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Durham, NC, United States

Comas L.H.,Pennsylvania State University | Comas L.H.,U.S. Department of Agriculture | Callahan H.S.,Barnard College | Midford P.E.,NESCent
Ecology and Evolution

Root traits vary enormously among plant species but we have little understanding of how this variation affects their functioning. Of central interest is how root traits are related to plant resource acquisition strategies from soil. We examined root traits of 33 woody species from northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We examined root trait distribution with respect to plant phylogeny, quantifying the phylogenetic signal (K statistic) in fine root morphology and architecture, and used phylogenetically independent contrasts (PICs) to test whether taxa forming different mycorrhizal associations had different root traits. We found a pattern of species forming roots with thinner diameters as species diversified across time. Given moderate phylogenetic signals (K = 0.44-0.68), we used PICs to examine traits variation among taxa forming AM or EM, revealing that hosts of AM were associated with lower branching intensity (rPIC = -0.77) and thicker root diameter (rPIC = -0.41). Because EM evolved relatively more recently and intermittently across plant phylogenies, significant differences in root traits and colonization between plants forming AM and EM imply linkages between the evolution of these biotic interactions and root traits and suggest a history of selection pressures, with trade-offs for supporting different types of associations. Finally, across plant hosts of both EM and AM, species with thinner root diameters and longer specific root length (SRL) had less colonization (rPIC = 0.85, -0.87), suggesting constraints on colonization linked to the evolution of root morphology. We examined root traits of 33 woody species co-existing in Northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We found patterns of plants forming roots with thinner diameters as species diversified across time; and that the AM habit was associated with lower branching intensity (rPIC = -0.77) and thicker root diameter (rPIC = -0.41) and the EM habit. We discuss findings in light of selection pressures on root traits and trade-offs for supporting different types of fungal symbionts. © 2014 The Authors. Source

de Casas R.R.,NESCent | de Casas R.R.,Duke University | Kovach K.,Duke University | Dittmar E.,Michigan State University | And 3 more authors.
New Phytologist

Seed dormancy can affect life history through its effects on germination time. Here, we investigate its influence on life history beyond the timing of germination. We used the response of Arabidopsis thaliana to chilling at the germination and flowering stages to test the following: how seed dormancy affects germination responses to the environment; whether variation in dormancy affects adult phenology independently of germination time; and whether environmental cues experienced by dormant seeds have an effect on adult life history. Dormancy conditioned the germination response to low temperatures, such that prolonged periods of chilling induced dormancy in nondormant seeds, but stimulated germination in dormant seeds. The alleviation of dormancy through after-ripening was associated with earlier flowering, independent of germination date. Experimental dormancy manipulations showed that prolonged chilling at the seed stage always induced earlier flowering, regardless of seed dormancy. Surprisingly, this effect of seed chilling on flowering time was observed even when low temperatures did not induce germination. In summary, seed dormancy influences flowering time and hence life history independent of its effects on germination timing. We conclude that the seed stage has a pronounced effect on life history, the influence of which goes well beyond the timing of germination. © 2012 The Authors. New Phytologist © 2012 New Phytologist Trust. Source

Genes occasionally change their location in the genome through inter-chromosomal duplication and loss. These changes happen as mistakes during recombination or through retrotransposition. In Han and Hahn 2011,1 we surveyed the genomes of ten Drosophila species, to identify and characterize the gene transposition events in the history of these species. In the paper, we showed that the rate of gene transposition in Drosophila is higher than previously appreciated. To understand the process of gene transposition, we examined the sequences, locations and functions of the transposed genes. Based on the elevated rate of sequence evolution in transposed genes and the frequent movements near the centromeres and telomeres, we could not reject the hypothesis that these are mutations fixed through relaxed selection. But, by examining the functions of transposed genes more carefully, we found that genes with male-specific functions and genes with female-specific functions move in opposite directions involving the X chromosome. We also found an over-representation of chromosome related functions among the transposed genes. These observations suggest the possibility of particular selection pressures contributing to gene transpositions in Drosophila. © 2012 Landes Bioscience. Source

Soltis D.E.,University of Florida | Mort M.E.,University of Kansas | Latvis M.,University of Florida | Mavrodiev E.V.,University of Florida | And 5 more authors.
American Journal of Botany

Premise of the study: We sought novel evolutionary insights for the highly diverse Saxifragales by constructing a large phylogenetic tree encompassing 36.8% of the species-level biodiversity. Methods: We built a phylogenetic tree for 909 species of Saxifragales and used this hypothesis to examine character evolution for annual or perennial habit, woody or herbaceous habit, ovary position, petal number, carpel number, and stamen to petal ratio. We employed likelihood approaches to investigate the effect of habit and life history on speciation and extinction within this clade. Key results: Two major shifts occurred from a woody ancestor to the herbaceous habit, with multiple secondary changes from herbaceous to woody. Transitions among superior, subinferior, and inferior ovaries appear equiprobable. A major increase in petal number is correlated with a large increase in carpel number; these increases have co-occurred multiple times in Crassulaceae. Perennial or woody lineages have higher rates of speciation than annual or herbaceous ones, but higher probabilities of extinction offset these differences. Hence, net diversification rates are highest for annual, herbaceous lineages and lowest for woody perennials. The shift from annuality to perenniality in herbaceous taxa is frequent. Conversely, woody perennial lineages to woody annual transitions are infrequent; if they occur, the woody annual state is left immediately. Conclusions: The large tree provides new insights into character evolution that are not obvious with smaller trees. Our results indicate that in some cases the evolution of angiosperms might be conditioned by constraints that have been so far overlooked. © 2013 Botanical Society of America. Source

Burleigh J.G.,University of Florida | Bansal M.S.,Iowa State University | Bansal M.S.,Tel Aviv University | Eulenstein O.,Iowa State University | And 5 more authors.
Systematic Biology

Phylogenetic analyses using genome-scale data sets must confront incongruence among gene trees, which in plants is exacerbated by frequent gene duplications and losses. Gene tree parsimony (GTP) is a phylogenetic optimization criterion in which a species tree that minimizes the number of gene duplications induced among a set of gene trees is selected. The run time performance of previous implementations has limited its use on large-scale data sets. We used new software that incorporates recent algorithmic advances to examine the performance of GTP on a plant data set consisting of 18,896 gene trees containing 510,922 protein sequences from 136 plant taxa (giving a combined alignment length of >2.9 million characters). The relationships inferred from the GTP analysis were largely consistent with previous large-scale studies of backbone plant phylogeny and resolved some controversial nodes. The placement of taxa that were present in few gene trees generally varied the most among GTP bootstrap replicates. Excluding these taxa either before or after the GTP analysis revealed high levels of phylogenetic support across plants. The analyses supported magnoliids sister to a eudicot + monocot clade and did not support the eurosid I and II clades. This study presents a nuclear genomic perspective on the broad-scale phylogenic relationships among plants, and it demonstrates that nuclear genes with a history of duplication and loss can be phylogenetically informative for resolving the plant tree of life. © 2011 The Author(s). Source

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