Juvenile Hippocampus guttulatus from a neuston tow at the French-Belgian border

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The initial tolerance to sub-lethal Cd exposure is the same among ten naïve pond populations of Daphnia magna, but their micro-evolutionary potential to develop resistance is very different

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The potential for adaptation in a natural Daphnia magna population: broad and narrow-sense heritability of net reproductive rate under Cd stress at two temperatures

The existence of genetic variability is a key element of the adaptive potential of a natural population to stress. In this study we estimated the additive and non-additive components of the genetic variability of net reproductive rate (R-0) in a natural Daphnia magna population exposed to Cd stress at two different temperatures. To this end, life-table experiments were conducted with 20 parental and 39 offspring clonal lineages following a 2 x 2 design with Cd concentration (control vs. 3.7 mu g Cd/L) and temperature (20 vs. 24 A degrees C) as factors. Offspring lineages were obtained through inter-clonal crossing of the different parental lineages. The population mean, additive and non-additive genetic components of variation in each treatment were estimated by fitting an Animal Model to the observed R-0 values using restricted maximum likelihood estimation. From those estimates broad-sense heritabilities (H-2), narrow-sense heritabilities (h(2)), total (CVG) and additive genetic coefficients of variation (CVA) of R-0 were calculated. The exposure to Cd imposed a considerable level of stress to the population, as shown by the fact that the population mean of R-0 exposed to Cd was significantly lower than in the control at the corresponding temperature, i.e. by 23 % at 20 A degrees C and by 88 % at 24 A degrees C. The latter difference indicates that increasing temperature increased the stress level imposed by Cd. The HA(2) and CVG were significantly greater than 0 in all treatments, suggesting that there is a considerable degree of genetic determination of R-0 in this population and that clonal selection could rapidly lead to increasing population mean fitness under all investigated conditions. More specifically, the HA(2) was 0.392 at 20 A degrees C+Cd and 0.563 at 24 A degrees C+Cd; the CVG was 30.0 % at 20 A degrees C+Cd and was significantly higher (147.6 %) in the 24 A degrees C+Cd treatment. Significant values of h(2) (= 0.23) and CVA (= 89.7 %) were only found in the 24 A degrees C+Cd treatment, suggesting that the ability to produce more offspring under this stressful condition may be inherited across sexual generations. In contrast, in the less stressful 20 A degrees C+Cd treatment the h(2) (0.06) and CVA (7.0 %) were very low and not significantly higher than zero. Collectively our data indicate that both the asexual and sexual reproduction phases in cyclic parthenogenetic D. magna populations may play a role in the long-term adaptive potential of Daphnia populations to chemical stress (with Cd as the current example) and that environmental variables which influence the stress level of that chemical may influence this adaptive potential (with temperature as current example)

The micro-evolutionary potential of Daphnia magna population exposed to temperature and cadmium stress

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The initial tolerance to sub-lethal Cd exposure is the same among ten naive pond populations of Daphnia magna, but their micro-evolutionary potential to develop resistance is very different

Genetic variation complicates predictions of both the initial tolerance and the long-term (micro-evolutionary) response of natural Daphnia populations to chemical stressors from results of standard single-clone laboratory ecotoxicity tests. In order to investigate possible solutions to this problem, we aimed to compare the initial sub-lethal tolerance to Cd of 10 naïve natural pond populations of Daphnia magna as well as their evolutionary potential to develop increased resistance. We did so by measuring reproductive performance of 120 clones, i.e. 12 clones hatched from the recent dormant egg bank of each of 10 populations, both in absence (Cd-free control) and presence of 4.4 μg Cd/L. We show that the initial tolerance, defined as the reproductive performance of individuals of the first generation exposed to Cd relative to that in a Cd-free control was not significantly different among the 10 studied pond populations and averaged 0.82 ± 0.04 over these populations. Moreover, these populations' initial tolerances were also not significantly different from the mean initial tolerance of 0.87 ± 0.08 at 4.0 μg Cd/L measured for a group of 7 often-used laboratory clones, collected from a range of European ecotoxicity testing laboratories. This indicates that the initial response of naïve natural pond populations to sub-lethal Cd can be relatively accurately predicted from ecotoxicity test data from only a handful of laboratory clones. We then used estimates of broad-sense heritability of Cd tolerance (H(2)) - based on the same dataset - as a proxy of these populations' capacities to evolutionarily respond to Cd in terms of the development of increased resistance, which is here defined as the increase with time of the frequency of clones with a higher Cd tolerance in the population (accompanied with an increase of mean Cd-tolerance of the population above the initial tolerance). We show that the populations' estimated H(2) values of Cd-tolerance cover almost the entire theoretically possible range, ranging from not significantly different from zero (for five populations) to between 0.48 and 0.81 (for the five other populations). This indicates that, unlike the initial tolerance to Cd, the (long-term) micro-evolutionary response to Cd may be very different among natural pond populations. Therefore, we conclude that it may be very difficult to predict the long-term response of an unstudied population to chemical stress from tolerance data on a sample of other populations. It is therefore suggested that new methods for forecasting long-term responses should be explored, such as the development of predictive models based on the combination of population-genomic and tolerance time-series data.publisher: Elsevier articletitle: The initial tolerance to sub-lethal Cd exposure is the same among ten naïve pond populations of Daphnia magna, but their micro-evolutionary potential to develop resistance is very different journaltitle: Aquatic Toxicology articlelink: http://dx.doi.org/10.1016/j.aquatox.2013.10.016 content_type: article copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe

Will genetic adaptation of natural populations to chemical pollution result in lower or higher tolerance to future climate change?

Evolved co-tolerance or cross-tolerance to chemical pollution and a future climate change stressor is observe