Complex genetic patterns and a phylogeographic disjunction among New Zealand mud snails Zeacumantus subcarinatus and Z. lutulentus

The comparative analysis of genetic structure and phylogeography of marine species can reveal the relative importance of common biogeographic barriers and species-specific evolutionary histories. In the present study, mitochondrial COI sequences from a total of 724 individuals collected from 38 localities throughout New Zealand during 2006 and 2007 were used to examine the genetic structure and demographic histories of the intertidal gastropods Zeacumantus subcarinatus and Zeacumantus lutulentus. For both species, results revealed isolation of populations located along the northern South Island and southern and western North Island, and extensive genetic structure throughout the remainder of their ranges. Despite this, long-distance dispersal and secondary admixture of divergent haplotypes was evident, especially for the widespread Z. subcarinatus. These findings reveal the importance of common barriers to gene flow and highlight how the interaction of inherent dispersal limitations of direct-developing marine organisms and periodic long-distance movements can produce complex genetic patterns.