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Genetic diversity within social insect colonies has proven to confer important benefits. At the population level, genetic diversity is ultimately determined by the genetically effective population size (Ne), which due to the combination of eusociality, haplodiploidy and complementary sex determination, is far more constrained in the eusocial Hymenoptera (ants, bees and wasps) than in other insect taxa. In consequence, strong selective pressures are expected to have shaped the mating systems of these insects in order to maintain genetic diversity and avoid the negative effects associated with inbreeding depression. Using the army ant Eciton burchellii and the honeybee Apis mellifera as study models, I addressed the impact of mating systems on the genetic structure of wild populations of eusocial Hymenoptera. Both species share important characteristics, such as obligate queen multiple mating, dependent colony foundation and extremely male-biased sex ratios, but differ in the patterns of mating and dispersal. First, I proved the existence of a genetic component for worker caste determination in E. burchellii, showing that high genetic variation combined with a genetic component to worker caste determination, may increase homeostasis in systems with complex division of labour. Relying on sibship reconstruction analyses I then showed that dispersal and polyandry seem to enhance gene flow and minimize the deleterious effects associated with the small effective population size of army ants and honeybees. Finally, I provide an insight into the mode by which sexual selection operates in both groups, illustrating that whereas female choice in army ants seems to promote outbreeding, male-male competition among honeybee drones is mainly based on environmental cues, and thus not likely to constrain genetic diversity. My results highlight the importance of dispersal and gene flow as key factors shaping the evolution of mating systems in highly eusocial Hymenoptera.
Insects display a staggering diversity of mating and social behaviours. Studying these systems provides insights into a wide range of evolutionary and behavioural questions, such as the evolution of sex, sexual selection, sexual conflict, and parental care. This edited volume provides an authoritative update of the landmark book in the field, The Evolution of Insect Mating Systems (Thornhill and Alcock, 1983), which had such a huge impact in shaping adaptationist approaches to the study of animal behaviour and influencing the study of the evolution of reproductive behaviour far beyond the taxonomic remit of insects. This accessible new volume brings the empirical and conceptual scope of the original book fully up to date, incorporating the wealth of new knowledge and research of the last 30 years. It explores the evolution of complex forms of sex determination in insects, and the role of sexual selection in shaping the evolution of mating systems. Selection arising via male contest competition and female choice (both before and after copulation) are discussed, as are the roles of parasites and pathogens in mediating the strength of sexual selection, and the role that parental care plays in successful reproduction. The Evolution of Insect Mating Systems is suitable for both graduate students and researchers interested in insect mating systems or behaviour from an evolutionary, genetical, physiological, or ecological perspective. Due to its interdisciplinary and concept-driven approach, it will also be of relevance and use to a broad audience of evolutionary biologists.
Insects and arachnids display the most impressive diversity of mating and social behaviour among all animals. This book investigates sexual competition in these groups, and the variety of ways in which males and females pursue, persuade, manipulate, control and help one another, enabling us to gain a better understanding of how conflicts and confluences of interest evolve together. Each chapter provides a comprehensive review of mating systems in particular insect and arachnid groups, discusses intrinsic and extrinsic factors responsible for observed mating strategies, and suggests fruitful avenues for further research. The book culminates in a synthesis, reviewing the date in terms of the theory of sexual conflict. This broad-based book will be of immense value to students and researchers interested in reproductive strategies, behavioural ecology, entomology and arachnology.
Sperm Competition and the Evolution of Animal Mating Systems describes the role of sperm competition in selection on a range of attributes from gamete morphology to species mating systems. This book is organized into 19 chapters and begins with the conceptualization of sperm competition as a subset of sexual selection and its implications for the insects. The following chapter describes the relationship between multiple mating and female fitness, with an emphasis on determining the conditions under which selection on females is likely to counteract selection on males for avoiding sperm competition. Other chapters consider the female perspective on sperm competition; the evolutionary causation at the level of the individual male gamete; and the correlation of high paternal investment and sperm precedence in the insects. The remaining chapters are arranged phylogenetically and explore the sperm competition in diverse animal taxa, such as the Drosophila, Lepidoptera, spiders, amphibians, and reptiles. These chapters also cover the evolution of direct versus indirect sperm transfer among the arachnids or the problem for kinship theory presented by multiple mating and sperm competition in the Hymenoptera. This book further discusses the remarkable potential for sperm competition among certain temperate bat species whose females store sperm through winter hibernation and the mixed strategies and male-caused female genital trauma as possible sperm competition adaptations in poeciliid fishes. The concluding chapter examines the predictions concerning testes size and mating systems in the primates and the possible role of sperm competition in human selection. This book is of great value to reproductive biologists and researchers.
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.
This up-to-date review examines key areas of animal behaviour, including communication, cognition, conflict, cooperation, sexual selection and behavioural variation. Various tests are covered, including recent empirical examples.
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.
