ScholarWorks@UNO

Developmental Plasticity of Grasshoppers Fed Different Diets

Developmental plasticity, the ability of a single genotype to produce multiple phenotypes, is an important adaptive pathway for organisms that experience environments that vary over time. Insects often exhibit alternative morphologies that match environmental conditions experienced in a particular generation. We asked whether the generalist feeding grasshopper Melanoplus differentialis was capable of adaptive change in morphology when fed on hard and soft diets. We predicted that grasshoppers fed a hard diet would allocate significantly more energy to mandibles and mandibular muscles than those fed a soft diet. We measured the dimensions of the head capsule and other body parts to determine if a developmental tradeoff existed between investment in feeding structures and other body structures. We found that females fed the hard diet were significantly larger in all body dimensions measured than females fed the soft diet. In contrast, males fed the hard diet were significantly smaller in all body dimensions than males fed the soft diet. The results did not support the idea that this species shows developmental plasticity in energy allocation to different body parts, but does suggest that sex-specific responses to food characteristics alter the course of development. Since females invest more in reproduction than males, we suggest that female development is keyed to reaching a body mass threshold required for egg production, regardless of the time required, while male development may be keyed to reaching adulthood as quickly as possible, regardless of body size, to maximize access to mates during adult life.