Peculiarities of early ontogeny of dwarf forms of Arctic charr Salvelinus alpinus complex (Salmonidae) from Lakes Tokko and Bol’shoe Leprindo (Transbaikalia). 2. Reciprocal hybrids

Growth, peculiarities and anomalies of the ossification and development of skeletal elements, as well as body proportions and meristic characters of laboratory-reared larvae and fry of two lacustrine dwarf forms of Arctic charr Salvelinus alpinus complex from lakes Tokko and Bol’shoe Leprindo (Transbaikalia) were studied. Retardations of the formation of blood cells, anomalies of morpho- and osteogenesis, and increased mortality of unhatched embryos, free embryos and prelarvae of reciprocal hybrids were revealed. Initial characteristics of prelarvae, linear growth, rate of osteogenesis, body proportions, and colouration of hybrid individuals matched matroclinal developmental pattern. Heterochrony of the ossification of vertebral centra was revealed in prelarvae of the hybrid between females from Lake Tokko and males of the deep-water form from Lake Bol’shoe Leprindo. Their ossification was displaced to an earlier stage in the typical ossification and differentiation sequence of skull bones and fin rays, which indicates the presence of respective regulator in parental genome. Such effect was not observed in reciprocal hybrid; however, it demonstrated earlier ossification of predorsalia than the pure form from Lake Bol’shoe Leprindo. The formation of morphological features in the ontogeny of hybrid larvae and juveniles as compared with parental forms was traced. All lethal anomalies of reciprocal hybrids and non-lethal anomalies influencing their viability as well as accelerated use of yolk by hybrids between the females from Lake Bol’shoe Leprindo and males from Lake Tokko, which resulted in mass mortality of prelarvae and weak development of the skeleton of early larvae are considered as the elements of post-zygotic reproductive isolation between pure forms of gen. Salvelinus from the two lakes. This isolation is obviously incomplete since part of hybrid individuals developed normally, though their fertility remains unknown.