Seasonal change in female choice for male size in the two-spotted goby

Mate choice may vary according to various factors, such as mate availability and variation in mate quality. We tested seasonal changes in female choice regarding male size in a marine fish, the two-spotted goby, Gobiusculus flavescens. In this species, males occupy nests in which females lay their eggs and males thereafter provide exclusive parental care of the eggs until hatching. Females are predicted to prefer large males if, for example, they are better at competing for and defending nests. In this species, the opportunity for females to be selective should decline over the breeding season as the availability of males decreases. We therefore predicted a reduction in female choosiness with season. We conducted mate choice tests, during the early (May) and later (June) part of the breeding season, in which females were allowed to choose between males differing in body length. Females chose large males early in the season, but became unselective with respect to male size later on. This change in mate choice may be caused by a reduction in overall choosiness as a result of the decline in male availability with season. Alternatively, the change could be caused by a switch in choice cues used by females if factors other than male size become more important for female reproductive success later in the breeding season. Further studies are needed to test between these alternative explanations. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.