Interspecific recognition and discrimination based upon olfactory cues in northern swordtails

Female Xiphophorus montezumae were attracted to olfactory cues from conspec ific and heterospecific (X. cortezi and X. nigrensis) males when given a ch oice between the stimulus and water. When given a choice between conspecifi c and heterospecific cues, females only demonstrated a strong preference fo r the conspecific stimulus when it was matched against X. nigrensis. Female X. nigrensis were attracted to olfactory cues from their close relative, X . cortezi, but did not respond to cues from the more distantly related X. m ontezumae. They preferred the scent of their own males to the olfactory cue s of both heterospecific species. Our results indicate that X. cortezi and X. nigrensis share an apomorphic change in some aspect of their olfactory c ue-receiver system that is not shared with X. montezumae. We also uncovered an asymmetry in response based on olfactory stimuli in these fishes: X. mo ntezumae is moderately attracted to the cue from X. nigrensis whereas X. ni grensis does not respond to the cue from X. montezumae at all.