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1. Rapid evolution of genome‐wide gene expression and plasticity during saline to freshwater invasions by the copepod Eurytemora affinis species complex

   https://doi.org/10.1111/mec.15681  

   Posavi, Marijan; Gulisija, Davorka; Munro, James B.; Silva, Joana C.; Lee, Carol Eunmi (November 2020, Molecular Ecology)

   Abstract Saline migrants into freshwater habitats constitute among the most destructive invaders in aquatic ecosystems throughout the globe. However, the evolutionary and physiological mechanisms underlying such habitat transitions remain poorly understood. To explore the mechanisms of freshwater adaptation and distinguish between adaptive (evolutionary) and acclimatory (plastic) responses to salinity change, we examined genome‐wide patterns of gene expression between ancestral saline and derived freshwater populations of theEurytemora affinisspecies complex, reared under two different common‐garden conditions (0 versus 15 PSU). We found that evolutionary shifts in gene expression (between saline and freshwater inbred lines) showed far greater changes and were more widespread than acclimatory responses to salinity (0 versus 15 PSU). Most notably, 30–40 genes showing evolutionary shifts in gene expression across the salinity boundary were associated with ion transport function, withinorganic cation transmembrane transportforming the largest Gene Ontology category. Of particular interest was the sodium transporter, the Na⁺/H⁺antiporter (NHA) gene family, which was discovered in animals relatively recently. Thirty key ion regulatory genes, such as NHA paralogue #7, demonstrated concordant evolutionary and plastic shifts in gene expression, suggesting the evolution of ion transporter function and plasticity during rapid invasions into novel salinities. Moreover, freshwater invasions were associated with the evolution of reduced plasticity in the freshwater population, again for the same key ion transporters, consistent with the predicted evolution of canalization following adaptation to stressful conditions. Our results have important implications for understanding evolutionary and physiological mechanisms of range expansions by some of the most widespread invaders in aquatic habitats. 

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2. Tolerance to salinity and thermal stress by larvae and adults of the serpulid annelid Ficopomatus enigmaticus

   https://doi.org/10.1111/ivb.12271  

   Peria, Jessica; Pernet, Bruno (November 2019, Invertebrate Biology)

   Abstract The serpulid annelidFicopomatus enigmaticusis a widely distributed invader of shallow‐water, brackish habitats in subtropical and temperate regions, where it has numerous damaging ecological and economic effects. Its distributional pattern suggests that temperature and salinity play important roles in limiting its distribution, but because other factors often covary with these, drawing strong conclusions from these patterns is difficult. In an effort to more clearly identify the effects of these factors, we examined tolerance to acute thermal (16–28°C) and salinity (0–35 psu) stress by larvae (5‐day exposure, unfed) and adults (14‐day exposure, unfed) ofF. enigmaticusin the laboratory experiments. Larvae showed higher mortality at the highest temperature tested 28°C; adult survival was unaffected by temperature. Neither larvae nor adults survived exposure to pure freshwater (0 psu), but survived well at salinities ranging 3.5–35 psu. In addition, high salinity did not slow tube growth in adults. These results suggest that salinity stress, in particular, does not directly limit the distribution ofF. enigmaticusto low‐salinity habitats. Experimental work on the distribution ofF. enigmaticusis uncommon in the literature, but is likely needed to identify the abiotic or biotic factors that limit the distribution of this frequently invasive species. 

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3. Salinity Alters Toxicity of Commonly Used Pesticides in a Model Euryhaline Fish Species (Menidia beryllina)

   https://doi.org/10.3390/toxics9050114  

   Hutton, Sara; St. Romain, Scott; Pedersen, Emily; Siddiqui, Samreen; Chappell, Patrick; White, J.; Armbrust, Kevin; Brander, Susanne (May 2021, Toxics)

