• Canada;
  • comparative phylogeography;
  • disjunct distributions;
  • Gerridae;
  • Gerris;
  • mitochondrial DNA;
  • morphological identification;
  • nuclear DNA;
  • western United States


Aim  To perform a comparative analysis of distribution and genetic diversity in three closely related water strider species (Gerris) in order to shed light on a putative disjunct distribution in Gerris gillettei.

Location  Canada and the western United States.

Methods  Entomological collections from Canada and the United States were surveyed for records of Gerris pingreensis, G. gillettei and Gerris incognitus in order to establish the distribution range of each species. Using samples from present populations, mitochondrial and nuclear DNA sequence variation were used to construct minimum-spanning networks. Distribution patterns and genetic diversity were then compared among species.

Results  Our results showed that G. incognitus is a genetically distinct species with an unsuspected disjunct distribution. Gerris pingreensis and G. gillettei were found to share genetic polymorphism and they displayed spatial differences only in terms of haplotype distribution, suggesting that they form a single species.

Main conclusions  Distributional and molecular information uncover unusual distribution patterns and underline taxonomic uncertainty in a group of three closely related Gerris species. Vicariance and failure to recolonize following the last glaciation could explain the G. incognitus disjunction. Morphological and DNA-based species identifications suggest different post-glacial recolonization processes for G. pingreensis and G. gillettei. The putative discontinuous range of G. gillettei may be explained as disjunct phenotypes of a single species.