PARENT SESSION
Poster Session #52: Evolutionary Ecology.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Selection by natural enemies and divergence of gall size among populations of Eurosta solidaginis.

Craig, Timothy^*,1, Itami, Joanne^*,1, ¹ University of Minnesota-Duluth, Duluth

ABSTRACT- Geographical populations of Eurosta solidaginis, a tephritid fly that induces galls on goldenrod, Solidago altissima, differed in gall size and shape. Eurosta galls produced by populations in prairie habitats in Minnesota were significantly larger and rounder than galls from populations in forest habitats. Previous studies have shown that gall size is a trait influenced by both the plant and insect genotype. These studies have also shown that natural enemies exert selection on gall size. Birds have higher attack rates on larger galls, and a parasitoid has higher attack rates on smaller galls. The causes of mortality differed between the forest and prairie sites sampled in Minnesota. We found that bird predation was low or absent in the prairie sites, supporting the hypothesis that large galls evolved in the absence of selection by avian predators for small galls.

KEY WORDS: gall, parasitoid, tritrophic interactions, natural selection