Data from: Morphological and genetic analysis of sympatric dace within the Rhinichthys cataractae species complex: a case of isolation lost

We assayed 12 morphometric traits and two meristic characters (N = 582; 23 sampling locations) to test for diagnosability of the two dace, as well as to test for morphological differentiation by mtDNA type in sympatry. We then employed a 10-locus microsatellite DNA assay (N = 374; 12 sampling locations) to test for genetic distinction between Nooksack dace and longnose dace in sympatry. We found that the two dace could not be reliably differentiated morphologically: there was overlap in all characters measured, and sampling location had a much larger effect on morphology than mtDNA group.

Microsatellite analysis showed no distinction by mtDNA type in localities with sympatric dace, indicating complete admixture between the sympatric Nooksack dace and longnose dace. The Nooksack dace and longnose dace provide an example of ‘ephemeral speciation’: two lineages that, despite an estimated 1.1 Myr of isolation, have developed no apparent barriers to reproduction and appear to have collapsed into a single interbreeding population where they come into secondary contact.

Nonetheless, the zone of secondary contact and the diagnosability of the Nooksack dace in terms of mtDNA represent significant aspects of the evolutionary legacy within R. cataractae and support its conservation importance. Usage notes jruskey_usat-data_genepop-format Microsatellite DNA genotypes in base pairs jruskey&taylor_morphological-data Morphological data for Ruskey and Taylor. All are in mm except two counts