Phylogeography of the snakeskin chiton Sypharochiton pelliserpentis (Mollusca: Polyplacophora) around New Zealand: are seasonal near-shore upwelling events a dynamic barrier to gene flow?

We present a phylogeographic study of the New Zealand and Australian intertidal chiton Sypharochiton pelliserpentis that was conducted to ascertain levels of population connectivity and to investigate the effect of previously hypothesized general phylogeographic boundaries. The analysis incorporated both cytochrome oxidase subunit 1 sequence data (approximately 700 bp) and RFLP data from 29 populations around New Zealand, and from one Australian population, for a total of N = 472. The major population structure observed was a strong disjunction between northern and southern populations (Phi(ST) = 0.47), with the genetic breaks located at Cloudy/Clifford Bay and Farewell Spit, at the northern tip of the South Island. This finding corresponds with a common phylogeographic barrier observed in a number of other marine invertebrates, highlighting its significance and ubiquity. Athird barrier to gene flow was identified between Spirits Bay and Ahipara, around the northern tip of the North Island. All three of these areas that exhibit significant population disjunctions have strong near-shore upwelling along with water current movement offshore, and these features are prevalent during the time of year when S. pelliserpentis spawns. That these seasonal hydrographic patterns contribute to the population structuring of S. pelliserpentis is supported by comparison with other phylogeographic studies of marine invertebrates, where the strength of this barrier seems to correlate with spawning season. (C) 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 552-563.