Across the Southern Alps by liver capture? Freshwater fish phylogeography in South Island, New Zealand

We used DNA analysis of galaxiid fish to test a hypothesis of localized hea dwater capture in South Island, New Zealand. The restricted western, but wi despread eastern, distributions of three nonmigratory freshwater fish speci es suggest that part of the east-flowing Waiau River has been captured by t he west-flowing fuller River. However, mitochondrial control region (Kimura 2-parameter distance = 4.1-5.4%) and microsatellite flanking sequences do not support a relationship between Waiau (N = 4 fish sequences) and western populations (N = 8) of Galaxias vulgaris. Instead, the point of capture is probably to the north-east, perhaps the Nelson lakes region. Phylogenetic analysis indicates that western populations, along with populations in the north-east (N = 18), represent a previously unidentified monophyletic Evolu tionarily Significant Unit, possibly a cryptic species. We suggest a genera l caveat for zoogeographic conclusions based on distributional data alone.