Showing papers in "Integrative and Comparative Biology in 1981"

Cellular and dynamic aspects of oocyte growth in teleosts

Abstract: SYNOPSIS. Four principal stages of oocyte growth are recognized among teleosts. During gonadotropin-independent primary growth, multiple nucleoli form as well as a Balbiani body which eventually disperses throughout the ooplasm. The first gonadotropin-dependent stage involves the formation of yolk vesicles, the precursors to the cortical alveoli. True vitellogenesis follows during which vitellogenin is sequestered from the maternal blood and packaged into yolk granules or spheres. The latter generally fuse centripetally at some time during oocyte growth to give a continuous fluid phase surrounded by a peripheral layer of cytoplasm containing the cortical alveoli. Maturation represents the final stage and is accompanied in many teleosts by water uptake; among marine teleosts with pelagic eggs, most of the final egg volume may be achieved by this process. Ovaries may be synchronous, asynchronous, or group-synchronous. Among the latter, a clutch of oocytes may be recruited from an asynchronous population of earlier stages into any of the subsequent stages. In teleosts which spawn repeatedly, recruitment of new clutches can usually be associated with the transition of a previously recruited clutch from one stage to the next. Teleosts thus offer examples of virtually every conceivable type of ovarian physiology and provide a wealth of experimental material for exploring the cellular and hormonal mechanisms which regulate oocyte recruitment and growth throughout ovarian recrudescence.

Cellular Organization of the Testis and Spermatogenesis in Fishes

Abstract: Synopsis. Tubular structure of the teleost testis can be divided into two basic types distinguished from each other by the distribution of spermatogonia. In most teleosts, spermatogonia occur along the length of the tubules, but in atheriniform fishes they are confined to the terrriinus of the tubule. Variations in these testis-types are discussed particularly in light of modifications leading to the production of spermatozeugmata or spermatophores. Teleost boundary cells are located immediately outside of the tubule basement mem? brane. Previous reports homologizing "lobule boundary cells" with Leydig or Sertoli cells are in error. Leydig cells have been described for species of teleosts wherein they have previously been thought to be absent and are a typical component of the interstitium. Sperm morphology reflects mode of reproduction. Nuclear elongation, coupled with possible elongation of the sperm midpiece, is characteristic of most species wherein fer? tilization is internal. Teleost sperm lack an acrosome.

Viviparity: The Maternal-Fetal Relationship in Fishes

Abstract: SYNOPSIS. Viviparity in the vertebrate line first makes its evolutionary appearance among fishes. It has independently evolved in a number of divergent piscine lineages. The 54 families of extant fishes that bear living young include 40 families of chondrichthyans (sharks and rays), one montypic family of coelacanths ( Latimeria ), and 13 families of teleosts. There is fossil evidence for viviparity in holocephalans and chondrosteans. Viviparity predominates among sharks and rays (40 families, 99 genera, 420 species) but is less widespread among teleosts (13 families, 122 genera, 510 species). Following an historical introduction, the organization of the female reproductive system, sites of gestation, developmental sequences and superfetation are considered. The evolution of viviparity establishes specialized maternal-fetal relationships, viz. , 1) developmental, 2) morphological, 3) trophic, 4) osmoregulatory, 5) respiratory, 6) endocrinological, and 7) immunological. While the latter four categories are briefly noted the major emphasis is on the trophic relationship and its morphological and developmental basis. First, a general overview is presented and then the maternal-fetal trophic relationships in each of the major groups of fishes are systematically reviewed. Pertinent anatomical, histological, ultrastructural, developmental, physiological, and biochemical studies are considered. Viviparous fishes are either lecithotrophic, i.e. , exclusively yolk dependent, or matrotrophic, i.e. , in receipt of a continuous supply of maternal nutrients during gestation. Nutrient transfer is accomplished by 1) oophagy and adelphophagy, 2) placental analogues, and 3) the yolk sac placenta. Placental analogues include: external epithelial absorptive surfaces, e.g. , skin, fins, gills; trophonemata, modifications of the uterine epithelia for the secretion of histotrophe or “uterine milk”; branchial placentae, close apposition between gill epithelia and either uterine or ovarian epithelial villi; the yolk sac; pericardial amnion and chorion; follicular pseudoplacenta, close apposition between follicle cells and embryonic absorptive epithelia; hypertrophied gut; and trophotaeniae, external rosette or ribbon-like projections of the embryonic gut. Among chondrichthyans, the yolk sac placenta (840–1,050%), trophonematal secretion and embryonic absorbtion of histotrophe (1,680–4,900%) and oophagy and adelphophagy (1.2 × 106%) are the most efficient methods of nutrient transfer. Among teleosts, the follicular pseudoplacenta (1,800–3,900%), trophotaeniae (8,400%) and absorption of ovarian histotrophe through surface epithelia and a hypertrophied gut (1,100–34,000%) are the most efficient. These values stand in contrast to the 30%40% loss of dry weight characteristic of oviparous fishes and viviparous lecithotrophes.

