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Limited nucleotide divergence over large spatial scales in the asterinid sea star Patiriella exigua

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DNA sequence data were collected from two segments of the mitochondrial genome for four populations of the sea star Patiriella exigua, a potentially hermaphroditic species with occasional self-fertilisation, and with a benthic, apparently non-dispersive larval stage. The populations, covering nearly all the range of this species in Australia, included samples from the Yorke Peninsula (South Australia), Tasmania (Woodbridge) and two from the Sydney region, New South Wales (Gordons Bay, Edwards Beach). Six haplotypes were observed in the Yorke Peninsula sample, three in Woodbridge, nine in Edwards Beach and nine in Gordons Bay. The evolutionary relationships between the samples included in this study are close, with average Tamura-Nei nucleotide distances between populations being at most 0.006. Migration between the NSW, Tasmanian and South Australian regions is, however, extremely rare. All haplotypes are restricted to single samples except for four found in both Edwards Beach and Gordons Bay. Monophyly of the haplotypes in Yorke Peninsula and Woodbridge suggests that much of their evolution has occurred locally or regionally and that migration has been low for long periods. This pattern strongly contrasts with the absence of lineage assortment in Echinodermata with extensive planktonic larval stages.

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