Showing papers in "Integrative and Comparative Biology in 1983"

Morphology, Performance and Fitness

Abstract: Synopsis. Selection can be measured in natural populations by the changes it causes in the means, variances and covariances of phenotypic characters. Furthermore the force of selection can be measured in conventional statistical terms that also play a key role in theoreticai equations for evolutionary change. The problem of measuring selection on morphological traits is simplified by breaking the task into two parts: measurement of the effects of morphological variation on performance and measurement of the effects of performance on fitness. The first part can be pursued in the laboratory but the second part is best accomplished in the field. The approach is illustrated with a hypothetical analysis of selection acting on the complex trophic morphology of snakes.

Interpreting Geographic Variation in Life-History Traits

Abstract: The geographic variation in the length of the larval period and the size at metamorphosis of the wood frog, Rana sylvatica, is examined for populations in the tundra of Canada, the mountains of Virginia, and the lowlands of Maryland. We argue that the observed differences in developmental plasticity, heriisbilities and genetic covariances of traits among localities result from differential selection pressures in each environment, and are related to the physiological constraints inherent in development and to the degree of compromise between the timing and size at metamorphosis allowed in each environment. In Maryland populations fitness has been maximized by evolutionary changes in size alone; body size in this population is canalized, has low heritability and is highly correlated with juvenile survival relative to developmental time. In Canada, minimum developmental time yields maximum fitness; the length of the larval period in this population is canalized and genetically monomorphic relative to body size. In contrast, fitness in the Virginia populations has been determined by correlated and pleiotropic effects of genes on both developmental time and larval body size, and both traits are equally canalized, affect juvenile survivorship equally and display moderate heritabilities. These results stress the importance of interpreting variation in life-history traits relative to constraints inherent in development and those imposed by the environment. Heritability and survivorship data support the general notion that fitness traits should have low levels of additive genetic variation, but also suggest that antagonistic pleiotropy may act to preserve genetic variation in fitness traits under simultaneous selection, and caution against inferring evolutionary importance of individual traits without considering the possible presence of pleiotropy .

Alternative Concepts of Reproductive Effort, Costs of Reproduction, and Selection in Life-History Evolution

Abstract: An outline for an organismic theory of reproductive tactics is presented to develop the demographic theory of optimal reproductive tactics into a more realistic theory of life-history evolution. Reproductive effort—denned as the proportion of resources invested in reproduction—and the costs in somatic investment do not automatically result in survival costs. Both the conditions where survival costs are produced and the conditions where reproduction can take place without survival costs are specified. Compensation and threshold hypotheses are put forward to allow weaker correlations between reproduction and survival than the trade-off hypothesis, which assumes direct impacts by reproductive effort on survival. Furthermore, reproductive tactics are unlikely to be moulded by the demographic forces of selection only. An empirical example is shown where residual reproductive value played no significant role in the evolution of reproductive tactics. Selection probably operates not on separate life-history traits but on whole organisms through their entire life-history. The structural and physiological intercouplings between separate traits can result in phenotypic opportunity sets where selection can mould life-history traits only within the constraints of the opportunity sets. Optimization theory has provided an efficient technique for modelling and making predictions. However, organismic selection does not necessarily optimize adaptive strategies but eliminates unfit strategies. Life-history theory, and evolutionary theory in general, can be developed along alternative logical lines when different hypotheses are generated on how selection operates.

Developmental Plasticity: Developmental Conversion versus Phenotypic Modulation

Abstract: The developmental mechanisms by which the environment may alter the phenotype during development are reviewed. Developmental plasticity may be of two forms: developmental conversion or phenotypic modulation. In developmental conversion, organisms use specific environmental cues to activate alternative genetic programs controlling development. These alternative programs may either lead to alternative morphs, or may lead to the decision to activate a developmental arrest. In phenotypic modulation, nonspecific phenotypic variation results from environmental influences on rates or degrees of expression of the developmental program, but the genetic programs controlling development are not altered. Modulation, which is not necessarily adaptive, is probably the common form of environmentally induced phenotypic variation in higher organisms, and adaptiveness of phenotypic plasticity therefore cannot be assumed unless specific genetic mechanisms can be demonstrated. The genetic mechanisms by which developmental plasticity may evolve are reviewed, and the relationship between developmental plasticity and evolutionary plasticity are examined.

