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Showing papers in "Biological Reviews in 1984"


Journal ArticleDOI
TL;DR: Wild, native fish demonstrate an excellent homing ability, judged from percent return to the home river and straying to non‐native watersheds.
Abstract: Summary (1) Based on data from the literature, the phenomenon of homing in salmonids is examined with special reference to the Atlantic salmon. Wild, native fish demonstrate an excellent homing ability, judged from percent return to the home river (1–3 %) and straying to non-native watersheds (less than 3 % of returning fish). (2) The homing ability in wild fish is shown to be closely related to the existence of reproductively isolated populations between and within watersheds, as demonstrated by data from salmonid ecology and biochemical genetics. (3) Two main hypotheses have dominated the literature on salmonid homing during recent years: (a) An ‘imprinting’ hypothesis based on a process of learning of stream odours during seaward migration, coupled with sun-orientation for open sea navigation, (b) A ‘pheromone’ hypothesis related to odours from fish and based on inheritance and the seasonal migrating schedules of discrete populations. (4) The olfactory sense has been demonstrated as mandatory for salmonids, both in near range and open sea navigation. According to genetic, sensory and ecological aspects of homing, the pheromone hypothesis is therefore concluded to be the most appropriate. (5) Fish produced from artificially fertilized eggs, released within native systems or transplanted, demonstrate a reduced homing ability. Since hatchery-raised fish demonstrate a survival in sea equivalent to that of wild fish, a genetic disturbance of navigational ability has been suggested, resulting from the production of population hybrids by man. (6) Studies made in the fields of behaviour, electrophysiology and chemistry strongly suggest that population-specific fish odours are involved in home-stream recognition by salmonids. (7) An evaluation of ‘imprinting’ experiments related to artificial organic compounds reveals that: (a) the odorant properties of the applied chemicals must be questioned, (b) imprinting related to olfaction may be based on a weak theoretical foundation, (c) returns obtained in census experiments may be adequately explained through ecological interpretations, and (d) behavioural preferences obtained from exposure to non-natural compounds may be founded on mechanisms not associated with homing. (8) A logical link between the use of olfaction and the role of genetics in salmonid homing is emphasized, together with its practical implications for salmonid management.

