Why is female choice not unanimous? Insights from costly mate sampling in marine iguanas.

Females do not unanimously choose the single 'best' male, even when female choice is strong, such as in leks, or in polygynous mating situations. A po ssible explanation is that females base their choices on limited informatio n, perhaps because gathering information is costly. We tested this hypothes is by continuously observing individual female marine iguanas throughout th e mating period in order to document the information they gathered about ea ch potential mate. Females actively visited approximately five additional m ales during the 3 d prior to copulation, compared to the males seen on thei r normal foraging routes. Females were more likely to visit large-bodied ma les, but preferentially copulated with the male that had the highest displa y rate of all males they visited. Females that mated on a dense territory c luster mated with more active males than did those that mated on dispersed territories. However, females on a dense cluster also lost more body mass, potentially as a consequence of high rates of interaction with males. This mass loss may represent an important cost and result from postural changes in response to male attention. Such costs may explain why females only gath er a certain amount of information and why females on dispersed territories choose less active mates. Lack of complete information introduces subjecti vity into female choice: what is perceived as best by one female may not be perceived as best by another. Thus, lack of complete information may preve nt unanimity of female choice.