Dietary Correlates of the Origin and Radiation of Snakes

Abstract: Stomach analyses of living families and of a fossil containing prey were used to address possible dietary correlates of the history of snakes. Aniliids, morphologically primitive among living snakes, feed on relatively heavy, elongate vertebrates. Large aniliids eat larger prey than do small individuals but, as in advanced snakes, they also take small items. Living boids, structurally intermediate between aniliids and advanced snakes, feed on relatively heavy prey of a much greater variety of shapes than do aniliids. An Eocene fossil that might be a boid contains a relatively large crocodilian in its gut. These findings, previous studies, and morphological considerations suggest that very early snakes used constriction and powerful jaws to feed on elongate, heavy prey. This would have permitted a shift from feeding often on small items to feeding rarely on heavy items, without initially requiring major changes in jaw structure relative to a lizard-like ancestor. Subsequent morphological changes could then have allowed boids to utilize a broad range of prey types, including many of those currently eaten by advanced snakes. More recent dietary themes include the consumption of even heavier prey by highly venomous elapids and viperids, and frequent feeding on relatively small items by some other advanced snakes.

Phenotypic Plasticity in Life-History Traits: Demographic Effects and Evolutionary Consequences

Abstract: Although much life-history theory assumes otherwise, most life-history traits exhibit phenotypic plasticity in response to environmental factors during development. Plasticity has long been recognized as a potentially important factor in evolution, is known to be under genetic control, and may or may not be adaptive. The notion of adaptive plasticity contrasts with the idea that developmental homeostasis is a major evolutionary goal. The conflict was resolved in principle by Ashby's cybernetic analysis of homeostasis, which showed how plasticity in “response variables” might act to screen “essential variables” from the impact of environmental disturbance. To apply this analysis to life-history plasticity, it must be incorporated into a demographic model. An approach is presented here using life cycle graphs and matrix projection models. Plasticity in response to temporal variation leads to time-varying matrix models: plasticity in response to spatial variation leads to models structured by criteria other than age. The adaptive value of such plasticity can be assessed by calculating its effects on a suitable measure of fitness: long-term growth rate for time-invariant models, expected growth rate discounted by variance for time-varying models. Three examples are analyzed here: plasticity in the rate of development from one instar to the next in a stage-classified model, plasticity in multiplicative yield components, and plasticity in dormancy as a response to environmental cues. Development rate plasticity is adaptive if reproductive value increases from the instar in question to the next, maladaptive otherwise. Plasticity in yield components reduces fitness variance, and hence is adaptive, if the responses of successive developmental steps ( e.g. , flowers/stem, seeds/flower) are negatively correlated. Plasticity in dormancy is adaptive if it responds to the same factor(s) influencing mortality, but with opposite sign. A number of important problems, including trade-offs between genetic and phenotypic adaptation and the distinction between continuous and discontinous plasticity remain to be solved.

Optimal Degree of Skew in Cooperative Societies

Abstract: Synopsis. An optimization model is employed to determine the outcome of within-group conflict in cooperative societies. The model assumes that selection acts simultaneously on the stronger, dominant members of the group to secure more benefits for themselves at the expense of subordinates, and on subordinates to leave the group in response to this usurpation if they can do better elsewhere. When it is in the interest of the dominant to maintain the group, the dominant will be limited in its opportunity to bias the benefits in its favor by the options available to subordinates outside the group. The resulting differ? ences in fitness or net pay-off among group members due to usurpation by dominants define the degree of skew. Ecological factors affect both the net benefit of grouping and the options for leaving, and thus establish the limits of skewing. The assumptions and rules governing this interaction are first outlined using a game theory approach. A continuous model for predicting the exact degree of skew is then developed. This analysis shows that the degree of skew increases when the benefit of group breeding relative to solitary breeding increases, and when the degree of relatedness among group members increases. Finally, the trade-offs between breeding with relatives versus nonrelatives are analyzed from a dominant relative's point of view. The results of two empirical studies on a social bird and a social wasp are compared to the predictions of these models. The exceptionally good fit to the models is interpreted as evidence in favor of the "social manipulation" approach to "helpinsr" and "altruism" in cooperatively breeding species.

