Native fish avoid parasite spillback from multiple exotic hosts: consequences of host density and parasite competency

Abstract

Disease-mediated impacts of exotic species on their native counterparts are often ignored when parasite-free individuals are translocated. However, native parasites are frequently acquired by exotic species, thus providing a mechanism through which native host-parasite dynamics may be altered. In Argentina, multiple exotic salmonids are host to the native fish acanthocephalan parasite Acanthocephalus tumescens. Field evidence suggests that rainbow trout, Oncorhynchus mykiss, may be a major contributor to the native parasite's population. We used a combination of experimental infections (cystacanth-juvenile worm transmission from amphipod to fish; postcyclic-adult worm transmission between definitive fish hosts) and dynamic population modelling to determine the extent to which exotic salmonid hosts may alter A. tumescens infections in native freshwater fish. Experimental cystacanth infections demonstrated that although A. tumescens establishes equally well in native and exotic hosts, parasite growth and maturity is superior in exotic O. mykiss. Experimental postcyclic infections also showed greater establishment success of A. tumescens in O. mykiss, though postcyclic transmission did not result in greater parasite size or maturity. