Climate change in a Minnesota prairie: Fitness and adaptation in a population of partridge pea

Background/Question/Methods

The capacity of a population to adapt to a changing environment is dependent on its additive genetic variance for fitness: V_A(W). Since R.A. Fisher described his Fundamental Theorem of Natural Selection (FTNS) it has been theorized that V_A(W) is likely to be negligible or even zero. If this value were minuscule, the likelihood of ongoing adaptation based on standing genetic variation would be low. To evaluate the capacity for ongoing adaptation I have applied the FTNS. Using a pedigreed population of an annual legume, Chamaecrista fasciculata, I established a common garden within a restored prairie and recorded complete lifetime fitness. I grew cohorts in 2013 and 2014 to account for the effect of year-to-year environmental variation. I have addressed statistical challenges posed by the compound nature of the fitness distribution by using Aster models for life history analysis. Calculations of additive genetic variance are made possible through the recently developed random effects capability of Aster models.

Results/Conclusions

Additive genetic variance for fitness was found to be substantial and highly statistically significant, supporting a prediction that mean fitness would increase by six seeds per individual due to natural selection. This result of significant genetic variation is particularly remarkable for two main reasons: first, it rebuts the theory that this variation is minimal and second, under any non-zero value fitness is expected to increase.