Effects of multiple mating and male harassment on female fecundity and longevity in the seed beetle Callosobruchus maculatus.
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Polyandry is a common mating system in many species, however females may experience considerable costs related to multiple mating including male harassment, energy use and in some cases physical damage. Male harassment of females may occur when there is sexual conflict related to mate choice or mating frequency. Females may, however, benefit from polyandry either indirectly by having more genetically viable offspring, or by increasing the genetic diversity among offspring. She may also gain direct benefits when the males provide resources, e.g. in the form of nuptial gifts like spermatophores, containing nutrients and water. These costs and benefits create a trade-off in multiple matings, with the optimum number of matings often differing between males and females. In the seed beetle Callosobruchus maculatus, males invest resources in spermatophores benefiting females, but females also might experience costs due to mating harassment and direct harm during copulations. By manipulating the female’s exposure to males, either by varying the sex ratio or the period of time exposed, we test the effect of multiple mating on female longevity and fecundity. Female life span and fecundity (number of eggs laid) were higher in the group that was exposed to males for a short-term compared to females permanently exposed to males. For the permanently exposed females, life span decreased with the number of males, but there was no such effect on fecundity (eggs laid). These results indicate that there is both benefits and costs related to multiple mating. Females in the group with permanent exposure seemed to pass a threshold where the costs of male harassment outweighed the benefits of multiple mating resulting in a negative effect on longevity.
PublisherThe University of Bergen
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