A quantitative framework for evaluating transgenerational phenotypic plasticity under environmental change

Amanda Kate Pettersen , Frank Seebacher

Rapid environmental change has intensified interest in inter- and trans-generational phenotypic plasticity (TGP) as a mechanism underlying populations responses to changing environments. Parental environments frequently induce shifts in offspring phenotypes, and it is often implicitly assumed that these generational responses enhance offspring fitness and thus population persistence. However, evidence for phenotypic change alone is insufficient to demonstrate adaptive value, particularly when fitness is inferred from performance proxies rather than survival or reproduction. Here, we argue that a more agnostic null hypothesis is required when evaluating the fitness consequences of TGP: that phenotypic shifts across generations can be neutral, detrimental, and context-dependent, rather than inherently beneficial. We present a quantitative analytical framework that integrates selection analysis into multigenerational experiments to evaluate whether TPG aligns with variation in offspring fitness. This approach does not seek to identify the mechanistic basis of TGP, nor to disentangle plasticity from genetic or epigenetic causation, but instead provides a diagnostic test of whether observed phenotypic shifts are associated with positive, negative, or absent selection. Because the framework requires only individual-level phenotypic and fitness measurements, it can readily be incorporated into existing multigenerational studies spanning a range of study systems, without additional complexity to experimental designs. Integrating selection analysis into studies of TGP provides a tractable and comparable framework for evaluating whether intergenerational responses enhance, constrain, or have no effect on population persistence under environmental change.