Patterns of Evolutionary Diversification in a World‐Significant Hotspot of Salmonid Diversity: A Study of Landlocked Salvelinus Fish of the Kronotskoe‐Uzon Area, Kamchatka

ABSTRACT

Freshwater fish are prone to forming polymorphisms beneficial for resource partitioning and rapid adaptation. Genetically distinct ecomorphs emerge in a mosaic, forming local centers of biodiversity. The mechanisms behind this process are of particular interest, as they facilitate the study of speciation. Here we examine the patterns of evolution in the endemic charrs (genus Salvelinus ) that populate the Kronotskoe‐Uzon drainage system. This is one of the most phenotypically diverse and complicated assemblages of salmonids on Earth. By analyzing SNPs in SLAF sequences of 107 specimens covering all local diversity and 55 specimens from nine populations of the potential ancestor, we investigated the phylogenetic relationships, the timeline of diversification, genetic structure, and historical gene flow within the population system. Our findings suggest that the endemic assemblage diverged from the widespread anadromous Salvelinus malma of eastern Kamchatka, which probably invaded the basin in several waves. Ten of the 14 genetically distinct ecomorphs diversified in Lake Kronotskoe at the center of the drainage system. The assemblage formed in the post‐LGM—Holocene time as a result of inter‐lake multistep adaptive radiation and specialization of hybridogenic populations, as well as the secondary expansion of endemic charrs into peripheral waterbodies. The steps of ecomorph divergence coincide well with the main geological and paleoclimatic events in the area. Although the diversity of Kronotskoe‐Uzon charrs is unique, faunal radiation has proceeded through several archetypal ecological modes implemented by freshwater fishes in dozens of reservoirs across the Holarctic. The reason for this increased diversity is the active habitat restructuring and enhanced ecological opportunities provided by the large lake–river system in the moderate climate.