Biological reviews of the Cambridge Philosophical Society最新文献

The relationship between phylogenetic reconstruction and evolutionary theory is reassessed. It is argued here that phylogenies, and evolutionary principles, should be analysed initially as independently from each other as possible. Only then can they be used to test one another. If the phylogenies and evolutionary principles are totally consistent with one another, this consilience of independent lines of evidence increases confidence in both. If, however, there is a conflict, then one should assess the relative support for each hypothesis, and tentatively accept the more strongly supported one. We review examples where the phylogenetic hypothesis is preferred over the evolutionary principle, and vice versa, and instances where the conflict cannot be readily resolved. Because the analyses of pattern and process must initially be kept separate, the temporal order in which they are performed is unimportant. Therefore, the widespread methodology of always proceeding from cladogram to evolutionary 'scenario' cannot be justified philosophically. Such an approach means that cladograms cannot be properly tested against evolutionary principles, and that evolutionary 'scenarios' have no independent standing. Instead, we propose the 'consilience' approach where phylogenetic and evolutionary hypotheses are formulated independently from each other and then examined for agreement.

Developmental stability reflects the ability of a genotype to undergo stable development of a phenotype under given environmental conditions. Deviations from developmental stability arise from the disruptive effects of a wide range of environmental and genetic stresses, and such deviations are usually measured in terms of fluctuating asymmetry and phenodeviants. Fluctuating asymmetry is the most sensitive indicator of the ability to cope with stresses during ontogeny. There is considerable evidence that developmental stability, and especially fluctuating asymmetry, is a useful measure of phenotypic and genetic quality, because it covaries negatively with performance in multiple fitness domains in many species, including humans. It is proposed that developmental stability is an important marker of human health. Our goal is to initiate formally the integration of the sciences of evolutionary biology, developmental biology and medicine. We believe that this integrative framework provides a significant addition to the growing field of Darwinian medicine. The literature linking developmental stability and disease in humans is reviewed. Recent biological theoretical treatments pertaining to developmental stability are applied to a range of human health issues such as genetic diseases, ageing and survival, subfertility, abortion, child maltreatment by parents, cancer, infectious diseases, physiological and mental health, and physical attractiveness as a health certification.

Amphibians occupy a wide range of habitat types from arid deserts to deep freshwater lakes; they may spend most of their life underground or high in cloud forest canopy. Some are found north of the Arctic Circle and can tolerate freezing conditions, while others have evolved a range of adaptations to avoid desiccation in some of the hotter areas of the world. The skin plays key roles in the everyday survival of amphibians and their ability to exploit a wide range of habitats and ecological conditions. The normal functions of the skin are surveyed and Eisner's biorational approach to chemical prospecting--seeking clues from an animal's behaviour and its interactions with its environment to reveal the presence of chemical compounds with potential medical or veterinary applications--is applied to amphibians. The biology and natural history of amphibian skin, its glands and their secretions are briefly reviewed. Four categories of compounds are found in the granular or poison glands, these are: biogenic amines, bufodienolides (bufogenins), alkaloids and steroids, peptides and proteins. Toads, particularly members of the genus Bufo, are identified as a particularly convenient and useful source of granular gland secretions. The potential medical-pharmaceutical significance of products derived from amphibian skin secretions is discussed. The need for a humane approach to this work is noted.

In the 1790s, Robert Townson established the main features of the water economy of terrestrial amphibians: rapid evaporative water loss in dry surroundings, 'drinking' by absorption of water through the abdominal skin pressed against moist substrates, and use of the urinary bladder as a reservoir from which water is reabsorbed on land. This knowledge was of little interest to the establishment in the first half of the nineteenth century of experimental physiology as a basic medical discipline, when frogs became models in the elucidation of general physiological processes. Townson's pioneer contributions to amphibian physiology were forgotten for 200 years (Jørgensen 1994b). During (1901) and particularly Overton (1904) restored knowledge about amphibian water economy to the level reached by Townson, but the papers had little impact on the young science of animal physiology because they primarily aimed at elucidating the transport of fluids across membranes. Frog skin remained a model preparation in such studies throughout the century. With the establishment of terrestrial ecology early in the century, the relations of animals, including amphibians, to water became a central theme. Concurrently with comparative studies of amphibian water economy in an ecological setting, the subject proceeded as an aspect of animal osmoregulation. Adolph (1920-1930) and Rey (1937a) established the highly dynamic nature of water balance in amphibians in water and on land. Their observations indicated functional links between environment, skin and kidneys, the nature of which remained to be explored. Thorson & Svihla (1943) reopened the ecological approach in a comparative study of the relations between amphibian habitat and tolerance of dehydration. By mid-century, the central themes of amphibian adaptations to terrestrial modes of life were re-established, except for the function of the bladder as a water-depot. During the following decades, a rich literature appeared, particularly focusing on adaptations of amphibians to arid environments. Thus, in the 1970s, it was found that 'waterproofing' of the highly permeable skins by means of skin secretions had evolved independently in several families of tropical arboreal frogs, and that a number of amphibians that aestivate whilst burrowed in dry soil could reduce evaporation by forming cocoons from shed strata cornea. In 1950-1970 the role of bladder urine as a water depot in terrestrial amphibians was recognized: this did not change the established view of water balance in terrestrial amphibians as alternating between dehydration on land and rehydration in response to the deficit in body water. Amphibians may, however, maintain normal water balance whether the ambient medium is water or air by means of little understood integrated mechanisms in control of cutaneous drinking behaviour, water permeability of the skin and bladder wall, and urine production.

