Expression of a life‐history trade‐off in a seed beetle depends on environmental context

Abstract

Within populations of the seed beetle Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), female longevity is positively correlated with fecundity, both phenotypically and genetically. Yet manipulations of egg‐laying rate (through deprivation of seeds or mates) consistently suggest a trade‐off between these traits. In this study, females were exposed to four levels of seed availability and the relationship between fecundity and longevity was examined both across and within environments. The expected trade‐off was observed across environments, as females with few or no seeds laid fewer eggs and lived longer than females with many seeds. Within environments, however, the relationship was inconsistent; individual longevity and fecundity were positively correlated when seeds were abundant, uncorrelated when seeds were few and negatively correlated when seeds were absent. Body mass at adult emergence was positively correlated with fecundity, but its effect was stronger when seeds were present than when they were absent. After the effects of mass were statistically controlled, longevity and fecundity remained positively correlated among females with many seeds and negatively correlated among those without seeds. Thus, even a single technique (phenotypic correlation) can produce divergent conclusions about the ‘cost of reproduction’ in insects. The reversal in the correlation appears to depend on variation in reproductive allocation; when seeds are scarce or absent, differences in reproductive effort among individuals may be large enough to overwhelm differences in resource acquisition.

The Genetic Architecture of Life Span and Mortality Rates: Gender and Species Differences in Inbreeding Load of Two Seed-Feeding Beetles

“…Having evolved to use dry seeds, and most recently having evolved in a storage environment, C. maculatus larvae develop and adults mature, mate, and complete reproduction using metabolic water and the resources acquired during larval development (i.e., they are capital breeders) (Messina and Slade 1999). Access to adult resources has a small positive effect on female fecundity and improves adult life span (Fox 1993;Fox and Dingle 1994;Tatar and Carey 1995).…”

Key themes in the study of seasonal adaptations in insects II. Life-cycle patterns

“…Consequently, trade-offs may not be visible if the input or availability of resources is too variable (Messina and Slade, 1999;Brown, 2003;Messina and Fry, 2003). Laboratory experiments suggest that time and size trade-offs are restricted to stressful situations (Fischer and Fiedler, 2002), or at least that trade-offs tend to disappear in uncrowded conditions (Cortese et al, 2003).…”

Evolutionary genetics of lifespan and mortality rates in two populations of the seed beetle, Callosobruchus maculatus

“…This beetle's short generation time and ease of laboratory rearing in a seminatural storage environment make it an excellent animal for life history studies. Having evolved to use dry seeds, and most recently having evolved in a storage environment, C. maculatus larvae develop and adults mature, mate and complete reproduction using only metabolic water and the resources acquired during larval development (ie, they are capital breeders; Messina and Slade, 1999). In some bruchids (eg, Bruchus pisorum) adult feeding (on pollen, floral or extra-floral nectarines, or leaf fungi) is common and these nutrients are used for maturation of eggs (eg, Clement, 1992).…”