Macroparasite Fauna of Alien Grey Squirrels (Sciurus carolinensis): Composition, Variability and Implications for Native Species

Abstract

Introduced hosts populations may benefit of an "enemy release" through impoverishment of parasite communities made of both few imported species and few acquired local ones. Moreover, closely related competing native hosts can be affected by acquiring introduced taxa (spillover) and by increased transmission risk of native parasites (spillback). We determined the macroparasite fauna of invasive grey squirrels (Sciurus carolinensis) in Italy to detect any diversity loss, introduction of novel parasites or acquisition of local ones, and analysed variation in parasite burdens to identify factors that may increase transmission risk for native red squirrels (S. vulgaris). Based on 277 grey squirrels sampled from 7 populations characterised by different time scales in introduction events, we identified 7 gastro-intestinal helminths and 4 parasite arthropods. Parasite richness is lower than in grey squirrel's native range and independent from introduction time lags. The most common parasites are Nearctic nematodes Strongyloides robustus (prevalence: 56.6%) and Trichostrongylus calcaratus (6.5%), red squirrel flea Ceratophyllus sciurorum (26.0%) and Holarctic sucking louse Neohaematopinus sciuri (17.7%). All other parasites are European or cosmopolitan species with prevalence below 5%. S. robustus abundance is positively affected by host density and body mass, C. sciurorum abundance increases with host density and varies with seasons. Overall, we show that grey squirrels in Italy may benefit of an enemy release, and both spillback and spillover processes towards native red squirrels may occur.

Diversity and host specificity of coccidia (Apicomplexa: Eimeriidae) in native and introduced squirrel species

“…Therefore, in both cases, additional investigation is needed to Finally, the low Eimeria species richness observed in two alien squirrel species suggests parasite-release which might facilitate the establishment of these species in the invaded range. A loss of species has been indeed already demonstrated for the macroparasite fauna of both alien species in Italy (Mazzamuto et al 2016;Romeo et al 2014). In order to verify this mechanism the next step should be to assess the pathological effect of these Eimeria species and quantify their impact on squirrel's fitness.…”

“…In contrast to SQPV or nematodes introduced by the alien grey squirrels (Collins et al 2014;Romeo et al 2014Romeo et al , 2015, the possible transmission and the potential role of monoxenous coccidia in mediating the competition between native and invasive squirrels in Italy were not confirmed. …”

Macroparasites of introduced parakeets in Italy: a possible role for parasite-mediated competition

“…For instance, grey squirrels introduced into Italy may acquire native squirrel fleas (Ceratophyllus sciurorum sciurorum), thereby increasing their transmission risk to native European red squirrels (Romeo et al 2014).…”

“…Although there is a potential for parasite spillback from non-native species to impact native communities (Romeo et al 2014), this phenomenon has been rarely documented in biological invasions because it is generally assumed that native parasites are unimportant when assessing the impacts of alien species (Kelly et al 2009). Moreover, it is difficult to evaluate the native or non-native status of many parasite species because the inventories of parasites and their geographic range are incomplete for many countries (Kelly et al 2009).…”

Ectoparasite load in the crested porcupine Hystrix cristata Linnaeus, 1758 in Central Italy

“…This result suggests a possible loss of ectoparasites during the history of introduction of H. cristata in Italy (e.g., Torchin et al 2003). The introduction of alien species increases incidence, pathogenicity, and geographical range of native parasites locally acquired (Romeo et al 2014). Therefore, if the crested porcupine keeps increasing its range, ectoparasite infestations in the newly colonized areas should be further investigated, with a special attention deserved to P. irritans, which has the human as a primary host (Buckland and Sadler 1989;Beaucournu and Launay 1990).…”