When it comes to sex drives, female fish prefer meh in their male partners.
To find out which males are interesting for female mosquitofish and whether the level of male sexual activity plays any role at all in their choice of partner, Carolin Sommer-Trembo and her colleagues Dr. David Bierbach (Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin) and Professor Martin Plath (Northwest A&F University, Yangling) let females choose between males which displayed different levels of sexual activity. To exclude the possibility that specific males were chosen because of their appearance (morphology) or other behavioural characteristics and to control precisely the degree of sexual activity of the males, the researchers worked with computer-animated stimulus males which were presented to the females on monitors.
The result was that females preferred males which displayed a moderate level of sexual activity whilst they clearly avoided males with a greater sex drive. The researchers assume that this is due to cost-benefit considerations, since females who find themselves in the close vicinity of sexually very active males often not only suffer injuries to their genitalia but also scarcely have an opportunity to feed as they are constantly busy avoiding the males’ advances.
The situation is different when a group of females encounters a rampant male determined to mate. “Under natural conditions, female mosquitofish often form shoals to protect themselves from male harassment, just like other fish do to protect themselves from predators”, explains Carolin Sommer-Trembo. In the group, females showed far greater acceptance towards sexually very active males, since the cost-benefit ratio shifts under these circumstances.
In evolution, a high sex drive does not always pay off. Female mosquitofish swim away from over-impetuous lovers because they leave them hardly any time to feed and also tend to injure their genitalia more often.