Unidirectional introgression within the genus Dolomedes (Araneae: Pisauridae) in southern New Zealand

We investigated the genetic structure of mitochondrial DNA (COI) and nuclear DNA (actin 5C) for variation within and among populations of two nurseryweb spider species: Dolomedes aquaticus Goyen, 1888 and D. minor Koch, 1876. Specimens were collected from intermediately disturbed braided rivers located in southern South Island, NewZealand. The genetic variation was compared against morphological characteristics to identify traits, both genetically and phenotypically, that indicate past occurrences of introgression. Haplotypes clearly assignable to D. aquaticus were also present in specimens of D. minor, supporting previous research suggesting introgression of mtDNA from D. aquaticus to D. minor. No evidence was found to indicate introgression from D. minor to D. aquaticus, suggesting that the introgression is asymmetrical and that the isolation mechanisms that may be in place to prevent such an occurrence are more successful within one species. In addition, the distribution patterns of identical haplotypes were found to provide an indication for when and where introgression took place.