G M Davis

Publications (12)14.14 Total impact

• Article: Anatomical variation in cryptic mudsnail species: Statistical discrimination and evolutionary significance

  T. Wilke, M. Pfenninger, G. M. Davis
  [show abstract] [hide abstract]
  ABSTRACT: In the present paper, the brackish-water mudsnail genus Hydrobia is used to assess the degree of anatomical differentiation among cryptic species. Detailed anatomical data for seven populations from four taxa are compared to genetic data in order to test whether there are discrete anatomical differences among taxa, whether it is possible to partition the total anatomical variation into hierarchical among-taxa and among-population components, to find those anatomical characters that statistically discriminate taxa, and to make inferences about the mode of evolution. A qualitative anatomical analysis did not yield any character states that could be used to differentiate among taxa, and a PCA of quantitative anatomical characters did not discriminate among species. Moreover, no significant variance component could be detected in the nested analysis of morphological variance among lineages and/or populations. However, discriminant analyses (DA) with mtDNA lineages as grouping variables resulted in highly significant discrimination models for sexes combined, females and males. The DA's retained up to 16 variables and LIP to six of them showed significant differences among lineages. Generally, shell characters were performing better than soft body characters. The poor performance of soft body characters is attributed to an unusually high intraspecific variability in Hydrobia. Anatomical, ecological, and biogeographical characteristics that could have contributed to the high variability are discussed. The evolution of anatomical variables among lineages was rested for deviation from expectations derived from a stochastic evolution model. The test showed that the null hypothesis of stochastic evolution according to the Brownian motion model could not be rejected, indicating that anatomical characters in Hydrobia are neither Subject to diversifying nor to constrained evolution. Based on genetic and supportive anatomical data, one of the taxa in the study, Hydrobia sp. A, is considered to be a new species and formally described as Hydrobia dierbaensis n.sp.
  Proceedings of the Academy of Natural Sciences of Philadelphia 01/2002; 152:45-66. · 0.83 Impact Factor
• Article: [Preliminary study on cytochrome C oxidase 1 gene of Oncomelania hupensis from Miao River area in Hubei province].

  C H Shi, C P Qiu, M Y Xia, Z Feng, G M Davis
  [show abstract] [hide abstract]
  ABSTRACT: To study the mitochondrial cytochrome C oxidase 1(CO1) gene of Oncomelania snails from Miao River area in Hubei Province. Oncomelania snails were collected from Miao River area, including upstream and downstream. Genomic DNA was extracted from the tissue of the snail. PCR was used to amplify a fragment of the CO1 gene. Sequences of the CO1 fragment were determined directly from the purified PCR products by an automated sequencer. Sequences for each individual were assembled and edited using ESEE 3.0 s. A distance matrix was computed using program DNADISt of PHYLIP(3.57). Unrooted maximum likelihood trees were calculated from program FITCH. The amplified CO1 gene of the snail was a fragment of 638 bp in length. Sequence analysis showed that the accumulated variable sites were significant different between upstream and downstream populations, being 29 and 46, respectively. From the number of variable sites in the gene, snails in this area were roughly separated into two groups. Each of them was a mixture of both upstream and downstream snails. Same haplotypes were confirmed to be present among the collected sites along the river. From the distance matrix of sequence divergence, the population upstream vs downstream differed by 0.0221 +/- 0.0105. There were more variation in downstream population than that in upstream. Gene flow was identified in these populations. The phylogenetic trees suggest the existence of two groups, but all of them belong to 0. h. hupensis.
  Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 02/2001; 19(1):41-4.
• Source

  Available from: jcu.edu.au

  Article: Evolutionary relationships between trematodes and snails emphasizing schistosomes and paragonimids.