Sexual selection has long been recognised as driving the evolution of diverse morphological and behavioural traits in animals. Decades of concerted research into the topic has uncovered reproductive adaptations ranging from the beautiful to the horrific, and insects provide some of the most striking examples from all parts of that spectrum. The diversity of insects, their mating systems, and their reproductive adaptations has made them crucial to our understanding of sexual selection and the evolution of sexual reproduction itself. Their natural amenability to observation and experimentation has granted us many useful and informative model systems for that endeavour. In particular, the Orthoptera (crickets, grasshoppers, katydids, wētā and their allies) have provided many model species for the study of acoustic mate calling, nuptial provisioning, intrasexual combat, the economics of reproduction that contribute to sexual conflict, and countless other topics in the realm of reproductive ecology. The current research delves into the diversity of mating system traits exhibited by the order, with a comprehensive review of the literature, as well as targeted evolutionary hypothesis testing via the phylogenetic comparative method. I then investigate in detail the reproductive ecology of New Zealand cave wētā, which are fascinating representatives of a globally distributed but hardly-studied orthopteran family, the Rhaphidophoridae. Firstly I investigate orthopteran reproductive ecology with analyses of sexual evolution across the order. I test for phylogenetic signal, ancestral character states and correlated evolution with data derived from a comprehensive literature search, using a synthetic supertree assembled for that purpose by tree grafting. The results of this approach indicated trends of strong evolutionary conservatism in orthopteran sexual traits, and a probable ancestral mating system that involved protandry, male-male combat and mate-guarding, acoustic mate-calling, and female-biased sexual size dimorphism, but without coercive mating or exaggerated weaponry. Although I was able to model the evolution of these traits, phylogenetic comparisons did not provide evidence in support of correlated evolution between them. I then move from broad questions to detailed examination of sexually dimorphic antennal structures in New Zealand cave wētā (Rhaphidophoridae: Pachyrhamma sp). Using scanning electron microscopy, I describe the morphology of microsensory hairs (sensilla) in P. waitomoensis and P. acanthocera and test for sexual dimorphism in the length, as well as presence and absence of these. This reveals numerous sensilla with unique morphology that may be particular to the group, and suggests possible sensory functions based on their individual characteristics. In addition, I provide the first detailed examination of intriguing, horn-like antennal cuticular structures that are restricted to males of these species. The two kinds of protrusive structure have some qualities that suggest a secretory function, indicating that male pheromonal communication may be an important aspect of those species' ecology. Subsequently, I investigate New Zealand cave wētā behavioural ecology with field-based approaches to observing P. waitomoensis. I examine the role of sexually dimorphic, elongated hind-legs in that species in the context of mate guarding, a central topic in the study of sexual selection. Interestingly, although males doggedly guard their mates with their exaggerated hind-legs, the limbs do not appear to function in warding off rivals. Because of that observation, I tested the novel hypothesis that the mate guarding behaviour and morphology of male P. waitomoensis instead serves to reduce disturbance to females by organisms other than sexual rivals of the male. Through several simple experiments with the wētā in their natural environment, I show a reduction in pair duration when females are disturbed, a disturbance-protection effect of male presence, a mating advantage to males that can guard their mates for longer, and a negative correlation between male hind-leg length and the likelihood of disturbance to the female. Taken together, these results provide an example of a mate guarding role in exaggerated trait evolution, and a novel function of mate guarding that may occur in other taxa. In addition, this highlights the importance of considering environmental context when examining behaviour, as well as raising the possibility that more potential female benefits of mate guarding may be observed if study organisms are observed in nature. After examining mate guarding, I continue the investigation of exaggerated trait evolution in P. waitomoensis by looking at the additional role of their elongated hind-legs in male-male-combat and competitive assessment. By comparing morphometric data with video recordings of intrasexual contest behaviour in the field, I showed that males with longer legs have greater chances of victory in combat. In addition, when the difference in leg-length between contestants was greater, fights escalated to a lesser degree. The observed relationship between contestant leg-length and contest escalation matched the predictions of the selfonly model of assessment, according to current contest theory. The results highlight the fact that fighting and weaponry are an important part of cave wētā reproductive ecology, and indicate that other Rhaphidophoridae with similar morphology may represent an overlooked trove of examples for exaggerated weaponry research in the Orthoptera. Lastly I approach the question of exaggerated weapon evolution from a different angle. Using software designed for entertainment war-gaming, I edited matches in order to pitch artificial intelligence contestants against one another under varied experimental conditions. By doing so, I was able to test the hypothesis that one-on-one duel scenarios favour arms superiority, a potential explanatory factor in the presence of extreme weaponry among various taxa, and in the occurrence of arms races in non-animal systems. I found that strong contestants enjoyed a greater advantage when fighting head-to-head, in contrast to the lack of any advantage in more chaotic skirmishes with multiple opponents. The advantage of superior weaponry showed the same pattern, in two different forms of contest. This suggests that conflict scenarios that are restricted to duels may contribute to weaponry escalation, in diverse systems. I thereby demonstrate a novel technique for approaching a difficult-to-test, broad evolutionary question, and show the potential for widely available and user-friendly consumer software to provide simulators for approaching scientific questions. Overall, this thesis summarises sexual selection research in the Orthoptera offers a hypotheses regarding ancestral mating systems in the order, provides new data on a poorly studied family, and tests a general hypothesis in a novel way. As well as reviewing and analysing existing knowledge and providing new discoveries in an overlooked group, this research opens and highlights novel avenues for investigation of orthopteran reproductive ecology, the examination of sexual selection, and the evolution of extreme weaponry.