The aim of this review is to consider variation in mating preferences among females. We define mating preferences as the sensory and behavioural properties that influence the propensity of individuals to mate with certain phenotypes. Two properties of mating preferences can be distinguished: (1) "preference functions'-the order with which an individual ranks prospective mates and (2) "choosiness'-the effort an individual is prepared to invest in mate assessment. Patterns of mate choices can be altered by changing the costs of choosiness without altering the preference function. We discuss why it is important to study variation in female mating behaviour and identify five main areas of interest: Variation in mating preferences and costs of choosiness could (1) influence the rate and direction of evolution by sexual selection, (2) provide information about the evolutionary history of female preferences, (3) help explain inter-specific differences in the evolution of secondary sexual characteristics, (4) provide information about the level of benefits gained from mate choice, (5) provide information about the underlying mechanisms of mate choice. Variation in mate choice could be due to variability in preference functions, degree of choosiness, or both, and may arise due to genetic differences, developmental trajectories or proximate environmental factors. We review the evidence for genetic variation from genetic studies of heritability and also from data on the repeatability of mate-choice decisions (which can provide information about the upper limits to heritability). There can be problems in interpreting patterns of mate choice in terms of variation in mating preferences and we illustrate two main points. First, some factors can lead to mate choice patterns that mimic heritable variation in preferences and secondly other factors may obscure heritable preferences. These factors are divided into three overlapping classes, environmental, social and the effect of the female phenotype. The environmental factors discussed include predation risk and the costs of sampling; the social factors discussed include the effect of male-male interactions as well as female competition. We review the literature which presents data on how females sample males and discuss the number of cues females use. We conclude that sexual-selection studies have paid far less attention to variation among females than to variation among males, and that there is still much to learn about how females choose males and why different females make different choices. We suggest a number of possible lines for future research.

Fetal growth and development is dependent upon the nutritional, hormonal and metabolic environment provided by the mother. Any disturbance in this environment can modify early fetal development with possible long-term outcomes as demonstrated by extensive work on 'programming'. Growth restriction resulting from a deficit in tissue/organ cell number (as measured by tissue DNA content) is irrecoverable. However, when the cell size (or cell protein content) is reduced, the effects on growth may not be permanent. Recent epidemiological studies using archival records of anthropometric measurements related to early growth in humans have shown strong statistical associations between these indices of early development and diseases in later life. It has been hypothesised that the processes explaining these associations involve adaptive changes in fetal organ development in response to maternal and fetal malnutrition. These adaptations may permanently alter adult metabolism in a way which is beneficial to survival under continued conditions of malnutrition but detrimental when nutrition is abundant. This hypothesis is being tested in a rat model which involves studying the growth and metabolism in the offspring of rat dams fed a low-protein diet during pregnancy and/or lactation. Using this rat model, it has been demonstrated that there is: (i) Permanent growth retardation in offspring nursed by dams fed a low-protein diet. (ii) Permanent and selective changes in organ growth. Essential organs like the brain and lungs are relatively protected from reduction in growth at the expense of visceral organs such as the liver, pancreas, muscle and spleen. (iii) Programming of liver metabolism as reflected by permanent changes in activities of key hepatic enzymes of glycolysis and gluconeogenesis (glucokinase and phosphoenolpyruvate carboxykinase) in a direction which would potentially bias the liver towards a 'starved' setting. We have speculated that these changes could be a result of altered periportal and perivenous regions of the liver which may also affect other aspects of hepatic function. (iv) Deterioration in glucose tolerance with age. (v) An increase in the life span of offspring exposed to maternal protein restriction only during the lactation period, and a decrease in life span when exposed to maternal protein restriction only during gestation. These studies show that hepatic metabolism and even longevity can be programmed by events during early life.

Serotonergic neurons are present in all phyla that possess nervous systems. In most of these phyla, serotonin modulates important behaviours, including feeding, sexual and aggressive behaviour. Serotonin exerts its effects by acting in three basic modes: as a classical neurotransmitter, as a neuromodulator, or as a neurohormone. In a number of invertebrate species, the neural circuitry underlying the effects of serotonin has been well characterized, whereas in vertebrates, the mechanisms by which serotonin affects behaviour are currently less fully understood. The following review examines the role played by serotonin in the generation and modulation of behaviour in successively more complex species, ranging from coelenterates to humans.

The aim of this review is to summarize newly available information on lemur social systems, to contrast it with the social organization of other primates and to relate it to existing models of primate social evolution. Because of their evolutionary history, the primates of Madagascar constitute a natural experiment in social evolution. During millions of years of isolation, they converged with other primates only in the most fundamental way in the evolution of solitary, pair-living and group-living species, but deviate in several respects within these basic categories of social organization. Solitary lemurs remain poorly studied, but their social organization appears to be broadly similar to that of other solitary primates, even though the unexpected lack of sexual dimorphism may indicate that similar types of social organization can give rise to different mating systems. The determinants of a solitary lifestyle remain elusive. Pair-living lemurs show striking convergences with other monogamous primates in several behavioural traits, but also deviate in that the majority of species are at least partly nocturnal and do not exhibit direct paternal care of dependent young. Group-living lemurs have not evolved single-male groups, male-bonded and multi-level societies, and polyandrous groups may also be lacking. Female philopatry is common, but female bonds are generally weakly developed and eviction of females from natal groups is not unusual. Group-living lemurs also differ from anthropoids in that their groups have even adult sex ratios, smaller average size and may split up on a seasonal basis. Feeding competition, predation risk and reproductive competition can not fully explain these unusual aspects of lemur social organization. It has therefore been suggested that the social consequences of the risk of infanticide and of recent changes in activity may be ultimately responsible for these idiosyncracies of group-living lemurs, an explanation largely supported by the available evidence. Thus, social factors and fundamental life-history traits, in addition to ecological factors, contribute importantly to variation in social systems among lemurs, and possibly other primates. However, neither the diversity of lemur social systems, nor the evolutionary forces and mechanisms operating in these and other primates are yet fully understood.

Resemblance between animal taxa may be due to convergence rather than to recent common ancestry. Constraints on biological materials and adaptation to particular habits or habitats will produce widespread convergence. How may we distinguish the two causes of resemblance? The relationship between convergence and taxonomy is discussed, demonstrating that the choice of taxonomic method will itself determine the extent to which convergence is perceived. In particular, cladistic analysis based on parsimony will tend to minimise and thus conceal convergence: neither the resulting cladogram nor a consistency index derived from it can be used to assess the prevalence of convergence. With any taxonomic system, there can be no substitute for evaluation of the morphological characters used. Complementary use of molecular characters shows promise: we wait further understanding of constraints in genetic evolution and of the possibilities of convergence at this level also. These general principles are illustrated with a range of examples from within and between invertebrate phyla: the phylogeny of Cnidaria and Platyhelminthes cannot be traced with certainty, but where the fossil record allows clear rooting, as for the echinoderms and in particular the echinoids, combination of morphological and molecular methods has made much progress. Sub-groups within a phylum, for example opisthobranch molluscs and the dipteran Phoridae, may show an uncontested phylogeny, and here studies have precisely identified convergence and shown that it may be the commoner cause of resemblance. Adaptation to exacting environments shown by terrestial and freshwater nemertines may also result in a predominance of convergent resemblance. Traditional grouping of phyla breaks down on re-examination of supposedly key characters, such as segmentation, body cavities, germ layers and symmetry, each of which must have had multiple origins: nor are developmental stages (especially not larvae) a reliable guide to relationships. Demarcation of phyla may be difficult, as with arthropods, and location of phyla is even more difficult, due to their early and rapid radiation. Over-simplified definition of characters has bedevilled invertebrate classification and the use of molecular data has not yet resolved the major controversies. The question "How common is convergence?' remains unanswered and may be unanswerable. Our examples indicate that even the minimum detectable levels of convergence are often high, and we conclude that at all levels convergence has been greatly underestimated.