Browsing by Subject "selfing syndrome"

Nectar production is one of several traits that are reduced in flowering plants that display the selfing syndrome, a suite of trait reductions often associated with the transition from outcross-fertilization to self-fertilization. However, the evolutionary mechanisms that contribute to reduced nectar has not been explored. In this dissertation, I use a pair of sister morning glories, Ipomoea lacunosa, a highly selfing species that displays the selfing syndrome, and I. cordatotriloba, a mixed mating species, to address the question: how did reduced nectar evolve in the selfing syndrome? Through a combination of approaches from quantitative genetics, population genomics, and transcriptomics, I describe the genetic architecture of nectar production and attempt to identify candidate genes that could lead to reduced nectar production – nectar volume and nectar sugar concentration – in I. lacunosa. QTL analyses indicate that nectar traits are polygenic and evolved independently from floral size traits, likely due to direct selection. Transcriptomic analyses reveal several sets of genes that are unique to each nectar trait, but both nectar volume and nectar sugar concentration also share some genes in common. Finally, through incorporating population genomic analyses, a short list of candidate genes was obtained that may explain how reduced nectar evolved in I. lacunosa and how nectar traits remain diverged between the two morning glory species even in regions of sympatry.

Accurate species descriptions are critical for understanding evolutionary relationships. Ipomoea “austinii” was proposed to be a new species found in the US, but conflicting evidence suggested that it was instead I. grandifolia. By examining cross-compatibility between these individuals and through genetic analyses, I find no cross-incompatibility and no genetic differentiation between I. “austinii” and I. grandifolia, thus suggesting that I. “austinii” should be reclassified as I. grandifolia.

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.