ИСТИНА

Segregation in the time and place of spawning is a major driver of sympatric speciation in fish, in particular in the case of intralacustrine Arctic charr morphs. In several lakes of Transbaikalia, Russia, deviations from typical autumn spawning of charr were recorded: summer spawning takes place in lakes Davatchan, Bol’shoe Leprindo and Tokko; winter spawning in Lake Maloe Leprindo (the first record of late winter spawning of Arctic charr in Russia). In these lakes, the profundal summer or winter spawning dwarf form is sympatric with littoral autumn-spawning small and/or large forms and presumably was outcompeted by them to the profundal zone in the course of intralacustrine divergence. The data from temperature loggers combined with laboratory rearing experiments idicate that effective spawning in the littoral zone is possible only in autumn or early winter, while at the depth of >25-30 m it is possible all year round, summer and late winter/spring spawning being two possible alternatives. Special attention is paid to the parapatric dwarf charr populations of interconnected lakes Maloe Leprindo and Bol’shoe Leprindo, which manifest contrasting spawning seasons, developmental temperatures and hatching time. Despite of 4o C difference in mean water temperature during egg development, these charr are similar in meristic characters and in life-history parameters connected with the exploitation of the niche of specialized planktophage, while profound morphological and ecological differences from sympatric large piscivorous form were observed. In both lakes, egg of the dwarf form develop in suboptimal unsheltered conditions of soft-bottom substrate. High egg mortality is compensated by two-fold increase of relative individual fecundity as compared with the large form, due to smaller egg diameter. The dwarf charr from the two lakes are genetically segregated and reproductively isolated from each other and from the large form. These observations illustrate the the mechanisms of the formation of reproductive barriers in the course of sympatric/parapatric speciation.