Speciational Evolution: a Phylogenetic Test With Allozymes in Sceloporus (Reptilia)

Abstract

The potential role of speciation in accelerating evolutionary divergence remains controversial. Earlier tests based on genetic and morphologic distances which indicated an absence of speciational evolution rely on problematic assumptions. We provide a phylogenetic test in which amounts of discrete character change relative to an outgroup are compared between sister taxa. Although this test is constrained by a need to assume similar extinction rates in groups compared, it provides conceptual improvements regarding monophyly, equal age of taxa, and distribution of homoplasy. Based on analysis of 68 informative allozyme characters for 19 lizard species in the genus Sceloporus [S. merriami, S. undulatus, S. occidentalis, S. virgatus, S. variabilis, S. cozumelae, S. chrysostictis, S. siniferus, S. clarki, S. olivaceus, S. spinosus, S. torquatus, S. dugesii, S. jarrovi, S. mucronatus, S. cyanogenys, S. poinsetti, S. grammicus and S. serrifer], significant speciational evolution and punctuational change is, at least, a viable explanation for the distribution of observed character changes.