Allozyme Differentiation and Biosystematics of the Californian Closed-Cone Pines (Pinus subsect. Oocarpae)

Abstract

Allozyme differentiation at 32 loci was studied in the three Californian species of Pinus subsect. Oocarpae: P. attenuata, P. muricata, and P. radiata, and in a small sample of a Latin American species of the subsection, P. oocarpa. The Californian species were previously known to comprise highly differentiated, disjunct populations, but with uncertain phylogenetic relationships among several populations and species. All populations had clear affinities for single species. The controversial Channel Islands (Santa Cruz Island) population of P. muricata and the Mexican Island (Guadalupe and Cedros islands) populations of P. radiata were distinct within their respective species, but clearly fell within each species complex. Con- to evidence from other traits, the Californian species were equally differentiated from one another allozymically, with no evidence of close relationships among pairwise comparisons of the three species. Pinus oocorpa, the putative ancestral species, was about two times more variable, and at substantial and approximately equal genetic distance from each of the three Californian species. Divergence of populations within species was generally clinal. The initial radiation of P. attenuata was in the Sierra Nevada, and subsequent divergence was toward the coast in the Siskiyou Mountains, and then south through the coast range to southern California. Divergence in both P. muricata and P. radiata occurred northward along the coast, with the southern island populations retaining ancestral alleles, and differentiation from P. oocarpa increasing northward within species. Genetic differentiation among species was twice that among populations within species.