Specializations of the Body Form and Food Habits of Snakes

Abstract: Viperid snakes have stouter bodies, larger heads, and longer jaws than snakes in other families; there are no major differences between the two subfamilies of vipers in these features. A suite of morphological characters that facilitates swallowing large prey finds its greatest expression among vipers, but certain elapid and colubrid snakes have converged upon the same body form. The number of jaw movements required to swallow prey is linearly related to the size of a prey item when shape is held constant. Very small and very large prey are not disproportionately difficult for a snake to ingest. Vipers swallow their prey with fewer jaw movements than do colubrids or boids and can swallow prey that is nearly three times larger in relation to their own size. Proteolytic venom assists in digestion of prey, and melanin deposits shield the venom glands from light that would degrade the venom stores. Ancillary effects of the morphological features of vipers, plus the ability to ingest a very large quantity of food in one meal, should produce quantitative and qualitative differences in the ecology and behavior of vipers and other snakes.

Optimal Foraging Theory and the Psychology of Learning

Abstract: The development of optimization theory has made important contributions to the study of animal behavior. But the optimization approach needs to be integrated with other methods of ethology and psychology. For example, the ability to learn is an important component of efficient foraging behavior in many species, and the psychology of animal learning could contribute substantially to testing and extending the predictions of optimal foraging theory.

The Evolution of Life-History Traits in Mosquitofish Since Their Introduction to Hawaii in 1905: Rates of Evolution, Heritabilities, and Developmental Plasticity

Abstract: !"#$%&'()*+',$'Synopsis. In 1905, mosquitofish were introduced to sugar plantation reservoirs in Ha? waii. Collections of at least 250 fish from each of 24 reservoirs, 4 stable and 20 fluctuating in water level, demonstrated that there were small but significant differences in the life history traits of fish from stable and fluctuating classes of reservoirs, and large and sig? nificant differences among stocks from individual reservoirs. Fish from 2 stable and 4 fluctuating reservoirs were then raised in individual containers with controlled food and temperature. Age and length at maturity, growth rates, and size of offspring all differed significantly among stocks. Broad-sense heritabilities were significantly greater than zero for female age at maturity for fish from one of two stable reservoirs, and for male mat? uration traits for fish from two of four fluctuating reservoirs. Rates of evolution, calculated from the maximum difference between the means of lab-raised stocks and assuming 140 generations since 1905 and continuous change, ranged from 0.1% to 0.5% of the average value of the trait per generation. The traits that changed more rapidly were also more phenotypically plastic, thus suggesting that phenotypic plasticity cannot account for stasis in the fossil record. The concept of plastic trajectories is introduced and exemplified, and predictions are made about how age and length at maturity should alter under stress for organisms with different demographic histories.

Effect of Food and Density on Development of Typical and Cannibalistic Salamander Larvae in Ambystoma tigrinum nebulosum

Abstract: Two subspecies of the tiger salamander, Ambystoma tigrinum, have a distinctive polymorphic life history that can include four adult morphs as well as typical and cannibalistic larval morphs. We evaluated the effect of environment on development of larval morphology in two laboratory experiments. In Experiment I, 180 larvae were raised in individual 3-liter containers and fed one of three food levels. Larvae in Experiment II received one of two levels of food, and were raised at three densities: one larva per 3 liters of water (50 containers), three larvae per 22 liters of water (18 containers), or seven larvae per 22 liters of water (18 containers). Cannibalistic morphs developed only in nine containers at the highest density, and their occurrence was independent of the two food levels. Our results suggest the typical and cannibalistic larvae which occur in some populations of Ambystoma tigrinum nebulosum is an environmentally induced developmental polymorphism that results from some individuals responding to the environment differently than others. This difference in response may or may not be associated with genetic differences between these morphs. Based on our results we cannot discriminate between two models that differ in their assumptions about the genetic background of individual larvae.

