1. To determine the consequences of dispersal and gene flow for temporary pond water mites (Hydrachnida), we compared distributional, genetic and morphological characters in the closely related species Arrenurus angustilimbatus and A. rufopyriformis. The former has larvae that parasitise and disperse on adult mosquitoes, whereas larvae of the latter forego any association with hosts.
2. Allometrically adjusted egg size and gonopore size were found to be useful characters for distinguishing between females of the two species.
3. Arrenurus angustilimbatus possesses a broader and more continuous geographic distribution than its ‘direct developing’ counterpart. Allozyme heterozygosity was higher and population differentiation lower in A. angustilimbatus. In addition, populations of A. rufopyriformis were morphologically divergent, whereas populations of A. angustilimbatus were not. Isolation by distance analyses on both genetic and morphological characters indicated that the results were not biased by different sampling regimes for the two species.
4. These results demonstrate the importance of mosquito parasitism for maintaining ecological and genetic linkages between A. angustilimbatus populations. More broadly, we hypothesise that insect-mediated dispersal has contributed to the ecological and evolutionary success of water mites, because the Hydrachnida lack other obvious adaptations for dispersing in space or time.