Graduate Defense: Paige Ellestad

Dissertation Information

Title: Anything: Uncovering the Hidden Diversity and Genomic Origin of the Threatened Vanilla Spice

Program: Doctor of Philosophy in Ecology, Evolution, and Behavior

Advisor: Dr. Sven Buerki, Curriculum, Instruction, and Foundational Studies

Committee Members: Dr. Stephen Novak, Biological Sciences; Dr. Marcelo Serpe, Biological Sciences; and Dr. Felix Forest, Biological Sciences

Abstract

Conserving the genetic diversity of crop species and their wild relatives has become a mounting concern as the detrimental effects of climate change, habitat destruction, and genetic erosion are being realized. In this epoch of unprecedented biodiversity loss, the genetic resources needed to improve crops may be at risk of extinction. Even one of the most iconic spices, vanilla, is threatened. Although it is so well-known, there is an unexpected lack of knowledge on its natural history and the ecological and evolutionary processes that have shaped its genetic resources. Overall, this hinders its effective preservation. To mitigate this gap of knowledge and help ensure the sustainability of this globally important spice, this thesis aimed to unravel the domestication of the main vanilla-producing species, Vanilla planifolia, in its cultivated center of origin, Mexico, by answering the fundamental questions: What is the native distribution of V. planifolia? What are its closest crop-wild relatives? How many vanilla species are cultivated in its center of origin? What domestication processes have shaped its genetic resources? and What is the genomic origin of cultivated vanilla? Results indicate that V. planifolia occurs within a larger distribution than previously expected, from Mexico to northern Brazil, along with ten closely related crop-wild relatives. In addition to the predominantly cultivated V. planifolia, two other crop-wild relatives, V. pompona and V. insignis, were found to be cultivated in Mexico. Genetic variability and high levels of genome-wide heterozygosity found within V. planifolia revealed the occurrence of multiple domestication events and past hybridization within cultivated vanilla. Signatures of introgressive hybridization between V. planifolia and V. pompona were discovered in a global V. planifolia cultivar, however, a parental origin for many Mexican cultivated accessions has yet to be identified. Considering the high levels of crop-wild relative diversity and the long history of cultivation by different cultural groups in Mexico, these results might provide evidence for regionally cultivated landraces, which may provide important sources of genetic diversity to potentially increase crop resilience in the face of climate change. Findings from this project provide a clearer illustration of vanilla’s genetic resources and support the urgent prioritization of biodiversity within this important region through the conservation of V. planifolia’s crop-wild relatives and landraces. These recommendations will help to benefit the livelihoods of farmers, encourage the protection of cultural diversity in Mexico, and ultimately help to ensure the sustainability of this iconic spice.