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Mark Wilkinson

Publications and source records attributed to Mark Wilkinson.

At least 19 recordsLinked to original sources
PubMed2007

Global patterns of diversification in the history of modern amphibians.

The fossil record of modern amphibians (frogs, salamanders, and caecilians) provides no evidence for major extinction or radiation episodes throughout most of the Mesozoic and early Tertiary. However, long-term gradual diversification is difficult to reconcile with the sensitivity of present-day amphibian faunas to rapid ecological changes and the incidence of similar environmental perturbations in the past that have been associated with high turnover rates in other land vertebrates. To provide a comprehensive overview of the history of amphibian diversification, we constructed a phylogenetic timetree based on a multigene data set of 3.75 kb for 171 species. Our analyses reveal several episodes of accelerated amphibian diversification, which do not fit models of gradual lineage accumulation. Global turning points in the phylogenetic and ecological diversification occurred after the end-Permian mass extinction and in the late Cretaceous. Fluctuations in amphibian diversification show strong temporal correlation with turnover rates in amniotes and the rise of angiosperm-dominated forests. Approximately 86% of modern frog species and >81% of salamander species descended from only five ancestral lineages that produced major radiations in the late Cretaceous and early Tertiary. This proportionally late accumulation of extant lineage diversity contrasts with the long evolutionary history of amphibians but is in line with the Tertiary increase in fossil abundance toward the present.

Amphibians↗
PubMed2006

On the origin of the Synodontis catfish species flock from Lake Tanganyika.

Species flocks within Great Lakes provide unique insights into the factors affecting diversification. Lake Tanganyika (LT) is of particular interest because it contains many endemic groups for which general factors affecting diversification can be discerned. Here, we present the first phylogenetic study of the LT Synodontis (Siluriformes, Mochokidae) species flock using mtDNA sequence data. Our data reveal some previously unrecognized species diversity and indicate that the LT species flock is not monophyletic, and that two closely related clades of endemics may have independently colonized LT. Other comparable small species flocks are characterized by a single colonization event. Molecular date estimates of the timing of the initial within-lake diversification of the LT endemics, based on a fossil calibration, are comparable to those reported for other groups, suggesting that extrinsic factors maybe important common causes of clade diversification. The basal divergence in the sampled Synodontis reveals an East-West African faunal split seen in many terrestrial, but few aquatic groups, the timing of which coincides with East African rifting events.

Africa, Eastern↗
PubMed2006

Are we meeting the standards set for endoscopy? Results of a large-scale prospective survey of endoscopic retrograde cholangio-pancreatograph practice.

OBJECTIVE: To examine endoscopic retrograde cholangio-pancreatography (ERCP) services and training in the UK. DESIGN: Prospective multicentre survey. SETTING: Five regions of England. PARTICIPANTS: Hospitals with an ERCP unit. OUTCOME MEASURES: Adherence to published guidelines, technical success rates, complications and mortality. RESULTS: Organisation questionnaires were returned by 76 of 81 (94%) units. Personal questionnaires were returned by 190 of 213 (89%) ERCP endoscopists and 74 of 91 (81%) ERCP trainees, of whom 45 (61%) reported participation in <50 ERCPs per annum. In all, 66 of 81 (81%) units collected prospective data on 5264 ERCPs, over a mean period of 195 days. Oximetry was used by all units, blood pressure monitoring by 47 of 66 (71%) and ECG monitoring by 37 of 66 (56%) units; 1484 of 4521 (33%) patients were given >5 mg of midalozam. Prothrombin time was recorded in 4539 of 5264 (86%) procedures. Antibiotics were given in 1021 of 1412 (72%) cases, where indicated. Patients' American Society of Anesthesiology (ASA) scores were 3-5 in 670 of 5264 (12.7%) ERCPs, and 4932 of 5264 (94%) ERCPs were scheduled with therapeutic intent. In total, 140 of 182 (77%) trained endoscopists demonstrated a cannulation rate >/=80%. The recorded cannulation rate among senior trainees (with an experience of >200 ERCPs) was 222/338 (66%). Completion of intended treatment was done in 3707 of 5264 (70.4%) ERCPs; 268 of 5264 (5.1%) procedures resulted in a complication. Procedure-related mortality was 21/5264 (0.4%). Mortality correlated with ASA score. CONCLUSION: Most ERCPs in the UK are performed on low-risk patients with therapeutic intent. Complication rates compare favourably with those reported internationally. However, quality suffers because there are too many trainees in too many low-volume ERCP centres.

