Something Fishy? Uncovering Patterns of Genetic Diversity and the Evolution of Resistance in Fish Populations
Populations of fishes are increasingly threatened by over-exploitation, pollution, habitat destruction, and climate change. In order to better understand the factors that can explain the amount of genetic diversity in wild populations of fishes, we collected estimates of genetic diversity (mean heterozygosity and mean rarefied number of alleles per locus) along with habitat associations, conservation status, and life history information for 463 fish species. We ran a series of phylogenetic generalized least squares (PGLS) models to determine which factors influence genetic diversity in fishes after accounting for shared evolutionary history among related taxa. We found that marine fishes had significantly higher genetic diversity than freshwater fishes with marine fishes averaging 11.3 more alleles per locus than their freshwater counterparts. However, contrary to our expectations, genetic diversity was not found to be lower in threatened versus not-threatened fishes. Finally, we found that both age at maturity and fecundity were negatively related to genetic variation in both marine and freshwater fishes. Our results demonstrate that both life history characteristics and habitat play a role in shaping patterns of genetic diversity in fishes and suggest that species-specific environmental preferences and life history information should be considered when prioritizing species for conservation. Sea lamprey (Petromyzon marinus) are hematophagous parasites that are invasive in the Great Lakes ecosystem. Since the late 1950s, control efforts have relied heavily on a chemical lampricide known as 3-trifluoromethyl-4-nitrophenol (TFM) to limit sea lamprey abundance in the Great Lakes. High but incomplete mortality associated with TFM exposure suggests that the lampricide may be a strong selective agent, which could result in rapid evolution of resistance. The objectives of this study are twofold: (1) to determine if sea lamprey populations with varied histories of exposure to TFM are evolving resistance using toxicological assays and a transcriptomics approach and (2) to determine what genes and physiological mechanisms underlie resistance. We found no differences in mortality among populations during our toxicological assays. However, our RNA-seq results revealed that the population with the longest history of exposure exhibited a greater transcriptional response relative to populations with a shorter or no history of exposure, and differentially expressed genes with functions related to TFM’s primary mode of action were nearly exclusive to the population with the longest history of exposure. Our findings, at this point in time, cannot rule out the possibility of the evolution of sub-lethal resistance in invasive sea lamprey populations and may have implications for the future management of Great Lakes sea lamprey.
Christie, Purdue University.
Evolution and Development|Ecology|Molecular biology
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