While it is true that members of most sexually reproducing species can be defined as either male or female, those who belong to the rest of the biological world are not so simply understood. Hermaphroditic creatures reproduce both as male and as female individuals, providing a fascinating glimpse into alternative sexual practices in nature and their ecological and evolutionary successes and failures. Eloquently written by an award-winning biologist and pioneer in molecular ecology, this primer on hermaphroditism traces the phenomenon throughout Earth's myriad species, accounting for the adaptive significance of alternative sexual systems. Accessible and richly illustrated, the text maps the evolutionary origins of hermaphroditism, as well as its historical instances and fictional representations, underscoring the relevance of dual sexuality to our biological, intellectual, and cultural making. John C. Avise describes the genetics, ecology, phylogeny, and natural history of hermaphroditic plants, fish, and invertebrate animals and details organisms that either reproduce simultaneously as male and female or switch routinely between one sex and the other. Filled with surprising creatures and compelling revelations, this textbook stands alone in its clear yet comprehensive treatment of hermaphroditism and its unique challenge to the supremacy of separate sexes.

When Richard Goldschmidt' coined the term "intersexuality" in 1915, he intended it to apply to normally dioecious species which exhibit some kind of mixture between male and female characters. However, as knowledge of the bewildering variability present in the sexual orga nization of members of the animal kingdom has increased, the original meaning of the word has changed. Today many authors define inter sexuality as "the presence of both male and female characteristics, or of intermediate sexual characteristics, in a single individual".2 This more extensive and widely accepted concept justifies the title of our book •. Among all the anatomical and physiological features of living organisms the reproductive system has a unique importance for the perpetuation of the species. Conversely, reproductive processes are of little or no account for the viability of the individual. Therefore, within the framework of general biology reproduction has all too often been looked at solely from the point of view of genetics. Lively discussions about genotypic versus phenotypic sex determination long dominated the sci entific literature on sexuality in animals; this one-sided emphasis has tended to obscure many important facets of an organism's ability to reproduce. Recent developments in current biological research have brought the classic problem of sex differentiation into focus again, and the rapid progress being made in comparative endocrinology has added a new di mension to the study of reproductive biology.

Marine fishes represent astonishing diversity with respect to practically every aspect of their biology. Reproductive modes and sexual patterns are especially fascinating and provide deep insight into general evolutionary problems. In this volume, chapters focus on reproduction and sexuality among groups of fishes defined by habitat, taxon, and the reproductive processes that are critical for reproductive success. The book illustrates how knowledge of reproductive biology among marine fishes can help identify vulnerable and potentially vulnerable species in the face of changing environmental conditions and increasing human-based pressures.

This book provides a comprehensive review of hermaphroditism in fishes. It focuses on the behavioral ecology of functional hermaphroditism in fishes and discusses its evolution. Approximately 99% of all vertebrate species consist of separate-sex individuals (gonochorists), i.e., pure males and pure females. The other 1% of vertebrate species are hermaphroditic, and almost all of them are fishes. Among hermaphroditic fishes, four major types of hermaphroditism are known: simultaneous (or synchronous) hermaphroditism, protandry (male-to-female sex change), protogyny (female-to-male sex change), and bidirectional sex change (or reversed sex change in protogynous species). The book examines the occurrence of hermaphroditism in relation to phylogeny and mating systems. It also reviews the hypotheses for the evolution of hermaphroditism, and the size-advantage model, which is the main theory for the evolution of sex change, tested in relation to the mating system. The appendix in the last chapter provides an annotated list of hermaphroditic fish species (ca. 500 spp.).

The unprecedented level of diversity recorded among the clones of self-fertilizing gynogenetic unisexuals and self-fertilizing simultaneous hermaphrodites challenges current ideas on the predominant role of recombination in promoting evolution of biological diversity. Though limited to a few species, the existence of self-fertilizing and cycli

This book presents the first unified conceptual and statistical framework for understanding the evolution of reproductive strategies. Using the concept of the opportunity for sexual selection, the authors illustrate how and why sexual selection, though restricted to one sex and opposed in the other, is one of the strongest and fastest of all evolutionary forces. They offer a statistical framework for studying mating system evolution and apply it to patterns of alternative mating strategies. In doing so, they provide a method for quantifying how the strength of sexual selection is affected by the ecological and life history processes that influence females' spatial and temporal clustering and reproductive schedules. Directly challenging verbal evolutionary models that attempt to explain reproductive behavior without quantitative reference to evolutionary genetics, this book establishes a more solid theoretical foundation for the field. Among the weaknesses the authors find in the existing data is the apparent ubiquity of condition-dependent mating tactics. They identify factors likely to contribute to the evolution of alternative mating strategies--which they argue are more common than generally believed--and illustrate how to measure the strength of selection acting on them. Lastly, they offer predictions on the covariation of mating systems and strategies, consider the underlying developmental biology behind male polyphenism, and propose directions for future research. Informed by genetics, this is a comprehensive and rigorous new approach to explaining mating systems and strategies that will influence a wide swath of evolutionary biology.

Darwin famously described special difficulties in explaining social evolution in insects. More than a century later, the evolution of sociality - defined broadly as cooperative group living - remains one of the most intriguing problems in biology. Providing a unique perspective on the study of social evolution, this volume synthesizes the features of animal social life across the principle taxonomic groups in which sociality has evolved. The chapters explore sociality in a range of species, from ants to primates, highlighting key natural and life history data and providing a comparative view across animal societies. In establishing a single framework for a common, trait-based approach towards social synthesis, this volume will enable graduate students and investigators new to the field to systematically compare taxonomic groups and reinvigorate comparative approaches to studying animal social evolution.

The study of alternative reproductive tactics (the behavioural strategies used by individuals to increase their reproductive success) is an evolutionary puzzle, and one of great interest to researchers. For instance, why do some males guard both nest and eggs, while others sneak into nests while pairs are spawning and fertilise those eggs? The field offers a special opportunity to study the evolution and functional causes of phenotypic variation, which is a general problem in the field of evolutionary biology. By integrating both mechanistic (psychological) and evolutionary (behavioural ecology) perspectives and by covering a great diversity of species, Alternative Reproductive Tactics addresses this integrated topic of longstanding interest, bringing together a multitude of otherwise scattered information in an accessible form that is ideal for graduate students and researchers.

Sex Determination, Volume 134, the latest release in the Current Topics in Developmental Biology series, contains current reviews in the field of vertebrate sex determination. It covers molecular pathways of sex determination in genetic and environmental species and encompasses both sex determination of somatic lineages and commitment of germ cells to male or female fate. Chapters in this new release cover, amongst other topics, Mapping the Sox9 Enhancer Elements, Epigenetic Regulation of Sex Determination, Evolution and Management of Sex Chromosomes, Regulation of Germ Cell Sex Identity in Medaka, Control of Sex Determination in Zebrafish, Sexually Dimorphic Germ Cell Identity in Mammals, and more. - Contains reviews written by leading experts in each field - Includes informative figures that illustrate principle points that are useful for teaching - Written in a style that is clear and simple

Cichlid fishes are amazing creatures. In terms of sheer number of species, they are the most successful of all families of vertebrate animals, and the extent and speed with which they have evolved in some African lakes has made them the darlings of evolutionary biologists. But what truly captivates biologists like George Barlow -- not to mention thousands of aquarists the world over -- is the complexity of their social lives and their devotion to family (most species of cichlids are monogamous and many pairs share the responsibility of raising offspring). In this wonderful book, Barlow describes the unusually high intelligence of these fishes, their complex mating and parenting rituals, their bizarre feeding and fighting habits, and the unusual adaptations and explosive rate of speciation that have enabled them to proliferate and flourish. A celebration of their diversity, The Cichlid Fishes is also a marvelous exploration of how these unique animals might help resolve the age-old puzzle of how species arise and evolve.