Two Decades of Homage to Santa Rosalia: Toward a General Theory of Diversity

Abstract: In 1959, in his seminal paper “Homage to Santa Rosalia,” G. E. Hutchinson asked, Why are there so many kinds of organisms? This paper focused attention on problems of species diversity and community organization that have occupied many theoretical and empirical ecologists for the last two decades. In the present paper I evaluate the attempt to answer Hutchinson's question by considering three topics. First, I reexamine the main themes which Hutchinson developed in “The Homage” and call attention to the central importance of energetic relationships in his view of ecological communities. Second, I examine the development of theoretical community ecology over the last two decades in an attempt to determine why some avenues of investigation, such as competition theory, have proven disappointing, whereas others, such as the theory of island biogeography, have enjoyed at least modest success. Finally, I suggest that future attempts to understand patterns of species diversity might focus on developing two kinds of theoretical constructs: capacity rules, which describe how characteristics of the physical environment determine its capacity to support life, and allocation rules, which describe how limited energetic resources are subdivided among species.

Defense and Dynamics in Plant-Herbivore Systems

Abstract: Recent theory about interactions between plants and their herbivores focuses on properties of individual plants that affect their resistance to herbivores, and it extrapolates from these individual properties to those of whole communities In this paper I question three major assumptions of this approach—costs of defenses, basic differences between classes of defenses, and step-wise coevolution—and recast the theory from a different community perspective I propose that major differences in defenses between plants with very different life-history characteristics arise from differences in community structure, especially the numbers of herbivore species involved in the interactions In particular, because of the diffuse pattern of herbivory on persistent plants, a new model of coevolution—diffuse coevolution—becomes appropriate when many species are involved Complex interacting assemblages have special properties that cannot be derived just by summing up all of the simple interactions that occur

Optimal foraging: Field tests of diet choice and habitat switching

Abstract: Synopsis. The application of optimal foraging theory to questions of predator behavior, and evidence bearing on the utility of this construct, are reviewed. Experimental tests of simple models predicting prey choice are examined with particular reference to the sizeselection of prey by fish. Laboratory estimates of model parameters are then used to predict prey choice in the field and data from several field tests are presented which corroborate these predictions. When parameters are habitat specific this permits predic? tions of net return from foraging in different habitats and consequendy predictions of habitat use and switching. Field data gathered to test these predictions demonstrate that fish feed in the richer habitats and switch habitats when the profitability of one drops below that of another. Examples are provided showing how these models can then be used to relate behavioral and morphological differences between species and questions at higher levels such as the nature of species interactions and community structure. It is suggested that this may be one of the more useful applications of optimal foraging theory. Finally, some of the criticisms of the theory and important questions requiring further study are discussed.

Social Modulation of Circulating Hormone Levels in the Male

Abstract: SYNOPSIS. In many species, social interactions rapidly modulate circulating hormone levels in the male. Sexual interaction or mere exposure to a conspecific female results in rapid, transient elevation of both plasma luteinizing hormone and testosterone concentrations in a variety of species. In contrast, aggressive interactions result in decreased plasma gonadotropin and testosterone levels and increased levels of adrenal corticoids. In general, these changes are more profound and of longer duration than those accompanying sexual interactions, particularly among subordinate males. These fluctuations in circulating hormone levels appear to be related to an individual's behavioral responsivity. For example, plasma concentrations of luteinizing hormone during a social encounter are positively correlated with the degree of sexual arousal shown by a male during the interaction. Similar correlations have been found between plasma androgen or corticoid levels and patterns of behavior shown by males during both sexual and aggressive interactions. The causal relationship between such rapid hormone fluctuations and behavior remains unclear. Are fluctuating hormone levels causing differences in behavior or aredifferent patterns of behavior causing differences in plasma hormone levels between males? Or is the correlation between these two variables caused by their relationship to another unidentified factor? There are some data favoring the first possibility. Increasing the magnitude of socially induced hormone fluctuations during an aggressive encounter or preventingsuch fluctuations entirely significantly alters an animal's behavior. These data suggest that the endocrine system may play a more important role in an individual's minute-to-minute response to critical social stimuli than was previously realized.

