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|Title:||L'integrità dell'ecosistema marino antartico come presupposto per lo studio della reazione parassita-ospite: un approccio genetico ed ecologico||Authors:||Nardi, Valentina||Keywords:||Contracaecum osculatum;Anisakidae;Antarctic fish;Genetic variability;Allozymes;mtDNA;Parasitic infections;Marine trophic webs;Pesci antartici;Variabilità genetica;Allozimi;Livelli di infestazione;Rete trofica marina;BIO/07||Issue Date:||25-Jun-2015||Publisher:||Università degli studi della Tuscia - Viterbo||Series/Report no.:||Tesi di dottorato di ricerca. 26. ciclo||Abstract:||
1.Genetic and ecological data onthe two Antarctic sibling species, C. osculatum sp. D and C. osculatum sp. E (Nematoda: Anisakidae) from fish of the Ross Sea, over a temporal scale
ABSTRACT The Ross Sea, Eastern Antarctica, is considered a “pristine ecosystem” and a biodiversity “hotspot”. This provides a chance to investigate a marine ecosystem scarcely impacted by human. The sibling species Contracaecum osculatum sp. D and C. osculatum sp. E are parasites embedded in the natural Antarctic marine ecosystem, where they have been documented in sympatry both in their definitive host (Weddell seal) and in fish intermediate/paratenic hosts. Aims of this study were to: 1) identify the larvae of C. osculatum (s.l.) recovered in fish hosts, collected during XXVII Italian Expedition to Antarctica (2011-2012); 2) perform a comparative analysis of the contemporary parasitic load and genetic variability estimates of C. osculatum sp. D and C. osculatum sp. E with respect to past samples collected during expedition 1993-1994. In this aim, a total of 200 fish specimens belonging to four Antarctic species (Chionodraco hamatus, Trematomus bernacchii, T. hansoni, T. newnesi) were analysed for Contracaecum sp. larvae, whose genetic identification was undertaken using allozyme diagnostic markers (N = 1347) and sequences analysis of the mtDNA cox2 gene (519bp) (N = 496).
No significant differences were found in the infection levels by C. osculatum sp. D and sp. E - genetically recognised – on a temporal scale (2011-2012 versus 1993-1994). Whereas, statistical significant differences were found between the occurrence of C. osculatum sp. D and C. osculatum sp. E in different fish species, independently by the two sampling periods. Indeed, C. osculatum sp. E resulted more prevalent in T. bernacchii; while, higher percentage of C. osculatum sp. D occurred in C. hamatus and T. hansoni. The two species showed also differences in the host infection site: C. osculatum sp. D showed higher percentage of infection in the fish liver.
High genetic variability values at both nuclear (14 allozymes loci) and mitochondrial (mtDNA cox2) level were found in the two species in both the sampling periods (2011-2012 and 1993-1994). The parasitic infection levels by C. osculatum sp. D and sp. E and their estimates of genetic variability showed no statistically significant variation, over a temporal scale, i.e. between the two Antarctic campaigns, suggesting that the low habitat disturbance of the Antarctic region permitting the maintenance of stable ecosystem trophic webs, contributes to the maintenance of a high population size of anisakid nematodes and of their genetic variability.
2. Parasitic infection by larval helminths in Antarctic fish: pathological changes and impact on the host body condition.
