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No. 41: Sep-Oct 1985

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The deceitful she-males

"In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is 'female mimicry,' whereby males assume a female-like morphology or mimic female behavior patterns. In some species males mimic both female morphology and behavior. 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 trials, 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."

In the competitive mating trials, the she-males were successful in 29 out of 42 trials. The normal males won out in only 13! The authors ask the question: Why aren't all males she-males given such an advantage?

(Mason, Robert T., and Crews, David; "Female Mimicry in Garter Snakes," Nature, 316:59, 1985.)

Comment. Among the fishes, bluegills and salmon (and probably many others) have female-appearing males competing with normal males.

From Science Frontiers #41, SEP-OCT 1985. 1985-2000 William R. Corliss