Burg, Theresa

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Browsing Burg, Theresa by Author "Graham, Brendan A."

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    Cryptic genetic diversity and cytonuclear discordance characterize contact among Canada Jay (Perisoreus canadensis) morphotypes in western North America
    (Oxford Academic, 2021) Graham, Brendan A.; Cicero, Carla; Strickland, Dan; Woods, John G.; Coneybeare, Howard; Dohms, Kimberly M.; Szabo, Ildiko; Burg, Theresa M.
    Three distinct Canada jay (Perisoreus canadensis) morphotypes with easily recognizable plumage traits come into contact in western North America. Recent work demonstrated high genetic structure across the species’ range; however, patterns of genetic variation in these contact zones remain unknown. We categorized 605 individuals into one of three morphotypes (Pacific, Rocky Mountain, and Boreal) based on plumage, and genotyped individuals at the mtDNA control region and 12 microsatellite loci to assess the extent of hybridization between morphotypes. Our data showed cryptic genetic diversity and high cytonuclear discordance among morphotypes within contact zones, which is likely the result of recent and historical admixture. The distributions of the Boreal and Pacific morphotypes each showed a strong association with a single, distinct genetic group, whereas the Rocky Mountain morphotype exhibited higher genetic diversity and was associated with multiple genotypes. Our analyses show the importance of considering both plumage and genetic traits when examining contact zones between closely related taxa. Finally the data presented in this study reaffirm that the Pacific morphotype is distinct from the Boreal and Rocky Mountain morphotypes based on genetic, phenotypic and ecological data, indicating that the Pacific morphotype should be re-elevated to a full species.
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    Do phylogeny and habitat influence admixture among four North American chickadee (family: Paridae) species?
    (Wiley-Blackwell, 2021) Graham, Brendan A.; Gazeley, Ian; Otter, Ken A.; Burg, Theresa M.
    Hybridization is an important aspect of speciation, yet questions remain about the ecological and environmental factors that influence hybridization among wild populations. We used microsatellite genotyping data and collected land cover and environmental data for four North American chickadee species: black-capped Poecile atricapillus, mountain P. gambeli, chestnut-backed P. rufescens and boreal P. hudsonicus chickadees. Combining these datasets, we sought to examine whether there is evidence of admixture between four widely distributed North American chickadee species; whether admixture takes place more often between more closely related species pairs or between species pairs with more similar ecological preferences; and whether certain habitat types have higher rates of admixture than others. We detected admixture for five of the six species pairs analyzed (chestnut-backed–mountain chickadee pair showed no evidence of admixture), and found rates of admixture varied geographically, and within taxa pairs. Admixture was higher among less closely related species than more closely related species, although habitat similarity was not a significant predictor. Finally, rates of admixture were higher in urban parkland habitats than deciduous, mixed or coniferous forest habitats. Our work indicates admixture occurs frequently among North American parids, and habitat and environmental variation may play an important role in the frequency and geographic distribution of hybridization.
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    Genetic-environment associations explain genetic differentiation and variation between western and eastern North Pacific Rhinoceros Auklet (Cerorhinca monocerata) breeding colonies
    (Wiley, 2024) Graham, Brendan A.; Hipfner, J. Mark; Wellband, Kyle W.; Ito, Motohiro; Burg, Theresa M.
    Animals are strongly connected to the environments they live in and may become adapted to local environments. Examining genetic-environment associations of key indicator species, like seabirds, provide greater insights into the forces that drive evolution in marine systems. Here we examined a RADseq dataset of 19,213 SNPs for 99 Rhinoceros Auklets (Cerorhinca monocerata) from five western Pacific and ten eastern Pacific breeding colonies. We used partial-redundancy analyses to identify candidate adaptive loci and to quantify the effects of environmental variation on population genetic structure. We identified 262 candidate adaptive loci, which accounted for 3.0% of the observed genetic variation among western Pacific and eastern Pacific breeding colonies. Genetic variation was more strongly associated with pH and maximum current velocity, than maximum sea surface temperature. Genetic-environment associations explain genetic differences between western and eastern Pacific populations, however, genetic variation within the western and eastern Pacific Ocean populations appears to follow a pattern of isolation-by-distance. This study represents a first to quantify the relationship between environmental and genetic variation for this widely distributed marine species and provides greater insights into the evolutionary forces that act on marine species.
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    The influence of latitude, geographic distance, and habitat discontinuities on genetic variation in a high latitude montane species
    (Nature Publishing Group, 2018) Hindley, John A.; Graham, Brendan A.; Pulgarin-R., P. C.; Burg, Theresa M.
