fifty species of Phyllobothrium sensu lato have been found in about 100 of the 3000 species of elasmobranchs known to exist, it is estimated that a very large number of Phyllobothrium spp. remains to be discovered and described. The possible significance of this fact is discussed. Brief descriptions of the most well-known species of Phyllobothrium are given and reasons against listing synonyms for these are emphasized. Of the 100 species already allocated to the genus only twenty-two are accepted at present; further studies may show that only three of these, viz. P. lactuca, P. dagnallium and P. serratum, show the typical features of the genus, as originally described. Fourteen of the twenty-two may, eventually, be placed in Anthocephalum Linton, 1890, if this genus is revived; the erection of a new genus or genera may be necessary for the remainder. P. britannicum sp.nov., from Raja montagui, is provisionally placed near P. lactuca but the bothridia are only slightly bifid, their margins are not so folded and the species is euapolytic. P. minutum sp.nov. from R. fullonica closely resembles P. auricularia, P. foliatum and P. loculatum and may, eventually, fall as a synonym of one of these; at present they are all little-known forms. Reasons are given for provisionally retaining Crossobothrium and Monorygma, with about ten species in each. It is suggested that three species originally placed in Phyllobothrium may be allied to Sphaerobothrium lubeti Euzet, 1959. An examination of the type material of P. ketae Canavan, 1928, previously regarded as unique or as a neotenic form, has shown that the original description was partly based on a pseudophyllidean and possibly on the larvae of P. caudatum. A number of larvae of Phyllobothrium in invertebrates, teleosts and marine mammals, fourteen little-known species of the genus and invalid members are discussed. A detailed discussion is given of the ecology, host specificity and attachment of Phyllobothrium and allied genera to the gut mucosa of elasmobranchs. In a general discussion brief comments are made on life-history, the identification and classification of Phyllobothrium, self-fertilization and on 'segmentation'. Almost 200 references are cited.

54 citations


Journal ArticleDOI
TL;DR: A survey of duneland populations of the polymorphic snail Cepaea nemoralis, based on 170 samples from 53 localities on the British and Irish coasts, shows an overall distribution of morph frequencies consistent with the action of visual selection as discussed by the authors.
Abstract: A survey of duneland populations of the polymorphic snail Cepaea nemoralis, based on 170 samples from 53 localities on the British and Irish coasts, shows an overall distribution of morph frequencies consistent with the action of visual selection. Some geographical trends of variation can be discerned, but there is great variation, often over short distances within one group of dunes. A detailed investigation of this has been made at Point of Air, Flintshire. Here and at several other dune systems there is an association of the occurrence of dark browns with complex topography which suggests that they are favoured by very local climatic effects caused by the accumulation of cold air. If local temperature or other climatic factors is effective, the apparent agreement of duneland populations with what is expected as a result of visual selection may be misleading.

50 citations


Journal ArticleDOI
TL;DR: In this paper, six separate episodes of cryoturbation are placed in the time sequence and the vicissitudes of climate, erosion and aggradation are integrated with a time scale.
Abstract: New evidence in the area around Brandon, Warwickshire, has amplified our knowledge of the sequence of events in the Saalian, Eemian and Weichselian. Organically rich deposits have been found at the base of Avon No. 2 terrace (mid-Weichselian) and in the Baginton-Lillington Gravels (early Saalian.) and their biota, described elsewhere, throws additional light on the climate of parts of Middle and Late Pleistocene time. Six separate episodes of cryoturbation are placed in the time sequence. Certain gravels which occur, in one locality only, at the base of No. 4 terrace are believed to be Eemian, separated by a major time break from the normal gravels of No. 4 which are ascribed to the early Weichselian. The vicissitudes of climate, erosion and aggradation are integrated with a time scale.

