@article {166,
	title = {Influence of climatic niche suitability and geographical overlap on hybridization patterns among southern Californian oaks},
	journal = {Journal of BiogeographyJournal of Biogeography},
	year = {2014},
	pages = {n/a-n/a},
	abstract = {Aim Information on the association between geographical patterns of hybridization and the climatic niche requirements and co-occurrence of the species involved can provide important insights that further our understanding of the factors promoting the formation of hybrid zones. Here, we test whether climatic niche suitability explains patterns of hybridization beyond spatial overlap in distributions of the geographically restricted Engelmann oak (Quercus engelmannii) and the widespread scrub oak species complex (Quercus spp.). Location Southern California, USA. Methods We sampled Engelmann and scrub oaks across 31 localities and genotyped 343 individuals at nine microsatellite loci. We used climatic niche modelling to assess the suitability of habitats for each parental species and hybrids and to analyse whether climatic niche suitability in addition to co-occurrence are associated with observed spatial patterns of hybridization. Results Our data indicated that hybrid zones are located in areas that are geographically constrained by the presence of scattered patches of Engelmann oak within a matrix broadly occupied by scrub oaks. However, the climatic niche of hybrids differed from that occupied by both Engelmann and scrub oaks, suggesting the importance of climate on their establishment and persistence beyond the simple role of geographical overlap of parental species distributions. We also found that even moderate levels of introgression contributed to increased genetic diversity in Engelmann oak but not in scrub oaks. Main conclusions These results show that hybrid zones follow a mosaic pattern constrained by the presence of scattered patches occupied by Engelmann oak and climatically suitable~areas that favour the establishment of hybrids. The low rates of ongoing hybridization and the bimodal distribution of parental genotypes found here suggest that hybridization is not threatening Engelmann oak and this phenomenon could instead be promoting the acquisition of favourable alleles that may increase the adaptive potential of this vulnerable species.},
	keywords = {Ecological niche modelling, extinction through hybridization, genetic diversity, HYBRIDIZATION, introgression, Maxent, microsatellite markers, peripheral populations, Quercus engelmannii, southern California},
	isbn = {1365-2699},
	author = {Ortego, Joaqu{\'\i}n and Gugger, Paul F. and Riordan, Erin C. and Sork, Victoria L.}
}
@article {167,
	title = {Climatically stable landscapes predict patterns of genetic structure and admixture in the Californian canyon live oak},
	journal = {Journal of BiogeographyJournal of Biogeography},
	year = {2014},
	pages = {n/a-n/a},
	abstract = {Aim We studied which factors shape contemporary patterns of genetic structure, diversity and admixture in the canyon live oak (Quercus chrysolepis). Specifically, we tested two alternative hypotheses: (1) that areas with high habitat suitability and stability since the Last Glacial Maximum (LGM) sustain higher effective population sizes, resulting in increased levels of genetic diversity; and (2) that populations from areas with lower habitat stability show higher levels of genetic admixture due to their recurrent colonization by individuals originating from genetically differentiated populations. Furthermore, we analysed the relative importance of past and current habitat suitability and their additive effects on contemporary patterns of genetic structure. Location California, USA. Methods We sampled 160 individuals from 33 localities across the distribution range of the canyon live oak in California and then combined information from 13 nuclear microsatellite DNA markers and climate niche modelling to study patterns of genetic variation in this species. We used Bayesian clustering analyses to analyse geographical patterns of genetic structure and admixture, and circuit theory to generate isolation-by-resistance (IBR) distance matrices. Results We found that the degree of genetic admixture was higher in localities with lower inferred population stability, but that genetic diversity was not associated with habitat suitability or stability. Landscape genetic analyses identified habitat stability as the primary driver of population genetic differentiation. Main conclusions This study shows that habitat stability can be a major factor shaping genetic variation in wind-pollinated trees and supports the idea that stable regions contribute to genetic connectivity across different climatic periods. To our knowledge, this study is the first to report an association between patterns of genetic admixture and stability of local habitat.},
