Investment into offspring is assumed to have positive effects on offspring survival and reproduction Why then do we find a huge amount of variation in maternal investment between individuals in the same population?

A commonly held belief is that this variation is maintained because high levels of maternal investment is costly for the mother, and , because individuals have a limited amount of resources, these costs are traded off against the benefits of increased investment for the offspring.

In a recent paper, published in Frontiers in Zoology, we investigated the potential costs for mothers investing more resources in their eggs. We found that females who produce larger eggs, with more nutrients in them, have larger reproductive organs, and so have a larger increase in weight when starting to produce eggs. These larger reproductive organs lead to females that produce larger eggs having an increased metabolic rate (a larger energy demand). We found that, despite a higher energetic demand, females producing larger eggs did not trade-off reproductive investment against flight ability, and did not experience increased physiological damage.

Are these high investment females darwinian demons, with high reproductive investment and no costs? A larger body weight during egg production along with a higher energetic demand would mean that females need to find a greater amount of food, whilst being less manoeuvrable, making the risk of being predated much higher. Although we cannot demonstrate these costs in our captive population, these are likely serious costs of higher reproductive investment in the wild.