Audience effect alters mating preferences in a livebearing fish, the Atlantic molly, Poecilia mexicana

Audience effects occur when an observing (by-standing) animal influences the behaviour of an observed individual. We examined whether audience effects influence mate choice decisions in a livebearing fish, the Atlantic molly, Poecilia mexicana. We gave males an opportunity to choose between a conspecific and a heterospecific, Poecilia formosa, female (experiment 1) or a large versus small conspecific female (experiment 2), and we determined the males' association times near the two types of females. During the second part of each test we visually presented an audience male to the focal male, and we compared male association times between the two parts. In both experiments the focal males spent less time near the initially preferred female, and spent more time near the initially nonpreferred female when we presented a conspecific audience male during the second part of the tests. When we presented a heterospecific, Xiphophorus hellerii, male instead, the change in male preferences was significantly weaker. Male preferences were highly consistent when we presented no audience male during the second part of the tests (control). Our study highlights that the social environment has an important effect on male mate choice decisions, and even the mere visual presence of a conspecific competitor can affect the expression of mating preferences.