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N B Chilton

Publications and source records attributed to N B Chilton.

At least 73 records · Page 4Linked to original sources
PubMed1996

Strongylus asini (Nematoda, Strongyloidea): genetic relationships with other Strongylus species determined by ribosomal DNA.

Genomic DNA was isolated from adult Strongylus asini collected from zebra. The second ribosomal transcribed spacer (ITS-2) was amplified and sequenced using polymerase chain reaction (PCR) based techniques. The DNA sequence was compared with previously published data for 3 related Strongylus species. A PCR-linked restriction fragment length polymorphism method allowed the 4 species to be differentiated unequivocally. The ITS-2 sequence of S. asini was found to be more similar to those of S. edentatus (87.1%) and S. equinus (95.3%) than to that of S vulgaris (73.9%). This result confirms that S. Asini and S vulgaris represent separate species and supports the retention of the 4 species within 1 genus.

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PubMed1996

The ITS-2 rDNA of Teladorsagia circumcincta, T. trifurcata and T. davtiani (Nematoda: Trichostrongylidae) indicates that these taxa are one species.

There remains uncertainty about the species status of Teladorsagia circumcincta, T. davtiani and T. trifurcata. In this study, the second internal transcribed spacer (ITS-2) sequences of these taxa and 2 other members within the same subfamily (Ostertagiinae) were examined. Although some sequence variation was detected between and within single worms of each taxon of Teladorsagia, no unequivocal base differences were detected among their consensus ITS-2 sequence. In comparison, there was 9% sequence difference between O. ostertagi and O. leptospicularis and 13-15% difference between the genera Teladorsagia and Ostertagia. These findings indicate that T. circumcincta, T. davtiani and T. trifurcata represent a single species, T. circumcincta.

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PubMed1995

Characterisation of taeniid cestode species by PCR-RFLP of ITS2 ribosomal DNA.

Seven species of taeniid cestode (Echinococcus granulosus. E. multilocularis, Taenia hydatigena, T. ovis, T. pisiformis, T. multiceps and T. serialis) were characterised using a polymerase chain reaction-based restriction fragment length polymorphism technique (PCR-RFLP). The second internal transcribed spacer of ribosomal DNA (ITS2) was amplified from various geographical isolates of each of the seven species, digested separately with four restriction endonucleases and the fragments were separated by conventional agarose gel electrophoresis. PCR-RFLP produced characteristic patterns for each taeniid species examined. No variation in RFLP patterns was observed among different isolates of E. multilocularis and the species of Taenia, but distinct intraspecific variation was detected in E. granulosus. The present study indicates the usefulness of the PCR-RFLP of ITS2 for systematic, epidemiological and diagnostic purposes.

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PubMed1995

Differences in the second internal transcribed spacer (ribosomal DNA) between five species of Trichostrongylus (Nematoda: Trichostrongylidae).

The second internal transcribed spacer (ITS-2) of the ribosomal DNA of 5 species of Trichostrongylus has been sequenced. The ITS-2 of the 5 species was 237 or 238 bases in length, and had a GC content of approximately 30%. No evidence of intraspecific variation was detected in the ITS-2 sequence of T. colubriformis, T. vitrinus or T. retortaeformis, irrespective of the life cycle stage examined. There was evidence, however, of variation at five positions in the ITS-2 sequence of T. vitrinus samples and at one position in T. axei, indicating intra-individual variation in the sequence of different copies of the ribosomal DNA. Nonetheless, there were consistent sequence differences between the five Trichostrongylus species examined. The level of interspecific differences in nucleotide sequence was low (1.3-7.6%), with the species infecting birds (T. tenuis) being genetically more different to the four species found in mammals. Some of the nucleotide differences between species occurred at the recognition sites of endonucleases, which makes them of important diagnostic value for species identification. Also of significance are the recognition sites for several enzymes located within the regions of sequence homology for the five species of Trichostrongylus. These may prove useful in distinguishing between genera of trichostrongyle nematodes.

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PubMed1995

Differences in a ribosomal DNA sequence of Strongylus species allows identification of single eggs.

In the current study, molecular techniques were evaluated for the species identification of individual strongyle eggs. Adult worms of Strongylus edentatus, S. equinus and S. vulgaris were collected at necropsy from horses from Australia and the U.S.A. Genomic DNA was isolated and a ribosomal transcribed spacer (ITS-2) amplified and sequenced using polymerase chain reaction (PCR) techniques. The length of the ITS-2 sequence of S. edentatus, S. equinus and S. vulgaris ranged between 217 and 235 nucleotides. Extensive sequence analysis demonstrated a low degree (0-0.9%) of intraspecific variation in the ITS-2 for the Strongylus species examined, whereas the levels of interspecific differences (13-29%) were significantly greater. Interspecific differences in the ITS-2 sequences allowed unequivocal species identification of single worms and eggs using PCR-linked restriction fragment length polymorphism. These results demonstrate the potential of the ribosomal spacers as genetic markers for species identification of single strongyle eggs from horse faeces.

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PubMed1995

Differentiation of Haemonchus placei from H. contortus (Nematoda: Trichostrongylidae) by the ribosomal DNA second internal transcribed spacer.

