Life-history variation as a source of diversity for endemic white charr (Salmonidae) of the lower Kamchatka River.

Abstract

Sympatric fish morphs diversifying in their feeding pattern in fresh waters typically implement alternative migratory tactics so that omnivores become migrants and specialists-residents. Charrs of the genus Salvelinus populating the lower Kamchatka River (Northeast Asia) are a rare example wherein two related sympatric morphs both implement a variety of life-history tactics in parallel. Here the authors analyse the ecological diversity in the endemic piscivorous "white" morph that exploits resources of the Kamchatka River in sympatry with the partially anadromous invertivorous "Dolly Varden" (DV) morph. Eco-morphological criteria allowed the authors to validate the morph identification. The white charr (WC) was found to subdivide into the small-sized (up to 1.6 kg) fish inhabiting the lacustrine part of the ecosystem and the large-sized (up to 3.4 kg) fish inhabiting the main river channel. The persistent spatial segregation of the sub-groups was confirmed by significant differences in the life span, muscle δ13 С signature and parasite load. According to contrasting patterns of strontium accumulation in otoliths, the riverine WC is represented by resident and semi-anadromous individuals. At the same time, the lack of microsatellite DNA differentiation and allometric nature of the morphometric discrepancy point to the intra-population source of the WC polymorphism. The authors suggest that WC diverged from DV as a result of feeding specialization on the threespine stickleback numerous in the ecosystem since the temporary flooding by marine waters in the middle Holocene. The modern stickleback division into local stocks following the ecosystem differentiation into a river, side lake and estuary resulted in the WC life-history split and ecological radiation.