HYDROCHORAL DISPERSAL AS A FACTOR OF GENETIC INTEGRATION AND DIFFERENTIATION OF CONIFEROUS POPULATIONS

Sannikova N.S., Sannikov S.N.

Botanical Garden of the Ural Division RAS, Russia, stanislav.sannikov@botgard.uran.ru

The study of methods, paths and rates of dispersal of tree populations in postglacial epochs is necessary for establishment and interpretation of regular features of their origination, migration, range dynamics and genetic differentiation. According to radioisotope dating data of the palynological analysis, common pines spread after the waning ice from the Alps and the Carpathians at a rate of 350-600 km in 1000 years, while the Siberian spruce propagated from the Urals at a rate of up to 210 km in 1000 years in the Holocene. However, such a rapid dispersal could not proceed only by the anemochorous dissemination of their seeds since its rate is not over 50-60 km in 1000 years (Shimanyuk, 1955; Udra, 1988). Our experiments (Sannikov, 1976; Sannikov, Sannikova, 2007) suggest a theoretical possibility of the long-range rapid transport of common pine seeds by rivers.

The comparative experimental and large-scale studies of the rate and the range of anemochorous and hydrochorous dispersals of common pine populations and the analysis of their genetic integration and differentiation in adjacent river basins yielded the following results.

The maximum effective (for the further "relay-race" dispersal of populations) propagation rate of the pine self-sown at the center of the range on an optimal tilled substrate is not over 3000-3500 m in one reproductive year (30-35 years), i.e. 90-140 km in a millennium, even in mast years. In the fore-tundra zone, where the seed yield and the height of trees are several times smaller, the dispersal rate of pines probably is one order of magnitude slower.

Experiments demonstrate that winged seeds of pines remain afloat on the river water surface for up to 7-8 days and then sink. However, they preserve their germinating capacity (42%) for as long as one week and become fully non-emergent only in 22-24 days after sinking. If the average velocity of the river flow is about 2.5 km/h, the theoretical propagation range of seeds by rivers can be up to 500-600 km/year. It is many orders of magnitude larger than their anemochorous range. According to our observations, floatability of spruce seeds is a little worse. The floatability period of weeping birches is up to 10 days, while seeds of Crimean pines have no floating capacity at all. It was found that even along the rapid mountain river Lomnitsa in the Carpathians the dispersal of the self-sown of common pines and Norway spruces progresses at a rate of at least 17-20 km in a decade or 1700-2000 km in 1000 years. It may be assumed that the hydrochory is the dominant method of the dissemination of seeds and the dispersal of coniferous populations in plains of Northern Eurasia where rivers flow predominantly to the north.

This hypothesis is confirmed by a high genetic similarity of Pinus sylvestris populations in transects along river beds (Tobol, Dnepr, Northern Dvina, Angara, Selenga). Their Nei genetic distances (Nei, 1978) generally do not exceed the population class (0.007-0.008). At the same time, the distances are 1.5-2.5 times larger in transects crossing watersheds of adjacent rivers. The maximum differentiation (0.024±0.005) – at the level of geographical groups of populations – is found between adjacent basins of mountain rivers in the Ukrainian Carpathians, which are separated by ridges up to 800 m high. Finally, the analysis of paths of dispersal of Pinus sylvestris populations in the Holocene in Europe using the latest paleobotanical studies (Cheddadi et. al., 2006) shows that the paths are almost coincident with directions of river flows.

Thus, the hydrochory of seeds by rivers is undoubtedly one of the most important factors determining paths of the post-Pleistocene migration, the degree of genogeographical integration and differentiation of tree populations in Northern Eurasia.

The study was supported by RFBR (project No. 05-04-48667) and RF HSS foundation (grant No. 9692.2006.4).