Abstract
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.
Highlights
Temperature is one of the most pervasive abiotic factors directly affecting all levels of organismic organization of aquatic ectotherms
We previously found differences in thermal tolerance and thermal preferences between the winter-reproducing Baikal endemic littoral amphipod species Eulimnogammarus verrucosus (Gerstfeld, 1858), the summerreproducing Baikal endemic species E. cyaneus (Dybowsky, 1874), and the Holarctic Gammarus lacustris Sars, 1863 inhabiting adjacent water bodies
We hypothesize that the Holarctic G. lacustris is limited at the extreme low temperature (i.e. 1.5 °C) preventing this species from establishing a stable population in Lake Baikal, whereas the Baikal endemic amphipods possessing specific thermal adaptations to maintain a high energy metabolism in winter at low temperatures
Summary
Temperature is one of the most pervasive abiotic factors directly affecting all levels of organismic organization of aquatic ectotherms. Climate change alters the lake’s temperature regime, causing shorter w inters[18] and more frequent extreme heat events in summer[19,20] This may cause a mismatch between highly adapted species and their respective niche, causing a disruption of the lake’s immiscibility barrier. We previously found differences in thermal tolerance and thermal preferences between the winter-reproducing Baikal endemic littoral amphipod species Eulimnogammarus verrucosus (Gerstfeld, 1858), the summerreproducing Baikal endemic species E. cyaneus (Dybowsky, 1874), and the Holarctic Gammarus lacustris Sars, 1863 inhabiting adjacent water bodies. While the cold stenothermal amphipod fauna of Baikal may be stressed in summer by increased temperatures in the littoral, which could be disadvantageous, their ability to maintain a high metabolic activity in winter may outcompete Holarctic species like G. lacustris, which significantly reduces its metabolic activity during the w inter[25]. The superiority of Baikal endemic amphipods at low temperature may prevent the non-Baikal species to colonize the lake
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