Repeat exposure to hypercapnic seawater modifies growth and oxidative status in a tolerant burrowing clam

Abstract

Whereas low levels of thermal stress, irradiance, and dietary restriction can have beneficial effects for many taxa, stress acclimation remains understudied in marine invertebrates, despite being threatened by climate change stressors such as ocean acidification. To test for life-stage and stress-intensity dependence in eliciting enhanced tolerance under subsequent stress encounters, we initially conditioned pediveliger Pacific geoduck (Panopea generosa) larvae to (i) ambient and moderately elevated pCO2 (920 µatm and 2800 µatm, respectively) for 110 days, (ii) secondarily applied a 7-day exposure to ambient, moderate, and severely elevated pCO2 (750 µatm, 2800 µatm, and 4900 µatm, respectively), followed by 7 days in ambient conditions, and (iii) implemented a 7-day third exposure to ambient (970 µatm) and moderate pCO2 (3000 µatm). Initial conditioning to moderate pCO2 stress followed by second and third exposure to severe and moderate pCO2 stress increased respiration rate, organic biomass, and shell size suggesting a stress-intensity-dependent effect on energetics. Additionally, stress-acclimated clams had lower antioxidant capacity compared to clams under ambient conditions, supporting the hypothesis that stress over postlarval-to-juvenile development affects oxidative status later in life. Time series and stress intensity-specific approaches can reveal life-stages and magnitudes of exposure, respectively, that may elicit beneficial phenotypic variation.

Acclimatory gene expression of primed clams enhances robustness to elevated pCO2

“…Fine‐tuning, as expeditious/dynamic gene expression, may bolster tolerance to external environmental changes. Altogether, this study corroborates physiological traits of emergent organismal and cellular phenotypes (Gurr et al, 2021) with transcriptomics, highlighting how early life priming events can rapidly induce transcriptional plasticity that have the potential to enhance resilience under subsequent environmental challenges later in life.…”

“…The timing for primary exposure has naturalistic relevance, as postlarval development represents a transition from a free‐swimming stage to a sedentary life in the benthos (Goodwin and Pease, 1989), where bacterial carbon mineralization and low buffering capacity elevate p CO 2 and decrease calcium carbonate saturation (Cai et al, 2011). Survivorship over the pediveliger‐to‐juvenile transition was ~30% regardless of p CO 2 condition (4–5 × 10 3 juvenile geoduck per tray; Gurr et al, 2021). Juveniles acclimated under ambient and elevated p CO 2 , hereafter referred to as naïve and pre‐exposed clams, were divided at equal density into 36 replicate vessels ( N = 120 animals per vessel, N = 6 vessels per treatment), and subjected to a secondary 7‐day period under three p CO 2 conditions (ambient p CO 2 = 754 ± 15 μatm, moderate p CO 2 = 2750 ± 31 μatm, severe p CO 2 = 4940 ± 45 μatm) followed by 7 days of ambient recovery (896 ± 11 μatm) before replicates were split into 72 vessels ( N = 6 vessels per treatment) for a 7‐day third exposure in two conditions (ambient p CO 2 = 967 ± 9 μatm and moderate p CO 2 = 3030 ± 23 μatm; Figure 1); the time to reach target treatments (i.e., ambient to moderately elevated p CO 2 ) occurred more rapidly (~3 h) than the return to ambient conditions from elevated p CO 2 levels (~ 6–8 hr).…”

“…Geoduck clams (Panopea sp.) are long-lived molluscs of high economic value, and recent studies have corroborated their particular resilience to OA (Gurr et al, 2020(Gurr et al, , 2021Spencer et al, 2019).…”

“…Gene expression data were analysed for juvenile P. generosa acclimated at the pediveliger stage under ambient and moderately elevated p CO 2 conditions for 110 days (day 0) and then were subsequently re‐exposed in a reciprocal fashion to a second exposure of either ambient, moderately elevated p CO 2 , or severely elevated p CO 2 for 7 days (day 7), a 7‐day return to ambient p CO 2 (day 14), and a third 7‐day exposure to ambient or moderately elevated p CO 2 (day 21; Figure 1). Gurr et al (2021) review details regarding the rationale (i.e., timing and magnitude of p CO 2 conditions) and limitations of this hormetic framework.…”

Dynamic DNA methylation contributes to carryover effects and beneficial acclimatization in geoduck clams

“…While there are the fewest DMGs in the Wnt/Ca 2+ pathway on both Day 10 and Day 135, it remains possible there is a role for this in muscle or tissue growth. Gurr et al (Gurr et al 2021) reported that following preconditioning of geoduck to low pH stress there was a subsequent increase in biomass. Specifically in our study, the support for the Wnt/Ca 2+ pathway on Day 135 comes from differential methylation of RGS12 and FTM related to inositol triphophate Ca 2+ linked to potential triggering of the calcineurin NFAT pathway where AKAP5 and SL9A1 are positive regulators.…”