278 citations


Journal ArticleDOI
TL;DR: Living echinoderms are characterized by an extensive water vascular system developed from the larval left hydrocoel, a complex, multi‐plated endoskeleton with stereom structure, and pentamery.
Abstract: Summary 1. Living echinoderms are characterized by an extensive water vascular system developed from the larval left hydrocoel, a complex, multi-plated endoskeleton with stereom structure, and pentamery. Fossil evidence shows that stereom evolved before pentamery, but both were acquired during the Lower Cambrian. 2. Cladistic analysis of Lower Cambrian genera reveals very few characters in common between carpoids and true echinoderms, and that the split between them was the first fundamental evolutionary dichotomy within the Dexiothetica. 3. Helicoplacoids are stem group echinoderms with spiral plating and three ambulacra arranged radially around a lateral mouth. They are the most primitive echinoderms and the first to show a radial arrangement of the water vascular and ambulacral systems. Unlike later echinoderms, their skeleton shows no dorsal/ventral (aboral/oral) differentiation. They were probably sedentary suspension feeders. 4. Camptostroma is the most primitive known pentaradiate echinoderm and, in our view, possibly a common ancestor of all living groups. It had a short conical dorsal (aboral) surface with imbricate plating, a ridged lateral wall and a slightly domed ventral (oral) surface with five curved ambulacra in a 2-1-2 arrangement inherited from the triradiate pattern of the helicoplacoids. Interambulacral areas bore epispires and the CD interambulacrum contained the anus, hydropore and/or gonopore. All parts of the theca had plates in at least two layers. 5. All other echinoderms belong to one of two monophyletic subphyla, the Pelmatozoa and the Eleutherozoa. 6. Stromatocystites is the earliest known eleutherozoan and differs from Camptostroma in having a test with only one layer of plates and having lost the dorsal elongation. In Stromatocystites the dorsal surface is flat and the plating tesselate. Stromatocystites was an unattached, low-level suspension feeder. 7. The lepidocystoids are the earliest known pelmatozoans. They differ from Camptostroma in having an attached dorsal stalk which retained the primitive imbricate plating, and by developing erect feeding structures along the ambulacra. In Kinzercystis, the ambulacra are confined to the thecal surface and erect, biserial brachioles arise alternately on either side. Lepidocystis has a similar arrangement except that, the distal part of each ambulacrum extends beyond the edge of the theca as a free arm. 8. Pelmatozoans diverged more or less immediately into crinoids, with multiple free arms composed of uniserial plates, and cystoids sensu lato, which retained brachioles. Gogia (Lower to Middle Cambrian) is the most primitive known cystoid and differs from Kinzercystis principally in having all plating tesselate, while Echmatocrinus (Middle Cambrian) is the most primitive known crinoid and differs from Lepidocystis in lacking brachioles and in having more than five free arms with uniserial plates. 9. Post Lower Cambrian differentiation of pelmatozoan groups proceeded rapidly, exploiting the primitive suspension-feeding mode of life. Maximum morphological diversity was reached in the Ordovician, but thereafter crinoids progressively displaced cystoid groups and reached their peak diversity during the Carboniferous. The eleutherozoans were slower to diversify, but by the Arenig the earliest ‘sea-stars’ (in reality, advanced members of the eleutherozoan stem group) had reversed their living orientation and had begun to exploit a deposit-feeding mode of life. These in turn led to the ophiuroids, echinoids and holothuroids. 10. The basic echinoderm ambulacrum was already present in the helicoplacoids. It had biserial, alternate flooring plates and complexly plated sheets of cover plates on either side. The radial water vessel lay in the floor of the ambulacrum, external to the body cavity, and gave rise ventrally to short, lateral branches (fore-runners of tube feet) that were used to open the cover plate sheets, and dorsally was connected to internal compensation sacs which acted as fluid reservoirs (and were preadapted for a role in gaseous exchange). Plating on the cover plate sheets was organized and reflected the positions of the lateral branches from the radial water vessel. In Camptostroma, the cover plate sheets had biserially aligned rows of cover plates associated with the lateral branches. 11. Brachioles arose by extension of the lateral branches of the radial water vessel and associated serially aligned cover plates found in Camptostroma. They bear a single alternate series of cover plates. In Lepidocystis the ambulacra extended beyond the edge of the oral surface as true arms. Brachial plates of arms are homologues of primary ambulacral flooring plates, and arms bear multiple series of cover plates. Uniserial ambulacral plating is a derived condition and evolved independently in crinoids, paracrinoids and isorophid edrioasteroids. Pinnules in crinoids arose independently in inadunates and camerates by a progressively more unequal branching of the arms. Thus all parts of the subvective system in crinoids are internally homologous, whereas in cystoids, brachioles and arms (or ambulacra) are not homologous structures. 12. The position of the hydropore is the best reference point in orientating echinoderms. Carpenter's system of identifying ambulacra by letters, arranged clock-wise in oral view with the A ambulacrum opposite the hydropore, is consistent in all echinoderm classes. In all Lower Cambrian pentaradiate echinoderms the anus, gonopore and hydropore lie in the CD interambulacrum and this is accepted as the primitive arrangement. In helicoplacoids we tentatively suggest that the A ambulacrum spiralled down from the mouth while the two ambulacra that spiralled up represent the B + C and D + E ambulacra combined. 13. The pelmatozoan stem arose from a polyplated stalk, via a meric stem to a true column with holomeric (single piece) columnals. This happened independently in the crinoids and the cystoids. 14. Our analysis of echinoderm phylogeny leads us to recommend the following changes to the higher level classification of echinoderms: The phylum Echinodermata includes only those groups with radial symmetry superimposed upon a fundamental larval asymmetry. It has a stem group that contains the triradiate helicoplacoids and a crown group to which all other (pentaradiate) echinoderms belong. The crown group contains two monophyletic subphyla, the Pelmatozoa and the Eleutherozoa, and the Pelmatozoa contains two superclasses, the Crinoidea which are extant and the Cystoidea, which are extinct.

