The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, VA(W). Mean absolute fitness, (Formula presented.), is predicted to change at the rate (Formula presented.), according to Fisher's Fundamental Theorem of Natural Selection. Despite ample research evaluating degree of local adaptation, direct assessment of VA(W) and the capacity for ongoing adaptation is exceedingly rare. We estimated VA(W) and (Formula presented.) in three pedigreed populations of annual Chamaecrista fasciculata, over three years in the wild. Contrasting with common expectations, we found significant VA(W) in all populations and years, predicting increased mean fitness in subsequent generations (0.83 to 6.12 seeds per individual). Further, we detected two cases predicting “evolutionary rescue,” where selection on standing VA(W) was expected to increase fitness of declining populations ((Formula presented.) < 1.0) to levels consistent with population sustainability and growth. Within populations, inter-annual differences in genetic expression of fitness were striking. Significant genotype-by-year interactions reflected modest correlations between breeding values across years, indicating temporally variable selection at the genotypic level that could contribute to maintaining VA(W). By directly estimating VA(W) and total lifetime (Formula presented.), our study presents an experimental approach for studies of adaptive capacity in the wild.
Bibliographical noteFunding Information:
RGS designed the study with substantial input from SNS. All authors participated in planting and data collection, MWK performed the main analyses with contributions from SNS and RGS, MWK and RGS led the manuscript writing with input from remaining authors. The authors thank land managers: Larissa Mottl, Don Ramsden, Karen Schik, and Elizabeth Hill for site preparation. Amber Nashoba, Sam Weaver, Carlee Steppe, Becca Tucker, Bailey Choudhury, Linley Davidson, William Peterson, Sarah Jordan, Lauren Sawich, Greg Margida, Sam Sokolosky, Aidan Healey, Christine Solomon, Tim Burnette, Ana Pulak, and members of the Grinnell College BIO 305 (Evolution of the Iowa Flora) and BIO 368 (Ecology) classes supplied critical greenhouse and field assistance. The authors are grateful to Charles Geyer and Frank Shaw for guidance with aster modeling. This work was funded by a National Science Foundation grant (DEB 1257462) to RGS. USDA National Institute of Food and Agriculture Hatch project 1016272 supported SNS during the writing stages of this work. All data and R scripts are available at https://github.com/mason-kulbaba/adaptive-capacity.git
- Adaptive capacity
- Chamaecrista fasciculata
- Fisher's Fundamental Theorem of Natural Selection
- aster models
- genotype-by-environment interactions