Scientists have found out that female eastern mosquitofish tend to avoid overzealous Cassanovas when it comes to mating.
Generally speaking, aggressive males with strong sexual drives are the ones that tend to have an evolutionary advantage. However, this is not the case for the eastern mosquitofish, a small, freshwater fish. A study at the Goethe University Frankfurt has shown that the female of this species actually avoid such males, preferring those that are more moderate in their sexual advances.
Carolin Sommer-Trembo has been looking into this behaviour for her doctoral thesis. Together with colleagues Dr David Bierbach (Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin) and Professor Martin Plath (Northwest A&F University, Yangling), she discovered that the female mosquitofish behaved in this way because sexually aggressive males do not give them time to feed and tend to injure their genitalia more frequently.
This turned out to be a learnt behaviour, as virgin female mosquitofish do not exhibit this preference.
“The starting point for our studies was the question why males in some animal species differ pronouncedly and consistently in their sexual activity levels even when they are exposed to identical environmental conditions and don't need to compete. We wanted to know how this variation in male behavioural types is maintained, although selection ought to oust males which display low or average levels of sexual activity,” said Sommer-Trembo.
“Under natural conditions, female mosquitofish often form shoals to protect themselves from male harassment, just like other fish do to protect themselves from predators", Sommer-Trembo explained. If a group of females encounter sexually active males, they are more open to the male's advances. Under such circumstances, the females showed greater acceptance towards sexually very active males, since the cost-benefit ratio shifts under these circumstances.