Inter-population differences in salinity tolerance of adult wild Sacramento splittail: osmoregulatory and metabolic responses to salinity

Diverse Transcriptome Responses to Salinity Change in Atlantic Cod Subpopulations

Adaptation to environmental variation caused by global climate change is a significant aspect of fisheries management and ecology. A reduction in ocean salinity is visible in near-shore areas, especially in the Baltic Sea, where it is affecting the Atlantic cod population. Cod is one of the most significant teleost species, with high ecological and economical value worldwide. The population of cod in the Baltic Sea has been traditionally divided into two subpopulations (western and eastern) existing in higher- and lower-salinity waters, respectively. In recent decades, both Baltic cod subpopulations have declined massively. One of the reasons for the poor condition of cod in the Baltic Sea is environmental factors, including salinity. Thus, in this study, an oligonucleotide microarray was applied to explore differences between Baltic cod subpopulations in response to salinity fluctuations. For this purpose, an exposure experiment was conducted consisting of salinity elevation and reduction, and gene expression was measured in gill tissue. We found 400 differentially expressed genes (DEGs) involved in the immune response, metabolism, programmed cell death, cytoskeleton, and extracellular matrix that showed a subpopulation-dependent pattern. These findings indicate that osmoregulation in Baltic cod is a complex process, and that western and eastern Baltic cod subpopulations respond differently to salinity changes.

Responses to saltwater exposure vary across species, populations and life stages in anuran amphibians

To predict the impacts of environmental change on species, we must first understand the factors that limit the present-day ranges of species. Most anuran amphibians cannot survive at elevated salinities, which may drive their distribution in coastal locations. Previous research showed that coastal Hyla cinerea are locally adapted to brackish habitats in North Carolina, USA. Although Hyla squirella and Hyla chrysoscelis both inhabit coastal wetlands nearby, they have not been observed in saline habitats. We take advantage of naturally occurring microgeographic variation in coastal wetland occupancy exhibited by these congeneric tree frog species to explore how salt exposure affects oviposition site choice, hatching success, early tadpole survival, plasma osmolality and tadpole body condition across coastal and inland locations. We observed higher survival among coastal H. cinerea tadpoles than inland H. cinerea, which corroborates previous findings. But contrary to expectations, coastal H. cinerea had lower survival than H. squirella and H. chrysoscelis, indicating that all three species may be able to persist in saline wetlands. We also observed differences in tadpole plasma osmolality across species, locations and salinities, but these differences were not associated with survival rates in salt water. Instead, coastal occupancy may be affected by stage-specific processes like higher probability of total clutch loss as shown by inland H. chrysoscelis or maladaptive egg deposition patterns as shown by inland H. squirella. Although we expected salt water to be the primary filter driving species distributions along a coastal salinity gradient, it is likely that the factors dictating anuran ranges along the coast involve stage-, species- and location-specific processes that are mediated by ecological processes and life history traits.