Rapid Evolutionary Responses to Global Transformations in Salinity & Temperature

With climate change, rising temperature is resulting in drastic changes in the global water cycle, leading to changes in precipitation patterns. On land, these changes are leading to increases in droughts and flooding. Throughout aquatic habitats, salinity is rapidly changing throughout the globe. In high latitude coastal waters, increases in polar ice melt and precipitation are causing rapid salinity declines. In contrast, rapid evaporation is resulting in increasing salinities in lower latitude habitats, such as the Mediterranean Sea. It is critically important to understand how populations will respond to these rapid changes in order to forecast the probability of population extinctions under future climate change.

Our research program examines population responses to rapid changes in salinity, focusing on the common copepod Eurytemora affinis species complex. This copepod is a dominant plankton species in estuaries of Europe, North America, and Asia and serves as an important food source for major fisheries, such as herring, anchovy, sardine, and larval salmon. For instance, this copepod is abundant in the Seine estuary in France.

We examined how quickly the copepod populations could evolve in response to rapid salinity decline and which genes are involved. First of all, we found that ion transporter genes show signatures of natural selection (allele frequency shifts) in response to salinity change. Second, we localized these ion transporter proteins in the osmoregulatory organs of copepods, in the maxillary glands, swimming legs, and digestive tract. We found that the amount and localization of these ion transporters shift in response to salinity change and show evolutionary differences in expression between saline and freshwater populations. In addition, expression of these ion transporters shows evolutionary shifts in laboratory natural seleciton experiments. Finally, we have performed theoretical modelling of the alleles under selection to analyze the impacts of genome architecture (such as chromosome number) on the probabability of adaptation or extinction of populations. Our studies have uncovered important evolutionary genetic and physiological mechanisms that enable certain populations to survive under rapid environmental change.