Male swords and female preferences.

ent sword as a control. Because swordlessness is the ancestral state of the Xiphophorus clade, Basolo argues that the results of her experiment indicate that female preference for swords predates the evolution of the sword and concludes that coevolutionary models of sexual selection are inadequate. Basolo provides no direct evidence in support of a preexisting female sensory bias, but rejects the coevolutionary hypotheses of mate-choice evolution. Female platyfish may have exhibited a preference for artificially sworded males because these males were novel (2). The appropriate control for this possibility would be males with some other shapes attached that do not resemble any marking on males, a blue triangle, for example. Iffemales prefer males with a triangle to those without, then females are clearly attracted to novel males. Ifthis test shows that females are not attracted to novel males, then it would be necessary to demonstrate that females are attracted to the sword per se and not the context in which the sword is displayed. This is an important distinction, because the sensorybias hypothesis implicitly assumes that it is the character alone, not its context, that attracts the females. Such an experiment could be done by attaching a sword to areas other than the lower edge of the caudal fin. The most convincing support for the sensory-bias hypothesis would come from a demonstration that males show a mating preference for females bearing swords. This counterintuitive prediction derives from the hypothesis that a female sensory bias evolves in response to some environmental stimulus. Basolo gives the example that females may have evolved a search image for a favorite food and then preferred to mate with males that sported an appendage resembling this food. In such a scenario, males would be just