240 citations


Journal ArticleDOI
TL;DR: There exist two broad mating patterns in the fiddler crabs, which most western and Indo‐Pacific species mate on the surface of intertidal substrates near burrows females defend and males of many American species court from and defend burrows to which females come for mating.
Abstract: Summary 1. General accounts of the natural history and behaviour of fiddler crabs suggest there exist two broad mating patterns in the genus. Most western and Indo-Pacific species mate on the surface of intertidal substrates near burrows females defend. The sexes associate only briefly during courtship and mating. In contrast, males of many American species court from and defend burrows to which females come for mating. Copulation occurs underground in burrows plugged at the surface; the sexes usually remain together for at least several hours. Here we summarize and contrast recent detailed field studies of the mating systems of U. pugilator, an American species, and U. vocans, a species widely distributed in the western and Indo-Pacific. We indicate how differences in the breeding ecology of these two species may account for basic differences in modes of sexual selection leading to the two broad mating patterns in the genus. 2. U. pugilator burrows in protected sandy substrates in the upper intertidal and supratidal zone. During ebb tide, nonbreeding crabs leave burrows they occupy during high tide to forage on food-rich substrates in the lower intertidal zone. Reproductively active males remain in the burrow zone where they fight for and defend burrows from which they court. Large males win most fights for burrows and tend to defend burrows high on the elevation gradient, especially during periods with relatively high tides. Females usually approach and descend the burrows of several males before choosing their mates by remaining in males' burrows. Males remain underground with their mates for 1–3 days until after they oviposit their eggs. Some males then emerge and leave their burrows while others sequester their mates in the chambers where mating and oviposition has occurred, dig new chambers and resume courtship, perhaps attracting additional females. In either case, females remain underground for approximately 2 weeks, finally emerging to release their planktonic larvae. Burrows that do not collapse due to tidal inundation or flooding by groundwater are best for breeding and usually are located relatively high on the elevation gradient. Females choose mates indirectly by preferring to breed in burrows that will remain intact while they oviposit and incubate their eggs. Large males mate more often than small males because they are better able to defend burrows at locations females prefer to breed. The mating system of U. pugilator may be classified as resource-defence polygyny. 3. U. vocans burrows in open muddy substrates in the mid- to lower intertidal zone. At a site near Chunda Bay, Australia, where the reproductive behaviour of this species has been studied in depth, both sexes feed near burrows they defend. Females tend to occupy their burrows for longer periods and move shorter distances than do males. Mating occurs on the surface near the burrows that females defend. Females accept both resident and wandering males as mates. They show no preference for mating with larger males. Female choice may be based on other male morphological or behavioural characteristics. Females oviposit their eggs either while on the surface or in their burrows. They produce relatively small clutches and are active on the surface throughout their breeding periods. Males fight both their neighbours and wandering males. Large males tend to win fights and defend burrows in areas where large females, which produce relatively many eggs, are most dense. Such areas may offer greater protection from predators than areas occupied by smaller females. Small males mate about as often as large males but may father fewer larvae. The mating system of U. vocans is resource-free and promiscuous. 4. The mating systems of U. pugilator and U. vocans differ fundamentally in that female U. pugilator require access to a specific microenvironment to breed successfully, while female U. vocans do not. We suggest this difference occurs because of contrasts in clutch sizes and the mobility and movement patterns of feeding females. Female U. pugilator produce relatively large clutches and probably experience more intense selection from factors that can cause egg loss and mortality than do U. oocans, which produce clutches of sufficiently small volume to be protected by their abdominal flaps. Hence, the range of suitable breeding environments for U. pugilator is small compared to that for U. vocans. In addition, U. pugilator burrows in areas that are relatively food-poor, leading to daily migrations to and from food-rich substrates in the lower intertidal zone, preventing female defence of an area suitable for both breeding and feeding. U. vocans, however, burrows in areas sufficiently rich to support feeding, leading to relatively low female mobility and defence of burrows that are also suitable breeding sites. 5. Adaptive radiation of the genus Uca in the Americas is manifest by trends toward smaller adult size, higher population densities, more frequent microgeographic sympatry and increased terrestriality, compared to species in the western and Indo-Pacific regions. We outline the general features of the selection mechanisms tying each of these trends to the evolution of resource—defence mating systems. Intraspecific variation in the courtship behaviour and site of mating in U. lactea and U. vocans supports our contention that resourse—defence behaviour tends to occur at high population densities. Additional data are needed to evaluate the other hypotheses critically.

238 citations


Journal ArticleDOI
TL;DR: The Random Placement Hypothesis was the first of these and is the simplest, proposing that nothing other than a random placement of species and individuals over area is occurring, and must be tested and rejected before any other hypothesis can be considered viable.
Abstract: Summary 1. The species-area curve has been studied now for more than one hundred years. In this time four hypotheses have been proposed to account for this pattern - the Random Placement (or Passive Sampling) Hypothesis, the Habitat Diversity Hypothesis, the Equilibrium Theory (or Area Per Se Hypothesis), and the Disturbance Hypothesis. The Random Placement Hypothesis was the first of these and is the simplest, proposing that nothing other than a random placement of species and individuals over area is occurring. This should be considered the Null Hypothesis for species-area studies and must be tested and rejected before any other hypothesis can be considered viable. 2. The Habitat Diversity Hypothesis explains the species-area curve via the addition of new habitats with increasing area. It is supposed to result in a Power Function curve. It has been invoked a number of times but has not yet been shown experimentally to give rise to a species-area curve. 3. The Equilibrium Theory proposes that species become extinct faster on small islands as a result of the lower population sizes on such islands. This is probably the hypothesis most frequently invoked to account for the species–area curve. It is also said to result in a species-area curve of the Power Function form. Many of the tests of this hypothesis have, however, been inadequate and on only two occasions has the null hypothesis been tested. 4. The Disturbance Hypothesis also proposes that species become extinct faster on small islands, but in this case it is supposed to occur because disturbances are more frequent and more intense on these islands. This hypothesis has only rarely been considered yet it is consistent with many of the observations used to support the Equilibrium Theory. Furthermore, it has been shown experimentally, in one situation at least, to give rise to a species-area curve. 5. Two methods exist by which the null hypothesis of Random Placement can be tested. One is based on probability calculations; the other on sampling in the field. Both methods have been successfully used to test the null hypothesis, and to demonstrate biologically interesting and meaningful patterns. 6. The existence of a Power Function curve has been taken to indicate that the Equilibrium Theory is correct. Likewise, an Exponential curve has been taken by some as indicating that Random Placement is occurring. These views can be shown, theoretically and empirically, to be invalid. The fitting of a particular type of curve does not test any of the hypotheses described. 7. Species-area curves can be meaningfully used to measure the relative species diversity of a community, and biologically interesting patterns can be found by comparing communities in this way. 8. More intensive studies, testing the null hypothesis and performing manipulative experiments, are necessary if the processes underlying the species–area curve are to be understood.

