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Despite the importance of adaptation in shaping biological diversity over many generations, little is known about populations' capacities to adapt at any particular time. Theory predicts that a population's rate of ongoing adaptation is the ratio of its additive genetic variance for fitness, VA(W), to its mean absolute fitness, W¯. We conducted a transplant study to quantify W¯ and standing VA(W) for a population of the annual legume Chamaecrista fasciculata in one field site from which we initially sampled it and another site where it does not currently occur naturally. We also examined genotype‐by‐environment interactions, G × E, as well as its components, differences between sites in VA(W) and in rank of breeding values for fitness. The mean fitness indicated population persistence in both sites, and there was substantial VA(W) for ongoing adaptation at both sites. Statistically significant G × E indicated that the adaptive process would differ between sites. We found a positive correlation between fitness of genotypes in the "home" and "away" environments, and G × E was more pronounced as the life‐cycle proceeds. This study exemplifies an approach to assessing whether there is sufficient VA(W) to support evolutionary rescue in populations that are declining. [ABSTRACT FROM AUTHOR]

Genetic incompatibilities and low offspring fitness are characteristic outcomes of hybridization between species. Yet, the creative potential of recombination following hybridization continues to be debated. Here we quantify the outcome of hybridization and recombination between adaptively divergent populations of the North American legume Chamaecrista fasciculata in a large-scale field experiment. Previously, hybrids between these populations demonstrated hybrid breakdown, suggesting the expression of adaptive epistatic interactions underlying population genetic differentiation. However, the outcome of hybridization ultimately rests on the performance of even later generation recombinants. In experiments that compared the performance of recombinant F6 and F2 generations with nonrecombinant F1 and parental genotypes, we observed that increasing recombination had contrasting effects on different life-history components. Lifetime fitness, defined as the product of survivorship and reproduction, showed a strong recovery of fitness in the F6. The overall gain in fitness with increased recombination suggests that hybridization and recombination may provide the necessary genetic variation for adaptive evolution within species. We discuss the mechanisms that may account for the gain in fitness with recombination, and explore the implications for hybrid speciation and phenotypic evolution. [ABSTRACT FROM AUTHOR]

Cost-benefit models of the evolution of mutualism predict that the current state of mutualism results from trade-offs between fitness costs of mutualist traits and the fitness benefits of association. We test the assumptions of such models by measuring patterns of natural selection on a mutualist trait, extrafloral nectar production in Chamaecrista fasciculata. Selection was measured on plants from which ants had been excluded (removing the mutualist benefit of the trait), from which all insects had been excluded (removing costs of herbivory in addition to mutualist benefits), and unmanipulated plants (where both costs and benefits were present). Selection analysis based on half-sibling-mean regressions of fitness on the trait revealed no evidence of costs of extrafloral nectar production in the absence of all insects or in the absence of ants. However, examination of the selective surfaces for these treatments suggest that costs of nectar production may exist and are exacerbated by the presence of herbivory. In the presence of ants, natural selection favors high extrafloral nectar production, consistent with a fitness benefit to this mutualist trait in the presence of the mutualist partner. In this study, the interaction of costs and benefits did not produce an evolutionary optimum for the trait within the range of variation observed, suggesting that application of a cost-benefit framework to this trait will benefit from considering the influence of temporal and spatial variation on the quality of costs and benefits. [ABSTRACT FROM AUTHOR]

Presents a study which quantified gene flow from spatial genetic structure data in a metapopulation of Chamaecrista fasciculata. Materials and methods; Results; Discussion.

Provides information on a study which evaluated the genetic architecture of trait differentiation between two ecologically distinct populations of Chamaecrista fasciculata, a legume specie. Materials and methods; Phenotypic differentiation between populations; Cytoplasmic differentiation between populations; Nuclear genetic differentiation between populations.

Focuses on a study which evaluated adaptive differentiation between populations of the annual legume Chamaecrista fasciculata. Materials and methods; Results; Discussion.

Focuses on a study which presented a quantitative genetic design to quantify the contribution of epistasis to population divergence for fitness components of a native annual legume, Chamaecrista fasciculata. Materials and methods; Results; Discussion.

Presents information on a study which evaluated the effects of nuclear genes, cytoplasmic genes, and their interactions on local adaptation using geographically isolated Chamaecrista fasciculata. Discussion on the co-adaptation between cytoplasmic and nuclear genes; Methodology of the study; Results and discussion.