Climate change is inducing rapid salinity and temperature change in coastal habitats. Thus, the ability of populations to expand their ranges presents among the most serious global problems today. However, fundamental mechanisms that enable certain populations to rapidly adapt to novel habitats remain poorly understood. Recently, populations of the copepod Eurytemora affinis complex have experienced drastic changes in habitat salinity and temperature. These copepods are dominant grazers in aquatic habitats throughout the Northern Hemisphere and support major fisheries. Intriguingly, we discovered that evolutionary changes during salinity transitions repeatedly involve the same loci (and SNPs) in wild populations and laboratory selection lines far beyond expectations. In both wild populations and laboratory lines, ion transporter genes dominate as the functional category undergoing natural selection. Using extensive simulations, we found that this degree of parallelism was consistent with positive synergistic epistasis among alleles, where selection on one allele promotes selection on other related alleles. Our results were consistent with mechanisms of ion uptake from dilute habitats, requiring the coordinated action of cooperating ion transporter proteins. Interestingly, temperature adaptation resulted in selection acting on an entirely different set of loci, indicating tradeoffs between salinity and temperature adaptation. Here, we find strong support for a novel and potentially widespread mechanism, namely positive epistasis, in promoting parallel polygenic adaptation.

Tutorial/Invited: Invited

Primary Presenter: Carol Eunmi LEE, University of Wisconsin, Madison (carollee@wisc.edu)

Authors: