Browsing by Subject "Quercus"

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Open Access
Information processing without brains--the power of intercellular regulators in plants.
(Development, 2010-04) Busch, Wolfgang; Benfey, Philip N
Plants exhibit different developmental strategies than animals; these are characterized by a tight linkage between environmental conditions and development. As plants have neither specialized sensory organs nor a nervous system, intercellular regulators are essential for their development. Recently, major advances have been made in understanding how intercellular regulation is achieved in plants on a molecular level. Plants use a variety of molecules for intercellular regulation: hormones are used as systemic signals that are interpreted at the individual-cell level; receptor peptide-ligand systems regulate local homeostasis; moving transcriptional regulators act in a switch-like manner over small and large distances. Together, these mechanisms coherently coordinate developmental decisions with resource allocation and growth.
Open Access
Seed Dispersal, Gene Flow, and Hybridization in Red Oak
(2010) Moran, Emily Victoria
Understanding the ecological and evolutionary responses of plant species to shifts in climate (and other rapid environmental perturbations) will require an improved knowledge of interactions between ecological and evolutionary processes as mediated by reproduction and gene flow. This dissertation research examines the processes of seed dispersal, intra- and inter-specific gene flow, and reproductive success in two red oak populations in North Carolina; the variation in these processes from site to site; and their influence on genetic structure, population dynamics, and migration potential.

Using genetic and ecological data collected from two large long-term study sites, I develop a hierarchical Bayesian model to identify the parents of sampled seedlings and characterize the scale of effective seed and pollen dispersal. I examine differences in scale of dispersal between the Appalachian and Piedmont sites in light of the spatial genetic structure and ecological differences of the two sites. I then use the pedigree and dispersal estimates derived from these analyses to examine variation in reproductive success and to test hypotheses about the causes and consequences of such variation. Using parentage estimates and measures of genetic differentiation between species, I study the likely extent of hybridization in these mixed-species secondary forests. Finally, using the SLIP stand simulator, I explore the implications of new genetic dispersal estimates for migration potential in oaks.

I find that effective seed dispersal distances are longer than estimated using seed trap data. While at the Piedmont site the large number of seedling found >100 m from their mother trees suggests that animal dispersers play a vital role, at the Appalachian site seedling distributions conform more closely to the original gravity-created pattern of seed density. Individual trees vary widely in their reproductive success. Seedling production was found to be positively associated with annual seed production, but exhibited hump-shaped or reversing relationships with age (suggesting the effect of senescence) and growth rate (suggesting tradeoffs in allocation). Germination fraction was negatively associated with fecundity, suggesting that density-dependent mortality may be acting on the high concentrations of seeds near highly fecund adults. Due to overlapping generations and variation in individual reproductive success, effective population size is estimated to be less than half the size that numbers of "adult" individuals would suggest, with consequences for the relative strength of drift and selection. Hybridization may boost effective population size somewhat; my analyses suggest that inter-specific gene flow is common at both study sites. Finally, simulations show that dispersal has a relatively stronger effect on migration rate and population growth than fecundity or size at maturity, and that genetic estimates of seed dispersal can yield significantly higher rates of migration and/or population persistence than seed-trap based estimates under both competitive and non-competitive conditions.
Open Access
Sympatric parallel diversification of major oak clades in the Americas and the origins of Mexican species diversity.
(New Phytol, 2017-09-18) Hipp, Andrew L; Manos, Paul S; González-Rodríguez, Antonio; Hahn, Marlene; Kaproth, Matthew; McVay, John D; Avalos, Susana Valencia; Cavender-Bares, Jeannine
Oaks (Quercus, Fagaceae) are the dominant tree genus of North America in species number and biomass, and Mexico is a global center of oak diversity. Understanding the origins of oak diversity is key to understanding biodiversity of northern temperate forests. A phylogenetic study of biogeography, niche evolution and diversification patterns in Quercus was performed using 300 samples, 146 species. Next-generation sequencing data were generated using the restriction-site associated DNA (RAD-seq) method. A time-calibrated maximum likelihood phylogeny was inferred and analyzed with bioclimatic, soils, and leaf habit data to reconstruct the biogeographic and evolutionary history of the American oaks. Our highly resolved phylogeny demonstrates sympatric parallel diversification in climatic niche, leaf habit, and diversification rates. The two major American oak clades arose in what is now the boreal zone and radiated, in parallel, from eastern North America into Mexico and Central America. Oaks adapted rapidly to niche transitions. The Mexican oaks are particularly numerous, not because Mexico is a center of origin, but because of high rates of lineage diversification associated with high rates of evolution along moisture gradients and between the evergreen and deciduous leaf habits. Sympatric parallel diversification in the oaks has shaped the diversity of North American forests.