Adult↗
PubMed2006

Gbrowse Moby: a Web-based browser for BioMoby Services.

BACKGROUND: The BioMoby project aims to identify and deploy standards and conventions that aid in the discovery, execution, and pipelining of distributed bioinformatics Web Services. As of August, 2006, approximately 680 bioinformatics resources were available through the BioMoby interoperability platform. There are a variety of clients that can interact with BioMoby-style services. Here we describe a Web-based browser-style client--Gbrowse Moby--that allows users to discover and "surf" from one bioinformatics service to the next using a semantically-aided browsing interface. RESULTS: Gbrowse Moby is a low-throughput, exploratory tool specifically aimed at non-informaticians. It provides a straightforward, minimal interface that enables a researcher to query the BioMoby Central web service registry for data retrieval or analytical tools of interest, and then select and execute their chosen tool with a single mouse-click. The data is preserved at each step, thus allowing the researcher to manually "click" the data from one service to the next, with the Gbrowse Moby application managing all data formatting and interface interpretation on their behalf. The path of manual exploration is preserved and can be downloaded for import into automated, high-throughput tools such as Taverna. Gbrowse Moby also includes a robust data rendering system to ensure that all new data-types that appear in the BioMoby registry can be properly displayed in the Web interface. CONCLUSION: Gbrowse Moby is a robust, yet facile entry point for both newcomers to the BioMoby interoperability project who wish to manually explore what is known about their data of interest, as well as experienced users who wish to observe the functionality of their analytical workflows prior to running them in a high-throughput environment.

Journal Article↗
PubMed2006

Parental investment by skin feeding in a caecilian amphibian.

Although the initial growth and development of most multicellular animals depends on the provision of yolk, there are many varied contrivances by which animals provide additional or alternative investment in their offspring. Providing offspring with additional nutrition should be favoured by natural selection when the consequent increased fitness of the young offsets any corresponding reduction in fecundity. Alternative forms of nutrition may allow parents to delay and potentially redirect their investment. Here we report a remarkable form of parental care and mechanism of parent-offspring nutrient transfer in a caecilian amphibian. Boulengerula taitanus is a direct-developing, oviparous caecilian, the skin of which is transformed in brooding females to provide a rich supply of nutrients for the developing offspring. Young animals are equipped with a specialized dentition, which they use to peel and eat the outer layer of their mother's modified skin. This new form of parental care provides a plausible intermediate stage in the evolution of viviparity in caecilians. At independence, offspring of viviparous and of oviparous dermatotrophic caecilians are relatively large despite being provided with relatively little yolk. The specialized dentition of skin-feeding (dermatophagous) caecilians may constitute a preadaptation to the fetal feeding on the oviduct lining of viviparous caecilians.

Amphibians↗
PubMed2005

Novel puroindoline and grain softness protein alleles in Aegilops species with the C, D, S, M and U genomes.

DNA from six hexaploid, tetraploid and diploid species of Aegilops with the C, D, S, M and U genomes was amplified with specific PCR primers to identify sequences encoding puroindolines (Pins) a and b and grain softness protein (GSP), all of which are encoded by genes at the Ha (hardness) locus, with Ae. tauschii (DD) and bread wheat (T. aestivum) (AABBDD) cv Hiline being studied as controls. Seven new allelic forms of Pin a and Pin b were identified, including forms with mutations within or close to the tryptophan motif. In addition, five new forms of GSP were detected. In all species both genomic DNA from leaves and cDNA from developing grain were analysed. This revealed the presence of both silent genes (with premature stop codons) and multiple genes, with the latter being confirmed by Southern blot analysis. Freeze fracture analysis demonstrated that all except one accession (Ae. sharonensis) were soft textured. However, this difference cannot be accounted for by the sequences of the Pin alleles present in this line.

Alleles↗
PubMed2005

A hotspot of gene order rearrangement by tandem duplication and random loss in the vertebrate mitochondrial genome.

Most reported examples of change in vertebrate mitochondrial (mt) gene order could be explained by a tandem duplication followed by random loss of redundant genes (tandem duplication-random loss [TDRL] model). Under this model of evolution, independent loss of genes arising from a single duplication in an ancestral species are predicted, and remnant pseudogenes expected, intermediate states that may remain in rearranged genomes. However, evidence for this is rare and largely scattered across vertebrate lineages. Here, we report new derived mt gene orders in the vertebrate "WANCY" region of four closely related caecilian amphibians. The novel arrangements found in this genomic region (one of them is convergent with the derived arrangement of marsupials), presence of pseudogenes, and positions of intergenic spacers fully satisfy predictions from the TDRL model. Our results, together with comparative data for the available vertebrate complete mt genomes, provide further evidence that the WANCY genomic region is a hotspot for gene order rearrangements and support the view that TDRL is the dominant mechanism of gene order rearrangement in vertebrate mt genomes. Convergent gene rearrangements are not unlikely in hotspots of gene order rearrangement by TDRL.

