Estimating salinity stress via hsp70 expression in the invasive round goby (Neogobius melanostomus): implications for further range expansion

Abstract

Species invasions often occur on coasts and estuaries where abiotic conditions vary, e.g. salinity, temperature, runoff etc. Successful establishment and dispersal of non-indigenous species in many such systems are poorly understood, partially since the species tend to show genetic and ecological plasticity at population level towards many abiotic conditions, including salinity tolerance. Plasticity may be driven by shifting expression of heat shock proteins such as Hsp70, which is widely recognized as indicator of physical stress. In this study, we developed a qPCR assay for expression of the hsp70 gene in the invasive round goby (Neogobius melanostomus) and tested the expression response of fish collected from a brackish environment in the western Baltic Sea to three different salinities, 0, 10 and 30. hsp70 expression was highest in fresh water, indicating higher stress, and lower at brackish (ambient condition for the sampled population) and oceanic salinities, suggestive of low stress response to salinities above the population’s current distribution. The highest stress in fresh water was surprising since populations in fresh water exist, e.g. large European rivers and Laurentian Great Lakes. The results have implications to predictions for the species’ plasticity potential and possible range expansion of the species into other salinity regimes.

Sperm performance limits the reproduction of an invasive fish in novel salinities

“…Fish of freshwater origin kept in 16 PSU were the least likely to spawn, suggesting that despite higher sperm velocity in 16 PSU, these freshwater fish had limited reproductive ability. Lower energy reserves are commonly seen in freshwater round gobies (Kornis et al., 2012, Table 1; but see Green, Niemax, et al., 2020) and round gobies from brackish origin show increased stress levels in freshwater (Puntila‐Dodd et al., 2021). If more energy is required in adverse salinities (Behrens et al., 2017), initial low energy reserves of freshwater round goby are likely to limit their reproductive output even further.…”

Invader at the edge — Genomic origins and physiological differences of round gobies across a steep urban salinity gradient

“…The genomic brackish ancestry of the Gothenburg fish likely limits them from rapid colonization of freshwater systems, which may explain the lack of fish caught further upstream the Göta Älv river (red sampling sites, Figure 1 ) and the higher levels of the stress hormone cortisol in fish when kept at 0 PSU. A previous study also found the highest level of heat shock protein (hsp70) expression when round gobies caught from Guldborgsund were kept in freshwater (compared to 10 and 30 PSU salinities) (Puntila‐Dodd et al, 2021 ). These mechanisms point to higher stress in freshwater for the round gobies with brackish ancestry, and a reason they will avoid it.…”

“…Habitats are roughly categorized and separated with dotted lines according to salinity. Striped polygon shows the extent of the Gothenburg international shipping port, Scandinavia's largest port with over 5300 cargo vessels visiting in 2020 in particular, the western Baltic Sea, the northern Baltic Sea, and two large rivers in northern continental Europe, Elbe and Rhine (Azour et al, 2015;Puntila et al, 2018).…”

Invasive round goby shows higher sensitivity to salinization than native European perch

“…There are some studies indicating that round goby could be sensitive to freshwater salinity levels. For instance, heat shock protein 70 (hsp70) expression was highest in round goby in freshwater (0‰) compared to 10 and 30‰ salinities (Puntila-Dodd et al 2021). However, it is still perplexing that European perch from the same area seem to be more tolerant towards salinity, but other factors than sensitivity to abiotic factors can also be important for the establishment of invasive species, such as sensory biology (Abrahams et al 2017).…”