ABSTRACT: We examined pathological changes and relationship between body condition index
(BCI) and parasitic infection in 5 species of fish, including 42 icefish Chionodraco hamatus (Channichtyidae),2 dragonfish Cygnodraco mawsoni (Bathydraconidae), 30 emerald rock cod Trematomusbernacchii, 46 striped rock cod T. hansoni and 9 dusty rock cod T. newnesi (Nototheniidae)from the Ross Sea, Antarctica. All parasites were identified by a combination of morphology andmtDNA cytochrome-oxidase-2 sequence (mtDNA cox2) analysis, except Contracaecum osculatums.l., for which only the latter was used. Five larval taxa were associated with pathological changesincluding 2 sibling species (D and E) of the C. osculatum species complex and 3 cestodes includingplerocercoids of a diphyllobothridean, and 2 tetraphyllidean forms including cercoids withmonolocular and bilocular bothridia. The most heavily infected hosts were C. hamatus and C.mawsoni, with C. hamatus most often infected by C. osculatum sp. D and sp. E and diphyllobothrideans,while C. mawsoni was most often infected with tetraphyllidean forms. Histologically, allfish showed varying severity of chronic inflammation associated with larval forms of helminths.Diphyllobothrideans and C. osculatum spp. were located in gastric muscularis or liver and wereassociated with necrosis and mild to marked fibrosis. Moderate multifocal rectal mucosal chronicinflammation was associated with attached tetraphyllidean scolices. C. hamatus showed a strong negative correlation between BCI and parasite burden
3 The role of lantern fish (Myctophidae) in the lyfe cycle of cetacean parasites from western Meditterranean waters
ABSTRACT: Myctophids(lantern fish) andcephalopods play a key role in trophic webs from the continental slope and oceanic waters linking the zooplankton to top predators. Many cetaceans feed on both lantern fish and cephalopods, and such prey would thus be expected to bridge the trophic
gap in the life-cycle sof helminths infecting cetaceans. However, information on the life-cycles of most of these helminthes is extremely scanty. We examined the parasite fauna of myctophids and cephalopods in two areas from the western Mediterranean where at least 21 helminth taxa from cetaceans have been reported and both cetacean diversity and abundance is high. A total of 1012 individuals of 8 lantern fish species, namely, Ceratoscopelus maderensis, Lampanyctus crocodilus, Notoscopelus elongatus, Benthosema glaciale, Mycto- phum punctatum, Lobianchia dofleini, Diaphus holti and Hygophum benoiti, and 792 individuals of 2 cephalopod species, Alloteuthis media and Sepietta oweniana, were collected from the Gulf of Valencia and Alboran Sea (Spanish Mediterranean) during 2010–2012 and examined for larval helminths. All these species have been reported as prey forat least some cetacean species in the area. Only five helminth taxa were found. The nematodes Anisakis pegreffii and Anisakis physeteris were detected in N. elongatus and C. maderensis (overall prevalence for Anisakis: 8.1% and 0.5%,respectively).Their prevalence in N. elongatus was significantly higher than that from the other three myctophid species with n450 individuals. A single individual of Hysterothylacium sp. Was found in N. elongatus (prevalence:0.5%) and Raphidascarididaegen.spp.in N. elongatus and L. crocodilus (prevalence:20.3% and 0.7%,respectively). Juvenile didymozoid digeneans (Torticaecum type)were detected in N. elongatus and L. crocodilus (prevalence:18.5% and 4.3%,respectively).Two unidentified cestode plerocercoids were collected from N. elongatus. Our study suggests, for the first time, that myctophids could play a role as paratenic hosts in the oceanic life-cycle of A. pegreffii and A. physeteris in the western Mediterranean. None of the other larvae identified at least to family level infect cetaceans,but some of them can be transmitted to large predatory fish. The extreme scarcity of such cetacean parasites in this, and previous parasitological surveys of mesopelagic fish and cephalopods is at odds with the key role of these preys in the diet of oceanic cetaceans.
Il lavoro condotto per questa tesi di dottorato si inserisce nell’ambito del Progetto finanziato dal MIUR-PNRA 2009 dal titolo: “Diversità genetica spazio-temporale di endoparassiti delle regioni polari: uno studio per la valutazione dell’impatto dei cambiamenti globali sulle reti trofiche marine.
La tesi, è costituita da un’introduzione generale che comprende l’attuale tassonomia, il ciclo biologico e la distribuzione geografica delle specie di nematodi appartenenti al genere Contracaecum. Nei capitoli successivi sono stati presentati i risultati delle ricerche che rappresentano un avanzamento rispetto allo Stato dell’Arte. Alcuni di questi risultati sono stati già pubblicati su riviste internazionali, pertanto si è ritenuto opportuno mantenere in questa tesi, la struttura di pubblicazione.
Infine, nell’ultimo capitolo, è inserito un lavoro pubblicato che riguarda altri nematodi anisakidi, appartenenti al genere Anisakis. Il lavoro pur non essendo oggetto del titolo della tesi, è tuttavia inserito nel contesto delle ricerche sui nematodi anisakidi.
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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