Biomedical subjects

Roderic D M Page

Publications and source records attributed to Roderic D M Page.

10 recordsLinked to original sources

PubMed2005

An edit script for taxonomic classifications.

BACKGROUND: The NCBI taxonomy provides one of the most powerful ways to navigate sequence data bases but currently users are forced to formulate queries according to a single taxonomic classification. Given that there is not universal agreement on the classification of organisms, providing a single classification places constraints on the questions biologists can ask. However, maintaining multiple classifications is burdensome in the face of a constantly growing NCBI classification. RESULTS: In this paper, we present a solution to the problem of generating modifications of the NCBI taxonomy, based on the computation of an edit script that summarises the differences between two classification trees. Our algorithms find the shortest possible edit script based on the identification of all shared subtrees, and only take time quasi linear in the size of the trees because classification trees have unique node labels. CONCLUSION: These algorithms have been recently implemented, and the software is freely available for download from http://darwin.zoology.gla.ac.uk/~rpage/forest/.

Algorithms↗

PubMed2005

A Taxonomic Search Engine: federating taxonomic databases using web services.

BACKGROUND: The taxonomic name of an organism is a key link between different databases that store information on that organism. However, in the absence of a single, comprehensive database of organism names, individual databases lack an easy means of checking the correctness of a name. Furthermore, the same organism may have more than one name, and the same name may apply to more than one organism. RESULTS: The Taxonomic Search Engine (TSE) is a web application written in PHP that queries multiple taxonomic databases (ITIS, Index Fungorum, IPNI, NCBI, and uBIO) and summarises the results in a consistent format. It supports "drill-down" queries to retrieve a specific record. The TSE can optionally suggest alternative spellings the user can try. It also acts as a Life Science Identifier (LSID) authority for the source taxonomic databases, providing globally unique identifiers (and associated metadata) for each name. CONCLUSION: The Taxonomic Search Engine is available at http://darwin.zoology.gla.ac.uk/~rpage/portal/ and provides a simple demonstration of the potential of the federated approach to providing access to taxonomic names.

Classification↗

PubMed2005

Rates and patterns of gene duplication and loss in the human genome.

Gene duplication has certainly played a major role in structuring vertebrate genomes but the extent and nature of the duplication events involved remains controversial. A recent study identified two major episodes of gene duplication: one episode of putative genome duplication ca. 500 Myr ago and a more recent gene-family expansion attributed to segmental or tandem duplications. We confirm this pattern using methods not reliant on molecular clocks for individual gene families. However, analysis of a simple model of the birth-death process suggests that the apparent recent episode of duplication is an artefact of the birth-death process. We show that a constant-rate birth-death model is appropriate for gene duplication data, allowing us to estimate the rate of gene duplication and loss in the vertebrate genome over the last 200 Myr (0.00115 and 0.00740 Myr(-1) lineage(-1), respectively). Finally, we show that increasing rates of gene loss reduce the impact of a genome-wide duplication event on the distribution of gene duplications through time.

Evolution, Molecular↗

PubMed2004

Supertree algorithms for ancestral divergence dates and nested taxa.

MOTIVATION: Supertree methods have been often identified as a possible approach to the reconstruction of the 'Tree of Life'. However, a limitation of such methods is that, typically, they use just leaf-labelled phylogenetic trees to infer the resulting supertree. RESULTS: In this paper, we describe several new supertree algorithms that extend the allowable information that can be used for phylogenetic inference. These algorithms have been recently implemented and we describe here two illustrative applications. AVAILABILITY: These new algorithms are freely available for application at http://darwin.zoology.gla.ac.uk/cgi-bin/build.pl.

Algorithms↗

PubMed2004

Phylogeny of "Philoceanus complex" seabird lice (Phthiraptera: Ischnocera) inferred from mitochondrial DNA sequences.

The Philoceanus complex is a large assemblage of lice that parasitise procellariiform seabirds (petrels, albatrosses, and their relatives). We obtained mitochondrial 12S rRNA and cytochrome oxidase I DNA sequences from 39 species from diverse hosts and localities. Resolution of deeper relationships between genera was limited, however there is evidence for two major clades, one hosted by albatrosses, the other by petrels. Based on our results, the genera hosted by albatrosses are excellent candidates for detailed analysis of cospeciation. Our results also suggest that a previous estimate of a 5-fold difference in the relative rate of sequence evolution in lice and their avian hosts is an artefact of limited taxonomic sampling.

Animals↗

PubMed2004

Plant-insect interactions: double-dating associated insect and plant lineages reveals asynchronous radiations.

