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<p>The evolution of selfing from outcrossing is one of the most frequent mating system
transitions in angiosperms. Plants that are highly selfing typically exhibit a suite
of morphological traits termed a "selfing syndrome," including reduced corollas and
reproductive structures, loss of corolla pigmentation, little anther-stigma separation,
and a low pollen/ovule ratio. The overall consensus among scientist is that the morphological
changes that accompany the transition to selfing are adaptive and thus a product of
natural selection. Few attempts, however, have been made to determine whether traits
of the selfing syndrome are truly an operation of natural selection or if genetic
drift could be the acting force. My dissertation examines the roles that natural selection
and genetic drift played in the evolution of the selfing syndrome in Ipomoea lacunosa.
With the use of field observations, crossing data, and molecular analyses, I show
that I. lacunosa has evolved increased selfing ability, decreased anther-stigma distance
and smaller, white flowers, compared to its closest relative I. cordatotriloba. Furthermore,
using a standard QST - FST comparison, I evaluated the relative importance of selection
and drift in the evolution of the selfing syndrome in I. lacunosa. I also identified
the genetic basis of flower color divergence between I. lacunosa (white) and I. cordatotriloba
(purple) and examined patterns of variation to determine if selection or genetic drift
caused the divergence. Analyses revealed that the traits of I. lacunosa characteristic
of the selfing syndrome have evolved as a product of natural selection, not genetic
drift.</p>
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