237 citations


Journal ArticleDOI
TL;DR: LH is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre‐pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle.
Abstract: Summary (1) Luteinizing hormone (LH) is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre-pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle. Secretion is probably also pulsatile during the preovulatory surge of LH. (2) The secretion of LH is affected by the ovarian steroids, oestradiol and progesterone, both of which act principally to reduce the frequency of the pulses. During the luteal phase the two steroids act synergistically to exert this effect, and during anoestrus oestradiol acts independently of progesterone. Androstenedione secreted by the ovary apparently has no role in the control of LH secretion. (3) The amplitude of the pulses may also be affected by the steroids but there are conflicting reports on these effects, some showing that amplitude is lowered by the presence of oestrogen and others showing increases in amplitude in the presence of oestrogen and progesterone. (4) The secretion of LH pulses is affected by photoperiod, social environment and nutrition. Under the influence of decreasing day-length, oestradiol alone cannot reduce the frequency of pulses and the ewe experiences oestrous cycles. When day-length is increasing, the hypothalamus becomes more responsive to oestradiol which reduces the frequency of the pulses. (5) A hypothetical pheromone secreted by rams can increase the frequency of the LH pulses in anoestrous ewes and thereby induce ovulation, possibly by inhibiting the negative feedback exerted by oestradiol. (6) The relationships between nutrition and reproduction are poorly understood, but it seems likely that the effects of nutrition are mediated partly through the hypothalamus and its control of the secretion of LH pulses. (7) The pulses of LH secreted by the anterior pituitary gland are evoked by pulses of GnRH secreted by the hypothalamus. The location of the centre controlling the GnRH pulses and the neurotransmitter involved are not known.

231 citations


Journal ArticleDOI
TL;DR: It is proposed that the incorporation of a unique parasitic stage in the life‐cycle of unionaceans which involves an obligate relationship between a vertebrate host, usually a fish, and a highly modified larval stage, the glochidium, has had far‐reaching consequences with respect to overall morphology, extent of species' geographic ranges, and rate of speciation in the group.
Abstract: Summary It is proposed that the incorporation of a unique parasitic stage in the life-cycle of unionaceans which involves an obligate relationship between a vertebrate host, usually a fish, and a highly modified larval stage, the glochidium, has had far-reaching consequences with respect to overall morphology, extent of species' geographic ranges, and rate of speciation in the group. Glochidia are separable into three main types with respect to overall shape and attachment features, and are retained in variously modified brood pouches. When mature, glochidia are released in several different ways which reflect various adaptations involved in either attracting the fish host and/or increasing the probability of attachment. Glochidia do not seem capable of host selection, and the reaction of the host to the parasite seems to be the main factor in determining specificity. Release of glochidia is synchronized to correspond to periods of predictable host availability, such as during spawing migrations and nesting behaviour. Other adaptations include modifications of glochidial conglutinates to mimic host food items, and modifications of the unionacean mantle edges to attract hosts. In all cases, a good correlation exists between the type of lure used and host food preferences, but, despite these adaptations, host specificity among unionaceans seems low. Parasitism among unionaceans is postulated to be mainly advantageous in terms of predictability of dispersal by habitat-specific hosts, but parasitism is hypothesized to entail constraints in terms of the degree to which shell shape and life-habit can be diversified among unionaceans. The type of host parasitized is considered to affect the rate of diversification among populations and speciation among unionaceans: those that parasitize strictly freshwater hosts are more likely to exhibit highly individualistic populations in different drainages with respect to molecular genetic and soft-part characters, while those that parasitize anadromous or saltwater-tolerant hosts show little differentiation among widely distributed populations.

