A Rare Case of Permanent Introgressive Hybridization in Char of the Genus Salvelinus (Salmonidae: Salmoniformes) in the Utkholok River, Western Kamchatka

Hybrids between the whitespotted char Salvelinus leucomaenis and the northern Dolly Varden S. malma malma have been found to regularly occur and exist in the Utkholok River in western Kamchatka and constitute a significant part of the local char stock. Initially, hybrids were recorded in 1970–1971; however, a detailed description is provided for the first time. The diagnosis, description, morphometry, and skull morphology, as well as an analysis of the mtDNA CO1 gene and nuclear TNFα gene sequences and variation in six microsatellite loci, are considered. It has been established that in some of the craniological and meristic morphological traits and genetic markers the hybrids hold an intermediate position between the whitespotted char and northern Dolly Varden, whereas in other traits they are closer to whitespotted char or northern Dolly Varden. According to data of the genetic marker analysis, the hybrids are produced by female whitespotted char and male northern Dolly Varden. It has been shown that in the Utkholok River hybridization occurs constantly due to the disruption of the prezygotic isolation mechanism. A hypothesis is made that the process of permanent hybridization and the large number of hybrids are caused by the close proximity of the spawning grounds of the whitespotted char and northern Dolly Varden in the river tributaries. During the spawning of the whitespotted char, anadromous males, as well as mature male parr of both the whitespotted char and northern Dolly Varden, form a “gamete cloud” resulting in fertilization of whitespotted char eggs.