Evans, J.P., Box, T.M., Brooshooft, P., Tatler, J.R. & Fitzpatrick, J.L. 2010. Females increase egg deposition in favour of large males in the rainbowfish, Melanotaenia australis. Behavioural Ecology 21:465-469.
Through this study, the researchers address how sexual selection favours flexibility in maternal investment, using rainbowfish as a model species. Females were individually placed into large tanks, with both a small and a large male that were confined to containers within the tank. First, they observed the amount of time the female spent within one body length of the containers containing the males. After four days, either the large or the small male was released into the tank with the female, and they were allowed 4 more days to interact. The eggs produced by the female during this time were collected, counted and photographed. Results showed that during the initial 4 days, females spent 70% of their time within one body length of the large male, and they produced two times as many eggs when they mated with the large male (large males are phenotypically preferred). The variation in maternal investment defined within this study is important for understanding the effect of a mate’s phenotype on maternal investment, but it fails to address the effect of a mate’s genetic identity.