Abstract
Deciphering evolutionary processes occurring within contaminated populations is important for the ecological risk assessment of toxic chemicals. Whereas increased tolerance to contaminants is well documented in aquatic animal populations, whether such phenotypic changes occur through genetic adaptation is still debated. In that sense, several studies with the freshwater crustacean Gammarus concluded in a weak potential for genetic adaptation to cadmium (Cd), while others reported inheritable increased tolerance in Cd-contaminated populations. Using quantitative genetics and selection experiments, this study sought to further assess the potential of Gammarus populations to genetically adapt to Cd. By combining the control of the reproductive cycle of this species in the laboratory and protocols of individual Cd exposure, we conducted half-sib analyses to establish the genetic and environmental sources of variance in Cd sensitivity of neonates. Prior to experiments, computations allowed optimizing the experimental design in order to increase the power to detect additive genetic variance. The main findings are the existence of strong between-brood variability along with weak heritability of Cd sensitivity within Gammarus populations. This study also revealed a significant maternal effect on individual Cd sensitivity. This sheds new light on the importance of maternal influence in microevolutionary processes occurring in contaminated environments.
Highlights
Deciphering evolutionary processes occurring within longterm contaminated aquatic populations is important for the ecological risk assessment of toxic chemical contaminants (Bickham 2011; Coutellec and Barata 2011; De Coninck et al 2014)
If tolerance to contaminants frequently occurs in natural populations exposed to environmental contamination, water quality criteria established from short-term standardized ecotoxicity tests might be over protective; on the opposite, if tolerance is associated with fitness costs, especially expected in case of genetic adaptation which can lead to a loss of genetic diversity in populations, current values of water quality criteria might be under protective if tolerance frequently arises in contaminated environments (Klerks and Weis 1987; Weis 2002)
The Cd sensitivity of the juveniles produced by these individuals when mated for their second fertilization after Cd exposure with na€ıve females was compared to control offspring from unselected males
Summary
Deciphering evolutionary processes occurring within longterm contaminated aquatic populations is important for the ecological risk assessment of toxic chemical contaminants (Bickham 2011; Coutellec and Barata 2011; De Coninck et al 2014). The fact that long-term exposure to a pollutant can induce increased tolerance in aquatic animal populations is well documented (Johnston 2011). Whether such phenomena of increased tolerance occur through genetic adaptation and/or acclimation processes has not yet been fully elucidated, especially for field studies involving natural populations.
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