A NEGATIVE CORRELATION BETWEEN TRAIT AND MATE PREFERENCE IN XIPHOPHORUS-PYGMAEUS

Variation in female mating preferences was compared with variation in male traits across populations of Xiphophorus pygmaeus. Females of thi s species prefer the large courting males of X. nigrensis to their own small, non-courting males. It was predicted that if large, courting X . pygmaeus males were to occur, they would be preferred. The discovery , distribution and subsequent spread, of large X. pygmaeus males provi ded an unusual opportunity to analyse how sexual selection might act o n a trait not currently fixed in a species. The present study showed v ariation between populations in female preference for large male body size that was negatively correlated with the presence of large males. This variation in preference persisted over a 5-year period. Female pr eference for larger body size and courtship are evolutionarily decoupl ed from the male traits of large size and courtship in X. pygmaeus. Th is pattern is not consistent with indirect selection models (e.g. runa way selection), which predict that female mating preferences and male traits evolve in concert due to a genetic correlation between preferen ce and trait. (C) 1996 The Association for the Study of Animal Behavio ur