Physiological Control of Molting in Insects

Abstract: Synopsis. The initiation of a molting cycle in insects is neither a random nor a strictly periodic event. Insofar as molting can accomplish different things under different cir? cumstances, such as a change in size or a change in form, it is reasonable to asume that the timing of a molt must be adapted to these functions. The onset of a metamorphic molt, in particular, must be precisely controlled because the onset of metamorphosis terminates the growth phase of a larva and establishes the body size of the adult insect. This aspect of the control of molting has received relatively little attention and our knowl? edge of specific physiological mechanisms for the control of molt initiation is restricted to three species: the blood-sucking bug, Rhodnius prolixus, the greater milkweed bug, Oncopeltus fasciatus, and the tobacco hornworm, Manduca sexta. The present review discusses the state of our knowledge about the factors that render these insects competent to molt and about the stimuli that serve as a direct trigger for molting.

Saltatory Processes and Altricial to Precocial Forms in the Ontogeny of Fishes

Abstract: SYNOPSIS. Development is not a gradual but a saltatory process. A combination of qualitative changes in form and function—thresholds—creates boundaries between a succession of quantitative intervals—steps. Thresholds can be modified by an altered time of appearance of structures and functions (heterochrony), especially during early ontogeny, to form an operational basis for the prolongation of juvenile characters and adaptability into later ontogeny. Whereas such prolongation enables juvenilization in phylogeny, analogous principles may operate on a much shorter time scale to produce the r -selection-like altricial and the K -selection-like precocial trends in ontogeny. The inherited capacity to adjust constantly to the environment (heterochrony) selects for structural, biochemical and behavioral improvements. The tendency is toward the precocial but the way back to altricial forms is left open. The heterochronous adaptations in early ontogeny can “reverse” the vulnerable specialization, should the environment become less stable and/or the community less competitive. Juvenilization, capable of turning gerontomorphosis into paedomorphosis in evolution, and heterochronous shifts of character anlagen, capable of turning a precocial trend into an altricial trend in ontogeny are both part of the same biological process which operates during early ontogeny.

On the Diversity of Electric Signals in a Community of Mormyrid Electric Fish in West Africa

Abstract: SYNOPSIS. Communication through electric discharges is a rich and varied modality of social communication among mormyrid fishes of West Africa. Field studies permitted an analysis of the electric signals of over 20 species of Mormyridae living sympatrically in and near the Ivindo River of Gabon. Electric discharges can be classified according to their waveforms and can be shown to be species-specific in many cases. The waveform of the discharge is a signature which is a carrier for social communication signals. The paper asks: “Why is the signature, or carrier, adaptive?” An analysis points to competitive and cooperative forces in the evolution of electrical waveforms, not physical or habitat forces. Competition between species, as well as mutualistic interactions, appear important in explaining how electrical signatures are adaptive for: 1) channel privacy (noise immunity); 2) unique signals for species recognition ; and 3) electrolocation signals less vulnerable to jamming.

Morphogenetic Movements and Fate Maps of Vertebrates

Abstract: SYNOPSIS. Fate maps are totally lacking for hagfishes, rays, holocephals, dipnoi, holostei and mammals, and for all except two of the thirty or so orders of the huge teleost assemblage. Important errors have been found in earlier studies of the movements by closer control of marking techniques, but there are still major elements in the literature that remain unconfirmed. Recent studies on Salmo, Xenopus and chick suggest that a wider sampling of major vertebrate groups will uncover more unsuspected variations in this phase of embryology. Experimental results on the chondrostean sturgeon Acipenser are here compared and contrasted with those on Salmo and Xenopus . Though chondrostei and teleosts had a relatively recent common ancestry, the morphogenetic movements and fate map of Acipenser give no hint as to how the uniquely teleostean behavior could have arisen. Instead the experiments have shown in new elaborate detail how close the early development of Acipenser is to that of modern amphibia, closer to Xenopus than to Rana , closer to anura than to urodeles. The search for unity in the field of comparative morphogenetic movements is plagued by lack of breadth in the sample of vertebrates hitherto studied but also by a vocabulary too much loaded with ancient homological thinking. It is pointed out that when a group of movements, all called invagination—or all called epiboly, is studied closely it can be discovered that they may be doing quite different things, controlled by different environmental factors. General theory of this part of embryology requires the bringing together of the knowledge of cellular movements from in vitro and non-embryonic systems with the knowledge of the full variety of normal patterns of morphogenetic movements in the vertebrates. Before this can be accomplished, we will need a precise knowledge of what the cells are actually doing in all the sectors of these patterned movements, and in all the major patterns that the phylum has produced.