Coadapted Character Complexes Among Snakes: Fossoriality, Piscivory, and Durophagy

Abstract: Patterns of morphological variation among fossorial, piscivorous, and durophagic snakes reveal several principles underlying character co-occurrence. Homoplasy is widespread among all three groups. Alternative adaptive responses to specialized habits include modifications for cranial reinforcement in fossorial and cryptozoic snakes and columellar adjustments to accommodate large excursion of the quadrates in piscivores.Among durophagic species alternatives include dental attachment in both scincivores and crustacean-eaters. Although it may be difficult to distinguish primary adaptive responses from secondary ones, specialization frequently elicits pervasive modifications across manymorphological systems. Some are associated with the foraging microhabitat, such as valvularity in piscivores and arboreal adaptations in cochleophages. Others, such as mimicry in Dasypeltis and Scaphiodontophis , are defensive. Still others reflect special aspects of prey processing, such as hypertrophy of the gastric smooth muscle and presumptive salt glandin Fordoma , a cancrivore. The extent to which coordinated morphological responses necessarily accompany specialization is important in formulating hypotheses of macroevolutionary mechanisms.

Home Range in a Patchy Environment: Optimal Foraging Predictions

Abstract: Optimal foraging rules are used to simulate the home range of a central place forager in an environment with a patchy resource distribution. The model makes the following predictions: (1) Home range size is inversely related to maximum resource density and resource renewal rate. It is positively related to the animal's rate of movement. (2) The optimal home range shape in a patchy environment is elongate rather than circular, with a major to minor axisratio of about 2:1. This agrees well with observed values. (3) The proportion of the total home range used per foraging bout is positively related to the renewal rate of the environment. (4) The tendency of an animal to concentrate its activity in a subregion of the home range (rather than distributing its activity uniformly) will increase with the maximum resource density. This tendency is measured as the ratio of the area which will contain 65% of the occurrences of an animal to the area required to contain 95% of its occurrences. The values of the ratio predicted by this model agree closely with observed values.

Feeding Strategies in Marine Snakes: An Analysis of Evolutionary, Morphological, Behavioral and Ecological Relationships

Abstract: Analysis of 1,063 stomach contents from 39 species of sea snakes indicates that about one-third of the shallow, warm, marine, Indo-Australian fish families are preyed upon by sea snakes. Families of eels and gobies are taken by the greatest numbers of snake species. Most species of sea snakes feed on fish families whose members are relatively sedentary, dwelling along the bottom, within burrows or reef crevices. With one exception, a fish egg-eating specialization found uniquely in the Aipysurus-Emydocephalus lineage, the dietary habits of sea snakes cannot be categorized according to the snakes' three phylogenetic lineages. Eels, mullet-like, rabbitfish-like and goby-like fish forms are taken by all three lineages. Two or three snake species are generalists, and numerous ones specialize on eels, goby-like fish or catfish. There are differences among sea snake species in the relationship between snake neck girth and the maximum diameter of the prey; in the relationships of both snake gape measurements and fang length, to the type of prey taken; and in the relationship of snake shape and body proportions to the prey selected. Several modes of feeding have been observed among sea snakes: feeding in nooks and crannies in the bottom or in reefs, cruising near the bottom, and feeding in drift lines. Analysis of percent digestion of stomach contents and projections backward to the times of prey capture provides evidence for feeding periodicity. The greatest amount of diet overlap is for two species of sea snakes which do not both occur at the same locality. Where species do co-occur, diet overlap index values are lower. The numbers of species present as well as their relative abundances vary among localities as does the relative importance of generalists, eel-eaters, egg-eaters and other specialized feeders.

