Browsing by Subject "gene flow"

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    Phylogeography and landscape genetics of tigers (Panthera tigris) and elephants (Elephas maximus) in Thailand
    (2016-11) Klinsawat, Worata
    Habitat fragmentation and poaching have resulted in population declines in large mammals including tigers (Panthera tigris) and Asian elephants (Elephas maximus) throughout the Indochina biogeographic region in Southeast Asia. Tracking changes in demographic and genetic parameters of elusive, wide-ranging species remain a serious challenge. This dissertation applies noninvasive genetic sampling and phylogeographic and landscape genetic analyses to assess spatial genetic patterns and demography in the Indochinese tiger (P. t. corbetti) and elephants in Thailand’s Tenasserim Range. In Chapter 1, I describe changes in distribution and numbers of tiger and elephant populations in Thailand from 1987-2015. I found that tigers lost a greater percentage of their former habitat than elephants as a result of higher poaching intensity and their naturally low density. At both evolutionary and contemporary timescales, I combined mtDNA and microsatellite data to assess spatial genetic connectivity and demographic history of the Indochinese tiger (P. t. corbetti) in Chapter 2 and elephants in Chapter 3. Phylogeographic analyses based on mtDNA indicated that Amur tigers (P. t. altaica) are recently derived from Indochinese tigers, which is re-classified as a paraphyletic group by the placement of the newly discovered haplotype. Results support the hypothesis of northbound dispersal from Indochina to northeast Asia after the Last Glacial Maximum (LGM) 20 thousand years ago. Compared to the recent radiation in tigers, elephants have two deeply divergent mtDNA clades, which are highly admixed within the Tenasserim landscape. Results support the hypothesis that this landscape was the secondary contact zone during the postglacial period. High mtDNA and microsatellite diversity of tigers and elephants in Indochina, compared to other regions. is due to maintenance of their large and stable long-term effective population sizes. However, as a consequence of fragmentation and genetic drift in a recent timeframe, I estimated low gene flow and detected genetic differentiation into three clusters in tigers within Indochina and at least two clusters in elephants within the Tenasserim Range. My results highlight advantages of integrating genetic with ecological data to quantify impacts of modified landscapes on population dynamics and to devise appropriate management strategies for the species recovery.
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    The spatial scale of adaptation in common ragweed (Ambrosia artemisiifolia)
    (2019-09) Gorton, Amanda
    Environmental variation at both large and small spatial scales can influence the ecological and evolutionary trajectory of plant populations. Decades of common garden and reciprocal transplant experiments have demonstrated that local adaptation is widespread. However, most experiments examining local adaptation compare populations at a single spatial scale. For my dissertation, I combined field experiments and population genetics to examine how environmental variation at three spatial scales—small (i.e., among populations), regional (i.e., urban vs. rural), and continental (i.e., across latitudes)—shapes local adaptation in common ragweed (Ambrosia artemisiifolia L.). I found evidence for adaptation to urban environments and latitudinal gradients in climate. More specifically, I found evidence that phenotypic divergence at small spatial scales (e.g. within a city) can be greater than divergence found at larger spatial scales. Across latitudes, I found that photoperiod influences the fitness of common ragweed populations, and the relevant spatial scale for adaptation varies across life history stages. In addition, for northern populations of ragweed, I found that climate change is already causing maladaptation. Lastly, my population genomic work with RNA-seq identified new traits of interest that may be involved in local adaptation, including stomatal opening and closing and seed dormancy. I discuss these results with regard to how they can help us understand local adaptation more broadly and in turn predict how plants may respond to climate change.
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    Supporting data for "Direct tracking of pollen with quantum dots reveals surprising uniformity in dispersal distance across eleven populations of an annual plant"
    (2023-06-01) Kern, Brooke R; Carley, Lauren N; Moeller, David A; kern0193@umn.edu; Kern, Brooke R
    Pollen movement is a crucial component of dispersal in seed plants. We used quantum dot pollen labeling, a new technique that overcomes past limitations, to evaluate the spatial scale of pollen dispersal and its relationship with conspecific density within eleven populations of Clarkia xantiana ssp. xantiana, a bee pollinated, annual plant. We used experimental arrays in two years to track pollen movement across distances of 5 – 35 m within nine populations and across distances of 10 – 70 m within two additional populations. We tested for distance decay of pollen dispersal and whether conspecific density modulated dispersal distance. We also asked whether dispersal kernels varied among populations across an environmentally complex landscape. We did not observe a decline in labeled pollen receipt with distance over 35 m within eight of nine populations or over 70 m within either of two populations. Pollen receipt increased with conspecific density. Overall, dispersal kernels were consistent across populations.