Additive genetic variance for lifetime fitness and the capacity for adaptation in an annual plant

The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, V-A(W). Mean absolute fitness, W over bar , is predicted to change at the rate VA(W)W over bar , according to Fisher's Fundamental Theorem of Natural Selection. Despite ample research evaluating degree of local adaptation, direct assessment of V-A(W) and the capacity for ongoing adaptation is exceedingly rare. We estimated V-A(W) and W over bar in three pedigreed populations of annual Chamaecrista fasciculata, over three years in the wild. Contrasting with common expectations, we found significant V-A(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 V-A(W) was expected to increase fitness of declining populations (W over bar < 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 V-A(W). By directly estimating V-A(W) and total lifetime W over bar , our study presents an experimental approach for studies of adaptive capacity in the wild.