Female swordtails, Xiphophorus continens, prefer the scent of heterospecific males

Xiphophorus continens is one of two northern swordtail species that has only small, noncourting, sneaker males. In this study we discovered that female X. continens were strongly attracted to the scent of courting males of their close relative X. montezumae and that they preferred the odour of those males to the scent of conspecific males. The heterospecific attraction is asymmetric; female X. montezumae were not attracted to the scent of X. continens. These results suggest that the olfactory cue is in fact multicomponent, transmitting information about both the species identification (conspecific versus not a conspecific) and sexual status (sneaker male versus courting male) of the sender. These two 'bits' of information can interact in either a mutually reinforcing or an antagonist manner depending upon the choice being offered. Xiphophorus montezumae females choosing between X. montezumae/X. continens males are faced with mutually reinforcing cue components: 'conspecific + courting male' versus 'not a conspecific + sneaker male'. Xiphophorus continens females making the same choice, however, are faced with conflicting cue components: 'conspecific + sneaker male' versus 'not a conspecific + courting male'. We suggest that the strength of attraction to the conspecific based upon olfactory cues in these fishes represents the complex outcome of the female's attraction to the different components in the male-based cue. (c) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.