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

Abstract

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 × 2 design with Cd concentration (control vs. 3.7 μg Cd/L) and temperature (20 vs. 24 °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 (CV(G)) and additive genetic coefficients of variation (CV(A)) 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 °C and by 88 % at 24 °C. The latter difference indicates that increasing temperature increased the stress level imposed by Cd. The H² and CV(G) 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 H² was 0.392 at 20 °C+Cd and 0.563 at 24 °C+Cd; the CV(G) was 30.0 % at 20 °C+Cd and was significantly higher (147.6 %) in the 24 °C+Cd treatment. Significant values of h(2) (= 0.23) and CV(A) (= 89.7 %) were only found in the 24 °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 °C+Cd treatment the h(2) (0.06) and CV(A) (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).

Mothers and not genes determine inherited differences in cadmium sensitivities within unexposed populations of the freshwater crustacean Gammarus fossarum

“…The variability among clonal individuals appeared non-negligible within a single condition, for example, the 48 h LC50 of a given clone exposed to Cd range from 174 to 279 lg L À1 . The same significant residual variance was also present in the result of a quantitative genetics experiment on Cd sensitivity conducted with clones of Daphnia (Messiaen et al 2012).…”

“…The same significant residual variance was also present in the result of a quantitative genetics experiment on Cd sensitivity conducted with clones of Daphnia (Messiaen et al. ).…”

“…Nonetheless, Messiaen et al. () scrutinized the potential for adaptation to Cd in a natural Daphnia magna population by studying the heritability of the net reproductive rate under that order of magnitude of Cd stress (3.7 μg L −1 ). This led to relatively low estimations of h 2 (0.23 and 0.06 depending on the temperature).…”

“…For instance, adverse effects on reproduction have been observed in G. fossarum for Cd concentration of 3 lg L À1 (Geffard et al 2010), and Cd is known to disrupt vitellogenesis in Crustaceans (Yang et al 2015). Nonetheless, Messiaen et al (2012) scrutinized the potential for adaptation to Cd in a natural Daphnia magna population by studying the heritability of the net reproductive rate under that order of magnitude of Cd stress (3.7 lg L À1 ). This led to relatively low estimations of h 2 (0.23 and 0.06 depending on the temperature).…”

Mixed evidence for adaptation to environmental pollution

“…Forty‐two studies (21%) did not find statistical differences among treatments, regardless of the approach used. Only three studies (Dutilleul et al, ; Dutilleul et al, ; Dutilleul, Goussen, B., Bonzom, J.‐M., Galas, S. & Réale, ; Kelly, Padilla‐Gamiño, & Hofmann, ; Messiaen, De Schamphelaere, Muyssen, & Janssen, ; Messiaen, Janssen, Thas, & Schamphelaere, ; Messiaen, Janssen, De Meester, & De Schamphelaere, ) found evidence of a phenotypic response to pollution with an underlying advantageous genetic basis and also found the presence of a response to selection followed by a demographic response. These studies provided the most thorough insights on the adaptive potential of the studied organisms.…”