A Functional Approach to the Phylogeny of the Pharyngognath Teleosts

Abstract: Synopsis. Functional morphological analysis has revealed the existence of three functionally and morphologically different mechanisms underlying the tongue-parasphenoid and pharyngeal-parasphenoid bites in advanced teleost fishes. The bite is specialized differently in Pristolepis and the Anabantoidei, and in a primitive condition in both the Nandidae and Channiformes. These taxa belong to at least three unrelated lineages and do not share a common ancestry as was previously postulated. It has been possible to show how an originally primitive character can acquire a new biological and phylogenetic meaning by being integrated into a specialized functional complex. Based on functional data on the pharyngeal jaw apparatus, a new hypothesis is proposed stating that the Cichlidae, Embiotocidae, Labridae, Odacidae and Scaridae represent a monophyletic assemblage. This case study has demonstrated that reciprocal illumination of functional morphological and phylogenetic findings can lead to: (1) better tested and more precise phylogenetic hypotheses; (2) the construction of new hypotheses on the basis of specialized character complexes which were unrecognized by the use of a purely descriptive morphological approach.

Energy Metabolism in Fish Development

Abstract: SYNOPSIS. During oogenesis the fish oocytes accumulate several substances of which lipids and glycogen are the major energy substrates. Oocyte maturation is accompanied by an increase in all the enzymes of carbohydrate metabolism. After fertilization, respiration and glycogenolysis are increased and the energy charge is decreased. During early embryogenesis glycogen appears to be the only substrate of glycolysis. Glycolysis and the citric acid cycle are the main sources of energy for the biosynthetic activities and for the maintenance of embryo morphology. There are two patterns of ontogeny of glycolytic enzymes in trout embryos. One group of enzymes does not undergo appreciable changes whereas enzymes within the second group exhibit variable activities. Marked changes in enzyme activity occur during fertilization and gastrulation. Lactate dehydrogenase (LDH) is of particular interest. Its activity increases during gastrulation. This increase in LDH activity is followed by a change in the isozyme pattern and in the adenylate charge. 1mmunochemical and histochemical localization of LDH revealed that its cellular distribution depends on the position of the cells in the embryo. Moving cells had higher levels of LDH activity. The lactate dehydrogenase isozymes appear to play an important role in the regulation of energy metabolism during fish embryogenesis. These gene products are useful biochemical markers of cellular differentiation and organogenesis.

Population Variation in Continuously Varying Traits as an Ecological Genetics Problem

Abstract: The niche variation hypothesis is an adaptive explanation for variation within populations and for, the differences in variation between populations in morphological, physiological or behavioral traits. It has received only partial support from empirical tests and has been criticized on theoretical grounds. Recent quantitative genetic models have made an advance by exploring the effects of mutation, migration, mating pattern and selection on phenotypic variance. These models are reviewed and their most important features are integrated in a new model. In this model population variation is in a state of balance between the opposing forces of mutation and immigration, which tend to elevate variation, and selection and possibly genetic drift tending to decrease it. Populations exhibiting different levels of variation are interpereted as having different equilibrium points, and it is the task of empirical studies to determine the relative magnitudes of the opposing factors. An example is given from studies of Darwin's finches. Geospiza fortis varies more than G. scandens on Isla Daphne Major, Galapagos, in several morphological traits including beak and body size. This is explained, assuming equal mutation rates in the two species, as the result of more frequent genetic input to the G. fortis population, through occasional hybridization with immigrant G. fuliginosa , and relaxed stabilizing selection. Stabilizing selection is less intense on G.fortis than on G. scandens because the G. fortis population has a broader niche; there is both a within-phenotype and betweenphenotype component to the broad niche of G. fortis . The success of theory in explaining population variation is discussed, and it is concluded that empirical studies lag far behind theory.

Mechanisms of Hatching in Fish: Secretion of Hatching Enzyme and Enzymatic Choriolysis

Abstract: SYNOPSIS. Mechanisms of two constituent steps of the hatching process, i.e. , secretion of hatching enzyme from the gland cells and enzymatic choriolysis, in the Medaka, Oryzias latipes , are described. The ultrastructural changes of the hatching gland cells occurring at the initiation of electrically induced secretion as well as of natural secretion were the swelling of each gland cell and the separation of joints of the epithelial cells covering the gland cells, followed by a resultant exposure of the apical part of the gland cells. These changes, though their triggering mechanisms are not sufficiently clarified, suggest an intervention of some mechanical stimuli in the initiation of secretion. Decrease in electron density of the secretory granules also occurred immediately prior to the initiation of secretion. The secreted hatching enzyme was found to dissolve the inner layer of chorion by attacking the scleroprotein of the inner layer at some restricted sites and liberating a group of soluble glycoproteins of high molecular weights. This selective digestion appears to be the reason why choriolysis proceeds efficiently during a short period of time at hatching.