Amphibians↗
PubMed2005

New methods ring changes for the tree of life.

Relationships among prokaryotes and the origin of eukaryotes have both proven controversial, with results depending upon the gene sequences and methods used. Extensive horizontal gene transfer is one possible reason why inferring such deep phylogenetic relationships is difficult. In two recent papers, Lake and Rivera introduce new methods that can be used to reconstruct the genomic tree in the presence of horizontal gene transfers, but which suggest that a ring rather than a tree is a better representation of some parts of the history of life on Earth.

Journal Article↗
PubMed2005

The shape of supertrees to come: tree shape related properties of fourteen supertree methods.

Using a simple example and simulations, we explore the impact of input tree shape upon a broad range of supertree methods. We find that input tree shape can affect how conflict is resolved by several supertree methods and that input tree shape effects may be substantial. Standard and irreversible matrix representation with parsimony (MRP), MinFlip, duplication-only Gene Tree Parsimony (GTP), and an implementation of the average consensus method have a tendency to resolve conflict in favor of relationships in unbalanced trees. Purvis MRP and the average dendrogram method appear to have an opposite tendency. Biases with respect to tree shape are correlated with objective functions that are based upon unusual asymmetric tree-to-tree distance or fit measures. Split, quartet, and triplet fit, most similar supertree, and MinCut methods (provided the latter are interpreted as Adams consensus-like supertrees) are not revealed to have any bias with respect to tree shape by our example, but whether this holds more generally is an open problem. Future development and evaluation of supertree methods should consider explicitly the undesirable biases and other properties that we highlight. In the meantime, use of a single, arbitrarily chosen supertree method is discouraged. Use of multiple methods and/or weighting schemes may allow practical assessment of the extent to which inferences from real data depend upon methodological biases with respect to input tree shape or size.

Classification↗
PubMed2005

BioMOBY successfully integrates distributed heterogeneous bioinformatics Web Services. The PlaNet exemplar case.

The burden of non-interoperability between on-line genomic resources is increasingly the rate-limiting step in large-scale genomic analysis. BioMOBY is a biological Web Service interoperability initiative that began as a retreat of representatives from the model organism database community in September, 2001. Its long-term goal is to provide a simple, extensible platform through which the myriad of on-line biological databases and analytical tools can offer their information and analytical services in a fully automated and interoperable way. Of the two branches of the larger BioMOBY project, the Web Services branch (MOBY-S) has now been deployed over several dozen data sources worldwide, revealing some significant observations about the nature of the integrative biology problem; in particular, that Web Service interoperability in the domain of bioinformatics is, unexpectedly, largely a syntactic rather than a semantic problem. That is to say, interoperability between bioinformatics Web Services can be largely achieved simply by specifying the data structures being passed between the services (syntax) even without rich specification of what those data structures mean (semantics). Thus, one barrier of the integrative problem has been overcome with a surprisingly simple solution. Here, we present a non-technical overview of the critical components that give rise to the interoperable behaviors seen in MOBY-S and discuss an exemplar case, the PlaNet consortium, where MOBY-S has been deployed to integrate the on-line plant genome databases and analytical services provided by a European consortium of databases and data service providers.

Computational Biology↗
PubMed2004

Does a tree-like phylogeny only exist at the tips in the prokaryotes?

The extent to which prokaryotic evolution has been influenced by horizontal gene transfer (HGT) and therefore might be more of a network than a tree is unclear. Here we use supertree methods to ask whether a definitive prokaryotic phylogenetic tree exists and whether it can be confidently inferred using orthologous genes. We analysed an 11-taxon dataset spanning the deepest divisions of prokaryotic relationships, a 10-taxon dataset spanning the relatively recent gamma-proteobacteria and a 61-taxon dataset spanning both, using species for which complete genomes are available. Congruence among gene trees spanning deep relationships is not better than random. By contrast, a strong, almost perfect phylogenetic signal exists in gamma-proteobacterial genes. Deep-level prokaryotic relationships are difficult to infer because of signal erosion, systematic bias, hidden paralogy and/or HGT. Our results do not preclude levels of HGT that would be inconsistent with the notion of a prokaryotic phylogeny. This approach will help decide the extent to which we can say that there is a prokaryotic phylogeny and where in the phylogeny a cohesive genomic signal exists.

