Multi-generational responses of an elevated pCO2 tolerant laboratory marine polychaete strain to low pCO2.

We currently lack a firm understanding of the multi-generational responses of marine metazoans to rapid changes in pCO2. Consequently, we reared a marine polychaete, Ophryotrocha labronica, previously cultured for ~33 generations under a low and variable pH regime, under elevated pCO2 and low pCO2 conditions for six generations. After this time, reciprocal transplants were performed between pCO2 treatments using F7 individuals. The strain used was found to be tolerant to elevated pCO2 conditions. In generation F1 and F2 female fecundity was significantly lower, 47.0% and 16.0% respectively, in the low pCO2 treatment. However, from generation F3 onwards there were no differences between pCO2 treatments, indicating that trans-generational effects enabled the maximization and maintenance of reproductive output. Whilst the initial fitness recovery was likely driven by trans-generational plasticity (TGP), the results from reciprocal transplant assays performed using F7 individuals made it difficult to disentangle between whether TGP had persisted across multiple generations or if evolutionary adaptation had occurred. Nonetheless, both are important mechanisms to persist under climate change. Overall, our study highlights the importance of using multi-generational studies to more accurately understand how populations of marine metazoans may respond to the rapid changes in pCO2 predicted to occur over the next century.