Has the introduction of brown trout altered disease patterns in native New Zealand fish?

Abstract

SUMMARY1. It is well recognised that non-indigenous species (NIS) can affect native communities via the 'spillover' of introduced parasites. However, two other potentially important processes, the 'spillback' of native parasites from a competent NIS host, where the latter acts as a reservoir leading to amplified infection in native hosts, and the 'dilution' of parasitism by a NIS host acting as a sink for native parasites, have either not been tested or largely overlooked. 2. We surveyed the helminth parasite fauna of native New Zealand fish in Otago streams that varied in the abundance of introduced brown trout Salmo trutta, to look for evidence of spillback and ⁄ or dilution. Spillover is not an issue in this system, with trout introduced as parasite-free eggs. 3. Seven native parasite species were present across 12 sites; significant inverse relationships with an index of trout abundance (i.e. dilution) were documented for three species infecting the native upland bully Gobiomorphus breviceps, and one species infecting the native roundhead galaxias Galaxias anomalus.4. An inverse relationship between bully energy status and infection intensity of one parasite species suggests that parasite dilution could have positive effects on bully populations. Our failure to detect similar relationships for the other parasites does not preclude the possibility that dilution is beneficial to native fish, since parasites may have subtle or unmeasured impacts. 5. The parasite dilution patterns reported are compelling in that they occurred across several native host and parasite species; as such they have important implications for invasion ecology, providing an interesting contrast to the largely negative impacts reported for NIS. Mechanisms potentially responsible for the patterns observed are discussed.

Parasitism by water mites in native and exotic Corixidae: Are mites limiting the invasion of the water boatman Trichocorixa verticalis (Fieber, 1851)?

“…Most studies have focused on the effect of the loss of coevolved parasites during the introduction process ('Enemy Release Hypothesis', Torchin et al 2002Torchin et al , 2003Keane and Crawley 2002;Colautti et al 2004;Prenter et al 2004), and the introduction of exotic parasites arriving with alien hosts to the recipient community ('Parasite Spillover', Dobson and Foufopoulos 2001;Power and Mitchell 2004). However, with the exception of native parasites affecting exotic plants and invertebrates of economic importance, which have been the subject of studies of biological control (Williams et al 2003;Li et al 2012), the acquisition of new parasites by exotic species has been largely overlooked, even though it is potentially a frequent and important process (Kelly et al 2009b;Mastitsky et al 2010). Depending on the mechanism and the role played by the novel parasite, the consequences for the invasion success of the alien host and the impact on the recipient community can be highly variable.…”

Early life stages of exotic gobiids as new hosts for unionid glochidia

“…Exotic species are thought to benefit from a loss of parasite diversity as a consequence of leaving parasites behind and the inability of native-specialised parasites (i.e. the parasite attaches but fails to develop to its next life stage), exotic species can act as an infection sink, reducing the pool of parasites that could potentially infect native hosts ('dilution effect'; Kelly et al, 2009b). As a result, exotic hosts tend to be parasitised by a low number of generalist native parasite species (Kennedy & Bush, 1994;Poulin & Mouillot, 2003), though these parasites typically achieve high densities (Dunn, 2009).…”

Parasite communities of two three-spined stickleback populations in subarctic Norway—effects of a small spatial-scale host introduction

“…Potentially, parasites are brought along in this process, as introduced hosts can be infected with various parasites (Daszak et al 2000;Cleaveland et al 2002). Many studies have focused on the introduction of exotic species and host introduction on a large geographical scale Kelly et al 2009b;Vignon et al 2009;Lymbery et al 2010;Roche et al 2010;Gendron et al 2012), but few have addressed the effects of host introduction on a small spatial scale (e.g. local introduction).…”