Ocean warming and acidification are concomitant global drivers that are currently threatening the survival of marine organisms. How species will respond to these changes depends on their capacity for plastic and adaptive responses. Little is known about the mechanisms that govern plasticity and adaptability or how global changes will influence these relationships across multiple generations. Here, we exposed the emerging model marine polychaete Ophryotrocha labronica to conditions simulating ocean warming and acidification, in isolation and in combination over five generations to identify: (i) how multiple versus single global change drivers alter both juvenile and adult life-history traits; (ii) the mechanistic link between adult physiological and fitness-related life-history traits; and (iii) whether the phenotypic changes observed over multiple generations are of plastic and/or adaptive origin. Two juvenile (developmental rate; survival to sexual maturity) and two adult (average reproductive body size; fecundity) life-history traits were measured in each generation, in addition to three physiological (cellular reactive oxygen species content, mitochondrial density, mitochondrial capacity) traits. We found that multi-generational exposure to warming alone caused an increase in juvenile developmental rate, reactive oxygen species production and mitochondrial density, decreases in average reproductive body size and fecundity, and fluctuations in mitochondrial capacity, relative to control conditions. Exposure to ocean acidification alone had only minor effects on juvenile developmental rate. Remarkably, when both drivers of global change were present, only mitochondrial capacity was significantly affected, suggesting that ocean warming and acidification act as opposing vectors of stress across multiple generations.

International audienceOne outcome of contemporary climate trends is that the involvement of hypoxia and heat tolerance in determining individual fitness will increase in many fish populations. Large fish are believed to be more tolerant to hypoxia than small fish (Nilsson and Östlund-Nilsson, 2008) whereas thermal sensitivity is thought to decrease with body size (Clark et al., 2008). To better understand the bases of inter-individual variation in environmental adaptation performance, the current study examined hypoxia and heat tolerance in a fast growing (FGS; 288.3 ±14.4 g, 26.04±0.49 cm) and a slow growing (SGS; 119.95±6.41 g; 20.98±0.41 cm) strain of 1-year old rainbow trout (Oncorhynchus mykiss). This examination was conducted using two standardized challenge tests aimed at assessing individual incipient lethal oxygen saturation and incipient upper lethal temperature. Results to these tests were then cross-correlated with swim tests during which individual basal and active metabolic rate values were also measured. Measurements of permeabilized ventricular myofibers oxygen consumption were also conducted, as well as various organ-to-body-mass ratios. Experimental data showed that FGS was more hypoxia tolerant than SGS (13.4 to 16.7% air sat versus 14.7 to 18.9% air sat respectively). On the other hand, FGS was found less tolerant to heat than SGS (24.7-27.6 °C versus 28.5 to 29.7 °C respectively). Adding to the body size effect, another source of inter-individual variation in environmental tolerance was found. Residual analysis highlighted that whereas none of the individual morphometric and energetic traits correlated with hypoxia tolerance, permeabilized ventricular myofibers maximal oxygen consumption correlated well with individual tolerance to heat

Human‐assisted, trans‐generational exposure to ocean warming and acidification has been proposed as a conservation and/or restoration tool to produce resilient offspring. To improve our understanding of the need for and the efficacy of this approach, we characterized life‐history and physiological responses in offspring of the marine polychaete Ophryotrocha labronica exposed to predicted ocean warming (OW: + 3°C), ocean acidification (OA: pH −0.5) and their combination (OWA: + 3°C, pH −0.5), following the exposure of their parents to either control conditions (within‐generational exposure) or the same conditions (trans‐generational exposure). Trans‐generational exposure to OW fully alleviated the negative effects of within‐generational exposure to OW on fecundity and egg volume and was accompanied by increased metabolic activity. While within‐generational exposure to OA reduced juvenile growth rates and egg volume, trans‐generational exposure alleviated the former but could not restore the latter. Surprisingly, exposure to OWA had no negative impacts within‐ or trans‐generationally. Our results highlight the potential for trans‐generational laboratory experiments in producing offspring that are resilient to OW and OA. However, trans‐generational exposure does not always appear to improve traits and therefore may not be a universally useful tool for all species in the face of global change.