Sexual Dimorphism in Dispersal Traits for the Highly Invasive Western Mosquitofish (Gambusia affinis)

Biological invasions are driven by the transport, release/escape, establishment, and spread of organisms across biogeographic boundaries. While actions that prevent transportation and release/escapement are most efficient at thwarting the establishment of new invasions, control of existing evasions requires insight into ecological mechanisms that promote organism spread. The Western Mosquitofish ( Gambusia affinis ) is introduced globally because of its presumed benefits as a mosquito control agent, but the resulting invasions into nearby ecosystems have negative effects on native biota. Females of Western Mosquitofish have the ability to store sperm for multiple weeks, so movement of a single inseminated female could lead to secondary spread and new population establishment. Consequently, the global invasion success and secondary spread of Western Mosquitofish might be linked to greater movement ability among females, but we know little about female dispersal ability because existing studies are heavily biased toward evaluating males. Here, we investigate how six morphological traits linked to fish dispersal ability differ between male and female Western Mosquitofish. Our results reveal that traits correlated with movement capacity differed between males and females, with males having a perceived advantage for two traits (longer relative peduncle length and shorter relative body height) and females having a perceived advantage for three traits (larger caudal-fin aspect ratio, larger total length, and greater caudal-peduncle throttling). These findings suggest that females have greater capacity for dispersal relative to males and that future investigations on Western Mosquitofish and other ecologically and morphologically similar species should give greater focus to female movement ecology.