7 results on '"Norton, Andrew P."'
Search Results
2. Quantification and relative severity of inflated branch-support values generated by alternative methods: An empirical example
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Simmons, Mark P. and Norton, Andrew P.
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RUBIACEAE , *RECOMBINANT DNA , *MOLECULAR phylogeny , *DATA analysis , *MISSING data (Statistics) , *EMPIRICAL research - Abstract
Abstract: A supermatrix of 272 terminals from Rubiaceae tribe Spermacoceae that were scored for up to 10 gene regions (two nrDNA, eight plastid) was used as an empirical example to quantify sources of error in heuristic parametric (Bayesian MCMC and maximum likelihood) phylogenetic analyses. The supermatrix includes dramatic disparities in which terminals were sampled for which gene regions. The sources of error examined include poor quality tree searches, requiring a single fully resolved optimal tree, undersampling-within-replicates and frequency-within-replicates bootstrap artifacts, and extrapolation from one character partition to another such that synapomorphies that would only be ambiguously optimized by parsimony are optimized with high probability by parametric methods. Four of our conclusions are as follows. (1) The resolution and support provided by parametric methods for clades that lack unambiguously optimized (by parsimony) synapomorphies are less robust to the addition of terminals and characters than those clades that have unambiguously optimized synapomorphies. (2) Those tree-search methods which can create phylogenetic artifacts (frequency-within-replicates resampling, undersampling-within-replicates resampling, requiring a single fully resolved optimal tree, non-independent resampling among replicates) provide the greatest resolution and support irrespective of whether that resolution or support is corroborated by more conservative and better justified methods. (3) Partitioning data matrices cannot be relied upon to consistently obviate potentially dubious resolution and support caused by missing-data artifacts in likelihood analyses when the models require linked branch lengths among partitions. (4) Undersampling-within-replicates and frequency-within-replicates resampling artifacts are not unique to parsimony and should be accounted for in likelihood analyses by allowing multiple equally likely trees to be saved within each resampling pseudoreplicate and applying the strict-consensus bootstrap rather than the frequency-within-replicates bootstrap. [Copyright &y& Elsevier]
- Published
- 2013
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3. Alignment of, and phylogenetic inference from, random sequences: The susceptibility of alternative alignment methods to creating artifactual resolution and support
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Simmons, Mark P., Müller, Kai F., and Norton, Andrew P.
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NUCLEOTIDE sequence , *PLANT phylogeny , *AMINO acid sequence , *MATHEMATICAL optimization , *TOPOLOGY , *SIMULATION methods & models - Abstract
Abstract: We used random sequences to determine which alignment methods are most susceptible to aligning sequences so as to create artifactual resolution and branch support in phylogenetic trees derived from those alignments. We compared four alignment methods (progressive pairwise alignment, simultaneous multiple alignment of sequence fragments, local pairwise alignment, and direct optimization) to determine which methods are most susceptible to creating false positives in phylogenetic trees. Implied alignments created using direct optimization provided more artifactual support than progressive pairwise alignment methods, which in turn generally provided more artifactual support than simultaneous and local alignment methods. Artifactual support derived from base pairs was generally reinforced by the incorporation of gap characters for progressive pairwise alignment, local pairwise alignment, and implied alignments. The amount of artifactual resolution and support was generally greater for simulated nucleotide sequences than for simulated amino acid sequences. In the context of direct optimization, the differences between static and dynamic approaches to calculating support were extreme, ranging from maximal to nearly minimal support. When applied to highly divergent sequences, it is important that dynamic, rather than static, characters be used whenever calculating branch support using direct optimization. In contrast to the tree-based approaches to alignment, simultaneous alignment of sequences using the similarity criterion generally does not create alignments that are biased in favor of any particular tree topology. [ABSTRACT FROM AUTHOR]
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- 2010
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- View/download PDF
4. The relative performance of indel-coding methods in simulations
- Author
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Simmons, Mark P., Müller, Kai, and Norton, Andrew P.
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PLANT phylogeny , *PLANT evolution , *MISSING data (Statistics) , *GENETIC algorithms - Abstract
Abstract: We used simulations to compare the performance of 10 approaches that have been used for treating unambiguously aligned gaps in phylogenetic analyses. We examined how these approaches perform under the ideal conditions of correct alignments, as well as how robust they are to errors caused by use of inferred alignments. Our results indicate that 5th-state coding dramatically outperformed all other coding methods, which in turn all outperformed treating gaps as missing data or excluding gapped positions. Simple indel coding (SIC) and modified complex indel coding (MCIC) performed about the same, and generally outperformed the other indel-coding methods. The high performance of 5th-state coding was largely found to be a weighting artifact. We suggest that MCIC-coded gap characters be scored for all unambiguously aligned gaps in parsimony-based molecular phylogenetic analyses. When the number of terminals sampled precludes the use of MCIC, SIC may be used as an effective substitute. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
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5. Evaluating host use of an accidentally introduced herbivore on two invasive toadflaxes
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MacKinnon, Daniel K., Hufbauer, Ruth A., and Norton, Andrew P.
