Abstract
A comprehensive survey of several lakes in the Tuva Republic of Russia yielded, besides the ubiquitous Gammarus lacustris, the discovery of a small freshwater, lacustrine amphipod not previously recorded in this area. A comparative study of the Tore-Khol Lake gammarid population, probably conspecific with Gammarus koshovi (Bazikalova, 1946) originating from Khubsugul Lake, was conducted. The species, G. koshovi, is characterized by a specific habitus: a small-sized compact body, all limbs shortened, carpi of pereopods (PIII and PIV) reduced, coxal plates broad, and pereopod dactyli sturdy. It has been suggested that juveniles of the euryoecious G. lacustris or other large species could be confused with the relatively small G. koshovi. Consequently, we decided to present the distribution of gammarid species throughout south Siberia and Mongolia, referring to the sequences of works primarily by Soviet authors, which may be hard to access by international readers. We discuss affinity with related groups, distribution, and ecology of G. koshovi to better understand their evolution. Additionally, the zoobenthic species diversity of widely represented groups in the ecosystems of Tore-Khol Lake is briefly reviewed. An identification key for the Siberian Gammarus with 10 species is provided.
Highlights
The territory at the southern end of Central Siberia is rich in various mountain pools lying within the Sayan Province of the Lena-Yenisei subregion of the Palearctic (Leontyev 1957)
It should be noted that the amphipod fauna of the southern region of Central Siberia, and especially Tuva, is practically unknown (Dgebuadze et al 2010; Kirova 2019)
Specimens were dissected using a dissecting microscope Lomo MBS-9 and mounted on microscope slides in polyvinyl lactophenol (PVL) and stained with methylene blue (Sigma-Aldrich Company, Inc.); dissected appendages were covered with a coverslip and edged by clear nail polish
Summary
The territory at the southern end of Central Siberia is rich in various mountain pools (more than 430 lakes) lying within the Sayan Province of the Lena-Yenisei subregion of the Palearctic (Leontyev 1957). It should be noted that the amphipod fauna of the southern region of Central Siberia, and especially Tuva, is practically unknown (Dgebuadze et al 2010; Kirova 2019). The genus Gammarus J.C. Fabricius, 1775 is a large Holarctic / Sino-Indian epigean / subterranean group of amphipods that is typically found to be morphologically monotonous at high latitudes (Culver et al 1995), with a number of distinctly divergent narrowly localized endemic species at the southern border of the range (Sidorov et al 2018; Zheng et al 2020). Despite the obvious inconsistencies in morphological distances between recent species and paraphyly within the group, the genus Gammarus reveals a certain unity and is known from at least the Oligocene-Eocene era (Hou et al 2011). In a series of publications, it was shown that the amazingly diverse endemic amphipod fauna of Baikal Lake, consisting of more than 354 species (Takhteev 2019), had radiated from a putative Gammarus-like ancestor in the Oligocene (28 Mya), coinciding with the formation of the lake (Ogarkov et al 1997; Sherbakov et al 1999; MacDonald et al 2005; Hou & Sket 2016)
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