Year of Award

2019

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

Lila Fishman

Commitee Members

Zachary Cheviron, Scott Miller

Keywords

Adaptation, Mimulus guttatus, Population genetics, Mating-system evolution, microgeographic adaptation

Subject Categories

Ecology and Evolutionary Biology

Abstract

Local adaptation across habitat mosaics can generate phenotypic divergence in the face of gene flow; however, adaptive divergence in reproductive traits may also create barriers to genetic exchange within and among distinct habitats. In plants, life-history, phenology, and mating system traits may lead to divergent selection over short (microgeographic) spatial scales. Changes to these traits are likely to directly affect patterns of gene flow and genomic diversity. In this study, we combined field, common garden, and population genomic approaches to investigate phenotypic and genetic variation in Mimulus guttatus (yellow monkeyflowers) adapted to a complex geothermal soil mosaic in Yellowstone National Park (YNP). A previously-identified major locus underlying life-history divergence (out6) strongly sorts by habitat (thermal annual habitats [AH] vs. non-thermal perennial habitats [PH]) across YNP. Plants from AH and PH were also differentiated for self-pollination potential and flowering time traits in the common garden, consistent with adaptation to spring-flowering in thermal habitats. Genome-wide sequence data (ddRADSeq) reveals one highly differentiated (and ecologically extreme) AH population (AHQT), while the other AH and PH plants form four geographic populations. F’ST between the geographic regions varied but remained relatively high (~0.10) across all comparisons. F’ST between AH-AH sub-populations pairs were marginally more differentiated than PH-PH pairs (F’ST = 0.13 vs. 0.10, respectively). Slightly elevated differentiation of thermal annual populations mirrors the isolation of AHQT from all other populations and suggests that increased selfing and phenological assortative mating in thermal habits generate structure through reduced gene flow and increased drift. Individual inbreeding coefficients (FIS) were positively associated with mean progeny stigma-anther distance and significantly elevated in thermal annual habitats. This is consistent with the inference that thermal habitats select for efficient self-pollination, with consequences for individual and population variation. Overall, multi-trait adaptation to geothermal soils occurs despite ongoing gene flow with nearby nonthermal populations, and parallel selective pressures in extreme thermal soils have reassembled similar adaptive phenotypes on distinct genetic backgrounds. To varying degrees, thermal annuals exhibit genomic signatures of elevated population differentiation that suggest they may be in the early stages of developing local reproductive isolation.

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© Copyright 2019 Kory M. Kolis