TESTING PATTERN PREDICTIONS OF SEXUAL SELECTION - A FROG EXAMPLE

Some Southeast Asian species of the genus Rana possess an unusual suite of secondary sexual characteristics: fangs, hypertrophied jaw muscles, enlarged heads, and males larger than females. Phylogenetic analysis indicates that these frogs form a monophyletic group. Historical transformation analysis and comparative performance tests suggest that this functional complex evolved as a result of sexual selection. Patterns of dimorphism within the clade were used to test a series of predictions from the sexual selection literature. As predicted, closely related species differed most in their secondary sexual characteristics and sexual selection is likely to produce novelties. Contrary to predictions, more derived taxa did not show a greater degree of sexual dimorphism, sexual dimorphism did not increase with body size, and the evolution of new secondary sexual characteristics did not precede and therefore contribute to the loss of old characteristics.