Morphology and Genetics of the Ciscoes (Actinopterygii: Salmoniformes: Salmonidae: Coregoninae: Coregonus) from the Solovetsky Archipelago (White Sea) as a Key to Determination of the Taxonomic Position of Ciscoes in Northeastern Europe

Abstract

Background. The characteristic feature of the genus Coregonus is the multitude of nominal species of obscure identity. The northeastern Europe is inhabited by, inter alia—the vendace, Coregonus albula (Linnaeus, 1758)—considered the European cisco—and the least cisco, C. sardinella Valenciennes, 1848—often referred to as the Siberian species. There is a large area in where the ranges of both species overlap. Using morphological- as well as genetic tools we attempted to test the working hypothesis that the Coregonus fish (ciscoes) inhabiting the above-mentioned transitional zone represent a single species. Materials and methods. Within 1995–2009 we collected 344 ciscoes from five lakes in Bolshoy Solovetsky Island and determined diagnostic morphological traits for the two species. For some samples, the polymorphism of the creatine kinase isoloci (CK-A1,2*) and the fragment of mitochondrial DNA (mtDNA) encoding the sub-unit 1 of NADH-dehydrogenize complex (ND-1 fragment) was also studied. Results. According to one of the main taxonomical characteristics—the number of vertebrae—the cisco of Solovetsky Island occupies an intermediate position between C. albula and C. sardinella. The molecular markers, however, did not reveal any differences between the ciscoes of Bolshoy Solovetsky Island and the vendace found elsewhere. All specimens had the type allele of creatine kinase (CK-A*100) which was considered to be typical for C. albula at other locations as well as the haplotype E of mtDNA widespread in vendace populations. Conclusion. The cisco from Solovetsky Island is more similar to typical vendace. Differences in some morphological traits between Solovetsky Island populations and the vendace from elsewhere are likely to reflect adaptation to environmental conditions. Thus it appears that morphological criteria do not allow reliable differentiation between two forms of ciscoes as well as between least cisco and vendace because they are influenced by environmental conditions. We believe that the presence of populations with intermediate features is a strong argument for combining C. albula and C. sardinella into a single species (C. albula).