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The timing of a developmental transition (phenology) can influence the environment experienced by subsequent life stages. When phenology causes an organism to occupy a particular habitat as a consequence of the developmental cues used, it can act as a form of habitat tracking. Evolutionary theory predicts that habitat tracking can alter the strength, direction, and mode of natural selection on subsequently expressed traits.

To test whether germination phenology altered natural selection on postgermination traits, we manipulated germination time by planting seedlings in seven germination cohorts spanning 2 yr. We measured selection on postgermination traits relating to drought, freezing, and heat tolerance using a diverse combination ofArabidopsis thalianamutants and naturally occurring ecotypes.

Germination cohorts experienced variable selection: when dry, cold, and hot environments were experienced by seedlings, selection was intensified for drought, freezing, and heat tolerance, respectively. Reciprocally, postgermination traits modified the optimal germination time; genotypes had maximum fitness after germinating in environments that matched their physiological tolerances.

Our results support the theoretical predictions of feedbacks between habitat tracking and traits expressed after habitat selection. In natural populations, whether phenological shifts alter selection on subsequently expressed traits will depend on the effectiveness of habitat tracking through phenology.

 

Abstract Evolvable traits of organisms can alter the environment those organisms experience. While it is well appreciated that those modified environments can influence natural selection to which organisms are exposed, they can also influence the expression of genetic variances and covariances of traits under selection. When genetic variance and covariance change in response to changes in the evolving, modified environment, rates and outcomes of evolution also change. Here we discuss the basic mechanisms whereby organisms modify their environments, review how those modified environments have been shown to alter genetic variance and covariance, and discuss potential evolutionary consequences of such dynamics. With these dynamics, responses to selection can be more rapid and sustained, leading to more extreme phenotypes, or they can be slower and truncated, leading to more conserved phenotypes. Patterns of correlated selection can also change, leading to greater or less evolutionary independence of traits, or even causing convergence or divergence of traits, even when selection on them is consistent across environments. Developing evolutionary models that incorporate changes in genetic variances and covariances when environments themselves evolve requires developing methods to predict how genetic parameters respond to environments—frequently multifactorial environments. It also requires a population-level analysis of how traits of collections of individuals modify environments for themselves and/or others in a population, possibly in spatially explicit ways. Despite the challenges of elucidating the mechanisms and nuances of these processes, even qualitative predictions of how environment-modifying traits alter evolutionary potential are likely to improve projections of evolutionary outcomes.