Assessing the cues required for mate choice copying in the plainfin midshipman fish

When choosing a mate, females can rely on their own judgements of male quality or use social information from other females' choices. The use of social information to inform mating decisions is called mate choice copying. Theory predicts that mate choice copying should be strongest in species where females have few mates over the course of their life span because each mating constitutes a greater proportion of the female's expected reproductive value; however, most research on mate choice copying has thus far focused on species with highly promiscuous females. In this study, we use the plainfin midshipman, Porichthys notatus, a toadfish in which females typically choose one mate per year, to investigate whether females mate-choice copy and, if they do, which cues influence their decision making. We show that in the wild, plainfin midshipman females co-occur in nests more often than expected under random female choice. Additionally, we found that females in the laboratory did not base their mating decisions on the mere presence of another female or previously laid eggs; however, females were more likely to choose a male they had observed spawning with another female. Taken together, our results indicate that female plainfin midshipman do mate-choice copy, but only when they observe a spawning event. Understanding how different mating systems affect the strength of mate choice copying and which cues are necessary to elicit mate choice copying will help elucidate more broadly how this behaviour evolved and is maintained.