Relative Size of Males and Competition for Females Induces Homosexual Behavior in the Western Mosquitofish (Gambusia affinis) Under Laboratory Conditions

Abstract

In an ongoing experiment, we investigated how mating behaviors of male western mosquitofish Gambusia affinis change across a range of temperatures. During behavioral trials, we observed high levels of homosexual behavior between males when in a competitive situation. We observed that when two males are in competition for matings with females, the smaller male performed significantly more homosexual acts than the larger. These results suggest that a dominance relationship develops with males in competition, where large males may dominate small males by not allowing them to copulate with the female, thereby causing an increase in same-sex mating by smaller males. Although preliminary data also indicate a possible relationship between density of males and number of homosexual copulations, we were not able to statistically analyze the relationship because these observations occurred during an ongoing experiment. In a future study, we will seek to understand underlying causes of homosexual behavior in the western mosquitofish.