Effects of intragenerational pCO2 conditioning on metabolism, oxidative stress response, and DNA methylation of juvenile Pacific geoduck Panopea generosa
ABSTRACT: Moderate or intermittent oxidative stress is known to induce positive carry over effects and is a theorized driver of stress memory and enhanced lifespan. Stress conditioning may increase resilient phenotypes and epigenotypes advantageous for sustainable aquaculture. However, the importance of pCO2 stress intensity remains understudied for establishment of intragenerational adaptive mechanisms to cope with subsequent exposure. To test whether pCO2 stress elicits beneficial responses under subsequent encounters, we conditioned pediveliger (~30 days old) Pacific geoduck Panopea generosa for 120 days in ambient and elevated pCO2 conditions (920 µatm and 2870 µatm, respectively) before subjecting juvenile clams (~5 months old) to three exposure periods over 21 days (n = 7 d exposure-1). We measured standard metabolic rate, shell length, total antioxidant capacity, and whole tissue DNA methylation periodically under three conditions: ambient (740 ± 40 µatm), moderate (2715 ± 70 µatm), and severe pCO2 (4876 ± 101 µatm); this was followed by a period of ambient recovery (861 ± 45 µatm) before subsequent reciprocal exposure to two conditions: ambient (939 ± 31 µatm) and moderate pCO2 (2983 ± 79 µatm). Clams reared in elevated pCO2 had greater metabolic rates in response to moderate pCO2 than clams reared in ambient conditions, suggesting an effect of preconditioning on energy homeostasis, cellular stress response, and redox regulation. Additionally, clams both reared under elevated pCO2 and exposed to severe pCO2 exhibited both elevated metabolic rates upon re-exposure to moderate pCO2 and greater shell size indicating stress intensity-dependent effects on performance. Long-term pCO2 conditioning of postlarval geoduck decreased total antioxidant capacity regardless of subsequent exposure(s) suggesting early-life stress conditioning can modify redox status and protein/energy homeostasis. Sequencing is planned to determine the cellular and molecular mechanisms of adaptive tolerance and stress memory. Intensity-specific stress conditioning can reveal thresholds and life-stages that enhance the longevity of resilient phenotypes and epigenotypes for commercial production of this long-lived clam.