There has been much debate as to whether H. placei is a separate species to H. contortus. The aim of this study is to provide molecular information to assess the species status of H. placei. Using the polymerase chain reaction, the second internal transcribed spacer (ITS-2) of ribosomal DNA was amplified and sequenced. Comparison of the 231 base pair ITS-2 sequences showed no intraspecific variation in H. contortus, among one isolate from each of the United Kingdom. Switzerland and China and 5 isolates from within Australia, or among 3 Australian isolates of H. placei. Three (1.3%) nucleotide differences were detected between the ITS-2 sequences of H. contortus and H. placei. In addition, 2 diagnostic sites for the endonucleases BfaI and FokI allowed the delineation of H. placei from H. contortus. The data presented herein support previous morphological and genetic evidence that H. placei is a separate species to H. contortus.

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PubMed1995

Differences in a ribosomal DNA sequence of morphologically indistinguishable species within the Hypodontus macropi complex (Nematoda: Strongyloidea).

The nucleotide sequence of the second internal transcribed spacer (ITS-2) from ribosomal DNA has been determined for 3 members of the Hypodontus macropi species complex. Sequences were compared from nematodes collected from 3 species of Australian macropodid marsupial, Petrogale persephone, Macropus robustus robustus and Thylogale billardierii. The ITS-2 of each operational taxonomic unit ranged from 287 to 292 bases in length, and had a GC content of 36.6-40.1%. Differences in nucleotide sequence between nematodes from the different host species ranged from 25.0% to 28.3%. The data suggest that H. macropi from P. persephone represents a different species to those in M. r. robustus and T. billardierii. The unique feature of this study is that it represents a comparison of the ribosomal DNA sequences of nematode species which are morphologically indistinguishable but which have been demonstrated to be genetically distinct (i.e. cryptic) species based on electrophoretic data. The results also demonstrate further that morphological characters alone are often not adequate for species recognition. Differences between these 3 species of H. macropi in their recognition sites for restriction endonucleases, indicates that a PCR-RFLP approach could be used, in conjunction with allozyme electrophoresis, to establish how many species are present within the H. macropi complex.

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PubMed1995

Division of Giardia isolates from humans into two genetically distinct assemblages by electrophoretic analysis of enzymes encoded at 27 loci and comparison with Giardia muris.

Giardia that infect humans are known to be heterogeneous but they are assigned currently to a single species, Giardia intestinalis (syn. G. lamblia). The genetic differences that exist within G. intestinalis have not yet been assessed quantitatively and neither have they been compared in magnitude with those that exist between G. intestinalis and species that are morphologically similar (G. duodenalis) or morphologically distinct (e.g. G. muris). In this study, 60 Australian isolates of G. intestinalis were analysed electrophoretically at 27 enzyme loci and compared with G. muris and a feline isolate of G. duodenalis. Isolates of G. intestinalis were distinct genetically from both G. muris (approximately 80% fixed allelic differences) and the feline G. duodenalis isolate (approximately 75% fixed allelic differences). The G. intestinalis isolates were extremely heterogeneous but they fell into 2 major genetic assemblages, separated by fixed allelic differences at approximately 60% of loci examined. The magnitude of the genetic differences between the G. intestinalis assemblages approached the level that distinguished the G. duodenalis isolate from the morphologically distinct G. muris. This raises important questions about the evolutionary relationships of the assemblages with Homo sapiens, the possibility of ancient or contemporary transmission from animal hosts to humans and the biogeographical origins of the two clusters.

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PubMed1994

Species identification of trichostrongyle nematodes by PCR-linked RFLP.

Restriction fragment length polymorphisms (RFLP) of the second internal transcribed spacer (ITS-2) of ribosomal DNA were examined for 6 species of ruminant nematodes; Trichostrongylus colubriformis, T. axei, T. vitrinus, Haemonchus contortus, Teladorsagia circumcincta and Cooperia oncophora. The ITS-2 of each species was amplified by PCR and restricted with the endonucleases DraI, HinfI, RsaI and VspI. Using this approach, the 6 species could be distinguished. No intraspecific variation in RFLP's has been detected so far in the ITS-2 of these species, suggesting that this technique has considerable potential for the identification of eggs of different nematode species in faecal samples.

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PubMed1994

Influence of environmental factors on oviposition and egg development in Amblyomma limbatum and Aponomma hydrosauri (Acari: Ixodidae).

This study examined the influence of temperature and light on the length of the pre-oviposition period of engorged females of two Australian ixodid ticks, Amblyomma limbatum and Aponomma hydrosauri. The hatching success and development time of eggs of both species were also compared at different temperatures and relative humidities. Darkness was found to have no effect on the duration of the pre-oviposition time or reproductive output of females of either species. In contrast, the preoviposition period of females of both species decreased with increasing temperature. Amb. limbatum females had shorter pre-oviposition periods than Ap. hydrosauri at all temperatures examined. Temperature and relative humidity had a marked effect on the hatching success of eggs. Eggs of both species had reduced hatching success at low relative humidities. Eggs failed to hatch at temperatures below 21 degrees C. Ap. hydrosauri eggs also failed to hatch at 34 degrees C while Amb. limbatum eggs failed to hatch at 36 degrees C. Within the range of temperatures suitable for egg development, the hatching times of eggs of both species decreased with increasing temperature. Amb. limbatum eggs developed faster than Ap. hydrosauri eggs at temperatures greater than 25 degrees C, but slower at cooler temperatures. These differences in the duration of their preoviposition period, and the responses of females and their eggs to different temperatures and relative humidities correlate with the different climates the two species experience throughout most of their distributional range.

