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R S Thorpe

Publications and source records attributed to R S Thorpe.

28 records · Page 2Linked to original sources
PubMed2000

The dynamics of natural selection and vicariance in the Dominican anole: patterns of within-island molecular and morphological divergence.

The larger islands of the Lesser Antilles are ecologically and geologically complex and are inhabited by single, but morphologically variable, Anolis species. Although earlier work has indicated that a large part of the morphological variation in Anolis oculatus from Dominica can be attributed to selection, a history of recurrent volcanic activity over the last few million years suggests that vicariance may have also played a significant role. We report a study of variation in the cytochrome b gene of mitochondrial DNA across the island to address this issue. We uncovered a very high degree of polymorphism, with an overall gene diversity of 0.97 and a nucleotide diversity of 0.04. Sequences, on average, differ by 3.82% and the maximum pairwise divergence (corrected for multiple hits) is 9.29%. Most haplotypes are restricted to single localities (a pattern not changed by increasing the sample size). Phylogenetic analysis revealed the presence of two distinct lineages on the island with strong phylogeographic structure. One of these is geographically restricted to a relatively small part of the central Caribbean coast. Sublineages were also discernible within the other more widely distributed lineage, but resolution within and support for these sublineages was poor. The phylogeographic pattern is not congruent with generalized body shape and scalation, but is significantly correlated with color pattern. Even when correcting for this lineage effect with partial Matrix correspondence tests, the relationship between color pattern and vegetation is reaffirmed, suggesting that although both vicariance and selection have played a role in the morphological differentiation of this species, selection for current environmental conditions has been more important. We discuss the causes of the phylogeographic structure in light of the volcanic history of the island and highlight the exceptional instance of congruence between all morphological character systems and lineage boundaries, which occurs at the transition between the northern and southern Caribbean ecotypes.

Animals↗
PubMed1996

Diet and snake venom evolution.

Venom composition within snake species can show considerable geographical variation, an important consideration because bites by conspecific populations may differ in symptomatology and require different treatments. The underlying causes of this phenomenon have never been explained. Here we present evidence that the variation in the venom of the pitviper Calloselasma rhodostoma (Serpentes: Viperidae) is closely associated with its diet. We also evaluated other possible causes of geographic variation in venom using partial Mantel tests and independent contrasts, but rejected both contemporary gene flow (estimated from geographical proximity) and the phylogenetic relationships (assessed by analysis of mitochondrial DNA) among populations as important influences upon venom evolution. As the primary function of viperid venom is to immobilize and digest prey and prey animals vary in their susceptibility to venom, we suggest that geographical variation in venom composition reflects natural selection for feeding on local prey.

Animals↗
PubMed1996

Electrophoretic profiles and biological activities: intraspecific variation in the venom of the Malayan pit viper (Calloselasma rhodostoma)

The Malayan pit viper (Calloselasma rhodostoma) is of major clinical significance both as a leading cause of snakebite and as the source of ancrod (Arvin). Although its venom has been extensively studied, the degree to which venom composition varies between individuals is poorly known. We individually analysed the venoms of over 100 C. rhodostoma using isoelectric focusing. In all populations, females produced an intense band that was absent from all males, and significant ontogenetic variation was detected. Principal components analysis of the banding profiles also revealed strong geographic variation, which was significantly congruent with variation in the biological activities of the venom (phosphodiesterase, alkalinephosphoesterase, L-amino acid oxidase, arginine ester hydrolase, 5'-nucleotidase, thrombin-like enzyme, haemorrhagic activity). Studies of captive-bred snakes indicate that the intraspecific variation in venom is genetically inherited rather than environmentally induced. The intraspecific variation in venom composition and biological activity could be of applied importance to snakebite therapy, both in correct diagnosis of the source of envenomation and in the development of a more effective antivenom. Greater attention should be given to the source of C. rhodostoma venom used in research to ensure reproducibility of results.

5'-Nucleotidase↗
PubMed1994

Naja siamensis, a cryptic species of venomous snake revealed by mtDNA sequencing.

Because of possible variation in venom composition, an understanding of venomous snake systematics is of great importance for the optimization of antivenom treatment of snakebite patients. Intraspecific variation in the morphology of many venomous snakes complicates the definition and identification of some species when allopatric populations are involved. Selectively neutral or near-neutral mtDNA sequences can reveal evolutionary relationships obscured by ecogenetically-caused morphological variation. We use comparative sequencing of the cytochrome oxidase subunit 1 gene to reveal the existence of a widespread, cryptic species of spitting cobra from southeast Asia. This species, Naja siamensis, is widely sympatric with other Asiatic cobra species. This may be of considerable medical significance, and calls for further research into venom composition in Asiatic cobras.

Amino Acid Sequence↗
PubMed1991

Asiatic cobras: systematics and snakebite.

The population affinities of the Asiatic cobras of the genus Naja are investigated, using multivariate analysis of a range of morphological characters. This complex, which was formerly thought to be monospecific, consists of at least eight full species. In some cases, species whose bites require different antivenoms occur sympatrically. The new understanding of the systematics of the Asiatic cobra complex calls for a reappraisal of cobra antivenom use in Asia, and for more research into venom composition.

Animals↗
PubMed1984

Percutaneous Trucut lung biopsy in the diagnosis of localised pulmonary lesions.

In a prospective evaluation of percutaneous Trucut needle biopsy for localised intrathoracic lesions in 89 patients histological specimens were obtained in 81. Malignancy was diagnosed in 66 cases. Subsequently definitive histological reports were available in 18 of these patients with complete concordance of malignant cell type. Sixteen patients had non-malignant histological appearances, which were later confirmed objectively in six. In three patients there was no follow up information, but in the remainder the clinical course was entirely consistent with the histological appearances of the biopsy specimens. Adequate specimens were obtained from only two of the five lesions less than 2 cm in diameter. Lesions deeper than 8 cm from the site of biopsy were associated with significantly more haemorrhagic complications than more superficial lesions. Comparison with other series indicates that Trucut needle biopsy which produces histological specimens has greater diagnostic accuracy than cytological techniques for both malignant and non-malignant localised lesions. It is concluded that this technique has a definite place in the investigation of this common problem in carefully selected patients provided that strict attention is paid to the details of the technique.

Adult↗
PubMedDate not supplied

Heterologous amplification of microsatellite markers from colubroid snakes in European natricines (serpentes: natricinae).

Eighteen microsatellite loci developed for a range of snake species (New World natricines, elapids, crotalids) were tested against European natricines (Natrix natrix, N. maura, and N. tessellata) in cross-species amplification experiments. Five loci were polymorphic (average expected heterozygosity 0.749 for a population of N. natrix in Amsterdam, mean sample size 47.8) and three loci were monomorphic. The remainder could not be consistently scored or failed to amplify. Further tests on single individuals of a diverse set of eight species of colubroid snakes showed that 15 of the 18 loci could be cross-amplified in at least one of these species. We conclude that our results show promise for the utilization of these markers for experimental assessments of genetic variation in the phylogenetically closely related group of European natricine snakes with emphasis on N. natrix. The full suite of microsatellite markers now available for snakes may show additional potential for subsequent investigation across a broader range of colubroid snakes.

Animals↗