Molly deceives rivals about the female it fancies

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Male Atlantic mollies deceive competitors by feigning disinterest in the females that are their first mate choice, according to a study published in a recent issue of the journal Current Biology.

The study by researchers from the University of Potsdam and University of Oklahoma found that male Poecilia mexicana not only feign disinterest in their top choices, they also begin courting less desirable females to throw off their rivals (male mollies are known to copy the mate choices of other males).

Martin Plath and co-workers introduced a male molly to a tank already containing a large and a small female molly.

They then observed the behaviour of the male for five minutes, and repeated the experiment several times with different individuals.

The experiment was then immediately repeated, but in half of the trials, a male audience molly was also introduced to the tank.

This male audience molly was kept inside a transparent plastic cylinder such that it could be seen by, but not come in physical contact with, the other fish in the tank.

The authors found that in the first set of experiments, the male mollies directed significantly more mating behaviours (nipping and gonopodial thrusts) toward the larger female. In the presence of the audience male, however, the focal male switched interest, directing significantly more mating behaviours towards the smaller (and apparently less preferred) females.

The experiment was repeated, this time using a set consisting of a female Atlantic molly and a female Amazon molly (Poecilia formosa) of similar sizes.

The asexually-reproducing Amazon molly is a sexual parasite, using sperm from male Atlantic molly solely to trigger embryogenesis.

Because male Atlantic mollies make no genetic contribution to the offspring of Amazon mollies with whom they have mated, the authors predict that male Atlantic mollies would choose to mate with female Atlantic mollies over female Amazon mollies.

In the absence of an audience male, focal males did direct more mating behaviours towards the female Atlantic molly, but switched their attentions to the female Amazon molly in the presence of an audience male.

The authors postulate that this behaviour ...is used to deceive competitors about the focal male's preferred mate... and that ending deceptive signals and leading competitors away from a preferred female can be a powerful alternate mating strategy providing relief from sperm competition in highly dynamic mating systems like that seen in poeciliid fishes.

Deception appears to have evolved as a counter-strategy in a system with a high potential for male mate-choice copying.

For more information, see the paper: Plath, M, S Richter, R Tiedemann and I Schlupp (2008) Male fish deceive competitors about mating preferences. Current Biology 18, pp. 1138"1141.