T. Ya. Sitnikova

Genetic differentiation of the endemic Baikalian mollusk Baicalia carinata (Mollusca: Caenogastropoda)

In gastropod mollusk Baicalia carinata Dybowski, 1875, sampled in different sites of the Lake Baikal, comparison of 81 sequences of internal transcribed spacer 1 (ITS1) located between the genes for 18S rRNA and 5.8S rRNA, and of 100 sequences of the fragment of mitochondrial DNA cytochrome-c-oxidase subunit 1 gene (CO1) was performed. Molecular phylogenetic analysis showed that the endemic mollusk species studied formed at least two distinct populations, Southwestern and Eastern. Statistical significance of the species subdivision into two populations was evaluated using the Mann-Whitney rank test.

Genetic and morphological diversification in gastropods of the Baicaliidae family

The combined (“total evidence”) phylogenetic inference was based on the comparison of the intronic nucleotide sequences of the ATP synthase α-subunit gene of 11 gastropod species belonging to the rapidly evolving Baikalian endemic family Baicaliidae, the morphological description of these species, and the previously published sequences of the mitochondrial gene coding the first subunit of cytochrome c oxidase. The phylogeny based on the intron sequences agrees well with the morphology. It is shown that sister species usually have similar substrate preferences. Certain discrepancy in the phylogenetic tree topology and the taxonomy based on morphological traits is probably due to the rapid morphological evolution of mollusks of the family Baicaliidae.

Biogeochemical characteristics of dominant gastropod species from the stony littoral of southern Baikal

The trace element composition of dominant gastropod species from the littoral of southern Baikal was investigated. Both different mollusk species and their parts (shells and soft tissues) show specific trace element characteristics. The highest Sr and Ba contents were observed in Maackia herderiana. The highest Zn, Cu, and Cd and lowest Pb contents were detected in Megalovalvata baicalensis. Choanomphalus sp. shows high Mn and Ti and very low Sr, Cu, and Cd contents. Most of Cu, Zn, and Cd and a considerable fraction of Rb, Pb, Mo, Sc, Ce, W, Ga, Y, and Th are incorporated in the gastropod bodies. The maximum concentration of U is also characteristic of the body tissues. The foot tissues of Maackia herderiana and Megalovalvata baicalensis are depleted in the majority of elements compared with their bodies. Sr and Ba are prevalent in the mollusk shells, where high Mn contents were also detected. A close relationship was observed between the chemical compositions of the gastropods, stony substrate, and bottom water. Group concentration of trace elements is common in the species investigated. Relative to the bottom water layer, the gastropod species concentrate Ti, Mn, La, Co, Y, and V and show similarly low extraction of U, W, Mo, and Cs. Compared with the bottom sediments, the mollusks accumulate Sr. In addition, Maackia herderiana and Megalovalvata baicalensis accumulate Cd and Zn. Megalovalvata baicalensis is distinguished by the ability to concentrate Cu. The following sequence is formed by the gastropods with respect to their capacity to accumulate Cd, Zn, and Cu: Megalovalvata baicalensis > Maackia herderiana > Choanomphalus sp.

Kindred Relations of Baikal polychaete of the Manayunkia Genus [Polychaeta: Sedentaria: Sabellidae] according to CO1 and settlement history analysis

The aim of the study was to clarify the distribution history of polychaetes from the Manayunkia genus (Leidy, 1859) (Sedentaria, Sabellidae) in the northeast of Asia and their speciation in Baikal. The comparative analysis of the polymorphism of the CO1 gene’s Folmer fragment nucleotide sequences allowed us to establish the sequence of migration and speciation events in the history of freshwater polychaetes of the Manayunkia genus. The phylogenetic analysis and comparison of the hypotheses about the type of the Manayunkia migrations by means of the Bayesian criterion demonstrated that the Kolyma basin was the initial region from which the polychaetes entered the Baikal, where they were divided into three species (M. godlewskii, M. baicalensis, and M. zenkewitschii); among them, the M. godlewskii was a source of migrants in the system of Baunt lakes.

First report on bacteria of the family Spirochaetaceae from digestive tract of endemic gastropods from Lake Baikal

Detection of bacteria of the family Spirochaetaceae in the crystalline style of 11 species of endemic gastropods from Lake Baikal is reported. Investigation by transmission and scanning electron microscopy showed that these spirochetes belonged to the genus Cristispira.

