Assessing the distinctiveness of the Cultus pygmy sculpin, a threatened endemic, from the widespread coastrange sculpin Cottus aleuticus

Abstract

The Cultus pygmy sculpin is a cottoid fish endemic to Cultus Lake, southwestern British Columbia, Canada, and is listed as 'threatened' under the federal Species at Risk Act (SARA). The Cultus pygmy sculpin was first discovered and described as a 'dwarf' coastrange sculpin Cottus aleuticus in the 1930s. It matures at a smaller size than the 'normal' C. aleuticus, has a lacustrine life history rather than a fluvial one, has different morphological features, and appears to undertake diurnal feeding migrations into the water column to feed on Daphnia, but little else of its biology is known. We used molecular genetic and behavioural assays to further assess the level of differentiation between Cultus pygmy sculpin and stream-dwelling C. aleuticus from several locations. Mitochondrial DNA haplotypes were broadly shared between Cultus pygmy sculpin and coastrange sculpin, and there was no apparent phylogeographic structure. However, analysis of 8 microsatellite analysis loci indicated significant genetic differentiation between parapatric samples of both forms. Laboratory-based experiments showed that, in gen- eral, the Cultus pygmy sculpin was found higher in the water column and was more active off the bottom than coastrange sculpin, but these behavioural differences were influenced by the pres- ence of congeneric C. asper. Molecular and behavioural results support the recognition of the Cul- tus pygmy sculpin as a conservation unit distinct from 'typical' C. aleuticus because there is some level of genetic and behavioural discreteness between the forms, and behavioural differences may represent an important aspect of the pelagic life style of the Cultus pygmy sculpin.