Female mimicry in garter snakes

Abstract

In many diverse taxa, males of the same species often exhibit multiple mating strategies¹. One well-documented alternative male reproductive pattern is ‘female mimicry’, whereby males assume a female-like morphology^2–8 or mimic female behaviour patterns^9,10. In some species males mimic both female morphology and behaviour^2,7,11,12. We report here female mimicry in a reptile, the red-sided garter snake (Thamnophis sirtalis parietalis). This form of mimicry is unique in that it is expressed as a physiological feminization. Courting male red-sided garter snakes detect a female-specific pheromone and normally avoid courting other males. However, a small proportion of males release a pheromone that attracts other males, as though they were females. In the field, mating aggregations of 5–17 males were observed formed around these individual attractive males, which we have termed ‘she-males’. In competitive mating trails, she-males mated with females significantly more often than did normal males, demonstrating not only reproductive competence but also a possible selective advantage to males with this female-like pheromone.