Sexual conflict occurs when each sex attempts to maximize its reproductive fitness with different strategies. In the bean beetle Callosobruchus maculatus, there is a balance to the optimal number of matings for maximal female reproductive fitness. Females that mate with numerous males can have a boost to fecundity because male ejaculate is used for egg production, yet these females suffer internal damage and reduced longevity. For males, reproductive fitness reaches a peak through mating with as many females as possible. The mating behavior of this species is well studied, but unknown are potential environmental differences in the expression of the mating behavior phenotype. We implemented a half-sib breeding design across 4 lines (2 populations: Burkina Faso and South India x two rearing environments: cowpea or mung beans) to compare the influence of population and environment on mating behaviors and their heritability estimates. The two rearing environments represent a native and novel host species, as cowpeas are native to Burkina Faso population and mung beans are native to the South India population.
Results/Conclusions
Both population and rearing host environment had significant effects on all or some mating behaviors. For both rearing environments, beetles from the Burkina Faso lines mated 18-23% longer and took 55-64% longer to dismount than beetles from the South India lines, suggesting that the effects of population persist when switched to a novel host for several generations. For both populations, beetles reared on mung bean took 13-30% longer to dismount than beetles reared on cowpeas, suggesting that rearing host plays a key role in this mating behavior. Several heritability estimates differed between populations and/or rearing environments. For example, for total mating duration, heritability estimates were low except for Burkina Faso beetles reared on mung beans (h2 = 0.36). For dismount duration, the Burkina Faso lines had significant heritability estimates (h2 = 0.28 or 0.29), but not for the South India lines. Such environmental differences are suggestive of differential gene expression for heritable components of mating behavior. Models used to predict the outcome of selection on behaviors related to sexual conflict in this species and other species need to consider environmental differences in heritability estimates.