Trace Element Patterns in Shells of Mussels (Bivalvia) Allow to Distinguish between Fresh- and Brackish-Water Coastal Environments of the Subarctic and Boreal Zone

The accumulation of trace metals in the shells of bivalves allows quantitative assessments of environmental pollution and helps to reconstruct paleo aquatic environments. However, the understanding on how marine and freshwater mollusks control the level of trace elements in their shells remains very limited. Here, we compared the trace element composition of marine and freshwater bivalves from boreal and subarctic habitats, using examples of widely distributed species of marine (Mytilus edulis, M. trossulus) and freshwater (Anodonta anatina, Unio sp., Beringiana beringiana) mussels. Sizable differences in several trace element concentrations were detected between different species, depending on their environmental niches. A multiparametric statistical treatment of the shell’s elemental composition allowed to distinguish the impact of external factors (water and sediment chemical composition) from active metabolic (biological) control. In particular, the obtained results demonstrated that Ba:Ca and Pb:Ca ratios in mussels’ shells are closely related to the primary productivity of aquatic ecosystems. The Mn:Ca ratio allowed to constrain the environmental conditions of mussels’ species depending on the trophic state of inhabited waterbody. Overall, the marine mussels exhibited stronger biological control of trace element accumulation, whereas trace element pattern in shells of freshwater mussels was chiefly controlled by environmental factors. The obtained results might help to use the trace element composition of bivalves in distinguishing marine and freshwater habitats of mollusks in paleo environments

How an Ecological Race Is Forming: Morphological and Genetic Disparity among Thermal and Non-Thermal Populations of Aquatic Lymnaeid Snails (Gastropoda: Lymnaeidae)

Hot (geothermal) pools and streams, a specific type of aquatic biotopes having almost worldwide distribution, maintain rich faunas of animals belonging to various taxa. Snails (Gastropoda) represent one of such groups, which form populations in geothermal waterbodies of all continents. Some freshwater snail species produce morphologically distinct hot-water populations, whose rank is often debated (full species or thermal ‘ecotype’, or ‘race’). In this study, we used six species of pond snails (family Lymnaeidae) to investigate the morphological and genetic consequences of infiltration of freshwater snails into geothermal habitats. In particular, we aimed at studying the changes in shell shape and proportions as well as the formation of unique hot-water haplotypes and the occurrence of the latter beyond geothermal waterbodies. All six species studied demonstrate diminutive body size in hot sites accompanied, in four species, by apparent alterations in shell proportions. A phenomenon of phenotypic ‘juvenilization’, when adult and able to reproduce individuals demonstrate shell proportions characteristic for full-grown individuals living under ‘normal’ conditions, is described. Unique ‘thermal’ haplotypes, not found beyond the geothermal sites, were normally restricted to a single locality, and no signs of frequent ‘travels’ of snails from one thermal habitat to another are seen. In the vast majority of cases, these exclusive haplotypes are separated from their ancestors by only a few (1–3) mutational steps, which may indicate their relatively recent origin. We are inclined to relate both size reduction and ‘juvenilization’ to the life-cycle re-adjustment following the penetration of lymnaeids to thermal habitats. The ecological (‘thermal’) intraspecific races of different species, forming in geothermal habitats, exhibit, to a great extent, evolutionary predictability (=convergent evolution; =parallelisms). The dilemma ‘ecological race vs. young species’ in application to the taxonomy of these hot-water populations is briefly discussed

Genetic and Morphological Characterization of the Invasive <i>Corbicula</i> Lineages in European Russia

Despite the full attention of malacologists to the study of Corbicula clams, stimulated mainly due to their high invasive potential and unique breeding system, studies based on an integrative taxonomic approach to identify various invasive lineages of this genus in European Russia are still limited. Our fieldwork was conducted in the Don, Volga, and Caspian Sea basins. In total, four distinct morphotypes belonging to the European forms R, Rlc, S, and “Int” of Corbicula clams were distinguished. According to our molecular genetic data, two Corbicula lineages, relevant to the nominal species Corbicula fluminea and C. fluminalis, can be defined. We observed a discrepancy between mtDNA haplotypes and morphological features for all individuals that were sampled from the Don and Kura Rivers. Identified mismatch may be due to the androgenetic reproduction of Corbicula that leads to cytonuclear inconsistencies. The 28S rRNA polymorphism in C. fluminea and C. fluminalis from studied localities was recorded. This occurrence is perhaps due to hybridization events between forms R, S, and Rlc. The biogeographic origins of Corbicula invasive lineages are discussed. Corbicula fluminalis (FW17, form S) has been detected for first time in the native range, namely in Azerbaijan, Tajikistan, Turkey, and Myanmar. We assume that the invasion of C. fluminalis into reservoirs and watercourses of the Caspian Sea basin (Republic of Dagestan and Stavropol Krai of Russia) was from Western Asia and Transcaucasia, and the introduction of C. fluminea to the Don and Volga River basins was from unspecified European countries