Parasite dynamics in an invaded ecosystem: helminth communities of native wood mice are impacted by the invasive bank vole.

It is becoming increasingly evident that biological invasions result in altered disease dynamics in invaded ecosystems, with knock-on effects for native host communities. We investigated disease dynamics in an invaded ecosystem, using the helminth communities of the native wood mouse (Apodemus sylvaticus) in the presence and absence of the invasive bank vole (Myodes glareolus) in Ireland. Native wood mice were collected over 2 years from four sites to assess the impact of the presence of the bank vole on wood mouse helminth community dynamics both at the component and infracommunity level. We found evidence for dilution (Syphacia stroma), spill-back (Aonchotheca murissylvatici) and spill-over (Taenia martis) in native wood mice due to the presence of the bank vole. Site of capture was the most important factor affecting helminth community structure of wood mice, along with year of capture and host-age and the interactions between them.

Reduced helminth parasitism in the introduced bank vole (Myodes glareolus): More parasites lost than gained.

Introduced species are often less parasitised compared to their native counterparts and to ecologically similar hosts in the new environment. Reduced parasitism may come about due to both the loss of original parasites and low acquisition of novel parasites. In this study we investigated the intestinal helminth parasites of the introduced bank vole (Myodes glareolus) in Ireland. Results were compared to data from other European studies and to the intestinal helminth fauna of an ecologically similar native rodent in Ireland, the wood mouse (Apodemus sylvaticus). The helminth fauna of introduced bank voles exhibited low diversity with only 3 species recovered: Aspiculuris tianjinensis; Aonchotheca murissylvatici and Taenia martis larvae. In particular, no adult parasites with indirect life-cycles were found in bank voles suggesting that indirectly transmitted parasites are less likely to establish in invasive hosts. Also, the results of this study add support to the enemy release hypothesis.