	keywords = {California, climatic stability, Ecological niche modelling, gene flow, genetic diversity, genetic structure, interglacial refugia, palaeodistribution modelling, Quercus chrysolepis},
	isbn = {1365-2699},
	author = {Ortego, Joaqu{\'\i}n and Gugger, Paul F. and Sork, Victoria L.}
}
@article {169,
	title = {Historical patterns of oak population expansion in the Chautauqua Hills, Kansas},
	journal = {Journal of BiogeographyJournal of Biogeography},
	year = {2014},
	pages = {n/a-n/a},
	abstract = {Aim Rates of tree population expansion have increased in many North American landscapes that were mosaics of grasslands, savannas and woodlands historically. Consequences of woodland expansion include reduced economic return from grazing and changes in native biodiversity, but causes of woodland expansion are poorly understood. We address historical timing of blackjack oak (Quercus marilandica) and post oak (Quercus stellata) population expansion in tree{\textendash}grass ecosystems, roles of climate and land use in driving this expansion, and future stability of these woodlands. Location The Cross Timbers ecosystem in Kansas, USA. Methods Using increment cores, we quantified blackjack oak and post oak age structures in four woodlands on sites that were not wooded in the 1860s. We compared timing of oak regeneration with climate fluctuations (using the Palmer drought severity index) and land-use history. We quantified tree species composition within 5-m radii of sampled oaks. Results Recruitment of both oak species increased between 1925 and 1945. Modal age classes recruited from 1935 to 1960. Recruitment was associated with dry intervals at the two sites with north- or east-facing aspects. This association was driven by blackjack oak recruitment in dry intervals. Woodlands on the sites with south- and west-facing aspects contained only oaks, whereas those on the sites with north- and east-facing aspects contained saplings of fire-intolerant, shade-tolerant tree species. Main conclusions Our results contribute to growing evidence for woodland expansion in the region during dry climate intervals. The association between drought and recruitment was influenced by slope aspect and was more pronounced in the less fire-tolerant oak species. Although woodland expansion coincided with regional increases in fire frequency, drought and greater use of prescribed burning are likely to have reduced fire intensities by reducing fuel loads. These oak woodlands, which have developed during the 20th century, appear to form stable communities on xeric slopes but to be undergoing succession towards a mesophytic tree community on mesic slopes.},
	keywords = {Age structure, Cross Timbers, fire ecology, Kansas, mesophication, Quercus marilandica, Quercus stellata, tree recruitment, woodland dynamics, woody plant encroachment},
	isbn = {1365-2699},
	author = {Rogers, Thomas R. and Russell, F. Leland}
}
@article {153,
	title = {Molecular and morphological support for a Florida origin of the Cuban oak},
	journal = {Journal of BiogeographyJournal of Biogeography},
	volume = {40},
	number = {4},
	year = {2013},
	pages = {632-645},
	publisher = {Blackwell Publishing Ltd},
	abstract = {Aim  The origins of the Cuban biota are of long-standing interest in biogeography, and the source of a small live oak (Quercus series Virentes) population on Cuba remains unresolved. Based on morphological evidence, previous authors have hypothesized a Florida origin from either Q.~geminata or Q.~virginiana or both; a Mexican origin from Q.~oleoides; or a hybrid origin from both sources. We use molecular data and taxonomically informative leaf morphology to identify the source species and timing of colonization. Location  Cuba, Central America, Mexico and the south-eastern United States. Methods~ We collected representative samples of Cuban oaks and each putative source species and genotyped each sample at 12 nuclear microsatellites and two chloroplast DNA sequences. We estimated population structure using a Bayesian clustering analysis and F-statistics, pairwise migration rates among taxa, and divergence time using an isolation-with-migration model. We measured seven leaf traits and conducted an analysis of similarity (ANOSIM) to determine which putative source species was most similar to Cuban oaks. Results  Cuban oak contains one chloroplast DNA haplotype, which is common in southern Florida. Bayesian clustering analysis of microsatellites revealed that the Cuban oak forms a distinct and pure population cluster, and F-statistics showed that Cuban oaks are differentiated least from Q.~virginiana and most from Q.~geminata. Migration rates were highest out of Cuba to Q.