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

Abstract

The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, VA(W). Mean absolute fitness, trueW¯, is predicted to change at the rate VA(W)normalW¯, 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 normalW¯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 (normalW0.28em¯< 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 trueW¯, our study presents an experimental approach for studies of adaptive capacity in the wild.

Estimating the capacity of Chamaecrista fasciculata for adaptation to change in precipitation

“…2018; Kulbaba et al. 2019). The analysis in aster, like those in all generalized linear mixed models (glmm), proceeds on a transformed scale.…”

“…Pedigreed seed was produced following Kulbaba et al. (2019) from seed collected by Dr. V. Eckard in 2013 from the Conard Environmental Research Area in Kellogg, Iowa (41°40′44.2″N 92°51′24.9″W). We used a single population of C. fasciculata to keep the space and time requirements for pedigree generation feasible.…”

“…To obtain estimates of V A ( W ), from parental variance, on the original measurement scale, we applied a nonlinear back transformation of the values using fitness values from the plot that had the median fitness value among the five plots in that treatment (as in Kulbaba et al. 2019). We obtained estimates of for each treatment using fixed effect aster models.…”

“…We calculated Pearson's product‐moment correlation coefficient ( r ) as an indicator of the similarity between breeding values between treatments (Kulbaba et al. 2019), acknowledging that it only approximates the association between breeding values because it does not account for the uncertainty in their estimates.…”

“…(2018) and Kulbaba et al. (2019) directly estimated V A ( W ) and to quantify the rate of adaptation in multiple natural populations, and over multiple years, of C. fasciculata . Both studies found significant levels of V A ( W ) indicating capacity for ongoing adaptation of each population to its home environment.…”