Some males just don’t know when to quit.
When you think of guppies, you probably think of pretty little fish in the pet store. But male guppies are notorious sexual harassers. They are so bad that they don’t even respect species boundaries, the cads! Male guppies will try to mate not only with a different species of guppy, they will try to mate with fish in an entirely different genus.
Picky they ain’t.
Of course, trying to mate with a female in the wrong genus is unlikely to yield any offspring, so it’s not really worth it for the males to try mating with the wrong genus. So while male guppies have the proverbial “one thing on their brain,” it is to their advantage to use their brain to try to learn which females to stop chasing.
In this experiment, Valero and colleagues tested male guppies’ responses to Skiffia bilineata females (pictured below). They had three conditions.
In one, two male guppies were put in a tank with female guppies for 2 weeks, then repaired in a new testing tank with either the same, familiar female guppies or new, unfamilar female guppies.
In the second, the set up was the same, except the females were Skiffia bilineata.
In the third, critical test, males were paired with females of both species, and then repaired with familiar or new females of both species (guppies and Skiffia bilineata). Half the time, the female guppy was new and the Skiffia bilineata) was familiar to the males; the other half of the time, the female guppy was familiar and the Skiffia bilineata) was new.
In the tests with two species of females, the males increased the proportion of times they tried to mate with the unfamiliar Skiffia bilineata females. Valero and coauthors suggest this means that the males had learned not to try to mate with females that had previously encountered.
When there was only one species, the guppies showed no changes towards females regardless of which species they were and regardless of whether they were familiar or not. The authors suggest that for the males to learn, they have to make a comparison between the different species.
Oddly, though, they did not change how often they displayed to those Skiffia bilineata females. Just the attempted copulations changed. This is surprising, as you might expect that learning would generalize across related sexual behaviours. The authors discuss the costs of sexual displays, but as far as I can see, have nothing to add that might explain why displays are unaffected but attempted copulations are.
Or maybe it’s just more proof that some males don’t know when to quit.
Valero, A., Magurran, A., & Garcia, C. (2009). Guppy males distinguish between familiar and unfamiliar females of a distantly related species Animal Behaviour DOI: 10.1016/j.anbehav.2009.05.018