Mucciolo, S. | bioRxiv Science

bioRxiv2023

Cold, but not for long enough: first insights into the tolerance to subzero temperatures of the invasive amphipod Dikerogammarus villosus

Dikerogammarus villosus is an invasive Ponto-Caspian amphipod, known to have colonized most of the major European freshwater bodies in the last few decades. Several studies assessing its tolerance related to higher temperatures have been performed; however, no records are present about its response to subzero temperatures. Therefore, in this study, we wanted to experimentally assess for the first time the tolerance of D. villosus to temperatures below 0{degrees}C. The animals were exposed to 0{degrees}C, -8{degrees}C, and room temperature for 2 and 24 hours, tracking their possible movements during the ice melting. Only long exposures at -8{degrees}C appeared to be fatal. These results provide new insights for more accurate predictive models regarding the future expansion of this invader.

ecology↗

bioRxiv2023

Distribution, diversity and diversification from a DNA barcoding perspective: the case of Gammarus radiation in Europe`s oldest inland waterbody - the ancient Lake Ohrid

AimA detailed, comparative DNA-barcoding and morphospecies based overview of the vertical and horizontal distribution of Lake Ohrid endemic Gammarus species-flock. Re-evaluation of the origin of the species-flock dating, identification of events that putatively influenced diversification patterns in the species-flock. LocationLake Ohrid: a deep and ancient lake of tectonic origin, biosphere reserve, UNESCO World Heritage Site, located on the Macedonia/Albania border. TaxonGammarus species-flock (Amphipoda, Crustacea) MethodsExtensive sampling and DNA barcoding of 600 individuals were carried out. DNA sequences were analysed using species delimitation methods, haplotype network reconstructions, Bayesian molecular dating and demographic analysis. The COI-based delimitation results were validated with nuclear 28S RNA data. ResultsThe species flock distribution has weak horizontal but clear vertical structure. The diversity across bathymetric gradients correlates with temperature and salinity; and the highest diversity with sublittoral and springs of lakes shore. Two new MOTUs representing putatively new species are revealed and supported also by the nuclear marker. The time of flock radiation overlaps with the time of lake formation. The COI gene shows signs of positive selection and an acceleration in substitution rate. The demographic changes of the flock happened during the last ky. Main conclusionsDistribution of the Gammarus species-flock is vertically structured, reflecting habitat zonation. Parapatric speciation as one of the mechanisms in flocks diversification is suggested. Detection of new MOTU suggests that the flocks diversity is still not fully revealed. Nevertheless, failure to recover three other MOTUs suggests the loss of gammarid diversity in the lake. This represents,together with the current threats to the lake ecosystem (i.e. climate changes, development of tourism), a clear call for conservation efforts. The speciation events and demographic changes within the flock relate presumably to glacial and postglacial water level changes and to colonisation of new depth ranges and the associated springs.

molecular biology↗