Genotype × environment interaction in the allometry of body, genitalia, and signal traits in Enchenopa treehoppers (Hemiptera: Membracidae)

Developmental plasticity may promote divergence by exposing genetic variation to selection in novel ways in new environments. We tested for this effect in the static allometry (i.e., scaling on body size) of traits in advertisement signals, body and genitalia. We used a member of the Enchenopa binotata species complex of treehoppers - a clade of plant–feeding insects in which speciation is associated with colonization of novel environments involving marked divergence in signals, subtle divergence in body size and shape, and no apparent divergence in genitalia. We found no change in mean allometric slopes across environments, but substantial genetic variation and genotype × environment interaction (G×E) in allometry. The allometry of signal traits showed the most genetic variation and G×E, and that of genitalia showed the weakest G×E. Our findings suggest that colonizing novel environments may have stronger diversifying consequences for signal allometry than for genitalia allometry.