The biology of post-invasion events

Abstract

In this contribution we consider the biology of invading organisms after they have become established. Adaptive radiation over the long term has been a favorite subject in evolutionary biology. Examples have been Darwin's finches in the Galapagos and the honeycreepers and Drosophila of Hawaii. Hawaiian honeycreepers have evolved from a finch-like ancestor into guilds of seed eaters, nectar feeders, and combined, nectar and insect feeders plus some species with unique beak structures. In the Hawaiian Drosophila sexual selection may have driven the extensive adaptive radiation and speciation in the group. The North American soapberry bug Jadera haemotoloma is an interesting model for post-invasion evolution in the short term. Some populations have moved onto introduced goldenrain trees Koelreuteria spp. and have evolved different stylet (mouthpart) lengths, as a function of fruit size, and new host preferences, all within the last 50 years. These rapid responses are possible because of high additive genetic variances for these traits. Similarly, there has been rapid evolution of life history variation in American shad introduced from east coast to west coast rivers. We postulate that invaders most likely to integrate successfully are those in which high levels of additive genetic variation are expressed in traits most likely to be adaptive in the new environment.