Sammendrag
The operational sex ratio (OSR) and variance in mate quality are two important criteria in determining which sex is the more choosy. A shift in OSR bias from one sex to the other could potentially create a change in choosiness. To test this, the two-spotted goby (Gobiusculus flavescens) is the ideal species. It is a small marine fish with a male biased OSR in the beginning of the breeding season and a female biased OSR by the end of the breeding season. Females develop an orange belly as they approach spawning and males have been shown to prefer colourful females over drab females. This study therefore used male mate choice tests for colourful females. This was done during two periods, one early and one late in the breeding season, to test for a change in male choosiness over the course of the breeding season. Males were expected not to be choosy early in the season but to become choosy late in the breeding season when there was a female biased OSR. However, the results were not as expected. Early in the breeding season, males preferred colourful females over drab ones. Late in the breeding season, males did not make a clear choice between the females. Instead of finding an increase in male choosiness, an apparent decrease in male choosiness was found. This result is puzzling, but it does shows plasticity in male mate choice, perhaps in response to other variables than OSR.
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