186 citations


Journal ArticleDOI
TL;DR: The focus of the review was on the evidence that supports or fails to support the importance of certain hydrolytic enzymes to the mammalian sperm acrosome reaction.
Abstract: Summary The mammalian sperm acrosome reaction is a unique form of exocytosis, which includes the loss of the involved membranes. Other laboratories have suggested the involvement of hydrolytic enzymes in somatic cell exocytosis and membrane fusion, and in the invertebrate sperm acrosome reaction, but there is no general agreement on such an involvement. Although reference was made to such work in this review, the focus of the review was on the evidence (summarized below) that supports or fails to support the importance of certain hydrolytic enzymes to the mammalian sperm acrosome reaction. Because the events of capacitation, the prerequisite for the mammalian acrosome reaction, and of the acrosome reaction itself are not fully understood or identified, it is not yet always possible to determine whether the role of a particular enzyme is in a very late step of capacitation or part of the acrosome reaction. (1) The results of studies utilizing inhibitors of trypsin-like enzymes suggest that such an enzyme has a role in the membrane events of the golden hamster sperm acrosome reaction. The enzyme involved may be acrosin, but it is possible that some as yet unidentified trypsin-like enzyme on the sperm surface may play a role in addition to or instead of acrosin. Results obtained by others with guinea pig, ram and mouse spermatozoa suggest that a trypsin-like enzyme is not involved in the membrane events of the acrosome reaction, but only in the loss of acrosomal matrix. Such results, which conflict with those of the hamster study, may have been due to species differences or the presence of fusion-promoting phospholipase-A or lipids contaminating the incubation media components, and in one case to the possibly damaging effects of the high level of calcium ionophore used. The role of the trypsin-like enzyme in the membrane events of the hamster sperm acrosome reaction may be to activate a putative prophospholipase and/or to hydrolyse an outer acrosomal or plasma membrane protein, thus promoting fusion. A possible role of the enzyme in the vesiculation step rather than the fusion step of the acrosome reaction cannot be ruled out at present. (2) Experiments utilizing inhibitors of phospholipase-A2, as well as the fusogenic lysophospholipid and cis-unsaturated fatty acid hydrolysis products that would result from such enzyme activity, suggests that a sperm phospholipase-A2 is involved in the golden hamster sperm acrosome reaction. Inhibitor and LPC addition studies in guinea pig spermatozoa have led others to the same conclusion. The fact that partially purified serum albumin is important in so many capacitation media may be explained by its contamination with phospholipase-A and/or phospholipids. Serum albumin may also play a role, at least in part, by its removal of inhibitory products released by the action of phospholipase-A2 in the membrane. The demonstration of phospholipase-A2 activity associated with the acrosome reaction vesicles and/or the soluble component of the acrosome of hamster spermatozoa, and the fact that exogenous phospholipase A2 can stimulate acrosome reactions in hamster and guinea pig spermatozoa, also support a role for the sperm enzyme. The actual site or the sites of the enzyme in the sperm head are not yet known. The enzyme may be on the plasma membrane as well as, or instead of, in the acrosomal membranes or matrix. A substrate for the phospholipase may be phosphatidylcholine produced by phospholipid methylation. It is possible that more than one type of ‘fusogen’ is released by phospholipase activity (LPC and/or cis-unsaturated fatty acids, which have different roles in membrane fusion and/or vesiculation. In addition to acting as a potential ‘fusogen’, arachidonic acid released by sperm phospholipase-A2 probably serves as precursor for cyclo-oxygenase or lipoxygenase pathway metabolites, such as prostaglandins and HETES, which might also play a role in the acrosome reaction. Although much evidence points to a role for phospholipase-A2, phospholipase-C found in spermatozoa could also have a role in the acrosome reaction, perhaps by stimulating events leading to calcium gating, as suggested for this enzyme in somatic secretory cells. (3) A Mg2+-ATPase H+-pump is present in the acrosome of the golden hamster spermatozoon. Inhibition of this pump by certain inhibitors of ATPases (but not by those that only inhibit mitochondrial function) leads to an acrosome reaction only in capacitated spermatozoa and only in the presence of external K+. The enzyme is also inhibited by low levels of calcium, and such inhibition, combined with increased outer membrane permeability to H+ and K+, and possibly plasma membrane permeability to H+ (perhaps by the formation of channels), may be part of capacitation and/or the acrosome reaction. The pH of the hamster sperm acrosome has been shown to become more alkaline during capacitation, and such a change may result in the activation of hydrolytic enzymes in the acrosome or perhaps in a change in membrane permeability to Ca2+. A similar Mg2+-ATPase has not been found in isolated boar sperm head membranes. However, that conflicting result could have been due to the use of noncapacitated boar spermatozoa for the preparation of the membranes or to protease modification of the boar sperm enzyme during assay. (4) Inhibition of Na+, K+-ATPase inhibits the acrosome reaction of golden hamster spermatozoa, and the activity of this enzyme increases relatively early during capacitation. A late influx of K+ is important for the acrosome reaction. However, this late influx may not be due to Na+, K+-ATPase, but instead may be due to a K+ permeability increase (possibly via newly formed channels) in the membranes during capacitation. It is suggested in this review that Na+, K+-ATPase has a role early in capacitation rather than directly in the acrosome reaction (although such a role cannot yet be completely ruled out). One possible role for the enzyme in capacitation might be to stimulate glycolysis (which appears to be essential for capacitation and/or the acrosome reaction of hamster and mouse spermatozoa). The function of the influx of K+ just before the acrosome reaction is probably to stimulate, directly or indirectly, the H+-efflux required for the increase in intraacrosomal pH occurring during capacitation. Direct stimulation of the acrosome reaction by a change in membrane potential resulting directly from K+-influx is not a likely explanation for the hamster results. However, the importance of an earlier membrane potential change, due to increased Na+, K+-ATPase during capacitation, and/or of later membrane potential changes resulting from the pH change, cannot be ruled out. Although K+ is required for the hamster acrosome reaction, other workers have reported that K+ inhibits guinea pig sperm capacitation. However, the experimental procedures used in the guinea pig sperm studies raise some questions about the interpretation of those inhibition results. (5) Ca2+-influx is known to be required for the acrosome reaction. Others have suggested that increased Ca2+-influx due to inhibition or stimulation of sperm membrane calcium transport ATPases are involved in the acrosome reaction. There is as yet no direct or indirect biochemical evidence that inhibition or stimulation of such enzymatic activity is involved in the acrosome reaction, and further studies are needed on those questions. (6) I suggest that the hydrolytic enzymes important to the hamster sperm acrosome reaction will also prove important for the acrosome reaction of all other eutherian mammals.