   Changing salinity in estuaries due to sea level rise and altered rainfall patterns, as a result of climate change, has the potential to influence the interactions of aquatic pollutants as well as to alter their toxicity. From a chemical property point of view, ionic concentration can increase the octanol–water partition coefficient and thus decrease the water solubility of a compound. Biologically, organism physiology and enzyme metabolism are also altered at different salinities with implications for drug metabolism and toxic effects. This highlights the need to understand the influence of salinity on pesticide toxicity when assessing risk to estuarine and marine fishes, particularly considering that climate change is predicted to alter salinity regimes globally and many risk assessments and regulatory decisions are made using freshwater studies. Therefore, we exposed the Inland Silverside (Menidia beryllina) at an early life stage to seven commonly used pesticides at two salinities relevant to estuarine waters (5 PSU and 15 PSU). Triadimefon was the only compound to show a statistically significant increase in toxicity at the 15 PSU LC50. However, all compounds showed a decrease in LC50 values at the higher salinity, and all but one showed a decrease in the LC10 value. Many organisms rely on estuaries as nurseries and increased toxicity at higher salinities may mean that organisms in critical life stages of development are at risk of experiencing adverse, toxic effects. The differences in toxicity demonstrated here have important implications for organisms living within estuarine and marine ecosystems in the Anthropocene as climate change alters estuarine salinity regimes globally. 

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4. Environmental Controls on the Distribution of Modern Benthic Foraminifera in the Florida Everglades and Their Use as Paleoenvironmental Indicators

   https://doi.org/10.2113/gsjfr.51.3.182  

   Verlaak, Zoë R.; Collins, Laurel S. (July 2021, Journal of Foraminiferal Research)

   null (Ed.)

   ABSTRACT This study examined the environmental factors that control the distribution of modern foraminiferal assemblages in the Everglades in order to provide baseline data for a paleoenvironmental study. Total assemblages from the surface 2 cm of 30 sites across the marsh and mangrove environments of southwest Florida were investigated. Eight environmental variables, including average salinity, salinity range, pH, total phosphorus, temperature, and dissolved oxygen, and total organic carbon and total inorganic carbon measured on bulk sediments, as well as the elevation and distance from the coastline were determined for each of the 30 sampling locations. In total, 82 species were identified, the majority of which were calcareous. Diversity decreases, dominance increases, and agglutinated taxa increase from the coastline inland. Rotaliina are equally abundant across the intertidal environment, whereas Miliolina are common near the coast and in lagoons or inland lakes. The most important factor controlling foraminiferal distribution is total organic carbon, followed by total inorganic carbon, distance from coastline, total phosphorus, and salinity. Jadammina macrescens and Miliammina fusca indicate lower salinities (<15 psu). Good indicators for higher salinities are Haplophragmoides wilberti (10–20 psu) and Arenoparrella mexicana (10–20 psu and 28–30 psu). Ammonia spp. prefer salinities >15 psu and Elphidium spp. >20 psu. Ammonia tepida, Helenina anderseni, Trochammina inflata, and A. mexicana prefer organic-rich sediments. Thus, the benthic foraminifera from Everglades sediments are excellent salinity proxies and can be used to determine the history of habitat change in this area as well as to assess past trends in the rate of sea level rise. 

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5. Resurrection genomics provides molecular and phenotypic evidence of rapid adaptation to salinization in a keystone aquatic species

   https://doi.org/10.1073/pnas.2217276120  

   Wersebe, Matthew J.; Weider, Lawrence J. (February 2023, Proceedings of the National Academy of Sciences)

   Ecologists and evolutionary biologists are increasingly cognizant of rapid adaptation in wild populations. Rapid adaptation to anthropogenic environmental change is critical for maintaining biodiversity and ecosystems services into the future. Anthropogenic salinization of freshwater ecosystems is quickly emerging as a primary threat, which is well documented in the northern temperate ecoregion. Specifically, many northern temperate lakes have undergone extensive salinization because of urbanization and the associated increase in impervious surfaces causing runoff, and the extensive use of road deicing salts (e.g., NaCl). It remains unclear whether increasing salinization will lead to extirpation of species from these systems. Using a “resurrection genomics” approach, we investigated whether the keystone aquatic herbivore,Daphnia pulicaria,has evolved increased salinity tolerance in a severely salinized lake located in Minnesota, USA. Whole-genome resequencing of 54Daphniaclones from the lake and hatched from resting eggs that represent a 25-y temporal contrast demonstrates that many regions of the genome containing genes related to osmoregulation are under selection in the study population. Tolerance assays of clones revealed that the most recent clones are more tolerant to salinity than older clones; this pattern is concomitant with the temporal pattern of stabilizing salinity in this lake. Together, our results demonstrate that keystone species such asDaphniacan rapidly adapt to increasing freshwater salinization. Further, our results indicate that rapid adaptation to salinity may allow lakeDaphniapopulations to persist in the face of anthropogenic salinization maintaining the food webs and ecosystem services they support despite global environmental change. 

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