The sympatric whitefishes Coregonus ussuriensis and C. chadary from the Amur River basin: Morphology, biology and genetic diversity

Data on morphology, biology and the molecular-genetic variability of the Coregonus ussuriensis (CU) and chadary whitefish C. chadary (Teleostei: Salmoniformes: Coregonidae) (CW) from the upstream and downstream reaches of the Amur River drainage are presented. These species differ in growth rate and morphological traits. Analysis of feeding has shown that CU is euryphagous, although during the summer this species has a significant proportion of fish and insect imago in its diet. Its habits considerably differ from the ecological niche of CW and other pidschian-like whitefishes inhabiting the water bodies of the southern part of Siberia. We have confirmed reliable distinctions between CU and CW in the numbers of gill raker and lateral line scales. The comparative analysis of the morphometric traits showed that a body shape of C. ussuriensis differs both from pidschian-like whitefishes and from C. chadary. The phylogenetic relationships among mtDNA haplotypes were reconstructed based on variability in mitochondrial genes 16 S-ND1 and ND3. The Coregonus species from the Amur River form a monophyletic clade sister to Lake Baikal omul and whitefishes lineage, with two distinct groups corresponding with two studied species. On the basis of our data, we suggest the hypotheses of sympatric and allopatric origins of these species. Two extant Coregonus species could have originated from: (i) a single ancestral whitefish related to Lake Baikal coregonids or (ii) two independent allopatric (Baikalian and south Siberian pidschian-like) forms that migrated to the Amur River basin, presumably asynchronously, with the subsequent hybridization and introgression that could have resulted in the complete replacement of mitochondrial DNA.