Bacteria↗
PubMed2004

Local endemism within the Western Ghats-sri Lanka biodiversity hotspot.

The apparent biotic affinities between the mainland and the island in the Western Ghats-Sri Lanka biodiversity hotspot have been interpreted as the result of frequent migrations during recent periods of low sea level. We show, using molecular phylogenies of two invertebrate and four vertebrate groups, that biotic interchange between these areas has been much more limited than hitherto assumed. Despite several extended periods of land connection during the past 500,000 years, Sri Lanka has maintained a fauna that is largely distinct from that of the Indian mainland. Future conservation programs for the subcontinent should take into account such patterns of local endemism at the finest scale at which they may occur.

Amphibians↗
PubMed2004

A subterranean generalist predator: diet of the soil-dwelling caecilian Gegeneophis ramaswamii (Amphibia; Gymnophiona; Caeciliidae) in southern India.

Biologists have paid relatively little attention to subterranean predators, especially their ecology. Although diets of some subterranean lower vertebrates suggest specialisation, there remains a lack of quantitative data. The diet of the caecilian amphibian Gegeneophis ramaswamii was investigated through analyses of gut contents of 67 specimens collected in randomised surveys at three localities in Kerala, southern India, in early and mid-monsoon. Although termites were the most frequently ingested items in the mid-monsoon, the specialist predator hypothesis was rejected because of differences in diet found in early monsoon samples, when earthworms contributed the greatest mass. That guts of some G. ramaswamii contained many individuals of only a single dietary taxon was interpreted as feeding on patchily distributed prey rather than specialisation. No ontogenetic differences in diet were apparent, but more sampling is required to investigate this further. Subadults largely feed on fewer items of the same prey as adults, though there is an indication that subadult diet is less diverse. The data do not support differences between male and female diet. High densities of G. ramaswamii, and perhaps of other terrestrial caecilians and subterranean lower vertebrates feeding on soil-ecosystem engineers (termites, earthworms and ants), might substantially impact soil ecology.

Amphibians↗
PubMed2004

Phylogeny of caecilian amphibians (Gymnophiona) based on complete mitochondrial genomes and nuclear RAG1.

We determined the complete nucleotide sequence of the mitochondrial (mt) genome of five individual caecilians (Amphibia: Gymnophiona) representing five of the six recognized families: Rhinatrema bivittatum (Rhinatrematidae), Ichthyophis glutinosus (Ichthyophiidae), Uraeotyphlus cf. oxyurus (Uraeotyphlidae), Scolecomorphus vittatus (Scolecomorphidae), and Gegeneophis ramaswamii (Caeciliidae). The organization and size of these newly determined mitogenomes are similar to those previously reported for the caecilian Typhlonectes natans (Typhlonectidae), and for other vertebrates. Nucleotide sequences of the nuclear RAG1 gene were also determined for these six species of caecilians, and the salamander Mertensiella luschani atifi. RAG1 (both at the amino acid and nucleotide level) shows slower rates of evolution than almost all mt protein-coding genes (at the amino acid level). The new mt and nuclear sequences were compared with data for other amphibians and subjected to separate and combined phylogenetic analyses (Maximum Parsimony, Minimum Evolution, Maximum Likelihood, and Bayesian Inference). All analyses strongly support the monophyly of the three amphibian Orders. The Batrachia hypothesis (Gymnophiona, (Anura, Caudata) receives moderate or good support depending on the method of analysis. Within Gymnophiona, the optimal tree (Rhinatrema, (Ichthyophis, Uraeotyphlus), (Scolecomorphus, (Gegeneophis Typhlonectes) agrees with the most recent morphological and molecular studies. The sister group relationship between Rhinatrematidae and all other caecilians, that between Ichthyophiidae and Uraeotyphlidae, and the monophyly of the higher caecilians Scolecomorphidae+Caeciliidae+Typhlonectidae, are strongly supported, whereas the relationships among the higher caecilians are less unambiguously resolved. Analysis of RAG1 is affected by a spurious local rooting problem and associated low support that is ameliorated when outgroups are excluded. Comparisons of trees using the non-parametric Templeton, Kishino-Hasegawa, Approximately Unbiased, and Shimodaira-Hasegawa tests suggest that the latter may be too conservative.

Amphibians↗