Lack of genetic evidence for the subspeciation ofPisaster ochraceus(Echinodermata: Asteroidea) in the north-eastern Pacific Ocean

Abstract

The existence of twoPisaster ochraceussubspecies has been proposed; one located northwards (P. ochraceus ochraceus)and the other southwards(Pisaster ochraceus segnis) from Point Conception. We used polymerase chain reaction–restriction fragment length polymorphism of the CO I and CO III mitochondrial genes to assess the degree of population structure from 126 samples collected along the western coast of North America, from Vancouver, Canada to Punta San Carlos, of Baja California, Mexico. The genetic structure was tested through molecular analysis of variance and by Monte Carlo simulations of the original data set. The phylogeographical pattern was deduced from a minimum spanning network analysis. No genetic structure was detected. Instead, a high degree of genetic homogeneity along the species distribution was evident from haplotype frequencies at each location. Two haplotypes,Po1andPo5, were predominant along the distribution and were considered ancestral because of their central position in the minimum spanning network. SincePisaster ochraceusdepicts a planktotrophic larval stage with very long duration before settlement, it seems to be able to surpass the biogeographical boundary that limits other species around Point Conception, thereby maintaining homogeneity of its genetic pool. Results of this study recognizeP. ochraceusas a single species.