  D Blair, G M Davis, B Wu
  [show abstract] [hide abstract]
  ABSTRACT: Snails and digeneans have been associated for at least 200 million years. Their inter-relationships over such a time-span must have been complex and varied. Few studies have attempted to explore these relationships in the light of knowledge of the phylogeny of both host and parasite groups. Here we focus on two important families of digeneans, the Schistosomatidae and the Paragonimidae, for which molecular phylogenies are available. We investigate the types of evolutionary relationships between host and parasite, operating at different phylogenetic depths, that might explain current host specificity and distributions of both associates. Both families of parasites utilise a number of highly diverged gastropod families, indicating that host extensions have featured in their histories. However, schistosomatids and paragonimids show different patterns of association with their snail hosts. As befits the apparently more ancient group, schistosomatids utilise snails from across a wide phylogenetic range within the Gastropoda. The genus Schistosoma itself has experienced one long-range host switch between pulmonates and caenogastropods. By contrast, paragonimids are restricted to two superfamilies of caenogastropods. Despite these differences, modern schistosomatid species appear to be more host specific than are paragonimids and host additions, at the level of host family, are far less common among species of schistosomatids than among paragonimids. Some species of Paragonimus exhibit remarkably low levels of host specificity, with different populations utilising snails of different families. Existing knowledge relating to the phenomenon will be presented in the context of phylogenies of schistosomatids, paragonimids, and their snail hosts. Discussion focuses on the usefulness of current theories of snail-digenean coevolution for interpreting these findings. In the past, much emphasis has been placed on the idea that digeneans engage in a one-to-one arms race with their snail host. We consider that phylogenetic tracking rather than an arms-race relationship might be a common alternative. Not being bound by the restrictions imposed by an arms race, some digeneans might be able to extend to new host species more easily than the literature suggests. Switches into related host taxa are most likely. However, ecologically equivalent but unrelated gastropod hosts may also be exploited. Given the right ecological setting, digeneans are able to switch across considerable phylogenetic distances. Examples from the Paragonimidae and Schistosomatidae are given.
  Parasitology 02/2001; 123 Suppl:S229-43. · 2.96 Impact Factor
• Article: Oncomelania hupensis (Gastropoda: rissooidea) in eastern China: molecular phylogeny, population structure, and ecology.

  T Wilke, G M Davis, C Cui-E, Z Xiao-Nung, Z Xiao Peng, Z Yi, C M Spolsky
  [show abstract] [hide abstract]
  ABSTRACT: The rissooidean snail genus Oncomelania is of medical interest as various taxa are hosts for the human blood fluke Schistosoma and the lung fluke Paragonimus; because of close co-evolved host-parasite-relationships, snail diversity may reflect parasite diversity. There is a considerable amount of confusion regarding the identity of smooth- and ribbed-shelled populations of Oncomelania hupensis in eastern China. We therefore studied the genetic variation, population structure, phylogenetic relationships and ecology of five smooth- and five ribbed-shelled populations in Hubei, Hunan, Anhui, Zhejiang, and Jiangsu provinces. Based on sequencing data of a fragment of the mitochondrial gene for cytochrome oxidase I from 80 individuals, we found little genetic variability within the ingroup-individuals studied here (average pi=0.01922). Moreover, within the ingroup, smooth-shelled individuals cluster together with ribbed-shelled individuals. We therefore consider all smooth- and ribbed-shelled populations of Oncomelania throughout the lower Yangtze River basin to belong to the subspecies O. hupensis hupensis. Our data indicate that ribbing in O. h. hupensis is associated with the annual floods of the Yangtze River. The greatest haplotype (d(H)) and nucleotide diversities (pi) are found in aggregates of ribbed-shelled snails along areas of the Yangtze River drainage subject to flooding. In areas not affected by flooding, the shells are smooth and genetic diversity decreases significantly.
  Acta Tropica 12/2000; 77(2):215-27. · 2.72 Impact Factor
• Article: The mudsnail genus Hydrobia s.s. in the northern Atlantic and western Mediterranean: a phylogenetic hypothesis

