Evidence for natural hybridization between Dolly Varden (Salvelinus malma) and bull trout (Salvelinus confluentus) in a northcentral British Columbia watershed

Abstract

Morphological and molecular analyses were used to identify sympatric Dolly Varden ( Salvelinus malma) and bull trout (Salvelinus confluentus) and their hybrids from streams tributary to Thutade Lake, Peace River drainage, northcentral British Columbia. Morphological analysis identified two groups of char resembling allopatric Dolly Varden and bull trout as well as a small number of morphologically intermediate fish. One of the morphologically intermediate char possessed both Dolly Varden and bull trout ribosomal DNA (rDNA) and growth hormone restriction fragment length differences (RFLDs) indicating its F1 hybrid status. Another morphologically intermediate fish exhibited a hybrid rDNA RFLD, but possessed a growth hormone RFLD consistent with a hybrid × hybrid mating or a hybrid × bull trout backcross. Both hybrid individuals had a diagnostic bull trout mitochondrial DNA (mtDNA) RFLD. As mtDNA is maternally inherited, our data imply that the F 1 hybrid resulted from a mating between a bull trout female and a Dolly Varden male, perhaps by small Dolly Varden males sneaking fertilizations during bull trout spawnings. This is the first record of Dolly Varden in the Peace River drainage, an d the first confirmation of natural hybrids between the two species. Despite apparent introgression, the two species appear to be maintaining themselves as distinct genomes.