GENETIC DIVERGENCE IN DIET- AND TEMPERATURE-INDUCED PLASTICITY OF GRASSHOPPER SIZE AND SHAPE

Populations of Melanoplus sanguinipes (Orthoptera: Acrididae) sampled from high and low elevation regions of the Southwest exhibit genetically divergent developmental reaction norms when raised under four combinations of diet and temperature. When measured in common environments, high elevation populations exhibit smaller adult body size and proportionally smaller wing and femur size than low elevation populations. In addition, low nutrient diets and low temperatures induce 10-20% plastic reductions in biomass allocation to wing and leg, relative to body size. Multivariate analyses of head, leg, wing, and thorax morphology reveal plastic changes in size and shape, despite overall population-level allometry of these traits. Quantitative genetic variation and genetic variation for plasticity (genotype x environment interaction) of leg and head size fluctuate in expression through nymphal ontogeny. Expression of genetic variation available for evolutionary change in morphological plasticity is greater in fourth nymphal instar than adult stages of ontogeny. The utility of multivariate analyses and the observed genetic and plastic variation in grasshopper morphology and ontogeny will be discussed with respect to studies of adaptive morphological evolution.