Context-dependent male mate choice: the effects of competitor presence and competitor size

Differences in the intensity of male–male competition for high- and low-quality females affect their value as mates. This can favor the evolution of mating preferences that vary with inherent male competitiveness and/or context-dependent mate choice. In the eastern mosquitofish (Gambusia holbrooki) we investigated how a male's choice of mate is influenced by his absolute size when alone (baseline mating preference) and by the presence and relative size of a competitor (context dependent). In standard 2-choice mating trials, we compared the time in association with the larger of 2 females in: 1) the absence of a rival; 2) the presence of a same-sized rival, and 3) the presence of a different-sized rival. We predicted which female the focal male would choose based on his estimated reproductive success. In all 3 social contexts, large and small focal males spent significantly more time with large females, but large males had a stronger association bias, indicating an effect of male size (competitiveness) on male mating preference. In contrast, neither the presence of a competitor nor his relative size affected the time the focal male spent with the large female. There was therefore no evidence that males facultatively adjust mate choice decisions to avoid competitors. This suggests that males do not maximize their expected reproductive success in the context of the current social setting.