Reticulate macro- and microevolution in an Australian soapberry bug on native and introduced host plants

Contemporary adaptation of plant-feeding insects to introduced hosts provides clear cases of ecologically based population divergence and speciation. However, the mechanisms that permit rapid evolution in response to altered selection, as well as the role of adaptation to native hosts in the ancestral populations, are often poorly known.  Among the host-associated ecotypes of the Australian soapberry bug, Leptocoris tagalicus, four are on naturalized Neotropical balloon vines. Three of these vines have much larger fruits than the native hosts, and the bugs on them have evolved longer beaks. The fourth vine does not inflate its fruit and hosts bugs with shorter beaks. Surprisingly, the genetic elements in the most extreme case of beak elongation were provided by hybridization of two distantly related native-host races with shorter beaks. Hence, ancestral differentiation on native hosts may inadvertently set the stage for rapid and extraordinary adaptation to novel hosts.