Females increase egg deposition in favor of large males in the rainbowfish, Melanotaenia australis

Females often partition their reproductive investment differentially according to variation in male phenotype. Although evidence for differential maternal investment is accumulating in species with resource-based mating systems, there is relatively little evidence for such effects in species lacking resources at reproduction. In this paper, we evaluate the potential for differential maternal investment in the Australian rainbowfish, Melanotaenia australis, an egg scattering freshwater fish with a non--resource-based mating system. We found that female preferences for relatively large males were reinforced through patterns of differential egg deposition that favored preferred males. We also found that females mated first to relatively large males exhibited a reduction in egg deposition when subsequently paired with smaller males, suggesting that patterns of maternal investment can be influenced by recent mating history. We found no evidence that these patterns of differential egg deposition were influenced by male aggression, which did not differ between large and small males. Sexual conflict through physical manipulation is therefore unlikely to account for these patterns. Instead, our findings are more consistent with a pattern of differential allocation, although future studies are needed to evaluate the fitness effects of egg allocation, and the predicted trade-off between current and future reproductive investment. Irrespective of the evolutionary mechanisms underlying these patterns, our results confirm that female rainbowfish exhibit rapid and flexible changes in their reproductive investment according to male sexual attractiveness. Copyright 2010, Oxford University Press.