The Role of Lysosomes in Molluscan Inflammation1

Abstract: Phagocytosis and related phenomena represent integral features of inflammation in all metazoans. Reviewed herein are the results of studies directed at understanding the role(s) of lysosomal enzymes synthesized and released from circulating hemocytes, especially granulocytes, of gastropods and bivalves as a result of challenge with exogenous, nonself materials. From what is known, most of the mechanisms underlying this inflammation-associated process parallel those of mammalian macrophages; however, immunoglobulins and most probably components of complement are not involved. The required energy for phagocytosis in molluscs appears to be derived from glycolysis alone. Furthermore, nitroblue tetrazolium reduction and the myeloperoxidase-H2O2-halide antimicrobial system, both characteristic of mammalian phagocytes, appear to be absent in molluscs. It is concluded that by studying phagocytosis by molluscan hemocytes, a great deal can be learned about the evolution of inflammatory response and its constitutent elements.

Size, Age and Demography of Metamorphosis and Sexual Maturation in Fishes

Abstract: Understanding what determines the timing of transitions between life-history stages in fishes is crucial to an understanding of their demography. Most theoretical treatments assume that these transitions are age dependent, but evidence accumulating from a variety of organisms indicates that size is an important variable also. In the starry flounder, Platichthys slellatus (Pallas), the onset of metamorphosis is more closely related to size than age. In the platyfish, Xiphophorus maculatus (Gunther), the onset of sexual maturation depends on both size and age. I compare these results with those reported for other organisms, and outline the expected ecological correlates of age- and sizedependent transitions between life history stages in general.

Chromatophore Organs, Reflector Cells, Iridocytes and Leucophores in Cephalopods

Abstract: The chromatophore organs of Lohgo are each composed of five types of cells: a central pigment cell: radially arranged, obliquely striated muscle fibers: neuronal processes; glial cells: and an investment of sheath cells. Sheath cells are absent in Octopus chromatophore organs. The cycle of expansion and retraction of a chromatophore organ may occur within the order of a second. It is clear that the muscle fibers expand the pigment cell and spread out the pigment granules. The pigment is contained within an unusual, filamentous, cytoplasmic compartment called the cytoelastic sacculus. This compartment has elastic properties. Reflector cells and iridocytes produce structural colors even though their components are colorless. Reflector cells in Octopus bear peripheral sets of leaf-like reflecting lamellae called reflectosomes: these contain proteinaceous platelets with a high refractive index (1.42). In each reflectosome the reflecting lamellae are separated by gaps that are about equal to the thickness of the lamellae, but have a lower refractive index (1.33). Reflectosomes are believed to reflect light and to function as thin-film interference devices. Iridocytes in squid and cuttlefish contain iridosomes that are also composed of sets of ribbon-like platelets but these are located centrally within the cell body. The platelets are usually oriented on edge with respect to the surface of the skin. The possibility that dermal iridocytes may act as diffraction gratings is discussed. Leucophores have thousands of processes that contain globules of protein with a high refractive index. These cells scatter light of all wave lengths and appear white in white light.

Thermal sensitivity as a specialization for prey capture and feeding in snakes

Abstract: Behavior can be regarded as a result of various processes of decision based on the information provided by the sensory organs. In this review the role of the so-called additional heat sense, next to vision, smell and mechanoreception is discussed with respect to the feeding behavior of snakes. The hierarchy of the sensory information in various phases of the feeding behavior differs between snakes possessing heat receptors ( e.g. , species of the Crotalinae and Pythoninae) and those without ( e.g. , species of the Viperinae and Colubrinae). Probably depending on the influence of ecological demands, visual or chemical cues are the main information in the behavioral phases before the strike However, in situations with little visual input, e.g. , in darkness, rodents' burrows, etc., hunting behavior is guided in the first place by radiation of warm objects in Crotalus, Python and Trimeresurus flavoviridis , and by substrate vibrations in Vipera aspis, Pituophis melanoleucus and Boa constrictor . I suggest that in the sensory hierarchy, heat information functionally replaces the mechanical information which is utilized by snakes without pit organs. Poststrike behavior on the other hand is mainly guided by chemical cues in all snakes.

