Data from: Adaptive divergence in a defense symbiosis driven from the top down

Most studies of adaptive radiation in animals focus on resource
competition as the primary driver of trait divergence. The roles of other
ecological interactions in shaping divergent phenotypes during such
radiations have received less attention. We evaluate natural enemies as
primary agents of diversifying selection on the phenotypes of an actively
diverging lineage of gall midges on tall goldenrod. In this system, the
gall of the midge consists of a biotrophic fungal symbiont that develops
on host-plant leaves and forms distinctly variable protective carapaces
over midge larvae. Through field studies, we show that fungal gall
morphology, which is induced by midges (i.e., it is an extended phenotype)
is under directional and diversifying selection by parasitoid enemies.
Overall, natural enemies disruptively select for either small or large
galls, mainly along the axis of gall thickness. These results imply that
predators are driving the evolution of phenotypic diversity in symbiotic
defense traits in this system, and that divergence in defensive morphology
may provide ecological opportunities that help to fuel the adaptive
radiation of this genus of midges on goldenrods. This enemy-driven
phenotypic divergence in a diversifying lineage illustrates the potential
importance of consumer-resource and symbiotic species interactions in
adaptive radiation.