Reproductive Behavior in the Rhesus Monkey: Social and Endocrine Variables

Abstract: SYNOPSIS. Social groups of rhesus monkeys ( Macaca mulatto ) living in outdoor environments exhibit a distinct seasonal mating pattern and female rhesus are observed to be sexually receptive for discrete periods averaging about 9 days duration. In the laboratory environment mating occurs throughout the year and, in the pair test, female rhesus are observedto be sexually receptive through all phases of a menstrual cycle, with a periovulatory peak incopulatory behavior. The apparent conflict between results from field and laboratory studies has been difficult to resolve because of methodological limitations inherent in each study environment. Studies conducted on social groups of rhesus monkeys housed in outdoor compounds, an environment in which the species typical seasonal mating pattern is preserved and which allowsfor concomitant measurement of behavioral and hormonal variables, provided information about the covariance between female sexual behavior and ovarian cycles. Female copulations were observed only in association with ovulatory cycles, and were limited to the follicular and peri-ovulatory phases of such cycles, demonstrating that copulatory behavior in female rhesus monkeys is strongly influenced by cyclic hormonal variables. The studies also revealed that females tend to conceive on the first ovulatory cycle of the season, that there was no synchrony of cycles among the females, and that the best predictor of the timing of ovulation in a particular female is reproductive outcome in the previous year.

Social Control of the Ovarian Cycle and the Function of Estrous Synchrony

Abstract: SYNOPSIS. The social signals among groups of females can either enhance or suppress ovariancyclicity. The ovarian cycle is not unitary, but is instead the integrated product of several different components which are each affected by social signals of different modalities. This interaction between female behavior and ovarian cycle components has different manifestations in different species. Depending on its temporal context and the social and physical environment, the same behavior/hormone interaction can take different forms. In some contexts, these interactions can be adaptive for the individual. In others, they can generate a strong epiphenomenon or artifact that may not confer a direct adaptive advantage itself, but still be necessary for other aspects of the coordination between social behavior and reproduction.

Hormonal Control of Epidermal Cell Development

Abstract: SYNOPSIS. During larval life the insect epidermis makes a larval cuticle and certain pigments due to the presence of juvenile hormone (JH) at critical times during the molt cycle. The presence of JH also permits growth of imaginal discs and maintains strictly larval epidermis. At metamorphosis the lepidopteran epidermis responds to a low level of 20- hydroxyecdysone (20HE) in the absence of JH by becoming pupally committed, then later it forms a pupal cuticle when more 20HE appears, even though JH is present. During the change of commitment, DNA synthesis occurs but is not essential, whereas both RN A and protein synthesis are. The major changes in the translatable mRNA population at this time are threefold: a decline in most larval cuticle mRNAs, a transient increase followed by a disappearance of a few larval cuticle mRNAs, and an appearance of at least one ‘pupal commitment’ mRNA and two to three mRNAs for small pupal cuticular proteins. Similar changes are seen in the protein synthetic patterns. Thus, a pupally committed cell is one which can no longer make larval products but which is not yet able to make most pupal products. Juvenile hormone prevents the change to pupal commitment by directing some of both the primary and the secondary actions of 20HE on the genome.

The Use of Functional and Adaptive Criteria in Phylogenetic Systematics

Abstract: SYNOPSIS. The controversy over whether functional data can contribute to phylogenetic inference has grown in recent years. Steps can be taken toward its resolution if the relevance of functional data is judged for each component of phylogenetic analysis. These components are (1)recognizing of basic taxa (species or supraspecific taxa), (2) formulating hypotheses of homology followed by character analysis, (3) evaluating character phylogeny, (4) formulating phylogenetic hypotheses, and (5) evaluating alternative phylogenetic hypotheses. It can be shown that functional data do not play a necessary or unique role in any of these components of phylogenetic analysis. Arguments to the contrary have failed to provide a rigorous, repeatable methodto incorporate functional data; proponents of a functional approach to phylogenetic reconstruction rely too often on subjective, authoritarian argumentation. Students of functional evolutionary morphology frequently have failed to understand the kinds of information necessary to study or apply the causal process of adaptation via natural selection. This information, required by the very nature of the theory itself, includes knowing the pattern of heredity of the phenotypic characters being studied, relating intrapopulational phenotypic variability to variation in fitness, and knowing a sufficient amount about population structure to specify the components of natural selection. Studies within functional evolutionary morphology are not designed to satisfy these requirements. Functional evolutionary morphology uses the concepts of adaptation and natural selection axiomatically, and thus such studies contribute nothing to our understanding of the evolutionary process because hypotheses about that process are not being evaluated. This also suggests that, if functional evolutionary morphology wishes to engage in analyses of the evolutionary dynamics of the phenotype, a reorientation of its research strategy and goals will be necessary.

