The role played by parasites and pathogens in biological invasions is increasingly recognised. In particular, alien species can lose part of their parasite fauna during the introduction process and this loss can positively affect their settlement and spread (enemy release hypothesis). Moreover, aliens can introduce in the environment new parasites that may spillover to naive native species or act as reservoir for local parasites, increasing their density and altering their epidemiology (spill-back hypothesis). Our aim is to investigate the macroparasite community of grey squirrels (Sciurus carolinensis) in Northern Italy to determine whether the alien species lost any parasite species, introduced new parasites to Europe or acquired local parasites. We also explored variation in grey squirrels' parasite burdens in order to point out potential factors that may increase disease risk for native species (in particular congeneric Eurasian red squirrels, S. vulgaris). A total of 279 grey squirrels were sampled between 2011 and 2013 in 7 study areas located in Northern Italy. Squirrels were captured using standard live-trapping techniques and immediately euthanised by CO2 inhalation. During post mortem examination, grey squirrels were first screened visually for ectoparasites, then their gut was extracted and dissected to collect gastro-intestinal content and search for gastro-intestinal helminths. Variation in the abundance of the most common helminth and ectoparasite species was then analysed through Generalised Linear Models (GLMs). We identified 6 gastro-intestinal nematode species and one cestode species. The most common helminths were the North American nematodes Strongyloides robustus (prevalence: 56.6%) and Trichostrongylus calcaratus (6.5%). All the other helminths were European species and were rare, with prevalence below 5%. Notably, grey squirrels acquired the red squirrel ossiurid Tripanoxyuris sciuri. The abundance of S. robustus varied with density of hosts in the area and with season and was positively affected by host body condition. The ectoparasite community was composed by 2 flea species, 1 sucking louse and 1 hard tick. The most common arthropods were the red squirrel flea Ceratophyllus sciurorum (26.0%) and the Holarctic sucking louse Neohaematopinus sciuri (17.7%). C. sciurorum abundance was affected by host density and season. Overall, parasite richness in Italian grey squirrel populations was much lower than in their native range, where 8 helminths and 7 ectoparasites with prevalence above 5% are reported. Several species common in North America are indeed missing and the number of acquired Palearctic parasites does not compensate the number of species lost. To test whether grey squirrels actually benefit from this parasite loss further research is needed. Two North American species were successfully introduced by grey squirrels. In particular, the nematode S. robustus has been reported in red squirrels co-inhabiting with the alien species, indicating that spillover from grey to red occurs. Also, the acquisition of the nematode T. sciuri and the flea C. sciurorum by grey squirrels is particularly alarming for the native species. Indeed, in grey squirrels we found a spring peak in C. sciurorum abundance, whereas, for red squirrels, an autumn peak is reported. Hence, where the two species co-inhabit, the normal seasonal distribution of C. sciurorum could be altered by the presence of grey squirrels, with an increased impact on red squirrels during spring. Examining whether the acquisition of these species actually has repercussions for red squirrels and investigating the consequences of S. robustus spillover for the native species should both be priorities for future research.

The macroparasite community of alien grey squirrels (sciurus carolinensis) in Italy: composition, variability and implications for native species conservation / C. Romeo, L.A. Wauters, N. Ferrari, P. Lanfranchi, A. Martinoli, B. Pisanu, D. Preatoni, N. Saino - In: Convegno Nazionale sui Piccoli Mammiferi : libro dei riassunti[s.l] : Gruppo piccoli Mammiferi - Associazione Teriologica Italiana, 2013. - pp. 23-23 (( Intervento presentato al 2. convegno Convegno Nazionale sui Piccoli Mammiferi tenutosi a Ercolano nel 2013.

The macroparasite community of alien grey squirrels (sciurus carolinensis) in Italy: composition, variability and implications for native species conservation

C. Romeo
Primo
;
N. Ferrari;P. Lanfranchi;N. Saino
Ultimo
2013

Abstract

The role played by parasites and pathogens in biological invasions is increasingly recognised. In particular, alien species can lose part of their parasite fauna during the introduction process and this loss can positively affect their settlement and spread (enemy release hypothesis). Moreover, aliens can introduce in the environment new parasites that may spillover to naive native species or act as reservoir for local parasites, increasing their density and altering their epidemiology (spill-back hypothesis). Our aim is to investigate the macroparasite community of grey squirrels (Sciurus carolinensis) in Northern Italy to determine whether the alien species lost any parasite species, introduced new parasites to Europe or acquired local parasites. We also explored variation in grey squirrels' parasite burdens in order to point out potential factors that may increase disease risk for native species (in particular congeneric Eurasian red squirrels, S. vulgaris). A total of 279 grey squirrels were sampled between 2011 and 2013 in 7 study areas located in Northern Italy. Squirrels were captured using standard live-trapping techniques and immediately euthanised by CO2 inhalation. During post mortem examination, grey squirrels were first screened visually for ectoparasites, then their gut was extracted and dissected to collect gastro-intestinal content and search for gastro-intestinal helminths. Variation in the abundance of the most common helminth and ectoparasite species was then analysed through Generalised Linear Models (GLMs). We identified 6 gastro-intestinal nematode species and one cestode species. The most common helminths were the North American nematodes Strongyloides robustus (prevalence: 56.6%) and Trichostrongylus calcaratus (6.5%). All the other helminths were European species and were rare, with prevalence below 5%. Notably, grey squirrels acquired the red squirrel ossiurid Tripanoxyuris sciuri. The abundance of S. robustus varied with density of hosts in the area and with season and was positively affected by host body condition. The ectoparasite community was composed by 2 flea species, 1 sucking louse and 1 hard tick. The most common arthropods were the red squirrel flea Ceratophyllus sciurorum (26.0%) and the Holarctic sucking louse Neohaematopinus sciuri (17.7%). C. sciurorum abundance was affected by host density and season. Overall, parasite richness in Italian grey squirrel populations was much lower than in their native range, where 8 helminths and 7 ectoparasites with prevalence above 5% are reported. Several species common in North America are indeed missing and the number of acquired Palearctic parasites does not compensate the number of species lost. To test whether grey squirrels actually benefit from this parasite loss further research is needed. Two North American species were successfully introduced by grey squirrels. In particular, the nematode S. robustus has been reported in red squirrels co-inhabiting with the alien species, indicating that spillover from grey to red occurs. Also, the acquisition of the nematode T. sciuri and the flea C. sciurorum by grey squirrels is particularly alarming for the native species. Indeed, in grey squirrels we found a spring peak in C. sciurorum abundance, whereas, for red squirrels, an autumn peak is reported. Hence, where the two species co-inhabit, the normal seasonal distribution of C. sciurorum could be altered by the presence of grey squirrels, with an increased impact on red squirrels during spring. Examining whether the acquisition of these species actually has repercussions for red squirrels and investigating the consequences of S. robustus spillover for the native species should both be priorities for future research.
Settore VET/06 - Parassitologia e Malattie Parassitarie degli Animali
Settore BIO/07 - Ecologia
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/233854
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