Genetic variation, population structure and cryptic species within the black mudfish, Neochanna diversus, an endemic galaxiid from New Zealand

To investigate the phylogenetic relationships and geographical structure am ong landlocked populations of the black mudfish, Neochanna diversus, mitoch ondrial DNA nucleotide sequence data were sampled from seven populations fr om the Waikato and Northland regions of New Zealand. The complete D-loop re gion was sequenced from 70 individuals, with 913 bp from the tRNA-pro end u sed in population and phylogenetic analysis. A tandem repeat array, which r anged in size up to 200 bp, was found in most populations at the 3' end of the D-loop that was not able to be aligned for analysis. Of the seven sites sampled, two from Northland exhibited significant sequence divergence from all other sites. There was also a clear distinction among remaining Northl and sites and those from the Waikato. An additional 518 bp segment of the 1 6S region was sequenced from all sites and compared with the other New Zeal and mudfish species, N. apoda, N. burrowsius and the Tasmanian mudfish Gala xias (Neochanna) cleaveri using Galaxias maculatus as an outgroup. Both D-l oop and 16S sequence data provided strong evidence for a cryptic species of mudfish present in Northland. The significant genetic structure apparent i n the black mudfish appears most probably to be attributed to geological co nditions during the Pliocene, where peat wetlands became apparent in the Wa ikato while Northland consisted of disjunct 'islands'. Conservation and man agement of these populations must take into account the historical processe s that have shaped these patterns of genetic diversity.