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PubMed1993

Sibling species within Macropostrongyloides baylisi (Nematoda: Strongyloidea) from macropodid marsupials.

Macropostrongyloides baylisi from four different species or subspecies of host were analysed electrophoretically at 27 enzyme loci. The results revealed the existence of two species, one in Macropus giganteus and the other in M. robustus robustus, M.r. erubescens and M.r. parryi, that had fixed genetic differences at 33% of loci. Populations of nematodes from two subspecies of M. robustus, M.r. robustus from Queensland and M.r. erubescens from South Australia, had fixed genetic differences at two (7.4%) of 27 loci and were considered to belong to the same species. No fixed genetic differences were detected between nematodes from M. parryi and M.r. robustus. A discriminant function analysis of morphological data assigned 96% of specimens to groups defined on the basis of the host species or subspecies from which they were obtained. This separation of Ma. baylisi into host-specific groups did not, however, totally correlate with the electrophoretic data. The species of M. baylisi in M. giganteus was genetically more distinct from the sibling species in M. robustus/M. parryi than to a related but morphologically dissimilar nematode, Ma. yamagutii from M. fuliginosus. This suggests an evolutionary parallel between host and parasite at the genetic level which is not reflected by morphological differences.

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PubMed1993

Lack of intraspecific variation in the second internal transcribed spacer (ITS-2) of Trichostrongylus colubriformis ribosomal DNA.

The nucleotide sequence of the second internal transcribed spacer (ITS-2) was determined for three populations of the parasitic nematode Trichostrongylus colubriformis which differed in their susceptibility to benzimidazole anthelmintics and/or in their geographical origin. No intraspecific variation was found in the ITS-2 sequence, indicating that this region of rDNA is inadequate to discriminate between resistant and susceptible populations of T. colubriformis, but it may prove useful for distinguishing between species of Trichostrongylus.

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PubMed1992

Apparent lack of genetic variation within Pelecitus roemeri (Nematoda: Filarioidea) from three Australian species of macropodid marsupial.

An electrophoretic study of Pelecitus roemeri from Macropus robustus, M. giganteus and Wallabia bicolor revealed no genetic differences at 23 enzyme loci. The genetic data support the existing morphological evidence that P. roemeri from these three hosts represents a single species. The data show no genetic variation between nematodes from the same or different host species collected in northern and southern Australia. This result is discussed briefly in relation to Price's model of parasite speciation.

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PubMed1992

An index to assess the reproductive fitness of female ticks.

This paper describes an index that assesses the reproductive fitness of female ticks. The Reproductive Fitness Index (RFI) is calculated by the number of eggs that hatch into larvae as a function of the body weight of the engorged female at the time of detachment from the host. The RFI has an advantage over existing reproductive indices because it takes into account the viability of eggs laid by females. This is of ecological significance because it provides a more accurate and biologically relevant measurement in intraspecific and/or interspecific comparisons of the reproductive fitness of females.

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PubMed1992

Interspecific differences in the movements of female ticks on reptiles.

Movements of females of two reptile ticks, Amblyomma limbatum and Aponomma hydrosauri were studied to determine whether the behaviour of the species on hosts was similar or different. Experiments were conducted to determine if the movement of females on hosts prior to mating was influenced by the delayed attachment of conspecific males. A field experiment was also undertaken to determine whether data obtained during laboratory experiments reflected the behaviour of females on hosts in the field. Both in laboratory and field experiments, a significantly greater proportion of Ap. hydrosauri females changed their site of attachment prior to mating. Individual Ap. hydrosauri females made significantly more positional changes than Amb. limbatum females. These interspecific differences occurred irrespective of the absence of conspecific males or presence of non-conspecific adults on hosts. These data may have important ecological implications in relation to the success of colonizing females at their parapatric boundary.

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PubMed1992

Detection by allozyme electrophoresis of cryptic species of Hypodontus macropi (Nematoda: Strongyloidea) from macropodid marsupials.

Allozyme electrophoresis of 98 Hypodontus macropi from eight different species of hosts using 24 enzymes revealed a complex of at least six sibling species, with 15-50% fixed genetic differences between taxa. Except for the taxon parasitizing Macropus rufus/M. robustus, pairs of parasite taxa were, in each case, sympatric at each locality examined, thus supporting the conclusion that they represent valid species. The existence of a series of host-specific nematode taxa explains many of the inconsistencies noted previously in the host distribution of H. macropi. Comparison of parasite allozyme phenograms with host phylogeny suggests that four of the speciation events could be attributable to cospeciation and two to host switching. A clear case of host switching between M. rufus/M. robustus and M. fuliginosus was found.

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