One Life Stage Cannot Predict Climate Resilience in Clams

Forecasts of whether marine species can adapt quickly enough to survive climate change usually rest on tolerance assays performed at a single developmental stage, tacitly assuming that what holds for a larva also holds for a juvenile. A new study of the hard clam Mercenaria mercenaria shows that this assumption fails in sign, not merely in degree. Across family-level, pedigree-conditioned and animal model estimates, larval tolerance to end-century ocean acidification and post-metamorphic tolerance to the same conditions were strongly negatively correlated, with a coefficient of r = −0.53 (95% CI [−0.69, −0.33]). Families whose larvae performed best under acidified seawater tended to produce the worst-performing juveniles after metamorphosis, and the top performers of each stage showed pervasive rank reversals.

A multivariate analysis of the among-family covariance matrix G reveals the mechanism behind this reversal. Under acidification, 57% of the among-family variance collapsed onto a single dominant axis that loaded positively on every larval trait and negatively on every post-metamorphic trait. Under ambient conditions, the same families showed no cross-stage covariance at all. In other words, acidification does not simply depress performance uniformly across the life cycle; it reorganizes the genetic architecture into a conflict between stages, so that genetic variation that benefits one stage actively works against the other.

The consequences for adaptation were explored under ramping RCP 8.5 forcing scenarios. In these simulations, the geometry of the cross-stage conflict dictated the direction, not merely the magnitude, of evolutionary change. Selection applied at a single stage systematically eroded the opposing axis of variation, whereas only balanced multi-stage selection preserved family diversity across the life cycle. Single-stage breeding or screening programs could therefore quietly eliminate the very genetic variation that later stages would need under continued acidification.

The authors conclude that, in organisms with complex life cycles, climate resilience is a geometric property of ontogeny that cannot be compressed into a single-stage measurement without inverting the sign of the answer. The findings are specific to one marine bivalve species and to family-level estimates of tolerance, and the covariance structure was characterized under experimental acidification conditions rather than observed across natural populations over time. Even so, the result cautions that adaptive capacity measured at one developmental stage may mispredict resilience in any species whose larval and adult forms face different physiological constraints.

Subject of Research: Evolutionary genetics of ocean acidification tolerance across life stages in a marine bivalve

Article Title: Tolerance measured at one developmental stage mispredicts climate resilience in an animal with a complex life cycle

Article References: Song, H., Shi, T., Yang, M., Liu, X., Li, Z., Shi, P., Wu, Y., Allam, B., Jeffs, A., Skelton, B., & Zhang, T. (2026). Tolerance measured at one developmental stage mispredicts climate resilience in an animal with a complex life cycle. PLOS Biology, 24(10), e3004079. https://doi.org/10.1371/journal.pbio.3004079

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004079

Keywords: ocean acidification, hard clam, Mercenaria mercenaria, life cycle, genetic covariance, larval tolerance, adaptation, marine bivalve, RCP 8.5, climate resilience, Tolerance, measured