The red-shouldered soapberry bug (Jadera haematoloma) is a textbook example of rapid adaptive change in the last ~60 years. Soapberry bugs feed on seeds of the soapberry family (Sapindaceae) by piercing the surrounding seedpod with its beak-like mouthparts. Historically, they fed on native soapberry species, but in the last ~60 years, related species of Asian soapberry trees have been introduced and spread throughout Texas and Florida. In this time frame, native populations of J. haematoloma have shifted onto these introduced trees. Compared with the native host plant in Texas (Sapindus drummondii), one of the Asian tree species in Texas (Koelreuteria paniculata) has a much larger pod. Corresponding to this difference, soapberry bug populations in Texas have evolved significantly larger beaks. The question remains: how did the soapberry bug evolve so quickly to the new host?

The answer to this question may emerge from features of the initial colonizers to new habitats. Soapberry bugs exhibit a flight-life history polymorphism, where there is a long-winged form that is the main disperser with a larger body, and a short-winged form that does not fly well with a smaller body. Long-wing morphs also have larger mouthparts that are beneficial on the new non-native host plant. This project will test whether the observed rapid adaptation from a native host plant, where smaller mouthparts are favored, to a non-native host plant, where larger mouthparts are favored, was promoted by differential dispersal as opposed to natural selection from standing phenotypic variation. To do this, field observational studies, a manipulative transplant experiment, lab tests of the genetic basis of dispersal phenotypes, as well as genetic tests for reductions in genetic variation within populations will be performed.

Soapberry bugs in Houston, TX.

Egan, S.P. & S. Carroll. RAPID: Testing the role of a dispersal-life history polymorphism as an important driver of rapid adaptive divergence. National Science Foundation – Evolutionary Processes – $103,000 (2017-2018).