Phylogenetic studies of insect/plant interactions: Tetraopes (Cerambycidae) and Asclepias (Asclepiadaceae)

摘要

Land plants and their insect enemies together constitute more than half of all known terrestrial species, yet we are only beginning to understand how the diversity of insect/plant assemblages is controlled.;The outstanding example of a historical model of insect/plant communities is Ehrlich and Raven's hypothesis of coevolution, which has profoundly stimulated research on insect/plant interactions. These authors postulated an endless evolutionary "arms race," whose elements are (1) origin of a new chemical defense in some plant lineage, which by reducing herbivore attack allows those plants to increase in abundance and eventually in diversity, and (2) subsequent origin of insect counteradaptations to these defenses, permitting insect radiation in the "adaptive zone" represented by the newly-diversified plant group. Present differences in diversity and ecological dominance among insect and plant groups are taken to represent different stages in the historical sequence of "escape and radiation.".;This thesis first sketches out the areas of inquiry accessible to an explicitly historical research program on the evolution of insect/plant interactions. While the available evidence is still quite sparse, the marks of evolutionary history seem readily apparent on both the composition and diversity of insect/plant communities.;Next is presented a phylogenetic study, explicitly designed to test Ehrlich and Raven's scenario, which treats the milkweed beetle genus Tetraopes, the most species-rich member of the distinctive assemblage of insects attacking the milkweed genus Asclepias. Evidence is presented that Tetraopes and Asclepias have diversified largely in concert and there is some suggestion that an escalation in hostplant chemical defense may mediate their interaction. However, each stage in this apparent escalation has evolved a single time, precluding statistical study of potential effects on rates of diversification.;Finally, a study of the potential correlation of novel plant defense, namely latex/resin secretory canals, with enhanced rates of plant diversification is presented. This study supports Ehrlich and Raven's proposition that evolutionary innovation in traits directly affecting insect/plant interactions spur adaptive radiations. More generally, this study provides support for an important theme of the New Synthesis: that ecological innovation can determine long-term evolutionary success.