A longevity cost of re-mating but no benefits of polyandry in the almond moth, <Emphasis Type="Italic">Cadra cautella</Emphasis>

Species where most but not all females mate monandrously can provide insight into the potential factors both promoting and restricting polyandry. Polyandry is typically explained by direct and/or indirect benefits models; however, polyandry may also confer costs via sexually antagonistic processes. The fitness of polyandrous and monandrous females may also vary with environmental conditions, such as availability of water. For some lepidopterans, water is a vital resource that increases fecundity and may be a direct benefit of multiple mating. Male lepidopterans transfer large spermatophores that may be an important water source for females, particularly for species living in water-depauperate environments. In such species, multiple-mating females may increase their reproductive output. We examined the fitness consequences of multiple mating in the almond moth, Cadra cautella. Males transfer substantial spermatophores; these have a large chitinous process attached, which decrease female longevity. To assess the impact of female mating treatment and water availability on female fitness, females mated once or twice, either with the same or different males, with half the females in each treatment receiving water. Water-fed females had dramatically increased fecundity, but we found no fitness benefits of multiple mating. Male longevity decreased with increased mating frequency and potentially his level of reproductive investment. Water-deprived females that mated twice died sooner than once-mated females, while multiple-mating females that received water lived longer than their water-deprived counterparts. It is interesting to note that the male’s spermatophore process did not affect female fitness or longevity. Why polyandry is maintained in this species is discussed.