Female preferences for dorsal fin and body size in Xiphophorus helleri: further investigation of the LPA bias in Poeciliid fishes

Abstract

Female preference for male fin elaborations in the family Poeciliidae may be driven by a perceptual preference for increased lateral projection area (LPA). Our research with sailfin and shortfin mollies suggests that increased LPA is more stimulating to females whether manifest as larger dorsal fin or body size. Like mollies, male Xiphophorus helleri possess a fin elaboration (sword) that even females of related but unsworded species find attractive. We hypothesize that the sword preference, like the sailfin preference in Poecilia , is the result of a bias for greater LPA. We addressed this hypothesis by testing female preferences for male body and dorsal fin size in X. helleri. Females preferred males of greater LPA when the fin:body size ratio was held constant. However, females showed no preference for enlarged dorsal fins when body size was held constant, instead favoring the dummy whose fin:body size ratio matched that of a typical male in the population. Therefore, although females preferred males with greater LPA, the LPA preference in X. helleri appears less permissive than that which favored the evolution of enlarged dorsal fins in mollies; constrained in X. helleri by an additional preference for a species-specific fin:body size ratio.