  T. Wilke, E. Rolán, G. M. Davis
  [show abstract] [hide abstract]
  ABSTRACT: The mudsnail taxon Hydrobia s.l. plays a major role in numerous ecological and parasitological studies. Yet, its taxonomy is confusing and its biogeography is poorly understood. A principal problem is that taxa of Hydrobia s.l. belong to morphostatic radiations – widely allopatric species radiations with little or no habitat diversification and a low level of anatomical change. So far, three morphostatic radiations can be identified within Hydrobia s.l.: Hydrobia s.s., Peringia, and Ventrosia. These radiations are identical with the putative genera of Hydrobia s.l. The purpose of the paper is to infer phylogenetic relationships within one of these radiations, Hydrobia s.s. in the northern Atlantic and western Mediterranean. A total of 22 populations, including topotypical populations of five commonly used taxa, were studied genetically using partial sequences of the mitochondrial cytochrome c oxidase subunit I gene. Based on molecular data and the species concept we define, the following species and subspecies were identified: Hydrobia acuta acuta (Draparnaud, 1805) [=H. minoricensis (Paladilhe, 1875)], H. acuta neglecta Muus, 1963, and H. glyca (Servain, 1880) (=H. joossei van Aartsen, Menkhorst and Gittenberger, 1984). One population from Djerba, Tunisia (Hydrobia sp. A) and one population from Mallorca, Spain (Hydrobia sp. B) are genetically distinct from all other taxa studied here. Both populations potentially represent new species. Due to the fact that only one population each has been studied, and so the degree of variation within these two taxa cannot be assessed, a final decision regarding their species level cannot yet be made.
  Marine Biology 11/2000; 137(5):827-833. · 2.28 Impact Factor
• Source

  Available from: ajtmh.org

  Article: Erhaia (Gastropoda: Rissooidea): phylogenetic relationships and the question of Paragonimus coevolution in Asia.

  T Wilke, G M Davis, X Gong, H X Liu
  [show abstract] [hide abstract]
  ABSTRACT: The human lung fluke Paragonimus is transmitted by gastropod taxa of two superfamilies: Ceritheoidea and Rissooidea. The question whether or not Paragonimus shows the same specificity of host-parasite coevolved relationship as the human blood fluke Schistosoma was inspired by the finding of two sympatric snail species as hosts for Paragonimus skrjabini in Fujian Province, China: Gammatricula and Erhaia. The former species can clearly be classified as Pomatiopsidae: Triculinae. The latter has previously been classified as Pomatiopsidae: Pomatiopsinae. However, this classification based on anatomical characteristics is uncertain. In order to obtain a robust phylogenetic hypothesis for Erhaia, we have studied three gene fragments from this taxon as well as from twelve related taxa. The data show that the species involved represent four families: Pomatiopsidae, Hydrobiidae, Cochliopidae (here raised to family status), and Amnicolidae. Erhaia fits securely into the Amnicolidae. This indicates that P. skrjabini has not coevolved with snail lineages. However, P. skrjabini has so far only been reported from rissooidean snails, whereas members of the Paragonimus westermani complex have only been found in ceritheoidean snails. The implication is that there is a host specificity on the superfamily level. However, Asian freshwater species of the Ceritheoidea and Rissooidea usually are not sympatric and often prefer different habitats. It is therefore possible that ecological niche partitioning plays the primary role for Paragonimus evolution.
  The American journal of tropical medicine and hygiene 05/2000; 62(4):453-9. · 2.59 Impact Factor
• Article: Gene sequencing for identification of Paragonimus eggs from a human case.