The prothoracicotropes: Source of the prothoracicotropic hormone

Abstract: SYNOPSIS. An in vitro assay for the insect prothoracicolropic hormone (PTTH) has been developed which measures the rate of ecdysone synthesized by Manduca sexta prothoracic glands (PG) stimulated in vitro by PTTH. This assay has been used to quantify PTTH in single neurosecretory cells (NSC) resulting in the identification of one NSC in each hemisphere of the brain as the prothoracicotrope, source of PTTH. The axonal and dendritic distribution of the prothoracicotrope has been determined by cobalt filling with silver intensification. From a comparison of the titers of PTTH in brains, corpora cardiaca and corpora allata during larval-pupal development, the corpus allatum has been identifiedas the neurohemal organ for PTTH. Electron microscopic analyses suggest that the acellular sheath surrounding the corpus allatum contains the axon terminals of the prothoracicotropes. There is at least one form of PTTH, ˜22,000 mol wt (big PTTH), and possibly a smaller form of about 7,000 mol wt (small PTTH). Bioassay and PTTH hemolymph titer data during the head critical period (HCP) for larval-larval development reveal that big PTTH is released as a single peak lasting ˜6 hr. By contrast, during the first HCP of the last larval instar PTTH is released over a period of ˜18 hr in three bursts, but its molecular weight has not been established with certainty. The kinetics of PG activation by these two forms suggest that big PTTH may function to activate the PG dramatically and thereby elicit molting, while small PTTH may activate the PG minimally at the time of cellular reprogramming.

Functional-Adaptive Analysis in Evolutionary Classification

Abstract: SYNOPSIS. Higher level systematic study can be divided into two parts, namely: (a) the formulation of classificatory and of phylogenetic hypotheses about groups and their testing against taxonomic properties of characters; and (b) the formulation of hypotheses about taxonomic properties of characters and their testing against empirical observations of these features. Thesecond step—character analysis—is most important because it constitutes the actualobjective testing within systematic study and provides the basis for one's conviction in the validity of a particular classification and/or phylogeny. Yet insufficient attention has been given to the methods used in the character analysis phase of systematics. Classifications and phylogenies are historical narrative explanations of the past evolutionary history of organisms. As such they must be based on and tested against the underlying theory of organic evolution. Classifications are not used to test the validity of mechanisms of evolutionary change; rather the reverse is true. For the construction of a classification or of a phylogeny, it matters absolutely how the organisms evolved—the classification and phylogeny depend completely on the accepted mechanisms of evolutionary change, not just on the hypothesis that organic evolution had occurred. Thus, the methods used in the character analysis phase of systematic study must be based on accepted mechanisms of evolutionary change. If the evolutionary change is adaptive, then functional and adaptive analyses form an integral part of the character analysis. Several commonly used methods of character analysis, most importantly that of outgroup comparison, are invalid because they are based on simple circularity, etc. The valid methods available for testing taxonomic properties, e.g. , homology, apomorphy, etc., of characters are poortests in that they have low resolving power, i.e. , poor ability to distinguish between correctand incorrect answers to individual tests. Additional methods must be used to establish a degree of confidence in particular answers of valid tests of low resolving power. A set of valid methods are outlined for testing character hypotheses about homology, apomorphy—plesiomorphy and synapomorphy, and for establishing the degree of confidence in the results of individual tests. Functional-adaptive analyses are a necessary and essential part of the valid methodsused to test and/or establish the degree of confidence in individual results for all hypotheses about taxonomic properties of characters.

Genetic and Endocrine Regulation of Vitellogenesis inDrosophila

Abstract: SYNOPSIS. Three yolk polypeptides (YPs) are major constituents of eggs. YPs are synthesized in the fat body and in ovary associated cells, secreted into the blood and sequestered into developing oocytes. YPs are translated as precursors which can be processed to lower molecular weight polypeptides by dog pancreatic microsomes, suggesting signal peptide removal. YP synthesis in both ovary and fat body is stimulated by juvenile hormone (JH), but 20-hydroxyecdysone (20HE) only stimulates YP synthesis in fat body. JH also induces YP sequestration into oocytes. The amount of RNA translatable into YPs increases sevenfold in the first day after eclosion. The increase can be blocked by ligating the abdomen to isolate it from anterior endocrine organs, and it can be restored by injecting these preparations with 20HE. Using electrophoretic variants, the YPs have been genetically mapped to the X chromosome: Yp1 and Yp2 are adjacent and Yp3 is distantly linked. Two mutants have been described which decrease the quantity of a single YP, map near the respective YP structural loci, are cis-acting and are not ovary autonomous in transplants. fs (1)1163 alters the structure of the primary translation product and is hypothesized to alter YP processing and secretion. Although Yp3 RI results in no detectable YP3, the mutant genome and mutant RNA contains sequences complimentary to cloned Yp3 gene. This mutant may result in blocked translation. Further analysis of Drosophila vitellogenesis using molecular and classical genetic techniques promises to help us understand how hormones regulate gene activity.

