Ecological predictions lead to the discovery of a benthic–limnetic sympatric species pair of threespine stickleback in Little Quarry Lake, British Columbia

Sympatric species pairs of benthic and limnetic threespine stickleback ( Gasterosteus aculeatus L., 1758 complex) are an important example of the role of ecology in speciation in nature. Four endemic pairs are known and each appears to have diverged independently as a consequence of adaptation to alternative environments. Using specific ecological and physical attributes hypothesized to be important to their evolution, we focused a search for further species pairs. Now, two decades after the last discovery, we describe another benthic–limnetic species pair from Little Quarry Lake on Nelson Island, British Columbia, Canada. Bimodality of genetic admixture values provides evidence of strong reproductive isolation between two morphological and genetic clusters, supporting the existence of a sympatric species pair within this lake. Close correspondence in shape to extant benthic and limnetic species pairs confirm their status as such. The remarkable similarity between them and other benthic and limnetic species pairs in levels of morphological differentiation, as well as extent of admixture and hybridization, points to similar processes underlying their origin. This discovery serves as an important reminder of the specificity of ecological factors that promote and maintain biodiversity, as well as the value of habitat conservation.