Measuring the effects of selection on the genome imposed by human-altered environment is currently a major goal in ecological genomics. Given the polygenic basis of most phenotypic traits, quantitative genetic theory predicts that selection is expected to cause subtle allelic changes among covarying loci rather than pronounced changes at few loci of large effects. The goal of this study was to test for the occurrence of polygenic selection in both North Atlantic eels (European Eel, Anguilla anguilla and American Eel, A. rostrata), using a method that searches for covariation among loci that would discriminate eels from 'control' vs. 'polluted' environments and be associated with specific contaminants acting as putative selective agents. RAD-seq libraries resulted in 23 659 and 14 755 filtered loci for the European and American Eels, respectively. A total of 142 and 141 covarying markers discriminating European and American Eels from 'control' vs. 'polluted' sampling localities were obtained using the Random Forest algorithm. Distance-based redundancy analyses (db-RDAs) were used to assess the relationships between these covarying markers and concentration of 34 contaminants measured for each individual eel. PCB153, 4'4'DDE and selenium were associated with covarying markers for both species, thus pointing to these contaminants as major selective agents in contaminated sites. Gene enrichment analyses suggested that sterol regulation plays an important role in the differential survival of eels in 'polluted' environment. This study illustrates the power of combining methods for detecting signals of polygenic selection and for associating variation of markers with putative selective agents in studies aiming at documenting the dynamics of selection at the genomic level and particularly so in human-altered environments.

Standard metabolic rate is 7-fold greater in the rat (a typical mammal) than in the bearded dragon, Amphibolurus vitticeps (a reptile with the same body mass and temperature). Rat hepatocytes respire 4-fold faster than do hepatocytes from the lizard. The inner membrane of isolated rat liver mitochondrial has a proton permeability that is 4-5-fold greater than the proton permeability of the lizard liver mitochondrial membrane per mg of mitochondrial protein. The greater permeability of rat mitochondria is not caused by differences in the surface area of the mitochondrial inner membrane, but differences in the fatty acid composition of the mitochondrial phospholipids may be involved in the permeability differences. Greater proton permeability of the mitochondrial inner membrane may contribute to the greater standard metabolic rate of mammals.

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Although the selective pressures of commercial fishing are well known, few studies have examined this phenomenon in recreational fisheries. This study used a unique population of largemouth bass ( Micropterus salmoides ) with lines bred for low (LVF) and high (HVF) vulnerability to recreational angling. We evaluated whether differential vulnerability to angling was correlated with physiological traits, including metabolic rate, metabolic scope, anaerobic capacity, and biochemical response to exercise. Indeed, angling selection affected the metabolic rate of fish significantly. The standard metabolic rate was 10%, maximal metabolic rate was 14%, and metabolic scope was 16% lower for LVF compared with HVF. Following exhaustive exercise, LVF required 1 h for lactate levels to recover to control values, whereas HVF required 2 h. Anaerobic energy expenditure was significantly lower for LVF, a finding consistent with the observation that LVF swam at a steadier rate during exercise. Although the reasons behind vulnerability to angling are complex, the phenotypic trait “vulnerability to angling” appears to be linked to a suite of physiological traits, including metabolism and the capacity for anaerobic activity. Thus, angling-induced selection might alter the physiological characteristics of wild largemouth bass populations, with unknown outcomes for long-term population viability.

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