178 citations


Journal ArticleDOI
TL;DR: Catch connective tissue is defined as the collagenous connectives tissue whose mechanical properties can be changed rapidly (in seconds or minutes) under nervous control.
Abstract: Summary (1) Catch connective tissue is defined as the collagenous connective tissue whose mechanical properties can be changed rapidly (in seconds or minutes) under nervous control. (2) Catch connective tissues are found in all five classes of Echinodermata. They function in tone control of the tissues and in autotomy. (3) The change in mechanical properties occurs in viscosity. (4) Muscle cells are not responsible for the viscosity change. (5) The viscosity change is controlled by nervous activities. Neurosecretory-like cells with large electron-dense granules are found in all the catch connective tissues so far studied. (6) The viscosity change is quite likely caused by the change in the ionic environment in the connective tissues, which alters the weak (non-covalent) interactions between extracellular macromolecules in the tissue.

158 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the selection and diel movements between microhabitats are related to diel changes in micrometeorological profiles and predation, feeding, and enhancement of sexual communication.
Abstract: Summary 1. Cockroaches are ubiquitous in most habitats where insects occur. Although most reports on cockroaches are physiological in nature, sufficient information is available to indicate that forest, desert, and cave-dwelling cockroaches select microhabitats on the basis of finely resolved environmental preferences. This is particularly true for oviparous females which select specific substrates for oviposition and embryogenesis. Selection and diel movements between microhabitats are related to diel changes in micrometeorological profiles and predation, feeding, and enhancement of sexual communication. 2. With some exceptions oviparous species live in wooded habitats; ovoviviparous species tend to occur in protected environments such as caves and logs. Oviparous species are exposed to greater predation, parasitism, and environmental pressures during embryogenesis than are ovoviviparous species, where internal incubation and some parental care reduce these risks. Most ovoviviparous species produce larger clutches, but the interval between broods is significantly longer than in oviparous species. Long gestation, clumping of food resources, and relatively little movement probably selected for male control of resources as a mate-attraction tactic in ovoviviparous species; agonistic interactions, and in some cases morphological specializations for fighting, and highly ritualized behaviours are common. In most oviparous species, volatile pheromone communication and resource-based aggregations are common. Rapid ovarian cycles and patchily distributed nutritional resources result in the need for greater mobility, and hence adults encounter greater risks.

138 citations


Journal ArticleDOI
TL;DR: Atavism can be produced by experimental manipulation within developing systems ‐increased growth of the chick fibula, enamel production from avian ectoderm, and balancer formation in amphibians.
Abstract: Summary 1. Atavisms emerge as evidence of localized modifications in development of an organ or of one of its parts. Different developmental processes can be triggered within the same organ rudiment, presumably in response to the same stimulus. We saw that that stimulus can have a genetic basis in a mutational event, which can be selected for. We also saw that atavism can be produced by experimental manipulation within developing systems -increased growth of the chick fibula, enamel production from avian ectoderm, and balancer formation in amphibians. Such atavisms are not based on heritable genetic changes. They indicate the developmental plasticity that exists within embryos and the relative ease with which development can be switched from one programme to another. 2. Examination of mutants (wingless chicks), limbless vertebrates and experimental manipulation of embryos, shows that cell death, inductive tissue interactions and altered patterns of growth are developmental mechanisms used in the formation of atavisms. 3. Differential development mechanisms can be triggered within the same organ at the same time to produce atavisms. In the guinea pig, formation of atavistic digit V involves prolongation of growth of metatarsal V whereas formation of atavistic digit I involves development of a new metatarsal I. 4. Secondary functional modifications ensure that the atavism is integrated with the other components of the functional unit, as illustrated by extra digits in horses or guinea pigs and fibulae in birds. Atavistic 2nd and 4th digits in horses arise by continued growth of their primordia. A consequent reduction in the growth rate of digit 3, the normal single functional digit, enables all three digits to attain approximately equal lengths and so potentially to function. The altered functional load transmitted to the limbs results in secondary but correlated alterations in muscles and skeletal elements in other portions of the limbs. The fact that embryonic digit 2 normally develops to a more advanced state than digit 4 explains why digit 2 more often develops atavistically, for if variation in growth rate is the basis for the atavistic digit, digit 2 has an advantage over digit 4. 5. Atavisms should not be an embarrassment to the evolutionary biologist. They are the outward and visible sign of a hidden potential for morphology change possessed by all organisms. Neither basic capacity to form the organ nor patterning information is lost. Modification of components of inductive tissue interactions helps to explain how organs are lost during evolution (also see Regal, 1977); retention of the basic mechanism explains how structures can be revived as atavisms (also see Rachootin & Thomson, 1981). Frequency of atavisms thus provides an indication of the degree of modification or loss of the underlying developmental programme.

126 citations


Journal ArticleDOI
TL;DR: In this paper, the authors propose a method to solve the problem of the problem: this paper...,.. ].. ).. ]... )...
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Journal ArticleDOI
TL;DR: Polyhedral bodies are present in several groups of autotrophic bacteria that assimilate inorganic carbon via the Calvin cycle, including members of the colourless sulphur‐ oxidizing bacteria, ammonia‐ and nitrite‐oxidizing bacteria and all cyanobacteria (blue‐green algae) examined.
Abstract: Summary 1. Polyhedral bodies are present in several groups of autotrophic bacteria that assimilate inorganic carbon via the Calvin cycle, including members of the colourless sulphur- oxidizing bacteria, ammonia- and nitrite-oxidizing bacteria and all cyanobacteria (blue-green algae) examined. Other groups of Calvin-cycle bacteria lack the inclusions, which have not been found in the purple photosynthetic bacteria, or in the hydrogen bacteria, with one exception in each case. Polyhedral bodies also occur in the chlorophyll b-containing photosynthetic symbiotic prokaryote, Prochloron, and in several cyanelles. The inclusion bodies have not been found in prokaryotes that cannot fix carbon dioxide via the Calvin cycle, or in eukaryotes. 2. Polyhedral bodies have been isolated from a colourless sulphur bacterium (Thiobacillus neapolitanus), two nitrifying bacteria (Nitrobacter agilis and Nitrosomonas sp.) and two cyanobacteria (Anabaena cylindrica and Chlorogloeopsis fritschii). Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the carbon dioxide-fixing enzyme of the Calvin cycle, has been found in the polyhedral bodies in each case, confirming that these inclusions in autotrophic bacteria be re-termed carboxysomes. 3. Knowledge of carboxysome composition has been constrained by difficulties in carboxysome isolation, although effective methods, including cell disruption in low-ionic-strength buffers followed by density-gradient centrifugation through silicon polymers, or sucrose, followed be preparative agarose electrophoresis, are now available. 4. Analysis of isolated T. neapolitanus, N. agilis and C. fritschii carboxysomes by dissociating sodium dodecyl sulphate-polyacrylamide gel electrophoresis has revealed the presence of 7–15 polypeptides, the most abundant being the large and small subunits of RuBisCO. Two polypeptides of the T. neapolitanus carboxysomes have been ascribed to the carboxysome membrane (shell), although the identity of other polypeptides is unknown. 5. DNA of unknown function has been reported in carboxysomes isolated from two Nitrobacter species and may be present in the organelles from T. neapolitanus. 6. RuBisCO occurs in both the carboxysomes and in soluble form in the cytoplasm of carboxysome-containing bacteria. Structural, kinetic, regulatory and immunological comparisons have demonstrated full or near identity between the cytoplasmic and carboxysomal forms of the enzyme. As with RuBisCO from chloroplasts and from almost all non-carboxysome-containing bacteria, the cytoplasmic and carboxysomal RuBisCOs each consist of eight large plus eight small subunits. All RuBisCOs are bifunctional enzymes, oxygen acting as a competitive inhibitor of carboxylation, and carbon dioxide acting competitively to inhibit the apparently wasteful oxygenase reaction. Carbon dioxide and oxygen fixation occur at the same site on the large subunit. Despite extensive study, the function of the small subunits is unknown. All RuBisCOs can exist in an inactive and active form, activation proceeding by an ordered reversible binding of carbon dioxide, followed by a divalent metal cation, to the large subunit, at sites distinct from the catalytic site. Identity of the activation and catalytic sites at lysine residues 201 and 175, respectively, on the RuBisCO large subunit in organisms as phylogenetically diverse as spinach and Rhodospirillum rubrum suggests a uniform mechanism of RuBisCO regulation throughout the Calvin cycle autotrophs. 7. Carboxysome function is unknown, although several possibilities exist. A role for the organelles in autotrophy has been assumed and studies on carboxysome function have centred on relations between the organelles and RuBisCO. Carboxysomes may serve as active sites of carbon dioxide fixation, act as CO2-concentrating compartments for RuBisCO, protect RuBisCO from adverse effects such as inhibition by oxygen and degradation by proteases, and/or act as general protein-storage bodies. Evidence and argument for and against each of these possibilities is presented from whole-cell and enzyme studies with sulphur bacteria and cyanobacteria, including specialist and nutritionally versatile strains. 8. The need for further knowledge of carboxysome composition, particularly including the structure and properties of the protein shell, to permit further understanding of carboxysome function is emphasized.

Journal ArticleDOI
TL;DR: A number of experimental approaches can be usefully employed to identify the molecular details of the events that occur in the mechanism of action of a‐adrenergic agonists in liver tissue.
Abstract: Summary 1. Although the mechanism of action of a-adrenergic agonists in liver tissue is somewhat complex, a number of experimental approaches can be usefully employed to identify the molecular details of the events that occur. 2. Receptors specific for α1-adrenergic agonists located on the plasma membranes of rat liver cells have been partially characterized using pharmacological agents, affinity labels and monoclonal antibodies. Much of this work has employed isolated plasma membrane fractions and does not take account of tissue-related factors which may now be studied in the intact perfused rat liver, following the development of an appropriate assay system. 3. Because a redistribution of cellular Ca2+ is central to the mechanism of action of a-adrenergic agonists in liver, it is important to first gain an understanding of basic cellular Ca2+ regulation. Knowledge about the compartmentation of cellular calcium and about Ca2+-translocation systems located in the mitochondria, plasma membrane and endoplasmic reticulum is now quite extensive. However, the role of mitochondria in the regulation of intracellular Ca2+ is still unclear; it now appears that the mitochondrial calcium content is much less than considered previously. This may have important implications for such a regulatory role. 4. The sequence of Ca2+ movements that may occur when a-adrenergic agonists interact with liver have been identified and are as follows: (a) Ca2+ is mobilized from an intracellular pool(s) (mitochondria plus endoplasmic reticulum and/or plasma membranes). (b) This elevates the cytoplasmic free Ca2+ concentration and leads to an efflux of the ion from the cell. (c) At this time, Ca2+-sensitive metabolic events in the cytoplasm are activated and an increase in Ca2+-cycling occurs across the plasma membrane. (d) Immediately after the hormone is withdrawn, there is a net influx of Ca2+ into the cell, and the intracellular Ca2+ pools and transmembrane fluxes are restored to the pre-induced states. In this model, Ca2+ movements across the plasma membrane play a key role in regulating the cytoplasmic Ca2+ concentration. 5. In the perfused rat liver it has been possible to define in quite precise terms the amounts and rates of Ca2+ mobilized in each of these stages. 6. Although several proposals for ‘second messengers’ to link the hormone-receptor interaction with initial Ca2+ mobilization have been made, at this time only polyphosphoinositide turnover appears to be a suitable candidate.

