Interactive effects of larval host and competition on adult fitness: an experimental test with seed beetles (Coleoptera: Bruchidae)

Abstract

Summary Resources and intensity of competition encountered during development can have significant consequences for adult fitness, yet their effects are rarely considered simultaneously. Furthermore, it is often assumed that these factors affect adult fitness only indirectly through their effects on body mass. Here, I examined the direct effects of larval host type and intensity of competition on mass at emergence and fecundity in two species of bruchid beetles (Callosobruchus spp.). There was no effect of competition treatments on mass at emergence of C. chinensis females reared in Adzuki or Mung Beans. Controlling for body mass, there was a significant effect of competition treatment on number of eggs laid by C. chinensis females that had been reared on Mung Beans, with those reared with a competitor laying significantly fewer eggs than females that had been reared in the absence of competition. Competition had a highly significant effect on mass at emergence of C. maculatus females reared in Mung Beans. In the absence of a significant effect of competition on mean mass at emergence in Adzuki Beans, females reared with two competitors laid significantly fewer eggs than did females reared with either one or no competitors. For certain combinations of bruchid species and resource type, thus, females laid fewer eggs for a given mass at emergence if they had been subject to competition during their larval phase. These results reveal subtle differences in the responses of closely related species with similar life histories to resources and competition during development, calling into question current generalizations about the direct effects of competition on fitness.