Long-term divergence in body size produced by food size in laboratory populations of Acheta domesticus (Orthoptera: Gryllidae)

Experiments were performed to test the hypothesis that food size can act as a selection pressure on body size. For 19–22 generations, two strains of house crickets were reared on small-sized food, large-sized food, or a mixture. Within both strains, small food consistently and significantly produced smaller individuals than did large food or mixed food. In the hybrid strain, rearing of all food-size lines on the same food size revealed that differences observed among the food-size lines had a genetic component. Within the commercial strain, all food-size lines were reared on the same food size during generations 16 and 19 in order to test for genetic divergence among the lines. No differences in body size were observed among the lines for generation 16. However, during generation 19, when populations from each line were reared on all three food-size treatments, the small-food line contained the smallest crickets only when reared on mixed food or large food. Although one cannot rule out alternative hypotheses of maternal effects or genetic drift, the hypothesis of genetic selection on body size by food size cannot be rejected with these data.