Journal ArticleDOI
TL;DR: The energy required for sustained physical activity in flying and running birds is obtained from fatty acids mobilized from adipose stores under the influence of hormones.
Abstract: Summary 1. The energy required for sustained physical activity in flying and running birds is obtained from fatty acids mobilized from adipose stores under the influence of hormones. There is some evidence that glucagon, insulin and growth hormone may be involved in this process. 2. Energy expenditure can increase up to 14 times and 12 times resting values in flying and running birds, respectively. Energy expenditure varies only slightly over the normal range of flight speeds in individual species, but in running birds there is a linear correlation between oxygen consumption and speed. The slope of this relationship is an inverse function of body weight and indicates the energy cost of transport in ml O2.kg-1.m-1. 3. Increased oxygen demands by the working muscles are met by increased ventilation and circulation. Increased oxygen delivery by the blood is achieved by rises in cardiac output and oxygen extraction. Cardiac stroke volume changes relatively little and the increased cardiac output results mainly from an increase in heart rate. Regional blood distribution during exercise may be determined not only by the demands of the locomotory muscles but also by the need to increase heat loss from the skin and respiratory tract. 4. Ventilatory movements during flight are frequently synchronized in a I:I fashion with wing movements. Increased ventilation during flight and running may be stimulated, not only by the need for increased gas exchange, but also in order to raise heat loss by respiratory evaporation. Thermal hyperventilation carries a risk of CO, washout from the lungs and consequent blood alkalosis. The risk is minimized in some species by appropriate alterations in the rate and depth of breathing, which help to confine excess ventilation to the respiratory dead space. 5. Metabolic heat produced during exercise is either lost from the respiratory linings and the skin, or stored by the body with a resultant rise in body temperature. Changes in peripheral blood perfusion and active regulation of the feathers may assist cutaneous heat loss. Respiratory evaporation usually accounts for less than 30% of the total heat loss, even at high air temperatures, and becomes progressively less efficient at higher exercise intensities. At high air temperatures and high exercise intensities, most of the metabolic heat is stored, and exercise duration is limited as the body temperature approaches the upper lethal limit.

Journal ArticleDOI
TL;DR: The bulk of either the phenolic or terpenoid regulators are localized within the vacuole, they can also be found within other cellular compartments where they may act upon metabolic pathways, modifying either cell multiplication or elongation.
Abstract: Summary 1. Plants contain growth regulators that are non-hormonal in nature. These regulators change in concentration during ontogeny and when applied exogenously, can either stimulate or depress growth. While the bulk of either the phenolic or terpenoid regulators are localized within the vacuole, they can also be found within other cellular compartments where they may act upon metabolic pathways, modifying either cell multiplication or elongation. 2. Non-hormonal growth regulators may affect the synthesis and/or destruction of phytohormones, mainly indole-3-acetic acid (IAA). These regulators behave non-specifically, modifying the actions of auxins, gibberellins and cytokinins upon growth. 3. A variety of both uncertainties and unresolved contradictions exist that have prevented a thorough elucidation of the mechanisms of actions of both phenolic and terpenoid regulators. These uncertainties and unresolved contradictions include lack of data regarding compartmentalization of many of the inhibitors. This raises the question of whether their intracellular concentrations become elevated sufficiently to affect metabolic pathways in vivo. Exogenously applied regulators of non-hormonal nature usually interfere with growth only at high concentrations. Therefore, the possibility cannot be excluded that under these conditions, reactions occur within the cell that are absent in vivo. 4. The specific properties of natural non-hormonal regulators are similar in certain respects to phytohormones. For example, both of them may be biogenetically bound within metabolic centres: shikimate (phenolics, indoles, alkaloids), bi-benzi (coumarins) or acetate-mevalonate (terpenoids, fluorens, sesquiterpenes, cytokinins). In addition, both non-hormonal regulators and phytohormones exhibit biological activity in growth bioassays. 5. Non-hormonal regulators may possess a number of useful purposes, e.g. test substances such as fusicoccin permit the investigation of the mode of action of phytohormones, specific inhibitors blocking special forms of growth and protectors of phytohormone activity in culture.