The ontogeny and evolution of sexual dimorphism in paraclinin blennies (Teleostei: Labrisomidae).

Abstract

Ontogeny of sexual dimorphism within the Paraclinini is quite complex both within and among species. Differential growth in males is not the main cause of adult dimorphism. Rather, allometric shifts in both sexes produce adult shapes with approximately equal frequency. A trait that appears exaggerated in one sex is not always produced ontogenetically by acceleration in growth of that trait. Larger male head size, for example, may result from neoteny in females (relative to juveniles) as often as acceleration in male growth. Females, rather than looking like large juveniles, are actually more different in shape from juveniles than are males. On this time scale then, females should be considered the divergent sex. Phylogenetic analysis revealed three main lineages within the tribe. These groups are probably stable, though positions of some of the other species may change as more data become available. The most primitive species are grandicomis, nigripinnis, and cingulatus. The position of Exerpes within the clade indicates that its single species should be included in the genus Paraclinus. Fairly extreme sexual dimorphism within Paraclinini seems to be the ancestral condition and has been variously modified within the clade. The trend is toward less extreme male and female difference with occasional reversal of a dimorphic character. The decrease in amount of dimorphism seems to have occurred primarily through neoteny (relative to ancestral allometry), acceleration, and post-displacement. Juvenile growth has also changed relative to ancestral juveniles, affecting of adult as well as juvenile proportions. These evolutionary changes are independent of and in no way reflect the ontogenetic paths producing dimorphism within a species.