ORCID Profile
0000-0002-4183-4533
Current Organisation
Natural History Museum
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Publisher: Springer Science and Business Media LLC
Date: 09-11-2020
DOI: 10.1186/S12915-020-00899-W
Abstract: Chromosome-level assemblies are indispensable for accurate gene prediction, synteny assessment, and understanding higher-order genome architecture. Reference and draft genomes of key helminth species have been published, but little is yet known about the biology of their chromosomes. Here, we present the complete genome of the tapeworm Hymenolepis microstoma , providing a reference quality, end-to-end assembly that represents the first fully assembled genome of a spiralian/lophotrochozoan, revealing new insights into chromosome evolution. Long-read sequencing and optical mapping data were added to previous short-read data enabling complete re-assembly into six chromosomes, consistent with karyology. Small genome size (169 Mb) and lack of haploid variation (1 SNP/3.2 Mb) contributed to exceptionally high contiguity with only 85 gaps remaining in regions of low complexity sequence. Resolution of repeat regions reveals novel gene expansions, micro-exon genes, and spliced leader trans-splicing, and illuminates the landscape of transposable elements, explaining observed length differences in sister chromatids. Syntenic comparison with other parasitic flatworms shows conserved ancestral linkage groups indicating that the H. microstoma karyotype evolved through fusion events. Strikingly, the assembly reveals that the chromosomes terminate in centromeric arrays, indicating that these motifs play a role not only in segregation, but also in protecting the linear integrity and full lengths of chromosomes. Despite strong conservation of canonical telomeres, our results show that they can be substituted by more complex, species-specific sequences, as represented by centromeres. The assembly provides a robust platform for investigations that require complete genome representation.
Publisher: Springer Science and Business Media LLC
Date: 05-11-2018
Publisher: Elsevier BV
Date: 02-2010
DOI: 10.1016/J.IJPARA.2009.07.012
Abstract: Trypanorhynch tapeworms (Platyhelminthes: Cestoda) are among the most erse and abundant groups of metazoan parasites of elasmobranchs and are a ubiquitous part of the marine food webs that include these apex predators. Here we present a comprehensive analysis of their phylogeny, character evolution and host associations based on 10years of s ling effort, including representatives of 12 of 15 and 44 of 66 currently recognized trypanorhynch families and genera, respectively. Using a combination of ssrDNA and lsrDNA (Domains 1-3) for 79 and 80 taxa, respectively, we maintain one-to-one correspondence between molecules and morphology by scoring 45 characters from the same specimens used for sequencing, and provide museum vouchers for this material. Host associations are examined through likelihood-based ancestral character state reconstructions (ACSRs) and by estimating dates of ergence using strict and relaxed molecular clock models in a Bayesian context. Maximum parsimony and Bayesian inference analyses of rDNA produced well-resolved and strongly supported trees in which the trypanorhynchs formed two primary lineages and were monophyletic with respect to the diphyllidean outgroup taxa. These lineages showed marked differences in their rates of ergence which in turn resulted in differing support and stability characteristics within the lineages. Mapping of morphological characters onto the tree resulting from combined analysis of rDNA showed most traits to be highly plastic, including some previously considered of key taxonomic importance such as underlying symmetries in tentacular armature. The resulting tree was found to be congruent with the most recent morphologically based superfamily designations in the order, providing support for four proposed superfamilies, but not for the Tentacularioidea and Eutetrarhynchoidea. ACSRs based on the combined analysis of rDNA estimated the original hosts of the two primary parasite lineages to be alternatively rajiform batoids and carcharhiniform sharks. This fundamental split provides independent support for rejecting the notion that rays are derived sharks, and thus supports the most recent molecular phylogenies of the Neoselachii. Beyond the basal split between shark- and ray-inhabiting lineages, no pattern was found to suggest that the trypanorhynchs have closely tracked the evolutionary histories of these host lineages, but instead, it appears that host-switching has been common and that the subsequent evolution of the parasites has been ecologically driven primarily through overlap in the niches of their shark and ray hosts. Using a relaxed molecular clock model calibrated by means of host fossil data, the ray-inhabiting lineage is estimated to have ersified around the Jurassic-Cretaceous boundary, whereas the shark-inhabiting lineage is estimated to have ersified later, in the Middle Cretaceous. Although the large error associated with the estimated ergence dates prevents robust conclusions from being drawn, the dates are nevertheless found to be consistent in a relative sense with the origins of their major hosts groups. The erection and definition of the suborders Trypanobatoida and Trypanoselachoida, for the major clades of trypanorhynchs parasitizing primarily rays and sharks, respectively, is proposed for the two primary lineages recovered here.
