Species recognition by male swordtails via chemical cues

Species recognition can often play a key role in female mating preferences. Far less is known about conspecific mate recognition from the male perspective. In many closely related taxa, females exhibit few obvious visual differences and males might have to attend to chemical cues in mate recognition, a possibility that has rarely been explored in vertebrates. Here, we examine male species recognition via odor cues in the swordtail fish, Xiphophorus birchmanni. In dichotomous choice experiments we first tested whether males respond to female odor cues. We found that males were attracted to conspecific female odor and those of a related allopatric congener, Xiphophorus malinche, over a water control. Males did not, however, respond to the female odor of the more distantly related sympatric platyfish, Xiphophorus variatus. We then gave male X. birchmanni the choice between conspecific and heterospecific female stimuli. Males, in this scenario, significantly preferred the conspecific odor when the alternative was platyfish. However, when offered odor cues of X. malinche, male X. birchmanni actually preferred the heterospecific female cue. The complex array of preferences reported here, previously documented only in females, underscores the need to consider the behavior of both sexes in dictating actual mating outcomes.