In the face of predators, long, passionate sexual encounters are not a luxury some male Bahamas mosquitofish can afford, and it has now been shown that they have evolved genitalia to match this un-luxurious lifestyle.
Image courtesy of Donald Hines
Reproduction is a risky business for animals, particularly for males. During active searches for females, mate calling and courting, males are vulnerable to predators. Even mating itself poses a challenge, as two agile individuals are transformed into one large lumbering prey item. As a consequence, animals which are susceptible to predation have reduced the time with which they spend searching, calling and courting and have reduced the duration of any one mating event. For example, Acharya and McNeil (1998) found moths to reduce mate seeking behavior under risk from bat predation, whereas Dunn et al. (2008) showed decreased courtship in the fiddler crab.
Males of Bahamas mosquitofish (Gambusia hubbsi) are no different and have evolved shorter mating events when under threat from predators. Justa Heinen-Kay and Brian Langerhans from North Carolina State University have now shown that the shape of the males’ genitalia has adapted for these brief encounters.
The research team collected Bahamas mosquitofish from blue holes (water filled vertical caves), either without or with predators present (e.g. the bigmouth sleeper, Gobiomorus dormitor). Fish collected from predator infested holes were found to have gonopodia (genitalia) with a more elongate distal tip which had more densely positioned bony segments. A longer tip was hypothesised to allow for sperm to be deposited further inside the female, increasing the efficiency of insemination and fertilisation during short mating events. In contrast, males from holes without predators would not require this altered shape as a greater time is spent with females, allowing for more cooperation and ease of sperm transfer. This study represents one of the few examples of genitalia shape divergence in fish resulting from predation risk.
By Matthew Everatt
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