Morphology and zoogeography of the burrower-like gammarid Gammarus koshovi (Bazikalova, 1946) (Crustacea, Amphipoda, Gammaridae) – An overlooked and poorly known species in the Siberian fauna

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.

Low annual temperature likely prevents the Holarctic amphipod Gammarus lacustris from invading Lake Baikal

Species with effective thermal adaptation mechanisms allowing them to thrive within a wide temperature range can benefit from climatic changes as they can displace highly specialized species. Here, we studied the adaptive capabilities of the Baikal endemic amphipods Eulimnogammarus verrucosus (Gerstfeld, 1858) and Eulimnogammarus cyaneus (Dybowsky, 1874) compared to the potential Holarctic Baikal invader Gammarus lacustris Sars, 1863 at the cellular level including the energy metabolism and the antioxidant system. All species were long-term exposed to a range of temperatures (1.5 °C to mimic winter conditions and the three species-specific preferred temperatures (i.e., 6 °C for E. verrucosus, 12 °C for E. cyaneus and 15 °C for G. lacustris). At 1.5 °C, we found species-specific metabolic alterations (i.e., significantly reduced ATP content and lactate dehydrogenase activity) indicating limitations on the activity level in the Holarctic G. lacustris. Although the two Baikal endemic amphipod species largely differ in thermal tolerance, no such limitations were found at 1.5 °C. However, the cold-stenothermal Baikal endemic E. verrucosus showed changes indicating a higher involvement of anaerobic metabolism at 12 °C and 15 °C, while the metabolic responses of the more eurythermal Baikal endemic E. cyaneus may support aerobic metabolism and an active lifestyle at all exposure temperatures. Rising temperatures in summer may provide a competitive advantage for G. lacustris compared to the Baikal species but the inactive lifestyle in the cold is likely preventing G. lacustris from establishing a stable population in Lake Baikal.

A new species of Gammarus Fabricius, 1775 (Crustacea: Amphipoda: Gammaridae) from extreme high-altitude Lake Tong Tso, Qinghai-Tibetan Plateau

A new species of the genus Gammarus Fabricius, 1775 is described from Lake Tong Tso, an extreme high-altitude lake in the Qinghai-Tibetan Plateau. Gammarus pontual sp. nov. is considered part of the Gammarus lacustris G.O. Sars, 1863 group, which is characterized by having the inner ramus of uropod 3 longer than half the length of the outer ramus, and by having both rami covered with plumose setae. The new species stands apart from their congeners, mainly, by the following combination of characters: head with cephalic lateral lobe truncated; gnathopods 1-2 propodus weakly armed, with 1 stout seta defining palm; palm longer than posterior margin of propodus, with 1 main stout seta medially; pereopods 5-7 basis slender, posterior margin crenulate; epimeral plate 1 posterior margin produced into a short spine, facial ridge present; epimeral plates 2-3 posteroventral corner sharply pointed; uropod 3 rami covered with plumose setae, inner ramus about 80% the length of the outer ramus; telson apex with 2 stout setae on each side.

Drastic changes of the amphipod fauna in northern Germany and the displacement of Gammarus lacustris G.O. Sars, 1864 to relict habitats/status

The amphipod fauna of Central Europe has changed dramatically over the last century. This change has increased dramatically over the past 30 years. This dynamic is well documented in northeast Germany. This study places it in a landscape-ecological context. An example of a displacement is Gammarus lacustris G.O. Sars, 1864, a circumpolar species with a variety of habitats, but relegated to relic habitats. The species turns out to be a very weak competitor. Already with the immigration of Gammarus roeselii Gervais, 1835 (probably in the 1960s), it became a relic species in northeast Germany. Massive waves of introduction of Pontocaspian species of the genera Dikerogammarus, Pontogammarus and Echinogammarus a few decades later intensified this process for this and other species.

The freshwater shrimp Gammarus lacustris (Malacostraca, Amphipoda) in lakes on the Hardangervidda mountain plateau, southern Norway: distribution and environmental requirements

The distribution of the amphipod Gammarus lacustris on the Hardangervidda mountain plateau was mapped by screening published data from 245 lakes in 11 and 16 catchments in western and central/eastern areas, respectively. These data are primarily based on stomach analyses of brown trout Salmo trutta. In central/eastern areas, G. lacustris was recorded in 79% of all the lakes examined, while there are only two former records (4%) in the western area. The distribution pattern of G. lacustris on Hardangervidda appears to be related to environmental conditions. The apparent absence of G. lacustris in the western area may be explained by a combined effect of cold water due to higher deposits of snow and water with low ionic strength as a consequence of its bedrock of Precambrian gneisses and granites with little or no moraine cover. However, lakes in central/eastern areas sustain G. lacustris in spite of dilute water, as G. lacustris has been recorded in 89 lakes of which 28% had calcium concentration <1.0 mg L-1, eight of them with pH <6.0. The lower lethal threshold for calcium concentration seems to be ~0.5 mg L-1. Gammarus lacustris was found in lakes at altitudes of 832 to 1396 m a.s.l. Furthermore, their occurrence increased significantly with lake size, being 69% in lakes <1.0 km2 and 97% in larger lakes. The number of refugia with better water quality is likely to increase with lake size. Gammarus lacustris is highly searched for as prey by all size groups of brown trout (15-45 cm). Access to proximity refugia that reduce predation pressure from fish may also increase with lake size. Climate changes are now in progress in this mountain area, and detailed mapping of G. lacustris is important in order to trace future range changes.