Biomedical subjects

A Hugall

Publications and source records attributed to A Hugall.

8 recordsLinked to original sources

PubMed1999

Reticulate evolution and the origins of ribosomal internal transcribed spacer diversity in apomictic Meloidogyne.

Among root knot nematodes of the genus Meloidogyne, the polyploid obligate mitotic parthenogens M. arenaria, M. javanica, and M. incognita are widespread and common agricultural pests. Although these named forms are distinguishable by closely related mitochondrial DNA (mtDNA) haplotypes, detailed sequence analyses of internal transcribed spacers (ITSs) of nuclear ribosomal genes reveal extremely high diversity, even within individual nematodes. This ITS diversity is broadly structured into two very different groups that are 12%-18% divergent: one with low diversity (< 1.0%) and one with high diversity (6%-7%). In both of these groups, identical sequences can be found within individual nematodes of different mtDNA haplotypes (i.e., among species). Analysis of genetic variance indicates that more than 90% of ITS diversity can be found within an individual nematode, with small but statistically significant (5%-10%; P < 0.05) variance distributed among mtDNA lineages. The evolutionarily distinct parthenogen M. hapla shows a similar pattern of ITS diversity, with two divergent groups of ITSs within each individual. In contrast, two diploid amphimictic species have only one lineage of ITSs with low diversity (< 0.2%). The presence of divergent lineages of rDNA in the apomictic taxa is unlikely to be due to differences among pseudogenes. Instead, we suggest that the diversity of ITSs in M. arenaria, M. javanica, and M. incognita is due to hybrid origins from closely related females (as inferred from mtDNA) and combinations of more diverse paternal lineages.

Animals↗

PubMed1997

Phylogenetic analysis of the Monogenea and their relationships with Digenea and Eucestoda inferred from 28S rDNA sequences.

Platyhelminth phylogeny is controversial. Phylogenetic analyses of the partial domain C1 and the full domains D1 and C2 (358 nucleotides) from the 28S ribosomal RNA gene for 21 species from the Monogenea, Digenea, Cestoda, and, as the outgroup, Tricladida reveal major departures from prevailing theory. The Digenea and not the Monogenea (Monopisthocotylea and Polyopisthocotylea) form the sister group of the cestodes; the Monopisthocotylea and Polyopisthocotylea are each monophyletic, but the Monogenea do not form a monophylum; the sister group of the Digenea + Cestoda is the Polyopisthocotylea; and Monopisthocotylea are the sister group of all other parasitic flatworms.

Animals↗

PubMed1997

Evolution of the AT-rich mitochondrial DNA of the root knot nematode, Meloidogyne hapla.

Mitochondrial DNA of the root knot nematode Meloidogyne hapla was investigated for intraspecific diversity and divergence from other parthenogenetic root knot nematodes. A 1,900-bp fragment containing COII, tRNAHis, 16S rRNA, ND3 and Cyt b genes has been cloned and sequenced from one individual and an 1,188-bp region within this region was sequenced from four other Australian isolates. M. hapla mtDNA is more than 80% AT-rich, like other Meloidogyne spp. Nucleotide diversity within M. hapla is some 10-fold higher than across three other parthenogenetic species of root-knot nematode (M. arenaria, M. javanica, and M. incognita), implying an earlier origin for M. hapla. Nucleotide divergence between M. hapla and its congener M. javanica is as great as that between Ascaris suum and Caenorhabditis elegans, members of different nematode subclasses, while amino acid sequence difference between Meloidogyne is more than twice as great. This is interpreted as an AT-bias-induced acceleration of the amino acid substitution rate, over and above saturation of nucleotide divergence in the strongly AT-biased DNA, on three lines of evidence: (1) in conserved blocks in 16S rDNA congeneric Meloidogyne have no more differences than between A. suum and C. elegans; (2) the Meloidogyne lineage has more amino acid changes relative to the Ascaris/Caenorhabditis lineage with respect to four of five outgroups, the exceptional outgroup being the only species (Apis) as AT-rich as Meloidogyne; and (3) between the two Meloidogyne there are more first and second but fewer third codon position changes than between the other nematode species. M. hapla is also found to contain a 102-bp tandem repeat of at least 40 copies; a size, arrangement, and position the same as in M. javanica, but sequence comparisons did not demonstrate homology between the two repeats.

Amino Acid Sequence↗

PubMed1995

Molecular support for vicariance as a source of diversity in rainforest.

The origin of high diversity in tropical rainforests is attributed to divergence amongst relatively mesic, late Pleistocene refuges. To test this hypothesis we analysed sequence variation within the mitochondrial DNA of populations of six rainforest-dwelling vertebrate species (one lizard and five birds) in the Wet Tropical rainforests of northeastern Australia. Vicariance among historical refuges was indicated by geographically congruent variation across a historical climatic barrier previously predicted by modelling. Sequence divergence across the barrier varied widely, being highest in species with lowest vagility and greatest restriction to rainforest. A high altitude, rainforest-restricted species was exceptional in lacking mtDNA variation. These data support the suggested role of vicariance in promoting evolutionary diversity in rainforests but also indicate variation in the timing of vicariance events, with most speciation or divergence events occurring well before the late Pleistocene. The relation between the amount of molecular divergence and current ecology suggests a sequence of isolation events, perhaps of increasing severity, occurring between the late Tertiary and the late Pleistocene.

Animals↗

PubMed1994

Low, but strongly structured mitochondrial DNA diversity in root knot nematodes (Meloidogyne).

