UV-blue structural coloration and competition for nestboxes in male eastern bluebirds

A population genetic model of sexual selection is constructed in which, at equilibrium, males signal their quality by developing costly ornaments, and females pay costs to use the ornaments in mate choice. It is shown that the form of the equilibrium is uninfluenced by the Fisher process, that is, by self-reinforcement of female preferences. This is a working model of the handicap principle applied to sexual selection, and places Zahavi's handicap principle on the same logical footing as the Fisher process, in that each can support sexual selection without the presence of the other. A way of measuring the relative importance of the two processes is suggested that can be applied to both theories and facts. A style of modelling that allows simple genetics and complicated biology to be combined is recommended.

It is generally believed that success in male-male competition genuinely reflects high quality and that female preference for dominant males should therefore be widespread. However, recent studies suggest that male dominance is not always attractive and that it does not necessarily predict superior parental quality, better genes or other forms of benefit to females. In fact, the costs of choosing a dominant male can sometimes outweigh the benefits. When traits selected by male-male competition do not reflect overall mate quality, females are expected to use other choice cues and might occasionally prefer subordinate males. Thus, male-male competition and female choice can sometimes work in different, or even opposing, directions.