Journal ArticleDOI
TL;DR: The surveys on the Berkshire Downs, the Purbeck Hills and part of lowland Somerset reported here show, together with previous ones, that both species can occur in lowland and chalk upland localities, but the distribution of the two species in any one locality is different.
Abstract: The snails Cepaea nemoralis and C. hortensis show an extensive and stable polymorphism involving the colour and banding pattern of the shell. The surveys on the Berkshire Downs, the Purbeck Hills and part of lowland Somerset reported here show, together with previous ones, that both species can occur in lowland and chalk upland localities, but the distribution of the two species in any one locality is different. This difference may be related to topography as on the Berkshire Downs and the Purbecks, or to habitat as in south-east Somerset. There are no regional differences in the C. nemoralis polymorphism, most morphs so far recognized being present in every locality. The colour polymorphism in C. hortensis is much more extensive in the southern localities than in those from central England and there are alo regional differences in the banding polymorphism. Two types of morph frequency variation occur in both species. The first described was variation with habitat, the second, variation related to geographical position. The surveys show that habitat variation occurs in both lowland and upland areas, although it does not necessarily occur in either. Thus both species show morph frequency variation with habitat round Oxford and on the eastern Berkshire Downs. Only C. hortensis shows such variation on the Purbeck Hills although C. nemoralis is present there. The evidence, although not conclusive, indicates that neither species shows habitat variation in lowland south-east Somerset, but there is good evidence that neither species shows such variation on the western Berkshire Downs, the Marlborough Downs or Salisbury Plain. The morphs showing frequency variation with habitat are not always the same in either species. Round Oxford, and on the eastern Berkshire Downs, brown, pink and banded C. nemoralis with at least the upper two bands missing, are at a high frequency in woods, and yellows and bandeds are at a high frequency in other habitats. C. hortensis , on the other hand, shows variation in the frequency of fused bands and yellow effectively unbandeds between habitats in these two localities. On the central Berkshire Downs, spread banded show habitat variation together with other morphs in C. nemoralis . On the Purbeck Hills where pinks, browns and unbandeds are common in C. hortensis the habitat variation is very similar to that of C. nemoralis round Oxford. Habitat variation is not restricted to strikingly different morphs. Different types of pink C. nemoralis show such variation on the Berkshire Downs, and fusions of the upper or more bands in C. hortensis also show variation there. All the variation of morph frequency described above is best explained on the hypothesis of visual selection. Morph frequency variations related to geography give rise to large areas of stable morph frequency irrespective of habitat, the so-called area effects. The surveys to date indicate that area effects are restricted in both species to upland localities. The Berkshire Downs survey of C. nemoralis shows that area effects and habitat variation are not mutually exclusive. In different localities, related on an east/west axis, most morphs may show habitat variation, some show habitat variation and some area effects, or most show area effects. Area effects may occur in both species in the same locality as on the western Berkshire Downs, where the limits of the various area effects in the two species are semi-coincidental, or they may only occur in one species, C. nemoralis , on the Purbeck Hills. There is no experimental evidence as to the cause of area effects but there is some evidence from the present surveys which supports Cain & Currey’s (1963 a, c ) suggestion that they are maintained by selection.

Journal ArticleDOI
TL;DR: A new theory of migration in butterflies is outlined and a calculation based on the results of this investigation suggested that a return flight would be a selective disadvantage to both P. rapae and P. brassicae.
Abstract: A new theory of migration in butterflies is outlined and present concepts are examined. During the course of evolution many butterflies have become adapted in the larval stage to foodplants that occur in small and scattered localities, the distribution of which changes constantly. It is argued that whenever this happens selection might be expected to produce a butterfly which flies from one foodplant site to another. Further it is argued that while they were crossing areas devoid of foodplants selection would have favoured those individuals that flew at a constant angle to the sun. At first all angles to the sun would be represented equally in the population but each individual would pass on to its offspring a bias towards its own particular angle. It is suggested that the temperature gradient experienced by a butterfly dispersing in this way would constitute a marked selective pressure. This selective pressure would cause an increase in the number of individuals flying at certain angles and a decrease in the number flying at others. The effects of temperature on rate of development and fecundity were demonstrated for Pieris rapae and P. brassicae in the laboratory. The effects of seasonal and geographical temperature variations on these two species in the field were also demonstrated. Based on these results the relative selective advantage of each flight direction was calculated for different times of the year. As a result of these calculations it was predicted that P. rapae should fly at 159° to the sun until 27 August, when it should fly at 0°. For P. brassicae it was predicted that the first brood should fly at 159° and the second brood at 339°. Observations of flight direction of these two species from August of one year to October of the following year agreed well with these predictions. The observations of flight direction also showed that P. rapae , and probably also P. brassicae and Vanessa atalanta , were using the sun as the environmental clue by which they were orientating themselves. There was no compensation for the sun’s movement during the day or season. Experiments showed that P. rapae is sensitive to photoperiod during the adult stage. It is by this means that the same individuals can change their flight direction from 159° to 0° at the most selectively advantageous time. A calculation based on the results of this investigation suggested that a return flight would be a selective disadvantage to both P. rapae and P. brassicae . Observation of these two species suggested that in neither does the southward movement function as a return flight, i.e. is equal in distance to the northward movement.

