Meeting Abstract
Grasshoppers develop larger head width and shorter leg length, relative to body size, when fed low nutrient, silica rich grasses compared to sibs fed a diet of high nutrient grasses. To elucidate how underlying genetic variation and plasticity of growth generate static allometry in Melanoplus sanguinipes (Orthoptera; Acrididae), I measured head and leg size of three nymphal instars and adults raised on either a low or high nutrient diet within a half-sib quantitative genetic experiment. A doubly-multivariate MANOVA of head growth, leg growth, and growth period per instar was used to analyze how these variables and additive genetic variation for plasticity (G x E interaction) contribute to scaling of functional allometry (trait x instar x G x E). Genetic variation for diet-induced plasticity of head and leg size varied through ontogeny, as did genetic variation for plasticity of growth in 3rd and 4th instar nymphs. Despite extensive genetic variation in plasticity of head width and leg length in the 4th instar, the static allometry between head and leg was stable within each diet because the patterns of G x E were concordant for head width, leg length and their coordinated growth. However, genetic variation for 4th instar morphological plasticity was suppressed in adults by negatively size-dependent compensatory growth in the last period of ontogeny. Bivariate reaction norms of adult head and leg size were parallel with diet specific scaling but no G x E. Thus, the hemimetabolous ontogeny of seemingly simple allometry between functional body parts comprised qualitatively different patterns of nutrient sensitive growth rates and periods and compensatory or targeted growth, all relevant to understanding development and evolution.
