The Evolution of Diet-Induced Development Plasticity in HeadMorphology of Grasshoppers

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Grasshoppers raised on hard grass diets develop relatively larger heads and mandibles than those raised on diets of soft herbaceous plants. This morphological pattern results from developmental or phenotypic plasticity, a change in the morphology expressed by a genotype in different plant environments. The red-legged grasshopper (Melanoplus femurrubrum) is ideally suited to studies of the evolution of adaptive phenotypic plasticity since preliminary experiments indicate that diet-induced plasticity in head size influences grasshopper feeding rates on different plants. The P. I. has proposed a series of ecological genetic experiments that will test theories of the evolution of phenotypic plasticity by measuring the heritability (genetic variation) of plastic shifts in head size and by measuring the intensity of natural selection on the same characters as they are expressed in two feeding environments (grass and forb). The relationship between phenotypic plasticity and grasshopper fitness will be estimated from measurements of growth, survival, and reproduction of grasshoppers fed in one plant environment (grass or forb) and then, later, shifted to a different feeding environment. The ability of grasshoppers to develop different head sizes in different plants environments enhances their survivorship and, hence, allows these destructive herbivorous pests to persist in many different environments. An understanding of the evolution of grasshopper developmental plasticity will provide basic knowledge about the conditions under which populations are likely to evolve the ability to occupy multiple environments and to potentially expand their distributions into new natural and agricultural habitats.