Mechanisms of Fertilization in Fishes

Abstract: SYNOPSIS. Sperm motility in fishes is, in general, initiated by simple dilution of the epididymal suspension. A few simple organic compounds and poorly characterized proteincontaining “factors” associated with fish eggs seem to enhance sperm motility. True chemotaxis in fish sperm has not been demonstrated. Ultimately, sperm-egg interaction leads to a large, transient increase in the concentration of free calcium in the egg's cytoplasm. This calcium increase is responsible for lifting the egg's developmental block; some mechanisms by which the calcium flux may accomplish this are discussed. A pH change is apparently not involved in turning on synthetic activity in fish eggs. Electrophysiological events and the fusion of cortical vesicles with the plasma membrane, which are among the earliest changes in the egg resulting from fertilization, are apparently not necessary for development of fish eggs. Synthesis of RNA and protein required for normal cleavage, axiation and organogenesis occurs during and soon after the calcium transient. Completion of the egg's second maturation division occurs within minutes after fertilization. Ooplasmic segregation (by some totally unknown mechanism) and opposition of male and female pronuclei complete the transformation of the egg into a functional zygote.

Environs: The Superniches of Ecosystems

Abstract: Evolution proceeds by natural selection of heritable variations of individual organisms based on direct influences of environment. However, indirect effects probably vastly outweigh direct ones in ecosystems. Therefore, why is evolution based on direct effects only? The ecological niche represents the point of direct contact between organisms and their environments. To encompass indirect influences, niches are extended to new structures, environs, which are units of organism-environment coevolution. The motive force for coevolution is closure of outputs back upon inputs of the organism members of ecosystems. Closure is achieved by biogeochemical cycling and feedback interactions, direct and indirect, between organisms. To the extent that closure does not occur, there is no imperative for organism-environment coevolution. Coevolution at the system level based on indirect effects is compatible with normal evolution at the individual organism level based on direct effects. The organism is the unit of the latter, but environs are the unit of coevolution.

Hormone Specificity, Androgen Metabolism, and Social Behavior

Abstract: SYNOPSIS The ability of different sex hormones to activate social signals can provide important clues to the biochemical mechanisms underlying these signals A pattern of hormone specificity in which testosterone (T) and estradiol (E), but not dihydrotestosterone (DHT), are effective suggests that conversion (aromatization) of T to E in the brain may be involved or required; a pattern in which T and DHT, but not E, are effective suggests that conversion of T to DHT may be involved The hormone specificity of social signals in diverse species of vertebrates is reviewed Aromatization seems to be of widespread behavioral significance in mammals andbirds A role for conversion of T to DHT is suggested for some signals Aromatization of T mayalso be important for the activation of adult female behavior in mammals and lizards, and for the early organization of behavior in mammals and birds Patterns of hormone specificity differ both across species for a given social signal, and within a given species when different signals are compared An attempt is made to integrate these findings by relating patterns of hormone specificity to hormone levels, steroid receptor and enzyme concentrations and distributions, signal function and dimorphism, and phylogenetic status

Portasomes as Coupling Factors in Active Ion Transport and Oxidative Phosphorylation

Abstract: SYNOPSIS. We propose that particles, 7–15 nm in diameter, observed on the apical plasma membranes of cation transporting cells of insect midgut, salivary glands, and Malpighian tubules are modified F1-F coupling complexes such as those found on phosphorylating membranes of mitochondria, chloroplasts, and bacteria. We suggest the generic term, portasome, to describe all of these particles and point out that they are located on the side of the membrane which is electronegative and has the low cation concentration, i.e. , on the input side in each case. Biophysical evidence identifies the portasome bearing membrane as the ion transporting membrane in several insect epithelia, some of which exhibit ion modulated ATPase activity. The activity of a K+-modulated ATPase from Manduca sexta midgut is increased in portasome enriched plasma membrane fractions. We propose that portasomes orient the scalar hydrolysis of negatively charged MgATP2− to less negatively charged MgADP thereby eliminating the attraction of MgATP2− to K+ with the result that the K+ ions are ejected to the opposite side of the portasome bearing membrane. This mechanism explains the coupling of the scalar hydrolysis of ATP to the vectorial active transport of K+ which leads to the establishment of a K+ electrochemical gradient. The reverse process, but with an H+ ionophore replacing a K+ ionophore in the portasome, would provide a mechanism for coupling the vectorial flow of H+, driven by a proton electrochemical gradient, to scalar ATP synthesis and thereby provide a mechanism for oxidative phosphorylation. Electrogenic active potassium ion transport would appear to have evolved from oxidative phosphorylation.

