In lieu of an abstract, here is a brief excerpt of the content:

Insects and flowering plants are among the most diverse macroorganisms on earth, and their mutual interactions provide little doubt that each group is in part responsible for the other’s diversity (Hairston et al. 1960; Ehrlich and Raven 1964; Strong et al. 1984; Novotny et al. 2006). However , exactly how diversification of flowering plants has affected the diversity of insects, and vice versa, is not well understood for the vast majority of plant and insect groups. Fossil evidence suggests that flowering plants were not associated with the initial modern diversification of insects that began 245 million years ago (Labandeira and Sepkoski 1993). Indeed, the basic diversity of the trophic machinery of insects was present in the fossil record 100 million years before the first fossil angiosperms. However, angiosperms do appear to be associated with a more recent diversification of insects, that is, diversification at the genus and species levels. One illustration of this association is Farrell’s (1998) study of herbivorous beetles in which sister groups of beetles that feed on angiosperms were found to be consistently more diverse than their relatives feeding on gymnosperms and ferns. The approach used in Farrell’s study makes some important assumptions, for example, that present feeding associations are indicative of past associations and that differences in numbers of species are not influenced unduly by other factors, such as asymmetrical extinction. The study demonstrates that the switch to angiosperms was associated with an increase in beetle diversity. But, exactly how does such an accelerated rate of diversification get started and to what extent do plants determine these processes? For some insect and plant groups, we have a fairly good understanding of the factors associated with insect diversification . For example, studies of plant chemistry and diversi- fication of Lepidoptera have provided evidence of the evolutionary arms races predicted by Ehrlich and Raven (1964) in their original hypothesis of insect-plant coevolution (Berenbaum and Feeny, this volume). Studies of pollination systems also illustrate how insects and plants are tightly tied to each other’s diversity (e.g., yuccas and yucca moths, [Pellmyr and Thompson 1992]; figs and figwasps [Silvieus et al., this volume]). These systems illustrate complex patterns of coevolution that can themselves be a locus for diversification , as, for example, when such systems are exploited by complex layers of insect interlopers (Kjellberg et al. 2005). For each of these systems, progress in understanding has come through the close examination of the insect/plant part of the system. In this chapter, we use remote islands to focus on the evolutionary patterns of insect-plant interactions . We examine studies that have used the features of remote islands to tease apart factors associated with recent host-associated diversification in an attempt to understand how host plants contribute to the process of insect speciation . We also point to some areas where future work is likely to be especially fruitful. Islands as a Model System Islands have been attractive systems for the study of evolutionary and ecological phenomena, particularly as it relates to adaptation and diversification (Carlquist 1980; Simon 1987; Wagner and Funk 1995; Gillespie and Roderick 2002; Percy 2003b; Emerson et al. 2006). Important features of islands include the following: (1) Islands offer discrete geographic entities with defined boundaries. (2) Gene flow between islands within an archipelago is often limited, and gene flow between islands and a continental source pool may—depending on the level of isolation—be greatly reduced or nonexistent. The extent of isolation will also depend upon the dispersal abilities of the organisms and, in particular, their ability to disperse over water. A reduction of gene flow allows island populations to evolve in isolation from continental populations through processes such as genetic drift and local adaptation. (3) Islands are usually 151 E LEVE N Host-Plant Use, Diversification, and Coevolution: Insights from Remote Oceanic Islands GEORGE K. RODERICK AND DIANA M. PERCY relatively small units so that the species can be more completely mapped and cataloged than is possible for continental regions. (4) Islands that are part of an archipelago offer multiple geographic replicates for studies of evolutionary and ecological processes. While islands can take many forms, here we limit our discussion to remote oceanic islands. As a group, remote oceanic islands are large enough to have a diversity of habitats. Further, because most are volcanic they can offer a diversity of geological landscapes, often with known ages and histories (e.g., Carson and...

Share