Finding a mate with desirable qualities is big business for humans. In today's society, advertisements are rampant for businesses promising to find you the perfect mate. Of course, whether we are conscious of it or not, the underlying driving force for this human behaviour is our biological desire to successfully transmit our genes. But, what if one didn't have to find the perfect mate? What if it were possible to improve the quality of young produced with a lower-quality mate to maximize reproductive success?Apparently, female birds have figured this `trick' out and can alter offspring quality before they hatch by manipulating the amount of vital nutrients present in their eggs. Kristen Navara and colleagues from the Department of Biological Sciences at Auburn University, Auburn, Alabama were interested in understanding this phenomenon in female birds.

Female birds invest in offspring by one of two contrasting strategies. Which strategy they use depends on environmental and social conditions, as well as the resource being allocated, for example nutrients. Some studies observed that females invest more resources in offspring sired by better-quality males; a phenomenon termed the `differential allocation hypothesis'. Conversely, in other studies, females contributed resources in a compensatory fashion, supplying more resources to offspring sired by lower-quality males and enhancing the offsprings' quality, making up for the poor quality of the father.

The team wanted to know what strategy wild female house finches(Carpodacus mexicanus) use to allocate antioxidants to their eggs. Antioxidants are chemicals important in protecting organisms against oxidative stress, which is caused by reactive oxygen species that damage cells and tissues. Knowing that males with more colourful plumage are more attractive,the team set out to find how the patterns of yolk antioxidants – vitamin E, vitamin A and three carotenoids – were affected by male quality and attractiveness. They measured the quantity of these nutrients in 36-h-old eggs and compared the antioxidant levels to the attractiveness of the father.

The team found that female house finches deposited antioxidants in their eggs in a compensatory fashion, putting more into eggs sired by less-attractive males. The team argues that this strategy enables females to improve the quality of young fathered by less-attractive males and take the edge off the unfavourable conditions experienced by these offspring. For example, the team explains that less-attractive finch males provide less food. Since house finches are short-lived individuals, the team proposes that focusing on current attempts at reproduction, rather than investing in future attempts, may be the only viable strategy to maximize the number of offspring that they can produce. In essence, females choose from the males that are currently available and make the most of what they have, rather than waiting for a better quality male to come along.

Navara, K. J., Badyaev, A. V., Medonca, M. T. and Hill, G. E. (
). Yolk antioxidants vary with male attractiveness and female condition in the house finch (Carpodacus mexicanus).
Physiol. Biochem. Zool.