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INSECT-plant relationships , *INVASIVE plants , *AGRICULTURAL pests , *INTRODUCED plants - Abstract
Abstract: The distribution of phytophagous insects is influenced by their preference for and performance on their host plants. Biological control agents of invasive plants that prefer and perform better on their target hosts are more likely to be both effective and safe.Brachypterolus pulicarius is an herbivore used in North America to combat two invasive plants, yellow toadflax and Dalmatian toadflax (Linaria vulgaris and Linaria dalmatica). Adult beetles prefer yellow toadflax over Dalmatian toadflax, and when beetles are redistributed onto Dalmatian toadflax, populations do not consistently establish. This leads to the hypothesis that beetle larvae will perform best on yellow toadflax. A reciprocal transfer experiment was conducted to test this hypothesis. Development rate, pupal mass and percent survival were measured to assess larval performance. Development time was influenced by an interaction between the source host and the test host, a pattern suggesting that it is important to consider both the collection host and redistribution host when releasing this beetle for the control of toadflax. Pupal mass of larvae reared on yellow toadflax was, on average, 13% greater than that of larvae reared on Dalmatian toadflax, supporting the hypothesis. Survival rate was not significantly influenced by source host, test host, or their interaction, suggesting that survival rates will be similar no matter the combination of collection host and redistribution host. These results, along with the preference that adult beetles show for yellow toadflax, do not support the redistribution of B. pulicarius onto Dalmatian toadflax in North America. [Copyright &y& Elsevier]
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- 2007
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6. Initiating plant herbivory response increases impact of fungal pathogens on a clonal thistle.
- Author
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Clark, Amy L., Jahn, Courtney E., and Norton, Andrew P.
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JASMONIC acid , *IMPACT response , *PLANT hormones , *NATIVE plants , *SALICYLIC acid , *STRIPE rust , *PLANT defenses , *FORAGE plants - Abstract
• Manipulating plant defense hormones increases the impact of fungal pathogens. • Jasmonic acid application increased the impact of CT-Rust on Cirsium arvense. • This effect was seen for belowground but not aboveground biomass. Cirsium arvense, or Canada thistle, is one of the most detrimental weeds for agricultural production. Native to south-eastern Europe, the species is now found in Many parts of Asia, North America and Australasia. In North America and New Zealand the species is considered invasive, displacing native vegetation and reducing the quality of forage in rangelands and pastures. The autoecious fungus, Puccinia punctiformis , or CT-rust, shows potential as a control agent but rarely reaches epidemic proportions in natural populations. Manipulating plant defense hormones could alter host susceptibility and allow CT-rust to have more widespread impact. To determine if applying hormones increases the infection by the fungal pathogen, Canada thistle plants were inoculated and sprayed with jasmonic acid (JA) and salicylic acid (SA). Results show that jasmonic acid application interacted with inoculation, increasing infection rates, both incidence and severity, and impact of CT-rust. We found that JA increased infection rates by nearly 20%. Infection consistently reduced root biomass and this reduction was 45% greater with the addition of JA compared to untreated control. Addition of JA at the time of inoculation could make it a more effective control agent for Canada thistle. [ABSTRACT FROM AUTHOR]
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- 2020
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7. Pre- and post-introduction patterns in neutral genetic diversity in the leafy spurge gall midge, Spurgia capitigena (Bremi) (Diptera: Cecidomyiidae)
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Lloyd, Casandra J., Hufbauer, Ruth A., Jackson, Aaron, Nissen, Scott J., and Norton, Andrew P.
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EUPHORBIA , *COMMUNICABLE diseases , *EPIDEMICS , *QUARANTINE - Abstract
Abstract: Many researchers have hypothesized that reduced genetic diversity in introduced populations of biological control agents can compromise the agent’s ability to establish and then adapt to novel environments. Strategies such as collecting from a wide geographic area or maintaining large colony sizes through the quarantine process have been used to minimize the loss of genetic diversity. Few studies have examined how the process of collection, quarantine, and establishment could affect patterns of genetic diversity in biological control agents. In this paper, we examine patterns in neutral genetic diversity in Spurgia capitigena, a gall midge introduced as a biological control agent of leafy spurge (Euphorbia esula) from its original collection site in Italy, a newly discovered population of the midge from southern France, and in two established populations in North America. By comparing the existing populations with historical samples collected shortly after the original introductions in 1991, we found that there is evidence of a mild bottleneck in both of the introduced populations. Further, we also examined the population structure in European populations of the fly collected from leafy spurge and a closely related species, cypress spurge (Euphorbia cyparissias) and found evidence for local restrictions in gene flow between populations on the two plants, but no evidence to support the current taxonomy of the genus with two distinct fly species. [Copyright &y& Elsevier]
- Published
- 2005
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