Activity of Head Muscles During Feeding by Snakes: A Comparative Study

Abstract: The adaptive radiation of colubroid snakes has involved the development of numerous prey capture specializations combined with conservation of a swallowing mechanism characterized by independent movements of the right and left toothed bones of the skull. Synchronized electromyographic and cinematographic recordings of swallowing in Nerodia, Elaphe, Heterodon and Agkistrodon , four diverse genera of colubroid snakes, allow a preliminary evaluation of the relationship between prey capture and swallowing. The results indicate that the movements of the palatopterygoid bar and advance of the mandible as closing of the jaws begins as well as patterns of muscle activity producing these movements are similar among the four genera. Conversely, the patterns of activity of external adductors and, to some extent, the depressor mandibulae differ among the four genera sampled. Analyses of bone movements during swallowing suggest that swallowing is effected primarily by the palatopterygoid bars. The mandibles and their connecting soft tissues mainly press the prey against the palatopterygoid teeth. The mandibular teeth evidently play little active role in swallowing. Also, the maxilla, which displays considerable morphological diversity among colubroid snakes, has little independent or direct function in swallowing, its teeth rarely contacting the prey. The data suggest that the heads of colubroid snakes have evolved two partially separated structural-functional units, a medial swallowing unit and a lateral prey capture unit.

Do Bumblebees Forage Optimally, and Does It Matter?

Abstract: Foraging behavior of bumblebees has been in the past analyzed from two major perspectives. On the one hand, behavioral mechanisms have been studied to learn more about the animal. On the other extreme, the animal has been used incidentally to examine optimal foraging theory (O.F.T.). Major problems have arisen when theory designed to answer evolutionary questions was used to determine proximal mechanisms. While O.F.T. could be highly useful in making predictions to point out useful problems, the bottleneck to our understanding at the present resides in the lack of experiments that test alternative hypotheses. Whether or not a bumblebee worker's foraging behavior is adaptive (enhances fitness), however, or is optimal (maximizes fitness) cannot yet be resolved by observations or experimentation on individual bees. However, calculations can show the potential energy costs and payoffs of alternative potential foraging behaviors. Rapid progress could be made by examining the mechanisms of foraging behavior that act to enhance foraging returns, without worrying about whether or not the behavior is “optimal.”

Population Biology of the First Replicators: On the Origin of the Genotype, Phenotype and Organism

Abstract: Prebiotic synthesis of short length macromolecules from precursor molecules results in a dynamic of spontaneous creation, which allows for growth from zero density. At this prereplicator stage in the evolution of life there is no life history, since the birth and death processes are intimately coupled through the physical chemistry of a single reaction. With the emergence of nonenzymatic, template-directed replication, the birth and death processes could diverge for the first time, since selection could act differently on the birth and death rates of the replicating molecule. Thus, with replication, natural selection and life-history evolution began. The genotype, or nucleotide sequence, of the replicating molecule gave rise to several phenotypic properties, the most important of which was its three-dimensional structure which in turn affected the birth and death processes. However, at this stage of nonenzymatic template replication, the phenotype was the physical structure of the genotype, nothing more: For the divergence of the phenotype from the genotype it was necessary for the replicator to produce a protein. It is shown here that the evolution of enzyme production is facilitated by the existence of population structure in the distribution of the macromolecules associated with replication. Initially, this structure was created passively by the localization of the macromolecules in rock crevices, suspended water droplets, etc. Ultimately, the replicator along with its proteins were localized in a protocellular structure and this became the first organism. Thus, initially, the organism was one extreme of the population structure of the macromolecules associated with life. The organism was the culmination of the encapsulation phase of evolution which proceeded through initial phases of passive localization.

