Invading parasites: spillover of an alien nematode reduces survival in a native species

Abstract

It is widely assumed that spillover of alien parasites to native host species severely impacts naïve populations, ultimately conferring a competitive advantage to invading hosts that introduced them. Despite such host-switching events occurring in biological invasions, studies demonstrating the impact of alien macroparasites on native animal hosts are surprisingly few. In Europe, native red squirrels (Sciurus vulgaris) are replaced by introduced North American grey squirrels (S. carolinensis) mainly through resource competition, and, only in the United Kingdom and Ireland, by competition mediated by a viral disease. In Italy such disease is absent, but spillover of an introduced North American nematode (Strongyloides robustus) from grey to red squirrels is known to occur. Here, we used long-term (9 years) capture-mark-recapture and parasitological data of red squirrels in areas co-inhabited by grey squirrels in Northern Italy to investigate the impact of this alien helminth on naïve native squirrels’ body mass, local survival, and reproduction of females. We found no negative effect of the alien parasite on body mass or reproductive success, but intensity of infection by S. robustus reduced survival of both male and female squirrels. Significantly, survival of squirrels co-infected by their native nematode, Trypanoxyuris sciuri, was less affected by S. robustus, suggesting a protective effect of the native helminth against the new infection. Hence, we demonstrate that alien S. robustus spillover adds to the detrimental effects of resource competition and stress induced by grey squirrels, further reducing the fitness of the native species in the presence of the invasive competitor.

Testing the parasite-mediated competition hypothesis between sympatric northern and southern flying squirrels

“…We recognize, however, that a caveat of our study is that it was a single year, which may only provide a snapshot of the complex interaction between hosts and parasite. In a different system, Romeo et al (2021) did not find a negative effect of S. robustus infection on body mass of native Eurasian red squirrels ( Sciurus vulgaris ), but found infection intensity reduced long-term survival. Therefore, long-term monitoring of S. robustus in our study area may be necessary to understand how this parasite may mediate competition between northern and southern flying squirrels as well as other sympatric sciurids.…”

Exotic Pet Trade as a Cause of Biological Invasions: The Case of Tree Squirrels of the Genus Callosciurus

“…A paradigm is the Squirrelpox virus (SQPV) transmitted by invasive grey squirrels, that act as healthy vectors, to native red squirrels, for which the disease is lethal in the vast majority of cases (e.g., [132]). As far as macroparasite-driven PMC is concerned, a spillover of an alien nematode (Strongyloides robustus) from grey squirrels, introduced in Italy, to the native red squirrels reduces the survival in infected animals with high parasite loads [43].…”

“…The most (in)famous invasive squirrel around the world is the Eastern grey squirrel, known for its spreading ability and its negative impact on native species and the environment [30,39]. Competitive exclusion through competition for food [40][41][42] and parasite-mediated com-petition are the main mechanisms that affect the survival and persistence of native red squirrel (S. vulgaris) populations in Europe [39,43].…”

A Review of Non-Invasive Sampling in Wildlife Disease and Health Research: What’s New?

“…However, we soon realised that our search missed several publications that might have been of interest. For instance, even some of our own papers using non-invasive methods were not retrieved (e.g., [215,216]). Other articles deserving of attention were pointed out to us by peer-reviewers such as a study using ticks to survey for pathogens in wombats [217], another one describing the use of a cytology cell sampler to collect samples from lesions in marine mammals [218], or yet another describing the use of drones to collect blow from them [219].…”