Publisher: The Royal Society
Date: 25-05-2016
Abstract: Australian spiny mountain crayfish ( Euastacu s, Parastacidae) and their ecotosymbiotic temnocephalan flatworms (Temnocephalida, Platyhelminthes) may have co-occurred and interacted through deep time, during a period of major environmental change. Therefore, reconstructing the history of their association is of evolutionary, ecological, and conservation significance. Here, time-calibrated Bayesian phylogenies of Euastacus species and their temnocephalans ( Temnohaswellia and Temnosewellia ) indicate near-synchronous ersifications from the Cretaceous. Statistically significant cophylogeny correlations between associated clades suggest linked evolutionary histories. However, there is a stronger signal of co ergence and greater host specificity in Temnosewellia , which co-occurs with Euastacus across its range. Phylogeography and analyses of evolutionary distinctiveness (ED) suggest that regional differences in the impact of climate warming and drying had major effects both on crayfish and associated temnocephalans. In particular, Euastacus and Temnosewellia show strong latitudinal gradients in ED and, conversely, in geographical range size, with the most distinctive, northern lineages facing the greatest risk of extinction. Therefore, environmental change has, in some cases, strengthened ecological and evolutionary associations, leaving host-specific temnocephalans vulnerable to coextinction with endangered hosts. Consequently, the extinction of all Euastacus species currently endangered (75%) predicts coextinction of approximately 60% of the studied temnocephalans, with greatest loss of the most evolutionarily distinctive lineages.
Publisher: Cold Spring Harbor Laboratory
Date: 09-04-2020
DOI: 10.1101/2020.04.08.031872
Abstract: Chromosome-level assemblies are indispensable for accurate gene prediction, synteny assessment and understanding higher-order genome architecture. Reference and draft genomes of key helminth species have been published but little is yet known about the biology of their chromosomes. Here we present the complete genome of the tapeworm Hymenolepis microstoma, providing a reference-quality, end-to-end assembly that represents the first fully assembled genome of a spiralian/lophotrochozoan, revealing new insights into chromosome evolution. Long-read sequencing and optical mapping data were added to previous short-read data enabling complete re-assembly into six chromosomes, consistent with karyology. Small genome size (169 Mb) and lack of haploid variation (1 SNP/3.2 Mb) contributed to exceptionally high contiguity with only 85 gaps remaining in regions of low complexity sequence. Resolution of repeat regions reveals novel gene expansions, micro-exon genes, and spliced leader transsplicing, and illuminates the landscape of transposable elements, explaining observed length differences in sister chromatids. Syntenic comparison with other parasitic flatworms shows conserved ancestral linkage groups indicating that the H. microstoma karyotype evolved through fusion events. Strikingly, the assembly reveals that the chromosomes terminate in centromeric arrays, indicating that these motifs play a role not only in segregation, but also in protecting the linear integrity and full lengths of chromosomes. Despite strong conservation of canonical telomeres, our results show that they can be substituted by more complex, species-specific sequences, as represented by centromeres. The assembly provides a robust platform for investigations that require complete genome representation.
Publisher: Elsevier BV
Date: 11-2007
DOI: 10.1016/J.ACTATROPICA.2007.07.008
Abstract: Dicrocoelium dendriticum (Rudolphi, 1819) and Dicrocoelium hospes (Looss, 1907) are recognised to affect the liver of domestic and wild ruminants. A third species, Dicrocoelium orientalis which was described from musk deer in the Baikal region of the former Soviet Union and re-named to Dicrocoelium chinensis (Sudarikov and Ryjikov, 1951) Tang and Tang, 1978 was isolated from other species of deer in Asian countries and from mouflon and roe deer in Europe. Scant information is available for D. chinensis, including the range of species that act as definitive and intermediate hosts. To provide morphological and molecular evidences differentiating D. chinensis versus D. dendriticum, 239 Dicrocoelium spp. specimens were collected from sheep, cattle and sika deer from different localities in Austria, Germany and Italy. Specimens were morphologically identified based on the testes orientation, overall size, and level of maximum body width and other morphometric measurements. From this s le, 10 specimens of D. chinensis and 25 of D. dendriticum from different hosts and geographical localities were characterized molecularly through sequencing of partial 18S rDNA (approximately 1400 bp) and ITS-2 (including the 5.8S and 28S flanking regions approximately 600 bp). Interspecific differences between D. dendriticum and D. chinensis of 0.14% and 3.8% were recorded in 18S rRNA and ITS-2 sequences, respectively. Phylogenetic analyses via Bayesian inference were conducted using sequences of ITS-2 (276 bp) and partial 28S (221 bp) of the above species of Dicrocoelium together with 20 species belonging to the Xiphidiata within the Plagiorchiida available in GenBank. Both gene regions were strongly concordant in differentiating the Dicrocoeliidae, Gorgoderidae and Plagiorchiidae and were in agreement with their current classification. Morphological and molecular characterization clearly differentiate D. dendriticum and D. chinensis as two distinct digeneans infecting ruminants. The implications on the separate status of D. chinensis on the etiology, biology and diagnosis of dicrocoeliosis are discussed.
Publisher: Informa UK Limited
Date: 24-02-2023
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Peter Olson.