Journal ArticleDOI
TL;DR: The available evidence, from pollen analysis and other sources, of changes in the climate of southern Britain in the last 6500 years suggests that the observed differences in morph frequencies can be related to known climatic changes, in agreement with present-day evidence.
Abstract: A number of samples of subfossil Cepaea nemoralis and hortensis from sites in southern Britain of archaeological interest, ranging in date from about 4500 b .c . to Romano-British and Anglo-Saxon, have been scored for frequency of the major banding morphs, and compared with present-day samples taken on each site or as near to it as these species could be found. In C. nemoralis there is a significant decrease of unbandeds from pre-iron Age samples to the corresponding ones for the present day, but no indication of systematic change from Iron Age samples to the present day. Spread banded also shows changes from pre-iron Age samples to present-day ones, but very little change from the early Iron Age to the present day. The smaller samples of C. hortensis available give no sign of a trend although there is much change from pre-iron Age times to the present; Iron Age samples and the corresponding present-day ones do not show the relative constancy of composition seen in C. nemoralis —as usual these two very closely related species are behaving differently. At the present day there is evidence (experimental and distributional) that the frequencies of banding morphs of C. nemoralis are affected by climate, unbandeds and mid-bandeds being favoured by better summers than those normal in Britain at present. The available evidence, from pollen analysis and other sources, of changes in the climate of southern Britain in the last 6500 years suggests that the observed differences in morph frequencies can be related to known climatic changes, in agreement with present-day evidence. One area effect (south-west M arlborough Downs) has contracted and become less intense since pre-iron Age times, as perhaps have others; in some cases a site has remained in an area effect, but the effect itself has changed. Two pairs of samples from lowland sites appear to have changed from frequencies indicating area effects in pre-iron Age times to others consistent with visual selection at the present day. Area effects seem to have been rather constant from the Iron Age to the present day.

Journal ArticleDOI
TL;DR: The fundi of fifty mammals have been drawn at a magnification of about x 16 and the appearances have been related to the usual classification of mammals and discussed with reference to habitat and some experimental observations of regional visual acuity.
Abstract: The fundi of fifty mammals have been drawn at a magnification of about x 16. The appearances have been related to the usual classification of mammals and discussed with reference to habitat and some experimental observations of regional visual acuity.

Journal ArticleDOI
TL;DR: A comparison of the series collected in 1924 with that collected in 1961 provides no evidence of consistent evolutionary change, and it is conceivable that the local distribution of pinks is the result of visual selection by rabbits.
Abstract: In 1924 one of us (C. D.), with the late Professor A. E. Boycott, F. R. S., collected random samples from populations of the polymorphic land snail Cepaea nemoralis L. on sand-dunes at Bundoran, County Donegal, Eire. In 1961, the other two revisited the area and sampled, as nearly as possible, the same localities. A total of 23857 live snails were collected and scored for various inherited shell characters. The data are considered from three points of view. First we have examined the distribution of morphs within individual samples, hoping to detect associations indicating linkage or selection. Secondly, we have studied the differences between contemporary samples and attempted to relate them to environmental factors. Thirdly, we have compared the two series (1924 and 1961) in order to detect any evolutionary changes that might have occurred. (1) Associations within samples In both series there are consistent linkage disequilibria involving the loci for shell-colour, for banded v. unbanded shell, for hyalozonate v. fully pigmented bands, and for white v. black lip. It is likely that these disequilibria are maintained by selection. There is also a suggestion of disequilibrium between the shell-colour locus and the loci determining the extent of band-fusions. We find no significant differences between adults and young in the proportions of any of the morphs. (2) Variation between samples Most of the characters show morph-ratio dines on an east/west axis. This pattern may be related to the fact that the western part of the area is predominantly mobile or semi-mobile dune, whereas the eastern part is generally more stable. The overall proportions of yellow and 9effectively unbanded’ shells very roughly correspond to those found by Cain & Sheppard (1954) hedgerows and rough herbage. They occupy the range of frequencies expected according to the hypothesis of visual selection by predators. Nevertheless, their precise distributions within the area are not evidently related to local changes of background, nor are the distribution of unbandeds ( sensu stricto ), hyalozonates, whites, white lips or fusions. There may possibly be come correspondence in the case of browns, 00300 and 00345, and it is conceivable that the local distribution of pinks is the result of visual selection by rabbits. A final interpretation must await further detailed studies of other sand-dune populations. (3) Comparison of the two series A comparison of the series collected in 1924 with that collected in 1961 provides no evidence of consistent evolutionary change. There may have been small local changes, which in our data would be indistinguishable from differences due to errors in relocating the sampling areas; but in general the populations seem to have remained stable. There have certainly been no changes comparable to those observed at Berrow, Somerset (Clarke & Murray 1962 a ). This apparent constancy may be related to the fact that the habitat at Bundoran has not greatly altered since 1924. At Berrow, on the other hand, the dunes have gradually become more stable, and larger parts of them have become overgrown with Hippophae . In each case the evolutionary situation seems to reflect the history of the habitat. It will clearly be of great interest to follow future developments at both localities.