Root-knot nematodes (genus Meloidogyne) have been the subject of recent and numerous studies of genetic variation because of the need to develop molecular diagnostics for the four globally distributed, parthenogenetic species that are significant agricultural pests. Our analysis of Meloidogyne mtDNA improves on previous studies: (i) by examining restriction site polymorphism among a large number of isolates also characterized for standard morphological, host range and allozyme phenotypes; (ii) by using higher resolution electrophoretic techniques; and (iii) by mapping variable restriction sites with reference to the complete nucleotide sequence. This revealed fivefold less sequence divergence (< 0.6%) between variants than estimated in previous restriction fragment length polymorphism (RFLP) studies, but perfect correspondence between mtDNA haplotype and allozyme (esterase) phenotypes. The mtDNA variation, although limited, is strongly structured with as much divergence between two lineages of Meloidogyne arenaria as between either of these and Meloidogyne javanica. The low diversity of mtDNAs suggests that these parthenogenetic lineages arose from distinct but closely related sexual females, a pattern seen in other parthenogenetic complexes. In contrast to the concordance between mtDNA and allozyme markers, there were several discrepancies between the traditional methods of identification. We suggest that further studies of these nematodes should focus on well defined genetic groups, whether or not these coincide with existing taxonomic units.

Animals↗

PubMed1994

Sequence evolution and phylogenetic signal in control-region and cytochrome b sequences of rainbow fishes (Melanotaeniidae).

The nucleotide sequences of segments of the cytochrome b gene (351 bp), the tRNA(Pro) gene (49 bp), and the control region (approximately 313 bp) of mitochondrial DNA were obtained from 26 fish representing different populations and species of Melanotaenia and one species of Glossolepis, freshwater rainbow fishes confined to Australia and New Guinea. The purpose was to investigate relative rates and patterns of sequence evolution. Overall levels of divergence were similar for the cytochrome b and tRNA control-region sequences, both ranging from < 1% within subspecies to 15%-19% between genera. However, the patterns of sequence evolution differed. For the cytochrome b gene, transitions consistently exceeded transversions, the bias ranging from 4.2:1 to 2:1, depending on the level of sequence divergence. However, in the control-region sequence, a bias toward transitions (2:1) was observed only in comparisons between very similar sequences, and transversions outnumbered transitions in comparisons of divergent sequences. Graphic comparisons suggested that the control region was saturated for transitions at relatively low levels of sequence divergence but accumulated transversions at a greater rate than did the cytochrome b sequence. These distinct patterns of base substitution are associated with differences in A+T content, which is 70% for the tRNA control-region segment versus 50% for cytochrome b. A test for skewness in the distribution of lengths of random trees indicated that both segments contained phylogenetic signal. Parsimony analyses of the data from the two regions, with or without weighting schemes appropriate to the respective patterns of sequence evolution, identified the same five groupings of sequences, but the relationships among the groups differed. However, in most cases the branches uniting different combinations of groups were poorly supported, and the differences among topologies were insignificant. Considering the observed patterns of base substitution and the results of the phylogenetic analyses, we deduce that both the control region and cytochrome b are appropriate for population genetic studies but that the control region is less effective than cytochrome b for resolving relationships among divergent lineages of rainbow fishes.

Animals↗

PubMed1993

Comparison of type I and type II Chlamydia psittaci strains infecting koalas (Phascolarctos cinereus).

The native Australian marsupial Phascolarctos cinereus, otherwise known as the koala, is prone to infection by the obligate intracellular parasite Chlamydia psittaci, which causes ocular 'pink eye' and urogenital 'dirty tail' diseases. Several chlamydial DNA probes to both chromosomal and plasmid sequences were used to type by Southern blot analysis 51 samples taken from wild and captive koalas from habitats on the eastern seaboard of Australia as far apart as Queensland and Victoria. Two types of C. psittaci were observed and called types I and II. Type II was found more frequently than type I and occurred in both ocular and urogenital samples, while type I showed a strong but not absolute preference for ocular sites. Cross-hybridization analyses indicated that type I and type II had about 10% DNA sequence identity to each other. DNA analyses showed that type II was very closely related to some ovine and bovine chlamydiae but type I could not be related to any other C. psittaci strain available. Light and electron microscopic analyses of infected BGM monolayers revealed that the two strains were similar in morphological characteristics. The type I strain was considerably more infectious than the type II strain in BGM cells and in the yolk sacs of embryonated eggs. A PCR based assay detected both type I and type II koala chlamydiae in samples that had been negative by Southern blot and tissue culture and provided the first evidence that both types can occur simultaneously at the one site of infection.

Animals↗

PubMed1989

Conserved DNA sequences in chlamydial plasmids.

Two 7.4-kb plasmids from Chlamydia psittaci have been cloned and characterized. These plasmids are quite distinct from the 6.2-kb C. psittaci and the C. trachomatis plasmids when compared by restriction endonuclease analysis. The plasmids show considerable cross-hybridization, with only a small region highly conserved and identified as a 4 X 22-bp tandemly repeated region. This sequence is identical in the two size categories of C. psittaci plasmids and differs from C. trachomatis plasmids by only 2 bp in the 22-bp motif. AT-rich clusters 5' to the repeat region which are present in C. trachomatis and Escherichia coli plasmids were absent from both classes of C. psittaci plasmids. Extensive regions are less highly conserved but show a sufficient degree of cross-hybridization to suggest that the plasmids are homologous.

Animals↗