    Examining the factors that influence contemporary genetic patterns is important given the alarming rate at which natural environments are changing. In particular habitat fragmentation and climate change are expected to influence the distribution and diversity of natural populations. In this study we used both mitochondrial control region (mtDNA) and microsatellite data to answer the following questions about genetic diversity and divergence in mountain chickadees (Poecile gambeli) a resident bird species in western North America: (1) Do populations exhibit similar levels of genetic diversity across the range? (2) What is the genetic affinity of western populations in Oregon and Washington? (3) Do genetic patterns exhibit isolation by distance, or are genetic patterns more heavily influenced by habitat discontinuity? We tested the effects of isolation by distance and habitat distribution on genetic structure by analyzing 266 samples from 17 sites across western Canada and the United States. We found a near significant relationship between genetic diversity and latitude, however, our results indicate that overall, latitude is not a strong predictor of genetic diversity. Our analyses of populations in Oregon and Washington revealed a mismatch between patterns detected with mtDNA and microsatellite data. In particular, Washington clustered with the Coast Range/Cascades/Rocky Mountain mtDNA group, but with populations in southern Oregon/California based on microsatellite data. These results suggest the presence of a contact zone in Washington between the two mtDNA clades Coast Range/Cascades/Rocky Mountain and southern Oregon/California clades. Finally, our study revealed a greater effect of isolation by distance than isolation by habitat for both mtDNA and microsatellite data. Overall the isolation by distance signal was greater for mtDNA than microsatellite patterns. The greater signal of isolation by distance on mtDNA patterns likely reflects the strong effects of Pleistocene glaciations in shaping genetic patterns in western North America.
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    Multilocus genetic analysis and spatial modeling reveal complex population structure and history in a widespread resident North America passerine (Perisoreus canadensis)
    (Wiley, 2017) Dohms, Kimberly M.; Graham, Brendan A.; Burg, Theresa M.
    An increasing body of studies of widely distributed, high latitude species shows a variety of refugial locations and population genetic patterns. We examined the effects of glaciations and dispersal barriers on the population genetic patterns of a widely distributed, high latitude, resident corvid, the gray jay (Perisoreus canadensis), using the highly variable mitochondrial DNA (mtDNA) control region and microsatellite markers combined with species distribution modeling. We sequenced 914 bp of mtDNA control region for 375 individuals from 37 populations and screened seven loci for 402 individuals from 27 populations across the gray jay range. We used species distribution modeling and a range of phylogeographic analyses (haplotype diversity, ΦST, SAMOVA, FST, Bayesian clustering analyses) to examine evolutionary history and population genetic structure. MtDNA and microsatellite markers revealed significant genetic differentiation among populations with high concordance between markers. Paleodistribution models supported at least five potential areas of suitable gray jay habitat during the last glacial maximum and revealed distributions similar to the gray jay’s contemporary during the last interglacial. Colonization from and prolonged isolation in multiple refugia is evident. Historical climatic fluctuations, the presence of multiple dispersal barriers, and highly restricted gene flow appear to be responsible for strong genetic diversification and differentiation in gray jays.
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    Pleistocene glacial cycles and physical barriers influence phylogeographic structure in Black-capped chickadees (Poecile atricapillus), a widespread North American passerine
    (Canadian Science Publishing, 2018) Hindley, J.; Graham, Brendan A.; Burg, Theresa M.
    The nonmigratory Black-capped Chickadee (Poecile atricapillus (Linnaeus, 1766)) has a continent-wide distribution extending across large parts of North America. To investigate the phylogeographic structure and verify possible refugia during the last glacial maximum, we sequenced a 678 bp region of the mitochondrial control region from 633 Black-capped Chickadees at 35 sites across North America and performed paleoecological distribution modeling. Two genetically distinct groups were found using multiple analyses: one in Newfoundland (Canada) and a widespread continental group, with additional substructure evident in western continental populations. While gene flow is low throughout the range, it is especially low in peripheral populations. The Newfoundland population has remained isolated from continental populations for at least 65 000 years and contains a number of fixed nucleotide differences. Within the continental populations, Black-capped Chickadees are subdivided into Pacific Coast, Alaska (USA), southeast Rockies, and main-northeast groups consistent with late Pleistocene vicariance events. Evidence of secondary contact was identified between Pacific and main-northeast populations in northwest British Columbia (Canada) and between southeast Rockies and main-northeast groups in Montana (USA). Paleoecological distribution modeling predicted suitable habitat in Alaska, off the coast of Newfoundland, and several locations across the southern United States during the last glacial maximum, whereas suitable habitat during the last interglacial was more similar to the contemporary distribution.