Divergent skull morphology between trophic separated lacustrine forms of Dolly Varden charr from Lake Kronotskoe, Kamchatka, Russia

Abstract

Trophic morphology divergence between two forms of Dolly Varden Salvelinus malma from Lake Kronotskoe (Kamchatka Peninsula, Russia): Salvelinus albus (omnivorous form) and Salvelinus schmidti (benthivorous form) was studied using the skull bone’s qualitative and measurable attributes. The strongest morphological differences between these two charr forms were associated with the jaw bone structures (i.e. premaxilla, maxilla, angulo-articular and dentary bones). There was an abrupt shift in bone structures with increasing body length in both morphs. S. albus of body length less than 350 mm had wider dentary, maxilla and angulo-articular bones than individuals of similar sized S. schmidti. In contrast, large (>350 mm) individuals of S. albus had narrower bone structures than individuals of S. schmidti. This divergent pattern of the bone structures in the jaws is closely linked with their different trophic niches measured by the contence of stable isotope (δ 13C, δ 15N) values in the tissues. S. albus have a narrow, long jaw bones and a terminal mouth and occupy an omnivorous niche with clear ontogenetic niche-shifts (i.e. benthivore and piscivore) by increasing in size. In contrast, S. schmidti have short jaw bones and a low mouth; also S. schmidti is exclusively benthivores through their entire ontogeny. These trophic traits indicate clear divergence between two lacustrine forms, which occupy different trophic niches but, at the same time, are not completely reproductively isolated.