Theories of Life-History Evolution

Abstract: SYNOPSIS. In order to assess current scientific understanding of life-history evolution, the alternative fundamental theories are formulated in a refutable form and compared with the available empirical evidence. The hypothesis that life-history does not evolve is rejected on the grounds that life-history can be readily modified by artifical selection. The hypothesis that life-history evolves according to mechanisms other than natural selection acting on genetic variation is shown to have no sound experimental basis. The hypothesis that life-history evolution depends primarily on group selection is undermined by the absence of the predicted group adaptations. The hypothesis that life-history is a unitary character which evolves in the same fashion as fitness is rejected because of the disparity between life-history genetics and basic theory concerning the evolution of fitness. The hypothesis that life-history is composed of a set of autonomous characters which are subject to mutation accumulation at later ages is refuted by the lack of any detectable increase in genetic variability with age and the evidence for the interdependence of lifehistory characters. It is concluded that the hypothesis of antagonistic interactions between life-history characters, generalized to take genetic variability into account, is the most satisfactory theory of life-history evolution available.

Androgen and Estrogen Actions in the Vertebrate Brain

Abstract: In all vertebrates gonadal secretions, through their actions on the central nervous system (CNS), control sex and sex-related behaviors and also regulate production of gonadotropin. Recently, major advances have been made in characterizing the molecular events which underlie these processes. Discussed in this paper are the nature and source of androgens and estrogens; their sites of action within the CNS as determined by steroid implant and autoradiographic studies; some manifestations of brain-steroid interactions, both “triggering” and “organizational”; evidence supporting a conventional genomic mechanism versus alternative modes of action; the critical role of androgen metabolizing enzymes in regulating the quality and quantity of active hormone in close proximity to targets; and some determinants of steroid access to the CNS. Information from nonmammalian vertebrates is reviewed in relation to the major body of knowledge derived from common laboratory species. The intent of this paper is to provide a biological perspective and to stimulate interest in the use of unconventional animal models for future studies.

Functional Evolution of Prolactin and Growth Hormone in Lower Vertebrates

Abstract: Some aspects of prolactin and growth hormone biology in fishes and amphibians are considered, including the nature of the secretory cells, the regulation of their activity, the chemistry of the hormones, and their physiological activity in relation to hydromineral metabolism and to growth and development. Inasmuch as most of the information is derived from only a small number of teleost and amphibian species, a broad evolutionary biology is difficult to derive without information from other fish groups especially, and a survey must be confined largely to a comparative biology of some representative higher bony fishes with some representative anurans and urodeles.

Phagocytosis and Encapsulation: Cellular Immune Responses in Arthropoda

Abstract: The least understood aspects of the cellular immune reactions of arthropods are the earliest events: the initial recognition of foreignness, and the resulting changes in hemocyte behavior and morphology There are indications that the recognition of a surface as foreign is based primarily upon its electrostatic charge, but more specific criteria may be utilized in some situations Phagocytes are capable of recognizing foreignness without the intervention of soluble opsonins but, in some arthropods, there is in vitro evidence that opsonins can increase the efficiency of phagocytosis It has been hypothesized, on the basis of ultrastructural evidence that encapsulation, a multicellular immune response, is induced when labile hemocytes rupture upon encountering a foreign object The released products may promote the formation of a sheath of ameboid hemocytes around the object This hypothesis is now supported by the results of experiments performed on an in vitro encapsulation system This system may prove useful in the purification of encapsulation—promoting factors; in determining the mechanism of their release from hemocytes; and in investigating the possibility that the various cellular immune reactions of arthropods have a common underlying mechanism

A Class of Patch-Use Strategies

Abstract: A class of models for economic, or optimal, foraging in a patchy habitat is characterized. All models in the class share a number of ecologically important properties, but there are important differences, as well. These models are well suited to studying properties of a variety of simple behavioral rules which foragers might use in deciding when to leave a patch. Several extensions and limitations of the class are also pointed out.

Evolution of Thyroid Function and Its Control in Lower Vertebrates

Abstract: The hypothesis is discussed that the general endocrine function of thyroid hormone in lower vertebrates is concerned with growth, development, and reproduction. Examples are given of possible heightened thyroid function during segments of the life cycles of lamprey, Pacific salmon, some amphibians, and some reptiles. Studies of the occurrence of components of the thyroid system in vertebrate classes suggest that pituitary control of the thyroid through thyroid stimulating hormone may be absent in agnathans and present in gnathostomes. The hypothesis is discussed that regulation of thyroid endocrine function through control of hormone metabolism and target tissue sensitivity is a phylogenetically ancient mechanism.

