Specialization, Speciation, and Radiation: The Evolutionary Biology of Herbivorous Insects

PREFACE

xiii This book examines the evolutionary biology of herbivorous insects, including their relationships with their host plants and natural enemies. It is a compendium pulling together many aspects of evolutionary study at different levels of biological organization, from individuals to clades. The inspiration for this book was a symposium I organized for the 2003 annual meeting of the Entomological Society of America, in memory of the late Thomas K. Wood, who worked on sympatric speciation in Enchenopa treehoppers . My goal for the symposium was to bring together people working on insect-plant evolution from several different perspectives, including those working on ecological and population genetics, behavior, speciation, macroevolution, and systematics. In chapter 16, Thompson notes that there has historically been a “conceptual tension between fields of study that focus on current selection, such as evolutionary ecology and population genetics, and fields that focus on higher-level patterns in the diversification of life, such as systematics and paleobiology.” During the symposium, there was a noticeable synergy that came from having people speak about evolutionary topics normally considered somewhat independent subdisciplines, but all united by the common theme of insect-plant interactions. These speakers were the nucleus of contributors to this volume, which doubled in chapter number after the inclusion of additional topics and authors. It is my hope that the common theme of insect-plant evolution will help readers to link ideas from micro- and macroevolutionary levels of study to overcome the conceptual tension that exists between them, and that this book will thereby contribute to a more holistic understanding of evolutionary process. Chapters are organized into three sections: Evolution of Populations and Species; Co- and Macroevolutionary Radiation; and Evolutionary Aspects of Pests, Invasive Species, and the Environment. The first section focuses on evolutionary mechanisms that maximize the fitness of individuals and the populations they comprise, and mechanisms that drive populations to speciation. The second section concentrates on the evolutionary forces that generate and maintain insect and plant biodiversity. Chapters in the third section draw on concepts developed in the first two, but relate specifically to insect-plant systems evolutionarily influenced—whether intentionally or inadvertently—by human activity. These three sections represent a logical continuum of inference about whole-organism evolutionary study. Evolution proceeds at the population level in an ecological context; species and speciation are at the crux of the evolutionary process in that they represent both the outcome of ecological and population genetic processes and the basic units of phylogenetic pattern; macroevolutionary processes and patterns build from the evolutionary process as a whole; finally, evolutionary study at various levels contributes to our understanding of practical biological problems that face society. Although the 23 chapters in this volume are divided, by organizational necessity, among sections, certain ideas and themes run throughout the book, occurring again and again. One such unifying theme is the importance of hostplant range and host-plant shifts in the evolution of herbivorous insects. Most insect herbivores have very intimate associations with their host plants. This characteristic is biologically and ecologically defining and has evolutionary implications at all levels. Some authors examine host-plant range at a genetically or ecologically mechanistic level. For example, Berenbaum and Feeny (chapter 1) look at the biochemical and genetic links between adult ovipositional preference and offspring performance that help determine host-plant range. Craig and Itami (chapter 2) examine adult PREFACE and offspring preference and performance, and host range in light of the ecological characteristics of plant resources, and M. C. Singer, Wee, Hawkins, and Butcher (chapter 22) discuss the evolution of host range in response to ecologically changing plant communities altered by human activity . M. S. Singer (chapter 3) looks at how a broad host-plant range can enhance individual herbivore fitness through escape from natural enemies. Most of the herbivorous insect speciation mechanisms examined in detail in section I (Cocroft, Rodriguez, and Hunt, chapter 7; Feder and Forbes, chapter 8; Funk and Nosil, chapter 9; Futuyma, chapter 10) center around hostplant shifts and host-use patterns (but see Scriber, Ording, and Mercader, chapter 6, for an exception, where life-history variation across hybrid zones is more important than host-plant use). Host shifts and host-plant range also feature prominently in chapters discussing broader patterns of evolutionary radiation. Roderick and Percy (chapter 11) use the special case of island systems to evaluate the relative importance of host shifts and geographic isolation in cladogenesis . Janz and Nylin (chapter 15) discuss how oscillations in host-plant range (with periods of wider...