Rapid Evolutionary Responses to Global Transformations in Salinity & Temperature

Our research program focuses on the evolutionary genetic and genomic mechanisms underlying physiological adaptation to habitat change, including biological invasions and climate change. With climate change, habitat salinity is changing rapidly throughout the globe. Our laboratory has completed several long-term evolution experiments (10-30 generations), which revealed a set of interacting ion transporter genes that enable plankton populations to survival rapid and drastic changes in salinity and temperature. With climate change, coastal waters are getting hotter and less saline in high latitude environments. Our experiments identify how quickly these populations could evolve and which genes are involved. The set of interacting genes that we identified in our experiments are the same ones that show signatures of natural selection across temperature and salinity gradients in wild populations in the Baltic Sea and in three locations in North America. The power of the laboratory experiments is in establishing that the genetic (allele frequency) shifts that correlate with environmental variables in the wild are the same genetic targets that are induced by the key variables alone in the laboratory. These results have been published in Nature Ecology & Evolution and Nature Communications.

      We have completed a genetic association study to link our candidate genes to their fitness effects. The goal of this experiment is to determine the extent to which specific alleles impact fitness (survival, egg number), so that we understand the demographic effects of beneficial alleles. We focused on the alleles that increased in frequency in the laboratory evolution experiment and determined their fitness effects. With this information we can begin to model how changes in allele frequencies in the wild will impact demographic changes in populations in the face of climate change. We have found a significant association between specific ion transporter alleles and survival of the copepods.

     We are the first lab to examine evolutionary shifts in in situ localization and expression of ion transporter alleles in the organism. We have found that salinity shifts are associated with evolutionary shifts in expression and localization of the key ion transporters Na⁺/K⁺-ATPase (NKA) and Na⁺/H⁺ antiporter (NHA) in the osmoregulatory leg, maxillary glands, and gut of the copepod. We discovered a novel mechanism through which populations of the copepod E. carolleeae can survive rapid reductions in salinity, specifically by expressing NHA in the gut. This mechanism has never been identified previously. Our work is enabling us to proposal a new model of ion transport from the environment, particularly for an organism that can rapidly evolve in response to climate change.