Evolutionary Genetics of Reduced Nectar Production in the Selfing Morning Glory, Ipomoea lacunosa (Convolvulaceae)

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.