We examined trends in expansion patterns and relative abundances of Dreissena bugensis in reservoirs and major river systems in eastern Europe. Based on our own data and data from the literature, it is apparent that trends were variable across river basins and not easily related to environmental conditions. In some cases these did not conform to the patterns typically found for dreissenids. In the early period of expansion beyond its native range in the Dnieper-Bug delta and estuary, D. bugensis rapidly replaced Dreissena polymorpha in the upper Dnieper River system, but increased only gradually and over time became less abundant relative to D. polymorpha in the DonManych River system. Contrary to the Dnieper and Don River systems, in the Volga River system considerable spatial variability in relative abundances was apparent, particularly in northern reservoirs. Moreover, even though D. bugensis usually displaces D. polymorpha as the dominant dreissenid, the latter can remain dominant in certain types of habitats where conditions are less favourable for the former. Suggested factors that may be responsible for differences in invasion patterns in the river systems may include differential responses to temperature, or to some other factor(s) associated with geographical latitude, the level of water mineralization, and selective predation by molluscivorous fish. In particular, the northward expansion of D. bugensis seems to be limited by temperature. The lack of long-term data on appropriate scales precludes linking these differences to specific features within the environment, but our comparisons indicate that the expansion of D. bugensis relative to D. polymorpha is more complex than previously believed.

The expressions of factorial (4) and stochastic (4) components of henotypic variance of bilateral characters are given, re arding simple connection of the latter to the iuctuatin as mmetry indicator, being traditionally usecffor assessment of developmental stability. The values of%oti components were calculated for 5 meristic characters in 172 samples of bream collected over most of its geographic range.The 4 values were to indicate possible effects of enetic disbalance and to measure environmental stress, while 4 was regarded as a rough estimate ofthe enetical heterogeneity. It was found that 4 values tended to grow in following situations: a) zones ofinterpopulational contacts or in populations with unusual morphology; b) zones of increased anthropogeneous pollution, in particular In the lower parts of the artificial reservoirs as compared to the upper arts and the majority of rivers and lakes. On the other hand, d values in lakes ap eared to be lower tgan in rivers, probably due to comparatively low enetic heterogeneity of the 1a; e opulations. The whole set of samples exhibits another clear trenrf ne ative correlation between z a n d 4, which seems to illustrate a well-known connection between fevelopmental homeostasis and heterozy osity. A conclusion may be made that the phenotypic variance com onents are useful in ecologica and genetical monitoring of large population systems, although the Zata are often difficult to interpret properly for separate populations.

No abstract

No abstract

We sampled sites in the lower Don River system, Russia between 1977 and 2004 (5 sites) or between 1999 and 2004 (10 sites) to determine relative trends in two dreissenid species, Dreissena bugensis and Dreissena polymorpha. The sites were located in the main river, in connecting reservoirs, and in a major tributary, the Manych River. For sites sampled beginning in 1977, D. bugensis was first found in the lower river in 1980 and then more upstream in 1991. The relative proportion of D. bugensis increased to reach a maximum of 30 -50 % of the dreissenid population by 1999. After 1999, this species decreased at 14 of the 15 sites. At sites in the Don River, the proportion that D. bugensis comprised of the total dreissenid population after 1999 declined from 25 -50 % to 10-18 %, whereas at sites in the Manych River the proportion declined from 65-75 % to 33 -43 %. The decline of D. bugensis relative to D. polymorpha is unique; in most other water bodies D. bugensis displaces D. polymorpha over time because of its superior physiological attributes. Reasons for the relative decline of D. bugensis are unclear, but we speculate that selective predation by fish may be a potential factor.