Quantitative genetic study of the adaptive process

Abstract

The additive genetic variance with respect to absolute fitness, V A (W), divided by mean absolute fitness, W, sets the rate of ongoing adaptation. Fisher's key insight yielding this quantitative prediction of adaptive evolution, known as the Fundamental Theorem of Natural Selection, is well appreciated by evolutionists. Nevertheless, extremely scant information about V A (W) is available for natural populations. Consequently, the capacity for fitness increase via natural selection is unknown. Particularly in the current context of rapid environmental change, which is likely to reduce fitness directly and, consequently, the size and persistence of populations, the urgency of advancing understanding of immediate adaptive capacity is extreme. We here explore reasons for the dearth of empirical information about V A (W), despite its theoretical renown and critical evolutionary role. Of these reasons, we suggest that expectations that V A (W) is negligible, in general, together with severe statistical challenges of estimating it, may largely account for the limited empirical emphasis on it. To develop insight into the dynamics of V A (W) in a changing environment, we have conducted individual-based genetically explicit simulations. We show that, as optimizing selection on a trait changes steadily over generations, V A (W) can grow considerably, supporting more rapid adaptation than would the V A (W) of the base population. We call for direct evaluation of V A (W) and W in support of prediction of rates adaptive evolution, and we advocate for the use of aster modeling as a rigorous basis for achieving this goal.

Microgeographic Patterns of Genetic Divergence and Adaptation across Environmental Gradients in Boechera stricta (Brassicaceae)

“…These results are compatible with migration-selection balance as an important cause of genetic variation within populations. Our field experiments show genetic variation in lifetime fitness and susceptibility to insect herbivory, suggesting that populations could evolve higher levels of fitness through ongoing natural selection in contemporary landscapes (Shaw and Shaw 2014). …”

“…Finally, genetic variation in fitness suggests that these regional pools of populations have the capacity to evolve higher fitness in contemporary environments, but changing conditions could alter this evolutionary potential. Not only do we need more estimates of genetic variation in components of fitness in nature (Shaw and Shaw 2014), but we need additional estimates in treatments that mimic future conditions to test the potential of global change to disrupt adaptive evolution.…”

The nature of nurture in a wild mammal's fitness

“…The loss of standing genetic variation through natural selection is particularly strong for fitness itself because selection on fitness is consistent and perfect. Levels of genetic variation in fitness are, therefore, expected to be very low [3,4], which could constrain the adaptive evolution of all traits in a population [5] unless some additional source of adaptive potential is available. Given the importance of genetic variance in fitness to evolution there have been surprisingly few estimates of its magnitude in nature [5,6], despite hundreds of measures of genetic variation in life-history traits in the wild [7].…”

“…Levels of genetic variation in fitness are, therefore, expected to be very low [3,4], which could constrain the adaptive evolution of all traits in a population [5] unless some additional source of adaptive potential is available. Given the importance of genetic variance in fitness to evolution there have been surprisingly few estimates of its magnitude in nature [5,6], despite hundreds of measures of genetic variation in life-history traits in the wild [7]. Furthermore, all previous measures of genetic variation in fitness considered only the effects of an individual's genotype on its own fitness, whereas it is now widely recognized that an individual's fitness can also be affected by the genotype of other individuals with whom it interacts socially [8,9].…”

“…As a result, many studies have now quantified MGEs on a wide variety of traits, including life-history traits, in many domesticated [19], laboratory [20] and wild animals brought into captivity [18,21], as well as in some free-living plants and animals [22 -25]. While quantitative genetic studies of specific traits are valuable for assessing their evolvability, genetic variation in fitness itself represents a fundamental measure of the adaptive potential of all traits within a population [5]. Since measures of fitness are applicable only to the environment in which they are measured, measures of genetic variation in the fitness of wild organisms require multigenerational studies of wild organisms in nature.…”