Journal ArticleDOI
TL;DR: This flora is interpreted as representing a vegetation of meadow birch woodland influenced by local edaphic conditions of a base rich sandy alluvial environment, which includes important aquatic associations and pioneer associations on sand substrates of different moisture contents.
Abstract: Part I This flora is interpreted as representing a vegetation of meadow birch woodland influenced by local edaphic conditions of a base rich sandy alluvial environment. It includes important aquatic associations and pioneer associations on sand substrates of different moisture contents. A thermophilous component indicating July mean temperature up to 15 $^\circ$ C is anomalous for this general vegetation type today and suggests that the vegetation was also influenced by the factor of delayed immigration of climax species. It is believed that this is due to the floras existence during an early interstadial of the Saalian, following the refrigeration which brought the Holstein to a close. Part II No pollen was obtained, but the plant macrofossils indicate a flora typical of the alluvial environment suggested by the sedimentary context. The vegetation was treeless and was sub-Arctic or even low-Arctic, though the occurrence of Groenlandia densa is anomalous. This plant occurs, however, at other mid-Weichselian sites, to which the Brandon flora shows general similarity.

Journal ArticleDOI
TL;DR: A fauna consisting of both vertebrates and invertebrates is described from an early Saalian deposit at Brandon, Warwickshire, being probably the first to be described from this time horizon.
Abstract: A fauna consisting of both vertebrates and invertebrates is described from an early Saalian deposit at Brandon, Warwickshire. Some 77 taxa, mostly Coleoptera, including 6 not now occurring in Britain, are recorded and though this is a very limited fauna, possibly due to rapidity of deposition, it is interesting as being probably the first to be described from this time horizon. The animal assemblage suggests deposition in a lake or slowly flowing river bordered by reeds and rushes with a Salix thicket on the surrounding ground. A climate cooler than that of today though not of arctic severity is indicated.

Journal ArticleDOI
TL;DR: The structure of the main portion of the axial organ of Arbacia lixula, Diadema antillarum and Paracentrotus lividus is described and Histochemical tests showed the presence of abundant PAS-positive material in the secretion, most of which was acid mucopolysaccharide.
Abstract: The structure of the main portion of the axial organ of Arbacia lixula, Diadema antillarum and Paracentrotus lividus is described. This portion, which lies at the confluence of the perivisceral coelom, water vascular and 'haemal' systems, is pre-eminently glandular. It has an irregular central lumen containing the contractile vessel and a spongy peripheral region permeated by three systems of cavities: the embayments of the central lumen, the lacunae and the canaliculi. The lacunae communicate with the contractile vessel and the canaliculi with the perivisceral coelom. These two systems are closely associated, being separated at the most by an attenuated epithelium which in many areas breaks down, allowing the contents of the lacunae to spill or proliferate into the canaliculi. The predominant histological features of the organ are associated with the production of secretion by the transformation of cells including amoebocytes within the lacunae, and in Diadema and sometimes in Arbacia, with the accumulation of large quantities of pigment. The organ is permeated by connective tissue, unevenly distributed muscle fibres and by varying numbers of amoebocytes. Secretion may be discharged into the lacunae, the central lumen, the canaliculi or directly from the free surface of the organ into the perivisceral coelom. Histochemical tests showed the presence of abundant PAS-positive material in the secretion, most of which is not glycogen, but the amount of glycogen is increased by carbohydrate feeding, after which it appears in the cells lining the canaliculi and some is secreted into the lacunae and canaliculi. Most of the PAS-positive substance proved to be acid mucopolysaccharide. The secretion also showed the reactions of lipid-bound and protein-bound reducing groups, together with other reactions of protein or amino acids and indole derivatives, at least one of which is a 3-indolyl compound, probably tryptophan. Both tyrosine and tryptophan are conspicuous in some amoebocytes. The possible function of some of these compounds is discussed. Tests for enzymes such as tyrosinase and alkaline phosphatase gave no clear indication of their presence. There was no indication of any significant amount of neutral fat or phospholipid. Variable and sometimes impressive amounts of brown and orange to red pigments occur in the axial organ. In Diadema and Arbacia the latter appears to be echinochrome A. The reddish pigment is mostly in the lacunae where it arises from the disintegration of amoebocytes, though in Arbacia it may possibly arise also within other lacunar cells. A possible function of this pigment is discussed. Brown pigment is widely distributed in the axial organ and is frequently associated with amoebocytes. In all three species this pigment proved to be melanin and an iron-containing pigment of nuclear origin. In Diadema, lipofuscin arising from phospholipid is also present. Melanin is liberated into the lacunae by the degeneration of amoebocytes, some of which contain tyrosine but when in the axial organ, appear to possess no active tyrosinase. Part, at least, of the iron-containing pigment can also be traced to amoebocytes.