Beyond the Gradient: Experimental Manipulations to Explore Causes of Natural Selection

Summary

As the architects (Lande and Arnold) of selection gradient analysis recognized, verifying the ecological causes of selection rests upon experimentation. My group has probed multiple causes of selection on plant phenology by manipulating environment and/or phenotype.

The optimal timing of transition out of dormancy to vegetative growth, and from growth to reproduction, depends on the plant’s internal, general, and social environments. In seasonal environments, optimal age at flowering is mediated by an internal trade-off between time allocated to growth and time allocated to reproduction. Resurrection experiments showed rapid evolution of this trade-off over 7 generations, when drought shortened growing seasons. Seasonal shifts pollinators and herbivore abundance can exert additional selection on flowering phenology. A phenotypic manipulation experiment that broke the inherent genotype-environment correlation between age at flowering (internal environment) and flowering date (general environment) showed that flowering during the “best week” of the season increases fitness over and above that caused by internal tradeoff. Finally, a phenotypic manipulation of plant germination time demonstrated how the social (competitive) environment can generate strong, frequency-dependent selection for early emergence.

Related publications

1.    Austen, E. J., & Weis, A. E. 2015. What drives selection on flowering time? An experimental manipulation of the inherent correlation between genotype and environment. Evolution, 69:2018-2033.

2.    Peters, M. A., & Weis, A. E. 2019. Isolation by phenology synergizes isolation by distance across a continuous landscape. New Phytologist, 224:215-1228.

3.    Franks, S. J., Sim, S., & Weis, A. E. 2007. Rapid evolution of flowering time by an annual plant in response to a climate fluctuation. Proceedings of the National Academy of Sciences, 104:1278-1282.