An increasing number of plant-insect studies using phylogenetic analysis suggest that cospeciation events are rare in plant-insect systems. Instead, nonrandom patterns of phylogenetic congruence are produced by phylogenetically conserved host switching (to related plants) or tracking of particular resources or traits (e.g., chemical). The dominance of host switching in many phytophagous insect groups may make the detection of genuine cospeciation events difficult. One important test of putative cospeciation events is to verify whether reciprocal speciation is temporally plausible. We explored techniques for double-dating of both plant and insect phylogenies. We use dated molecular phylogenies of a psyllid (Hemiptera)-Genisteae (Fabaceae) system, a predominantly monophagous insect-plant association widespread on the Atlantic Macaronesian islands. Phylogenetic reconciliation analysis suggests high levels of parallel cladogenesis between legumes and psyllids. However, dating using molecular clocks calibrated on known geological ages of the Macaronesian islands revealed that the legume and psyllid radiations were not contemporaneous but sequential. Whereas the main plant radiation occurred some 8 million years ago, the insect radiation occurred about 3 million years ago. We estimated that >60% of the psyllid speciation has resulted from host switching between related hosts. The only evidence for true cospeciation is in the much more recent and localized radiation of genistoid legumes in the Canary Islands, where the psyllid and legume radiations have been partially contemporaneous. The identification of specific cospeciation events over this time period, however, is hindered by the phylogenetic uncertainty in both legume and psyllid phylogenies due to the apparent rapidity of the species radiations.

Animals↗

PubMed2003

Dramatically elevated rate of mitochondrial substitution in lice (Insecta: Phthiraptera).

Few estimates of relative substitution rates, and the underlying mutation rates, exist between mitochondrial and nuclear genes in insects. Previous estimates for insects indicate a 2-9 times faster substitution rate in mitochondrial genes relative to nuclear genes. Here we use novel methods for estimating relative rates of substitution, which incorporate multiple substitutions, and apply these methods to a group of insects (lice, Order: Phthiraptera). First, we use a modification of copath analysis (branch length regression) to construct independent comparisons of rates, consisting of each branch in a phylogenetic tree. The branch length comparisons use maximum likelihood models to correct for multiple substitution. In addition, we estimate codon-specific rates under maximum likelihood for the different genes and compare these values. Estimates of the relative synonymous substitution rates between a mitochondrial (COI) and nuclear (EF-1alpha) gene in lice indicate a relative rate of several 100 to 1. This rapid relative mitochondrial rate (>100 times) is at least an order of magnitude faster than previous estimates for any group of organisms. Comparisons using the same methods for another group of insects (aphids) reveals that this extreme relative rate estimate is not simply attributable to the methods we used, because estimates from aphids are substantially lower. Taxon sampling affects the relative rate estimate, with comparisons involving more closely related taxa resulting in a higher estimate. Relative rate estimates also increase with model complexity, indicating that methods accounting for more multiple substitution estimate higher relative rates.

Animals↗

PubMed2003

Gene tree parsimony vs uninode coding for phylogenetic reconstruction.

have suggested that there are important weaknesses of gene tree parsimony in reconstructing phylogeny in the face of gene duplication, weaknesses that are addressed by method of uninode coding. Here, we discuss Simmons and Freudenstein's criticisms and suggest a number of reasons why gene tree parsimony is preferable to uninode coding. During this discussion we introduce a number of recent developments of gene tree parsimony methods overlooked by Simmons and Freudenstein. Finally, we present a re-analysis of data from that produces a more reasonable phylogeny than that found by Simmons and Freudenstein, suggesting that gene tree parsimony outperforms uninode coding, at least on these data.

Algorithms↗

PubMed2003

When do parasites fail to speciate in response to host speciation?

Cospeciation generally increases the similarity between host and parasite phylogenies. Incongruence between host and parasite phylogenies has previously been explained in terms of host switching, sorting, and duplication events. Here, we describe an additional process, failure of the parasite to speciate in response to host speciation, that may be important in some host-parasite systems. Failure to speciate is likely to occur when gene flow among parasite populations is much higher than that of their hosts. We reconstructed trees from mitochondrial and nuclear DNA sequences for pigeons and doves (Aves: Columbiformes) and their feather lice in the genus Columbicola (Insecta: Phthiraptera). Although comparisons of the trees from each group revealed a significant amount of cospeciation, there was also a significant degree of incongruence. Cophylogenetic analyses generally indicated that host switching may be an important process in the history of this host-parasite association. Using terminal sister taxon comparisons, we also identified three apparent cases where the host has speciated but the associated parasite has not. In two of these cases of failure to speciate, these comparisons involve allopatric sister taxa of hosts whose lice also occur on hosts sympatric with both of the allopatric sisters. These additional hosts for generalist lice may promote gene flow with lice on the allopatric sister species. Relative rate comparisons for the mitochondrial cytochrome oxidase I gene indicate that molecular substitution occurs about 11 times faster in lice than in their avian hosts.

Animals↗

PubMed2002

Going nuclear: gene family evolution and vertebrate phylogeny reconciled.

Gene duplications have been common throughout vertebrate evolution, introducing paralogy and so complicating phylogenetic inference from nuclear genes. Reconciled trees are one method capable of dealing with paralogy, using the relationship between a gene phylogeny and the phylogeny of the organisms containing those genes to identify gene duplication events. This allows us to infer phylogenies from gene families containing both orthologous and paralogous copies. Vertebrate phylogeny is well understood from morphological and palaeontological data, but studies using mitochondrial sequence data have failed to reproduce this classical view. Reconciled tree analysis of a database of 118 vertebrate gene families supports a largely classical vertebrate phylogeny.

Animals↗