Interspecific mate choice in sailfin and shortfin species of mollies

I examined interspecific patterns of female choice for three species of mollies: the 'sailfin' species, P. latipinna and two 'shortfin' species, P. orri and P. mexicana. Females of the sailfin species consistently preferred conspecific males across all male treatment combinations containing conspecifics. Females of the two shortfin species had lower levels of female preference and spent less time interacting with males during trials. The only consistent pattern of female choice in either shortfin species was a preference for the sailfin P. latipinna males over heterospecific shortfin males, but not over conspecifics. This finding suggests a potential bias by shortfin females for the sailfin male phenotype. Males of the three species differed in both behaviour and morphology. Length and relative position of the dorsal fin reliably separated P. latipinna from the two shortfin species. Body depth and shape distinguished males of the two shortfin species. Dorsal fin height was not a reliable cue for distinguishing sailfin males from males of either shortfin species. Males from different populations of the sailfin species P. latipinna differ in both size-specific behavioural rates and size-specific morphometry, particularly in the overall size-adjusted area of the dorsal fin. Increased rates of courtship displays and increased area of the dorsal fin separate males of P. latipinna from males of the two shortfin species as well. If the same traits used by females of P. latipinna for intraspecific discrimination are also important species-recognition signals, this suggests a potential role for sexual selection in contributing to the divergence of male phenotype during speciation of sailfin mollies. (C) 1998 The Association for the Study of Animal Behaviour.