RAPID: Testing the role of spatial sorting as an important driver of rapid adaptive divergence

William Marsh Rice University, Houston TX

Investigators

Abstract

Traits of organisms that enhance their rates of dispersal can be favored in populations that are rapidly colonizing new habitats. This is especially true if the dispersing individuals mate with similar, highly mobile individuals from surrounding populations. This process, termed "spatial sorting", generates offspring that are also rapid dispersers, regardless of how those genes affect the population's fitness in the new habitat. This project will perform the first large-scale field tests of spatial sorting in generating rapid evolution using populations of the red-shouldered soapberry bug (Jadera haematoloma), which has expanded and adapted from native to non-native food plants in the last 60 years. The rare episodic flooding from Hurricane Harvey has provided a unique opportunity to roll back the (short) evolutionary clock on soapberry bug populations by causing some populations to go extinct while others are still intact. Results from this study can be applied to understanding how invasive species colonize new habitats and ultimately displace native populations. This project also will support outreach public education on evolution in colonizing populations. One fundamental question is how could J. haematoloma populations evolve so quickly? The answer to this question may emerge from features of the initial colonizers. Soapberry bugs exhibits a flight 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 spatial sorting 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.