  Z S Chang, B Wu, D Blair, Y N Zhang, L Hu, S H Chen, M G Chen, Z Feng, G M Davis
  [show abstract] [hide abstract]
  ABSTRACT: To identify the etiologic agent from a paragonimiasis patient using molecular techniques. The complete nuclear ribosomal DNA second internal transcribed spacer (ITS2) gene sequence of eggs in sputum from a paragonimiasis patient was obtained by directly auto-sequencing its PCR product. ITS2 genes from eggs of Paragonimus westermani and Pagumogonimus skrjabini (both from animal hosts) were also sequenced for comparison. In addition, morphological comparisons were made with the eggs of the two species. The ITS2 gene from the human case was 100% identical with the sequence from the eggs of P. westermani from an experimentally infected dog but only 92% identical with the sequence from the eggs of P. skrjabini. Morphologically, the eggs from the human case more resembled those from P. westermani infected dog. The patient was diagnosed to be suffered from paragonimiasis westermani by gene sequence analysis.
  Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 02/2000; 18(4):213-5.
• Source

  Available from: jsczz.cn

  Article: [Allozyme-based genetic variation within an unstable "population" of Chinese Oncomelania hupensis (Gastropoda: Rissoacea: Pomatiopsidae)].

  Y Zhang, G M Davis, H X Liu, T Feng
  [show abstract] [hide abstract]
  ABSTRACT: To answer the following questions: 1. For Oncomelania snails collected two years apart from the same locality, has there been genetic divergence? 2. How much experimental error has there been in studying subsets of these populations? 3. As this is an unstable population, what has the net effect been on Hardy-Weinberg equilibrium (HWe)? Allozymes were studied using horizontal starch gel electrophoresis. Data collected from numbers of experiments were compiled. Data from each collection were divided into two equal subsets based on chronology of the experiments. Thirty-four loci were studied using 72 to 180 snails per subset. The mean number of alleles per locus ranged from 1.5-1.9. With each consecutive subset, the % polymorphic loci dropped from 38.2 to 17.6. The mean heterozygosity was very low: 0.033 to 0.049 and not significantly different from Hardy-Weinberg expectations. Ten loci and 11 alleles exclusive to the first group were eliminated from the overall study reducing the number of polymorphic loci from 19 to 10. There were significant departures from HWe at five loci having a substantial number of individuals for each allele. Nei's and Wright's D were 0.003 +/- 0.001 and 0.054 +/- 0.006 respectively. 1. There were significant errors seen primarily in the results scored in the earliest experiments. 2. These earlier errors involving scoring difficult to resolve loci, and interpretation of rare alleles that were not found in later experiment had no significant effect on overall genetic distance. 3. The use of Wright's D for closely related populations is explained. Results with Nei's D indicated no significant difference among the four subunits; Wright's D yielded significant difference between the collections made two years apart, attributed to the annual flooding of the Yangtze River mixing snails from different localities. 4. Major polymorphic loci were not in Hwe as predicted using the unstable population model. 5. One must study 25 or more individuals to find relatively rare alleles and study population genetics.
  Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 02/2000; 18(1):21-3 contd.
• Source

  Available from: Guevara Angel

  Article: A molecular perspective on the genera Paragonimus Braun, Euparagonimus Chen and Pagumogonimus Chen.

  D Blair, B Wu, Z S Chang, X Gong, T Agatsuma, Y N Zhang, S H Chen, J X Lin, M G Chen, J Waikagul, A G Guevara, Z Feng, G M Davis
  [show abstract] [hide abstract]
  ABSTRACT: The status of the genera Euparagonimus Chen, 1963 and Pagumogonimus Chen, 1963 relative to Paragonimus Braun, 1899 was investigated using DNA sequences from the mitochondrial cytochrome c oxidase subunit I (CO1) gene (partial) and the nuclear ribosomal DNA second internal transcribed spacer (ITS2). In the phylogenetic trees constructed, the genus Pagumogonimus is clearly not monophyletic and therefore not a natural taxon. Indeed, the type species of Pagumogonimus, P. skrjabini from China, is very closely related to Paragonimus miyazakii from Japan. The status of Euparagonimus is less obvious. Euparagonimus cenocopiosus lies distant from other lungflukes included in the analysis. It can be placed as sister to Paragonimus in some analyses and falls within the genus in others. A recently published morphological study placed E. cenocopiosus within the genus Paragonimus and probably this is where it should remain.
  Journal of Helminthology 01/2000; 73(4):295-9. · 1.38 Impact Factor
• Article: A molecular perspective on the genera Paragonimus Braun, Euparagonimus Chen and Pagumogonimus Chen

