Genetic differentiation in gill raker number and length in sympatric anadromous and nonanadromous morphs of sockeye salmon, Oncorhynchus nerka

The genetic and environmental basis for polymorphism in gill raker number a nd length in sympatric anadromous and nonanadromous morphs of sockeye salmo n, Oncorhynchus nerka, was investigated. Analysis of 30 full sib families i nvolving pure types and reciprocal hybrids revealed that the variation was partitioned significantly among families within cross types and among cross types in both traits. As in the wild, kokanee displayed more gill rakers t han sockeye; reciprocal hybrids displayed intermediate counts. Gill raker l ength also varied markedly among cross types, with pure sockeye displaying 19% longer gill rakers than comparable sized kokanee. This difference was i n the opposite direction predicted, given the common positive association b etween gill raker number and length in sympatric morphs of the same species in fishes. Gill raker number and length were generally not correlated with in cross types, suggesting independent divergence of the traits. The result s are discussed in relation to genetic and trophic divergence of the morphs and to factors selecting for differentiation in the two gill raker traits.