Social Inhibition of Maturation in Natural Populations of Xiphophorus variatus (Pisces: Poeciliidae).

According to analyses of field samples, social inhibition of maturation is at work in natural populations of the variable platyfish, Xiphophorus variatus. In the laboratory, adult males inhibit the maturation of juveniles; the inhibition is overcome as the juveniles increase in size. The proportion of maturing males in any field collection is related to the number of adult males present and the size of the juveniles. The more adults, the fewer maturing males are present; the larger the average juvenile, the greater the number of males maturing. The evolution of this system is best understood in terms of individual selection, but consequences of the system buffer the population against the effects of predation.