Ecological and Evolutionary Consequences of Habitat Tracking through Germination Phenology
Environmentally cued development is widespread across the natural world. Many organisms rely on abiotic and biotic cues to undergo developmental transitions like budburst, flowering, and mating at the appropriate times of year. The study of the timing of these transitions is known as phenology. Because the timing of development determines the environment experienced by the next life history stage, it has the potential to affect evolutionary processes that occur after development. Further, because the timing of development can filter the environment experienced by the next life history stage, it can be considered a form of “habitat tracking.” In this dissertation, I use manipulative laboratory and field experiments to quantify how germination phenology can alter the postgermination environment, show that the postgermination environment can itself be genetically determined, show that germination phenology is a form of habitat tracking, and test how germination phenology can affect trait expression, natural selection, and fitness.
In my first chapter, using the ecological and genetic model species Arabidopsis thaliana, I showed that when the timing of development is genetically controlled, and the timing of development affects the environment experienced by the next developmental stage, then the environment experienced after development can itself be inherited and can evolve. Further, I demonstrated that germination phenology is a form of “habitat tracking”, by enabling seeds to establish seedlings in a subset of the full environmental conditions available. In my second chapter, using ecologically diverse A. thaliana genotypes, I show that the timing of germination can affect natural selection on postgermination traits, and that postgermination traits can affect selection on germination phenology. In my third chapter, using two plants native to North Carolina, Phacelia purshii and P. fimbriata, I show that populations can vary naturally in their propensity to germinate in response to different environmental cues, that populations preferentially germinate in habitats that are beneficial for seedlings, and when placed in new geographic locations, populations may use phenology to track novel but beneficial environmental conditions.
My dissertation placed the common process of cued development into the well- established theoretical framework of habitat tracking and habitat selection. By doing so, I was able to generate and test novel predictions about potential consequences of phenological cueing that have not yet been explored—namely, that the post- development environment itself can be inherited, that the magnitude and frequency of natural selection can vary with changes in habitat tracking, that habitat tracking itself may evolve in response to traits expressed and environments experienced after development, and that habitat tracking through phenology may be an important mechanism that organisms can use to cope with climate change.
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