  D. Blair, B. Wu, Z.S. Chang, X. Gong, T. Agatsuma, Y.N. Zhang, S.H. Chen, J.X. Lin, M.G. Chen, J. Waikagul, A.G. Guevara, Z. Feng, G.M. Davis
  [show abstract] [hide abstract]
  ABSTRACT: The status of the genera Euparagonimus Chen, 1963 and Pagumogonimus Chen, 1963 relative to Paragonimus Braun, 1899 was investigated using DNA sequences from the mitochondrial cytochrome c oxidase subunit I (CO1) gene (partial) and the nuclear ribosomal DNA second internal transcribed spacer (ITS2). In the phylogenetic trees constructed, the genus Pagumogonimus is clearly not monophyletic and therefore not a natural taxon. Indeed, the type species of Pagumogonimus,P. skrjabini from China, is very closely related to Paragonimus miyazakii from Japan. The status of Euparagonimus is less obvious. Euparagonimus cenocopiosus lies distant from other lungflukes included in the analysis. It can be placed as sister to Paragonimus in some analyses and falls within the genus in others. A recently published morphological study placed E. cenocopiosus within the genus Paragonimus and probably this is where it should remain.
  Journal of Helminthology 11/1999; 73(04):295 - 299. · 1.38 Impact Factor
• Article: [Studies on allozyme of Gammatricula].

  X Zeng, C Chen, J Ding, G M Davis
  [show abstract] [hide abstract]
  ABSTRACT: To furnish molecular genetic evidences for taxonomy of Gammatricula. A total of 24 enzymes of 6 populations of Gammatricula songi and 1 population of Gammatricula chinensis collected from Kaihua County and Chunan County of Zhejiang Province were studied using horizontal starch gel electrophoresis. 29 loci were found. The percentages of polymorphic loci of G. songi populations were 6.9%-13.8%. All loci of G. chinensis were monomorphic. The Nei's distance among G. songi populations did not exceed 0.12. The Nei's distance between G. songi and G. chinensis was 0.73. The allozyme variations of inter-G. songi are limited, but the allozyme variation between G. songi and G. chinensis is significant.
  Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 02/1999; 17(2):84-6.
• Article: [Study on allele frequency in Oncomelania from the mainland of China].

  Y Zhang, T Feng, G M Davis
  [show abstract] [hide abstract]
  ABSTRACT: Nine populations of Oncomelania, field-collected from Anhui, Shanghai, Jiangsu, Zhejiang, Jiangxi, Hunan, Hubei, Sichuan and Yunnan were studied by horizontal starch gel electrophoretic method with 24 enzyme systems (AAT, AcPH, AK, AO, APH, CK, EST, GDH, GPI, G6PD, HBD, ISDH, LAP, LDH, ME, MDH, MPI, NADD, OCT, PGM, 6PGD, SDH, SOD, XDH) analyzed. 40 loci and 117 alleles were detected in the Oncomelania. Both of GPI and PGM-I, with 7 alleles, were the most variable loci. 22 loci had more than 3 alleles each. Of 40 loci examined in the 24 isozyme systems, 14 were found to be polymorphic, the proportion of multilocus enzymes being 58.3%. Our results showed that the genetic polymorphism existing in the populations of Oncomelania in the mainland of China. PGM and MDH, were found in both the populations of Oncomelania and strains of Schistosoma japonicum in the mainland of China. The results provided a new idea for studying snails and Schistosoma. Also, we found that there might be some correlation between the polymorphic locus and the feature of the shell of Oncomelania snail.
  Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases 02/1994; 12(3):172-7.