Abstract
Multiple parasite species simultaneously infecting a host can interact with one another, which has the potential to influence host-parasite interactions. Invasive species typically lose members of their parasite community during the invasion process. Not only do the founding population escape their parasites, but the rapid range expansion of invaders once in the invaded range can lead to additional stochastic loss of parasites. As such, parasite community dynamics may change along an invasion gradient, with consequences for host invasion success. Here, we use the bank vole, Myodes glareolus, introduced as a small founding population at a point source in the Republic of Ireland in c.1920's and its ecto- and endoparasites to ask: i) how does the parasite community vary across an invasion gradient, and ii) are parasite community associations driven by host traits and/or distance from the point of host introduction? We sampled the parasite community of M. glareolus at the proposed focal site of introduction, at mid-wave and the invasion front, and used a parasite interactivity index and statistical models to determine the potential for the parasite community to interact. Bank voles harboured up to six different parasite taxa, with a significantly higher parasite interactivity index at the foci of introduction (z = 2.33, p = 0.02) than elsewhere, suggesting the most established parasite community has greater opportunities to interact. All but one of four synergistic parasite community associations were driven by host traits; sex and body mass. The remaining parasite-parasite associations occurred at the mid-point of the invasion wave, suggesting that specific parasite-parasite interactions are not mediated by distance from a focal point of host introduction. We propose that host traits rather than location along an invasion gradient are more likely to determine parasite-parasite interactions in the invasive bank vole.
Highlights
The release of a species from the constraints of their native biotic community can give rise to changes in traits, resulting in explosive demographics within the invasive range (Colautti et al, 2004)
The interactivity index was associated with host traits; males at the focal point of introduction had a parasite community that was more likely to be interactive than females, this pattern was reversed elsewhere across the range
More detailed models examining specific parasite associations found that host traits were associated with three synergistic parasite community interactions, whilst an antagonistic interaction between parasites occurred at the mid-wave of the invasion range
Summary
The release of a species from the constraints of their native biotic community can give rise to changes in traits, resulting in explosive demographics within the invasive range (Colautti et al, 2004). Invasive species can be more fecund, larger in size and reach greater population sizes than their native counterparts (Blaustein et al, 1983; Keane and Crawley, 2002; Parker et al, 2013). A widely supported mechanism underlying these changed traits, and the success of invasive species is the enemy release hypothesis, whereby loss, or reduction of natural enemies; both predators and parasites, is translated into increased host fitness (Keane and Crawley, 2002). The regulatory effects of enemies are not equal, . The heterogeneity of enemy release is most clearly demonstrated by parasites, as opposed to predators, where the effects upon hosts range from acute infections to almost benign (Leggett et al, 2017). Parasites can have strong regulatory effects on their host population size (Hudson et al, 1998), have positive effects on life history traits (Telfer et al, 2002), and can even be essential for maintaining biodiversity at an ecosystem level (Hudson et al, 2006)
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