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<p>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.</p><p> </p><p>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. </p><p>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.</p>
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