Western range limits and isolates of eastern odonate species in Siberia and their putative origins

Macromia amphigena, Shaogomphus postocularis, and Sympetrum croceolum, ranging in NE China, Korea and Japan, have isolates at the NE margins of the Altai-Sayan mountain system: all 3 in SE West Siberia, M. amphigena and S. postocularis also in southern Central Siberia and M. amphigena in E Kazakhstan and W Mongolia. Ophiogomphus obscurus, Nihonogomphus ruptus, and Calopteryx japonica have continuous ranges protruding to the West from E. Asia to the Ob’ River basin and to 60° N latitude. Coenagrion ecornutum has a similar range but extends N in Siberia to 65° N and has an isolate in the S Ural Mts. C. lanceolatum, C. hylas and Somatochlora graeseri reach 70° N and also extend westward to the Ob’ River basin, but C. hylas has isolates in the Polar Urals and Bavaria, while S. graeseri is probably isolated in the Ural Mts. Of 4 other eastern spp. in Siberia, 2 reach 70° N, but Somatochlora exuberata extends westwards only to the sources of the Yenisey River and Coenagrion glaciale to Lake Baikal, while Cercion v-nigrum and Anisogomphus maacki just penetrate into SE Transbaikalia. Thus, 11 eastern odon. spp. have their western limits in Siberia (defined in a narrow sense, not including the Far East), In addition, 4 have more westerly isolates, 3 in the Urals and 1 in Bavaria. Siberia also includes the eastern limits of 21 western spp. 24 transpalaearctic spp. spread far to the N and 10 spp. occupy S Siberia only (or just occur locally), 2 Central Asian spp. barely penetrate into S. Siberia. Aeshna viridis is a doubtful amphipalaearctic species. Numerous palaeopalinological reconstructions suggest that during the Holocene climatic optimum, a continuous belt of broad-leaved forest was restored in Siberia, providing conditions for a recolonization of Siberia by Odon. Westward migrations of eastern spp. were favoured by the optimum occurring earlier in the east than in the west. Hence, many western spp. had no time to occupy all of Siberia and today the eastern limits of their ranges lie within the region. M. amphigena, S. postocularis and S. croceolum perhaps were the most stenotopic of those E. Asian spp. that colonized Siberia during the Holocene, and after the optimum, their ranges shrank to the peri-Altaian refugium. Their isolates there should be dated no earlier than 5-6 thousand yrs ago. C. v-nigrum and A. maacki are perhaps the least mobile of the eastern spp in Siberia.