Growth of Fish Retinas

Abstract: SYNOPSIS. This review discusses development and growth of the retina. A geometric model of retinal differentiation is proposed in which four phases are recognized; the first three are common to all vertebrate embryos. The last, post-embryonic growth phase has two alternate routes, one followed by birds and mammals and the other by fish and amphibians. All retinas grow by expansion, and retinal cells are spread apart as the retina enlarges. In fish (and larval amphibians), the retina not only expands but also adds cells. In these retinas a marginal germinal zone persists and continues to produce neurons, which are added appositionally in concentric annuh around the perimeter. The genesis of one class of photoreceptor cell, the retinal rods, is different from all other retinal neurons in that the proportion of rods increases with growth in central retinal regions far from the germinal zone. The source of these centrally-added rods is not yet established; several hypotheses are discussed. Alterations of synaptic connectivity within the retina and between retina and brain are suggested by the pattern of growth and cell addition. The capacity of adult fishes to generate new neurons and to form new synapses is a remarkable property, one which most animals abandon much earlier in life.

Interspecific Competition and Species' Distributions: The Ghosts of Theories and Data Past

Abstract: The idea that biological interactions between species restrict their distributions beyond limits set by the inorganic environment was established by plant ecologists well before the work of Volterra, Gause, and the development of modern niche theory. Mechanisms of competition between plant species, and the influence of predation and environmental factors on the outcome of interspecific competition, were demonstrated by extensive field experiments. These early botanical achievements were ignored by zoologists whose subsequent, independently derived ideas about competition paralleled those of plant ecologists to a remarkable degree. Application of niche theory to the real world was closely tied to the advent of the “modern synthesis.” The primary innovation of niche theory was not simply a new appreciation of the possible importance of competition between animals, but the incorporation of an evolutionary perspective to distributional problems largely absent among ecologists since Darwin.

Interaction Between Ecdysteroid, Eclosion Hormone, and Bursicon Titers inManduca sexta

Abstract: SYNOPSIS. The end of the molting process in the tobacco hornworm includes the rapid digestion of the old cuticle, molting fluid resorption, ecdysis of the old cuticle, and expansion and hardening of the new cuticle. The coordination of these processes is accomplished by three hormones. Each ecdysis during the life of Manduca appears to be triggered by eclosion hormone. Depending on developmental stage, the hormone comes either from the brain-corpora cardiaca complex or from the chain of ventral ganglia. The neural programs triggered by eclosion hormone include a neuroendocrine event, the release of the tanning hormone, bursicon, thereby ensuring that tanning of the new cuticle must follow ecdysis. Ecdysis, itself, appears to be controlled by the ecdysteroid levels since ecdysteroid injections delay ecdysis at physiological concentrations and in a dose dependent fashion. This delay is due to inhibition of eclosion hormone secretion and to the retardation of the terminal phases of the molt including the digestion of the old cuticle and the onset of sensitivity to eclosion hormone. Thus, eclosion hormone secretion and the ecdysis it triggers are coordinated with the end of development because both are influenced by the same endocrine signal—the decline in the ecdysteroid titer.

Hormonal Regulation of Female Reproductive Behavior in Fish

Abstract: Synopsis. Fundamentally different mechanisms regulate female sexual behavior in the ovoviviparous guppy and the oviparous goldfish. In the female guppy, ovarian estrogen evidently synchronizes cycles of sexual receptivity with endogenous cycles of ovarian mat? uration and also increases female attractivity at the time of maximum receptivity by stimulating the release of a sexual pheromone. In the goldfish, it appears that prostaglandin, released from the ovary or oviduct in conjunction with ovulation and the presence of ovulated eggs, acts on the brain to stimulate spawning behavior. In contrast to the situation in the guppy, steroid treatments alone (in the absence of ovulated eggs) fail to stimulate spawning behavior in the goldfish. It is proposed that endocrine mechanisms regulating female sexual behavior in the teleosts and in other vertebrates are less related to phylogeny than to the mode of reproduction employed. In the goldfish and several other externally fertilizing teleosts, where sexual behavior involves oviposition, female sexual behavior apparently is synchronized with ovulation by mechanisms which respond to elevated plas? ma prostaglandin as an indicator of the presence of ovulated eggs. In internally fertilizing species (guppy, reptiles, birds, mammals), where sexual behavior and fertilization are temporally dissociated, female sexual behavior is synchronized with ovulation by mecha? nisms which anticipate either an imminent spontaneous ovulation, or the potential for reflex ovulation, by responding to increases in plasma estrogen associated with follicular development.