Mitochondrial DNA sequence variation in a sea star (Leptasterias spp.) species complex

A 551-bp region of a PCR product containing the putative mitochondrial control region and flanking sequences was analyzed for sequence variation among 19 sea stars representing 10 previously described PCR-RFLP haplotypes within a cryptic species complex (Leptasterias spp.). Most (97%) of the sequence variation was interhaplotypic rather than intrahaplotypic, which greatly reduced the utility of sequence polymorphisms in this mtDNA region as markers of intrahaplotypic population structure and gene flow. The estimated number of transition and transversion substitutions per nucleotide site, corrected for multiple hits, was 0.0364 and 0.0158, respectively. Most of the sequence variation occurred in the first half of the putative control region. Phylogenetic analysis (both maximum parsimony and maximum likelihood) revealed three well-supported clades, but the position of two PCR-RFLP haplotypes was not completely resolved. Low intraspecific mtDNA sequence divergence over large geographic distances may be a general pattern for echinoderm species.