LEONARD, J.L.*; Univ. of California, Santa Cruz: Sexual Selection in Hermaphrodites: What Does It Look Like and Where Do We Find It?

Darwin believed that his theory of sexual selection would apply only to animals with sophisticated behavior and sensory systems. Modern emphasis on variance in mating success as an index of the opportunity for sexual selection offers a much different picture. Mating systems and structures in plants and many invertebrate animals are now viewed as products of sexual selection. However, hermaphrodites differ in many respects from the classic subjects of sexual selection theory. For example the degree of sexual dimorphism, which is sometimes used as a measure of sexual selection, is difficult to apply to hermaphrodites. It has also been suggested that sexual selection in hermaphrodites must be weak because sex allocation theory predicts that in male fitness should not be proportional to the number of mates but reach a plateau, in violation of Bateman�s principle. However, several phenomena that are commonly associated with sexual selection in dieocious taxa are widespread and highly developed in hermaphrodites. These phenomena include a) bizarre and expensive courtship and copulatory behavior; b) multiple mating and sperm competition; c) rapid evolution of genitalia, d) special structures associated with courtship and e) phally polymorphism. The skewed breeding sex ratios associated with sequential hermaphroditism have long been recognized as contributory to sexual selection. However, in many simultaneous hermaphrodites although the sex ratio at mating may be one to one, the actual reproductive sex ratio may also be skewed, creating a high potential for sexual selection. Since sexual selection theory is derived almost exclusively from consideration of dieocious organisms, the mating systems of hermaphrodites offer many opportunities for critical tests of the assumptions of predictions of sexual selection theory.