Fatty-Acid Composition of the Deep-Water Baikal Amphipod Polyacanthisca calceolata

The fatty-acid composition of the deep-water Baikal amphipod Polyacanthisca calceolata Baz., 1937, that was collected in the vicinity of hydrocarbon-gas releases (near the submerged mud volcano St. Petersburg) at depths of 1300–1400 m during the international expedition Miry in Baikal was studied for the first time. Gas-chromatography–mass-spectrometry (GC–MS) detected in the amphipod tissues 46 fatty acids, the principal ones of which were 16:0, 14:0, 18:0, 18:1n9, 16:1n7, 18:3n3, and 20:4n6. The high 18:1n9/18:1n7 ratio and low 16:1n7/16:0 and 20:5n3/22:6n3 ratios confirmed that the deep-water amphipod P. calceolata was a necrophage.

The species composition and distribution of free-living nematodes (Nematoda) in an area of natural oil and gas seeps in Lake Baikal

The species composition and quantitative parameters of free-living nematode fauna have been studied in an area of natural oil seeps off Cape Gorevoi Utes (Middle Baikal). A total of 34 species of 17 genera, 10 families, and 8 orders have been found, 18 of them endemic to Lake Baikal. The nematode fauna of bitumen volcanoes was found to be represented by three specialized species (Monhystera naphthera Gagarin et Naumova, 2010; Eumonhystera abyssalis Gagarin et Naumova, 2010; and Eutobrilus mirandus Gagarin et Naumova, 2011). Areas of the bottom with scattered oil seeps are dominated by eurybathic species endemic to Lake Baikal. The maximal values of nematode population density and maximum proportion of nematodes in the meiozoobenthos were recorded in areas directly adjacent to oil seeps.

Genetic and morphological heterogeneity of Lake Baikal endemic gastropod Benedictia fragilis (Dybowski, 1875)

Baikal endemic Benedictia fragilis gastropods distributed in a wide range of depths (from sublittoral to abyssal) of three lake basins are studied. The analysis of the nucleotide sequence of the COI mitochondrial gene fragment and internal transcribed nuclear DNA spacer (ITS1) demonstrates that the studied gastropods are represented in Lake Baikal by three genetic groups. The results of the studies on genetic diversity, phenotypic traits, and distribution allow us to assume that the detected groups are incipient allopatric (geographical) species. On the basis of the data obtained and geological and climatic history of Baikal, possible pathways of the B. fragilis resettlement in the lake and the emergence of three genetic groups are hypothesized.

Trophic relationships between macroinvertebrates and fish in St. Petersburg methane seep community in abyssal zone of Lake Baikal

Trophic relationships were examined for macroinvertebrates and fish inhabiting the St. Petersburg methane seep (central part of Lake Baikal, ~1400 m depth). The analyses of the values of carbon and nitrogen stable isotopes showed that all animals associated with the seep were heterotrophs with different feeding strategies; symbiotrophes were absent. Seep animals consumed combined food with different portion of methanederived carbon ranged from 2.7 to 89%. The average δ13С values varied in the range of–26.2‰ (in benthopelagic amphipods) to–64.5‰ (in gastropods). The trophic food web in the methane seep consists of filter feeders (pelagic amphipods, trophic position (TP) is 1.9), detritophages (gastropods, TP of 2.2, and burrowing amphipods, TP of 2.1), polyphages and necrophages (nectobenthic and benthopelagic amphipods of TP 2.8–3.2), and predators (planarians of TP 3.6–4.2 and cottoid fish of TP 3.0–3.8). Animals occupying similar trophic positions significantly differed in the δ13С values and have partially overlapping components of food.

Structure of biocenoses formed on bitumen mounds in the abyssal zone of Lake Baikal

For the first time, a study has been performed on specific small biocenoses of bitumen mounds formed in the region of natural oil seeps in the abyssal zone of Lake Baikal. These biocenoses consist of diatom detritus populated by archaea, bacteria, aquatic fungi, nematodes, and ostracods. Fungi and bacteria decompose petroleum hydrocarbons, thereby contributing to biodegradation of crude oil. Microorganisms together with planktonic diatoms settling onto bitumen form a substrate for invertebrates. It is hypothesized that the cohabitation of three distinctive nematode species (Eutobrilus mirandus, Monhystera naphthera, and Eumonhystera abyssalis) in the same bitumen biocenosis is possible due to their different feeding strategies and the presence of bacterial symbionts.