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Title:The winds of change: A study of post-glacial dispersal in pacific-northwest conifers
Author(s):Fernandez, Matias Cristobal
Director of Research:Hu, Feng Sheng
Doctoral Committee Chair(s):Heath, Katy D.
Doctoral Committee Member(s):Catchen, Julian M.; Malhi, Ripan
Department / Program:Plant Biology
Discipline:Plant Biology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Phylogeography, Migration, RAD-Seq, Western redcedar, Mountain hemlock
Abstract:Anthropogenic climate change has caused shifts in the abundances and geographic distributions of many organisms. Given the estimated rates of climate change in the coming decades, many plant species may be unable to migrate or adapt in time, thereby increasing their risk of extinction. The history of vegetation dynamics in response to past climatic events has important implications for understanding and predicting the biotic impacts of future climate change on organisms. Evidence is accumulating that small, isolated populations of trees have persisted in locally suitable habitats through dramatic climatic fluctuations during the last glaciation and the present interglacial period. Such "climate refugia" allow pockets of diversity to persist within a regional climate that is otherwise inhospitable for those species. It is important to understand climate refugia, as they are potential targets for conservation. Equally important, assessing how fast plants may migrate in response to climate change requires knowledge of past refugia and post-glacial migration patterns, especially in the case of long-lived tree species whose migration cannot be easily observed within a few decades to even centuries. Such data influence the design and predictive power of models used to project future change. This dissertation seeks to provide insight into the whereabouts of two key species of the PNW mesic forests during the last glaciation, their responses to past climate warming, and the role of heterogeneous mountainous landscapes in the persistence of refugia. The first principal chapter (Chapter 2) aims to address the methodology of inferring post-glacial species histories. Discerning ancient patterns in the abundance and distribution of vegetation requires an interdisciplinary approach. To infer the post-glacial vegetation and climate of putative refugia, we need paleoecological data from strategically selected sites. To infer past demographic events related to glacial refugia and post-glacial migration pathways, population genomic analysis is emerging as an important novel tool. Paleorecords are key to understanding range shifts in response to climatic fluctuations, but are prone to false-negatives when detecting small populations in climate refugia. Genetic data can improve inferences by providing evidence of population structure. Using the two disciplines in conjunction therefore provides a clearer understanding of post-glacial vegetation dynamics. The second principal chapter (Chapter 3) aims to determine the demographic history of two key species of the PNW mesic forests during the last glaciation, their responses to past climate warming, and the role of heterogeneous mountainous landscapes in the persistence of refugia. In the Pacific Northwest (PNW), mesic forest communities have two disjunct distributions: a coastal range and an interior range, separated from each other by a 160+ km barrier of dry rainshadow climate. Previous studies reveal conflicting information on the population dynamics leading to this disjunction. At coarse spatial scales, paleoecological records and paleoclimate simulations show that the interior range was uninhabitable by mesic species during the last glaciation and that mesic forests may have only recently arrived there during the late Holocene. This implies dispersal inland from the more accommodating southern coastal habitats as post-glacial conditions ameliorated. In contrast, the existence of many endemic species in the interior and deep genetic divergences among disjunct populations of several species strongly suggest the presence of a mesic glacial refugium within the interior range in northern Idaho. I examined the genetic variation of two mesic conifer species, western redcedar (Thuja plicata) and mountain hemlock (Tsuga mertensiana), across the PNW using the new RAD-Seq Genotyping-by-Sequencing method and combined the results with new paleoecological data from the same region to reconstruct the past population dynamics that resulted in their current distribution. The third principal chapter (Chapter 4) aims to investigate the possibility that the act of migrating may cause rapid adaptive changes that further enable a species response to climate shifts. Tree species must adapt or migrate in response to anthropogenic climate change, but there are concerns that some species may not be able to keep pace and risk extinction. There is a significant discrepancy between migration rates inferred from paleorecords and those observed in species tracking the modern climate. Recent studies have emphasized the potential for disjunct refugial populations to help explain this gap, but adaptation during migration may have also played a role. As the leading edge of a range shift expands, traits such as seed weight and wing size can undergo "spatial selection" where trees with better migration potential are more likely to populate the leading edge and seed the continued advance. Selection favoring the first to arrive and populate new terrain may have the effect of progressively concentrating adaptive alleles as migration continues. As a consequence, this may increase the rate of migration as better colonization ability is selected. We combined western redcedar sequencing results with common-garden seed phenotype measurements to analyze patterns of selection over the course of post-glacial migration.
Issue Date:2018-04-13
Rights Information:© 2018 Matias C. Fernandez
Date Available in IDEALS:2018-09-04
Date Deposited:2018-05

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