Differentiation of communities of macroinvertebrates and cottoid fish associated with methane seeps of different bottom landscapes of Lake Baikal

The paper presents the results of the study of communities of macroinvertebrates and cottoid fish inhabiting methane seeps of Lake Baikal. For the analysis, we used video surveillance and collection of animals carried out with the help of "Mir" deep-water submersible, as well as NIOZ-type box-corer samplers from the board of a research vessel. Posolskaya Bank and Saint Petersburg methane seeps are located in different basins (southern and middle) and at different depths (300–500 m and ~ 1400 m), characterized by the different underwater landscapes (slope of underwater upland and hills formed by gas hydrates), by the structure of gas hydrates and their depth location in sediments, as well as the composition of microbial mats and communities of microorganisms of bottom sediments. Both seeps are characterized by bubble discharge of methane gas and the formation of highly productive communities of large invertebrates and cottoid fish on seep habitats. Seep animal communities consisted of species-depleted invertebrates and fish of the surrounding deep-water benthal of the Lake. We showed the similarities and differences in the composition of the faunas of two seeps, as well as the quantitative characteristics of taxonomic groups of macroinvertebrates and cottoid fishes. Obligate species have not been revealed on the methane seep Posolskaya Bank. For the methane seep Saint Petersburg, the gastropod species Kobeltocochlea tamarae Sitnikova, Teterina et Maximova, 2021 (Caenogastropoda: Benedictiidae) was designated as an obligate species; among bottom cottoid fishes, Neocottus werestschagini (Taliev, 1953) (Cottoidei: Abyssocottidae) had possible a transitional state to obligate. We presented the data on the assimilation by seep animals of mixed photo- and chemosynthetic food with different proportions of methane-derived carbon. A hypothesis has been substantiated that deep-water seep areas could serve as refugium for the preservation of endemic fauna during the Pliocene-Pleistocene glaciations of Lake Baikal.

An annotated type catalogue of freshwater sculpins (Cottoidei) described by Lev Berg

The catalog is represented by type specimens of species and subspecies of cottoid fishes described by Lev S. Berg which are kept in the ichthyological collection of the Zoological Institute of Russian Academy of Sciences, St. Petersburg, Russia. The collection contains type specimens representing 14 taxa (species and subspecies) of the two families Abyssocottidae and Cottidae. In total, Lev S. Berg described one family, Cottocomephoridae, five genera, Abyssocottus, Asprocottus, Baicalocottus, Batrachocottus and Cottinella, 10 species and four subspecies. Four genera and 10 species are currently considered valid.

Have Niche, Will Travel. New Means of Linking Diet and Ecomorphology Reveals Niche Conservatism in Freshwater Cottoid Fishes

Synopsis Evolutionary transitions between habitats have been catalysts for some of the most stunning examples of adaptive diversification, with novel niches and new resources providing ecological opportunity for such radiations. In aquatic animals, transitions from saltwater to freshwater habitats are rare, but occur often enough that in the Neotropics for example, marine-derived fishes contribute noticeably to regional ichthyofaunal diversity. Here, we investigate how morphology has evolved in a group of temperate fishes that contain a marine to freshwater transition: the sculpins (Percomorpha; Cottoidea). We devised a novel method for classifying dietary niche and relating functional aspects of prey to their predators. Coupled with functional measurements of the jaw apparatus in cottoids, we explored whether freshwater sculpins have fundamentally changed their niche after invading freshwater (niche lability) or if they retain a niche similar to their marine cousins (niche conservatism). Freshwater sculpins exhibit both phylogeographical and ecological signals of phylogenetic niche conservatism, meaning that regardless of habitat, sculpins fill similar niche roles in either saltwater or freshwater. Rather than competition guiding niche conservatism in freshwater cottoids, we argue that strong intrinsic constraints on morphological and ecological evolution are at play, contra to other studies of diversification in marine-derived freshwater fishes. However, several intertidal and subtidal sculpins as well as several pelagic freshwater species from Lake Baikal show remarkable departures from the typical sculpin bauplan. Our method of prey categorization provides an explicit, quantitative means of classifying dietary niche for macroevolutionary studies, rather than relying on somewhat arbitrary means used in previous literature.

Karyotype characterization of the endemic piscine leech from Lake Baikal with vindication of Baicalobdella cottidarum Dogiel, 1957 (Piscicolidae, Hirudinea)

In this paper, we present for the first time data on karyotype analysis of leeches of the genus Baicalobdella (Piscicolidae) parasitizing Lake Baikal endemic cottoid fishes. Both mitotic and meiotic chromosomes are described. Leech testisacs were processed by a ?shaking-blotting? technique, and chromosomal preparations were stained with water-based fuchsine. Diploid and haploid chromosome sets demonstrated 2n=34 and n=17, respectively, with maximal chromosome length of 1.5-3.0 ?m. Comparative karyotype analysis of two ecological forms of Baicalobdella leeches revealed differences in chromosome numbers and its morphology. Previously studied Baicalobdella torquata (Grube, 1871) parasitizing Baikal amphipods had smaller diploid and haploid sets (2n=32, n=16). In addition to numerical superiority, differing patterns of chromosome size gradation and presence of satellite elements were found in the karyotype of piscine Baicalobdella leeches. This confirms the systematic position of the Baikal cottoid leech parasite as a separate species, validating the original name Baicalobdella cottidarum sensu Dogiel, 1957.