~oleoides. Molecular diversity, the ratio of allelic richness to allele size range, and effective population size of the Cuban oak were relatively low, suggesting a founder effect. Divergence time estimates fell entirely within the Pleistocene (628{\textendash}6~ka), considering a range of mutation rates and generation times. Cuban oaks were morphologically most similar to Q.~virginiana and least similar to Q.~geminata. Main conclusions  Molecular and morphological data support a Pleistocene dispersal of Q.~virginiana from Florida to Cuba, followed by isolation and divergence, then limited dispersal and introgression from Cuba to Q.~oleoides in Central America. Birds could have dispersed acorns to Cuba during a glacial period when sea levels were low. These results highlight the varied origin of the Cuban biota and the possible role of Pleistocene glaciations in the establishment of temperate taxa in the tropics.},
	keywords = {cpDNA, Cuba, founder effect, morphology, nuclear microsatellites, over-water dispersal, phylogeography, Quercus oleoides, Quercus sagraeana, Quercus virginiana},
	isbn = {1365-2699},
	author = {Gugger, Paul F. and Cavender-Bares, Jeannine}
}
@article {135,
	title = {Phylogeography and climatic niche evolution in live oaks (<i>Quercus </i>series <i>Virentes</i>) from the tropics to the temperate zone},
	journal = {Journal of BiogeographyJournal of Biogeography},
	volume = {38},
	number = {962-981},
	year = {2011},
	abstract = {Aim: We investigated the phylogeography, geographic variation in leaf morphology, freezingtolerance and climatic niches of two widespread evergreen sister oak species (Quercus) in theseries Virentes to gain insight into 1) the historical biogeographic explanations for populationgenetic structure and leaf morphological variation, and 2) the influence of genetically-basedvariation in freezing tolerance within and between species on climatic range limits and geneflow, and 3) to examine the evidence for contrasting impacts of Pleistocene glacial cycles ongenetic structure and diversity in tropical and temperate regions.Location: Southeastern U.S., Mexico and Central AmericaMethods: Nuclear microsatellites, non-recombining nuclear sequences within ITS and NIA-i3and chloroplast DNA sequences were obtained from samples collected throughout the range oftwo sister lineages of live oaks, represented by Quercus virginiana in the temperate zone andQuercus oleoides in the tropics. Divergence times were estimated for the two major geographicand genetic breaks. Differentiation in leaf morphology, analyzed from field specimens, wascompared to the molecular data. Freezing sensitivities of Q. virginiana and Q. oleoidespopulations were assessed in a common garden under controlled tropical and temperate climatesand compared to minimum temperature climatic niches for each species.Results: The geographic break between Q. virginiana and Q. oleoides was associated withstrong genetic differentiation of possible Miocene origin and with differentiation in freezingsensitivity, climatic envelopes and leaf morphology. A second important geographic and geneticbreak within Q. oleoides between Costa Rica and the rest of Central America showed aPleistocene divergence time and no differentiation in leaf morphology. Population geneticdifferentiation was greater but genetic diversity was lower within temperate Q. virginianacompared to tropical Q. oleoides, and genetic breaks largely corresponded to breaks in leafmorphology.Main Conclusions: Two major breaks, one between Mexico and the U.S. at the speciesboundary, and a more recent one within Q. oleoides between Honduras and Costa Rica implicateclimatic changes as potential causes. The latter break may be associated with formation of theCordillera Guanacaste followed by seasonal changes in precipitation. In the former case, an {\textquotedblleft}outof the tropics{\textquotedblright} scenario is hypothesized, in which acquisition of freezing tolerance in Q.virginiana permitted colonization of and expansion in the temperate zone while differences inclimatic tolerances between the species limited secondary contact. More pronounced Pleistocenechanges in climate and sea level in the southeastern U.S. relative to Central America may explainthe greater population differentiation within temperate Q. virginiana and greater genetic diversityin tropical Q. oleoides. These patterns are predicted to hold for other taxa that span temperateand tropical zones of North and Middle America},
	keywords = {Central America, chloroplast DNA sequences, climatic niches, freezing tolerance, leaf morphology, NIA-i3 and ITS, nuclear microsatellites, Pleistocene glacial cycles, rise, unglaciated eastern North America, sea level},
	author = {Cavender-Bares, Jeannine and Antonio Gonzalez-Rodriguez and Annette Pahlich and Kari Koehler and Nicholas Deacon}
}
