| Summary: | Due to the rapid changes in atmospheric pCO2 levels expected to occur over the coming centuries, as a result of increased CO2 emissions and the future implementation of CO2 mitigation strategies, and the current lack of understanding we have on the capacity of marine metazoans to adapt to these rapid changes, the aims of this study were to investigate the consequences of long-term acclimation / adaptation to elevated pCO2 and the potential for adaptive recovery to present pCO2. Here, I utilised a laboratory-bred strain of the marine polychaete Ophryotrocha labronica which has been cultured at pCO2 / pH levels predicted to occur by the year 2100 for approximately 30 generations. Taking advantage of this pre-experimental treatment, and to address the aims of this study, I firstly carried out a multi-generational selection experiment (six generations), in which present pCO2 levels were my experimental treatment and elevated pCO2 levels my control. Secondly, I carried out a reciprocal cross experiment with generation F7 to determine the extent of adaptive recovery to present pCO2 levels. Throughout the study I measured a range of life-history traits as well as metabolic rates. The only trait that was significantly affected by exposure to present pCO2 levels was female fecundity. In generation F1, female fecundity was significantly lower in the present pCO2 treatment, thus indicating that the pre-experimental treatment had resulted in adaptation to elevated pCO2 conditions. However, female fecundity significantly increased between generations F1 and F3, so that from generation F3-F7 a significant difference was no longer present. In the reciprocal cross experiment, there was no significant difference in fecundity between the present- present pCO2 cross and the present-elevated pCO2 cross, thus indicating that acclimation was responsible for increasing and maintaining fecundity levels in the present pCO2 treatment. This work has shown that rapid adaptation to elevated pCO2 conditions is possible in a marine metazoan, and for the first time that once adapted to elevated pCO2 conditions there is the potential for adaptive recovery to present pCO2 conditions.
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