Rapid miniaturization of Salvelinus fish as an adaptation to the volcanic impact

Volcanoes serve as natural laboratories expanding our understanding of the recent and past ecological and evolutionary processes. Here, we present data elucidating the developmental and phenotypic transformations providing rapid adaptation for the salmonid fish, Salvelinus malma , to volcanic impact. After being isolated by the mudflow in 1996, the locked descendants of sea-run charr managed to survive in the highly turbid and toxic environment. Initially, the population underwent a phase of high developmental instability accompanied by a surge in morphological deviations. Further, selection targeted the fish prone to migrate into the most toxic mainstream favoring a sedentary lifestyle at the less toxic spawning tributaries. In five–seven generations, the sedentary population recovered developmental homeostasis but diverged into a small-sized short-cycled form with low phenotypic variability. In response to toxicosis, the fish displayed an accelerated metabolic rate and precocious maturations. The spawners possessed fry morphology with no spawning dress. Sedentary fish also exhibited a decreased fecundity and did not build spawning nests. Thus, under the volcanic impact, S. malma demonstrated a rapid paedomorphic miniaturization, an evolutionary mechanism enabling to complete the reproductive cycle under the conditions of high risks of reaching the adaptive capacity limits.