Reproductive Strategies and the Origin of Parapatric and Sympatric Forms of Arctic Charr Salvelinus alpinus (Salmonidae) in the System of Lakes Bol’shoe Leprindo and Maloe Leprindo (Northern Transbaikalia)

In the system of lakes Bol’shoe Leprindo and Maloe Leprindo (Lena basin, Transbaikalia), spawning of two isolated populations of the dwarf form of Arctic charr Salvelinus alpinus was studied. The results supplemented with the data about the exterminated large form from these lakes, demonstrate a unique combination of sympatric and parapatric charr forms with autumn (large form), summer (dwarf form, Bol’shoe Leprindo) and first recorded in Russia winter-spring (dwarf form, Maloe Leprindo) spawning peaks. In both lakes, the dwarf form spawns in the profundal zone at silty bottom at the depth 25–58 m: in Bol’shoe Leprindo, from late June to October with peak in July-August when water temperature is 5–6°С, in Maloe Leprindo from January to July, with peak in January–March when temperature is 2.5–3.0°С. Eggs laid in July–August in Bol’shoe Leprindo develop for 3.0–3.5 months, eggs laid in January–March in Maloe Leprindo, for about 4.0–4.5 month; in both lakes they are actively consumed by burbot Lota lota. Due to smaller egg size the dwarf form has twice as high individual relative fecundity as the large form, which compensates for high egg mortality. It is supposed that the differences in spawning strategies were formed as the result of outcompeting of the dwarf form by the large form from the littoral to the profundal zone, where perennial low temperature favoured the prolongation and displacement of their spawning time. These differences determined reproductive isolation and genetic divergence between three charr populations.