αMelanocyte Stimulating Hormone: Chemical Nature and Mechanism of Action

Abstract: αMelanotropin (α-MSH) is a tridecapeptide, Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, synthesized and secreted by the pars intermedia of the vertebrate pituitary. This peptide hormone is derived from pro-opiomelanocortin, a precursor protein which contains within its structure the sequences of other melanotropic peptides (γ- and rβ-MSH, corticotropin), and possibly other hormones. α-MSH is the physiologically relevant melanotropin secreted by the pituitary and in most vertebrates plays the essential role in adaptive color changes through its action on integumental chromatophores. The initial actions of α-MSH are mediated at the level of the melanocyte membrane and involve signal transduction from receptor to adenylate cyclase on the intracellular surface of the membrane. This results in elevated cytosolic cyclic AMP levels followed by melanosome dispersion within dermal melanocytes and melanogenesis within epidermal melanocytes. The action of α-MSH on dermal melanocytes requires calcium for transduction of signal and cyclic AMP production. Melanosome dispersion per se does not, however, require extracellular calcium. Structure-function studies of α-MSH analogues and fragments have provided important insights relative to the structural requirements of the hormone for receptor binding and transduction. Substitution of certain residues within α-MSH has led to the development of melanotropins that exhibit extraordinary potency and prolonged biological activity

Early Development of the Hagfish Pituitary Gland: Evidence for the Endodermal Origin of the Adenohypophysis

Abstract: Synopsis. The adenohypophysis in early head fold stage hagfish embryos is at first a distinct differentiated thickening ofthe archenteric roof where it contacts the developing infundibular portion of the brain. This portion of the archenteron eventually becomes the dorsal epithelium of the nasopharyngeal duct. The later development of the adeno? hypophysis involves formation of multiple acinar outgrowths ofthe dorsal nasopharyngeal epithelium which together form a layered mass of follicular tissue adjacent to the neu? rohypophysis. This mode of origin of the adenohypophysis by endodermal polyinvagination and delamination differs from all other vertebrates, including the lampreys. The pertinence of this new information for considerations of monophyletic versus diphyletic evolutionary origins of the modern cyclostome groups is pointed out. The unusual devel? opment of the hagfish adenohypophysis presents some new and unanticipated puzzles within the general question of pituitary evolution.

Evolution of Neurohormonal Regulation of Reproduction in Lower Vertebrates

Abstract: Immunological and chromatographic studies demonstrate that the gonadotropin (GtH) releasing hormone (GnRH) in the brain of chondrichthyes, teleosts, reptiles and birds is different from luteinizing hormone-releasing hormone (LH-RH) of mammals. LH-RH is present in brain extracts from amphibia. The alterations in the structure of LH-RH found in various of the non-mammalian vertebrates are at positions 7 and 8; the structure of chum salmon GnRH is Trp7-Leu8-LH-RH, and in chickens is Gln8-LH-RH. A response to injection of LH-RH or its agonistic analogues, in terms of increased blood levels of GtH or a gonadal response such asovulation indicative of increased GtH secretion, has been found in all classes of vertebrates, and the cephalochordate amphioxus. This suggests a basic similaritiy of the GnRH receptors throughout vertebrates, and that the ancestral origin of the system was in the invertebrate chordates. Immunohistochemical studies demonstrate that many lower vertebrates have perikarya containing LH-RH-like material in the preoptic and ventrobasal hypothalamic regions. Brain lesioning studies provide functional evidence for GnRH from both locations in amphibia and only the ventrobasal hypothalamus in teleosts. Brain lesioning studies on goldfish suggest the presence of a GtH release-inhibitory factor (GRIF). Dopamine has GRIF activity in goldfish and common carp to modulate the actions of LH-RH and spontaneous release of GtH. How widespread this system for dual neurohormonal regulation of GtH secretion is in vertebrates is not known.