ALBERT

Description: Global biodiversity and ecosystems are highly impacted by anthropogenic activities, such as climate change and introduction of non-indigenous species (NIS). As numerous species from the Ponto-Caspian region have established in the North and Baltic Seas, as well as in the Laurentian Great Lakes, there have been large number of studies examining environmental tolerance of these species to determine their future spread potential. However, many of those studies were conducted only on adult stages, while neglecting possibility that early life history stages might not be equally resilient. To determine if juveniles would demonstrate the same environmental tolerance as their parents, we examined salinity tolerance of adults and juveniles of one Northern European (Gammarus salinus), one Ponto-Caspian (Pontogammarus maeoticus) and one North American species (Gammarus tigrinus). Additionally, we compared our study to that of Paiva et al. (2018). Our study determined that both adults and juveniles of all three species tolerated wide ranges of salinity, with juveniles of G. salinus tolerating slightly narrower salinity range, while those of P. maeoticus and G. tigrinus 12 g/Kg narrower salinity range than their parents. Even though, at the end of the experiments mortalities of adults among species were not so different irrespectively of the treatment, our study determined better performance of juveniles of G. salinus in higher salinities and those of P. maeoticus in lower salinities. Therefore, based on juvenile salinity tolerance, our study in a way supported findings of Paiva et al. (2018), where Northern European species perform better in higher, while Ponto-Caspian in lower salinities. As early life-history stages are often less tolerant to environmental variabilities than adults, as well as water chemistry and parasitism differ among habitats, it is of great importance to take into account all of these factors when predicting future resilience of ecosystems and biodiversity change.

Description: Invasions of freshwater habitats by marine and brackish species have become more frequent in recent years with many of those species originating from the Ponto-Caspian region. Populations of Ponto-Caspian species have successfully established in the North and Baltic Seas and their adjoining rivers, as well as in the Great Lakes-St. Lawrence River region. To determine if Ponto-Caspian taxa more readily acclimatize to and colonize diverse salinity habitats than taxa from other regions, we conducted laboratory experiments on 22 populations of eight gammarid species native to the Ponto-Caspian, Northern European and Great Lakes-St. Lawrence River regions. In addition, we conducted a literature search to survey salinity ranges of these species worldwide. Finally, to explore evolutionary relationships among examined species and their populations, we sequenced the mitochondrial cytochrome c oxidase subunit I gene (COI) from individuals used for our experiments. Our study revealed that all tested populations tolerate wide ranges of salinity, however, different patterns arose among species from different regions. Ponto-Caspian taxa showed lower mortality in fresh water, while Northern European taxa showed lower mortality in fully marine conditions. Genetic analyses showed evolutionary divergence among species from different regions. Due to the geological history of the two regions, as well as high tolerance of Ponto-Caspian species to fresh water whereas Northern European species are more tolerant of fully marine conditions, we suggest that species originating from the Ponto-Caspian and Northern European regions may be adapted to freshwater and marine environments, respectively. Consequently, the perception that Ponto-Caspian species are more successful colonizers might be biased by the fact that areas with highest introduction frequency of NIS (i.e., shipping ports) are environmentally variable habitats which often include freshwater conditions that cannot be tolerated by euryhaline taxa of marine origin.