Dissecting the evolutionary impacts of plant invasions: bugs and beetles as native guides

The introduction of plants into new biogeographical realms is a main repercussion of human trade. The responses of native insects to alien plants may provide insight into how invaders influence ecological processes in their new communities. We illustrate this point with results from our field and lab studies of seed-feeding insects on alien plants. Soapberry bugs (Jadera, Leptocoris) have colonized several species of weedy invasive plants (sapindaceous trees and vines) in the United States and Australia. After initial reduction in physiological performance, they evolved behavioral, morphological, physiological and life history adaptations permitting more efficient exploitation of those hosts. Those changes occurred quickly, in fewer than 100 generations (ca. 30-50 years). The underlying genetic changes are surprisingly complex, and also involve loss of function on native hosts. Contrasting with this is the bruchine beetle (Stator limbatus) on seeds of leguminous trees. Large numbers of S. limbatus oviposit on an alien tree in Arizona, but few offspring survive. The main influence on larval survival is a maternal effect determined by the host the mother experiences as her eggs mature. Adaptive plasticity in egg size and composition may ultimately permit successful exploitation of novel resources. Together, these studies show that both complex genetic and developmental factors influence the integration of ecological and evolutionary processes in environments altered by anthropogenically initiated plant invasions. Tractable insect study systems may be valuable guides to understanding biotic dynamics in a changing world.