Molecular approaches to systematic problems in parasitic nematodes : ribosomol DNA variation within cystidicola spp. (Nematoda: Habronematoidea) and the superfamily dracunculoidea
Notice bibliographique
Résumé
Morphological characters are traditionally used in nematode systematics, however, morphological convergence and marginal differences between close relatives can obscure species diversity and confound taxonomic studies. This thesis applies molecular approaches to systematic problems in two groups of parasitic nematodes where morphological data is ambiguous. Ribosomal DNA (rDNA) variable regions such as the first and second internal transcribed spacers (ITS-1 and ITS-2), and the D3 expansion loop of the large subunit have consistently distinguished nematode species and provided a limited basis for phylogenetic inference between close relatives. I assess rDNA variation within Cystidicola spp. (Nematoda; Habronematoidea) and the superfamily Dracunculoidea to examine species diversity in both groups, and phylogenetic relationships in the Dracunculoidea. Phenotypic variation in Cystidicola spp. suggests unresolved variation within the genus. Distinct life histories, host ranges, reproductive strategies, and adult and egg morphologies define the two recognized Cystidicola spp. Variable host specificity and egg morphology in Cystidicola farionis is difficult to interpret and could reflect genetic species-level variation. I sequenced four rDNA regions (ITS-1, ITS-2, 5.8S, D3) from Cystidicola spp. isolates from a total of seven host species and nine locations in Ontario (ONT), British Columbia (BC) and Finland (FIN). The ITS-1, 5.8S, and D3 regions displayed no inter or intraspecific variation. Two ITS-2 types were identified which differed at four nucleotide positions: the ITS-2 from C. farionis (BC) and C. stigmatura was identical and 365bp long; the ITS-2 from ONT and FIN C. farionis was identical and 368bp long. No relationship between egg morphology and genetic variation was apparent. ITS-2 differences between morphologically distinct C. farionis (ONT and FIN) and C. stigmatura were expected but comparison of this region among C. farionis isolates produced a surprising result. The ITS-2 distinguishes C. farionis (BC) from C. farionis (ONT and FIN) and suggests a closer relationship between C. farionis (BC) and C. stigmatura. Morphological resemblance among close relatives and a lack of phylogenetically informative characters in the superfamily Dracunculoidea reiterates this need for more precise taxonomic markers. I examined the D3 and ITS-2 regions from a total of nine dracunculoid species to distinguish cryptic species (e.g. Philonema spp.), place unidentified nematodes within the current classification system, and infer phylogenetic relationships within dracunculoid families (e.g. the Philometridae and Guyanemidae). I sequenced the D3 of two dracunculoid species, Philometroides huronensis and an unidentified nematode from Eopsetta exilis, adding these to an existing D3 data set of seven dracunculoids and sequenced the ITS-2 from all nine species. These regions varied in their ability to distinguish close relatives. The D3 region distinguishes Philonema agubernaculum and P. oncorhynchi but not Cystidicola spp. whereas the ITS-2 is identical in the former taxa and distinct in the latter. Both ITS-2 and D3 data supported previous suggestions that the family Philometridae may be artificial, and that members of the Guyanemidae are affiliated with some philometrids (e.g. Philonema spp.).
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,000 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».