Personality affects mate choice: bolder males show stronger audience effects under high competition

Males in various species adjust their mate choice to sperm competition risk and intensity arising when females potentially mate with several competing males. If males use social information and copy other males’ choices, this leads to an increased likelihood of sperm competition for both, the copying and the copied male. In livebearing fishes (Poeciliidae), males appear to avoid the risk of being copied by temporarily moving away from preferred females and approaching nonpreferred ones ("audience effect"), thereby exploiting the rival’s propensity to copy. Responding to rival presence with an audience effect bears the risk of losing the initially preferred female, which may swim away, but may help to reduce sperm competition intensity. Males may rate this risk–benefit ratio differentially depending on their personality, for example, more risk-taking (bolder) males might be more likely to respond to an audience. Using Atlantic mollies (Poecilia mexicana) as our study organism, we characterized focal and audience males along the boldness–activity behavioral axis. As overall competition levels are known to affect male mate choice, we subjected half of the males to a low competition (single-male housing) and the other half to a high-competition treatment (group housing) before they were tested in binary mate choice tests. Only males from the high competition treatment responded to rival presence with an audience effect. In congruence with our prediction, bolder males within this cohort showed a stronger audience effect. Our study exemplifies that (depending on the social context) bolder, not shyer, individuals can be more responsive to their social environment.