Stressful parental (usually maternal) environments can dramatically influence expression of traits in offspring, in some cases resulting in phenotypes that are adaptive to the inducing stress. The ecological and evolutionary impact of such transgenerational plasticity depends on both its persistence across generations and its adaptive value. Few studies have examined both aspects of transgenerational plasticity within a given system. Here we report the results of a growth-chamber study of adaptive transgenerational plasticity across two generations, using the widespread annual plant Polygonum persicaria as a naturally evolved model system. We grew five inbred Polygonum genetic lines in controlled dry vs. moist soil environments for two generations in a fully factorial design, producing replicate individuals of each genetic line with all permutations of grandparental and parental environment. We then measured the effects of these two-generational stress histories on traits critical for functioning in dry soil, in a third (grandchild) generation of seedling offspring raised in the dry treatment. Both grandparental and parental moisture environment significantly influenced seedling development: seedlings of drought-stressed grandparents or parents produced longer root systems that extended deeper and faster into dry soil compared with seedlings of the same genetic lines whose grandparents and/or parents had been amply watered. Offspring of stressed individuals also grew to a greater biomass than offspring of nonstressed parents and grandparents. Importantly, the effects of drought were cumulative over the course of two generations: when both grandparents and parents were drought-stressed, offspring had the greatest provisioning, germinated earliest, and developed into the largest seedlings with the most extensive root systems. Along with these functionally appropriate developmental effects, seedlings produced after two previous drought-stressed generations had significantly greater survivorship in very dry soil than did seedlings with no history of drought. These findings show that plastic responses to naturalistic resource stresses experienced by grandparents and parents can "preadapt" offspring for functioning under the same stresses in ways that measurably influence realized fitness. Possible implications of these environmentally-induced, inherited adaptations are discussed with respect to ecological distribution, persistence under novel stresses, and evolution in natural populations.
Bibliographical noteFunding Information:
The study was designed by S.E.S., carried out by T.H.-K., C. R., and J. H., and analyzed by T. H.-K. and J. H. The authors thank Lauren Nichols, Caleb Corliss, Nora Vogel, and Sophie Ackoff for experimental assistance, and Manolis Kaparakis of the Wesleyan Quantitative Analysis Center for statistical consultation. The authors are especially grateful to Dr. Silvia Matesanz for valuable discussion. The manuscript was written jointly by J.H. and S.E.S. We thank the symposium organizers, M. Wund, A. Moczek, I. Dworkin, F. J. Nijhout, and C. Ledon-Rettig, and acknowledge symposium support from the US National Science Foundation (IOS# 1153657) and the Society for Integrative and Comparative Biology.
Research funding was provided by Wesleyan University and Howard Hughes Medical Institute.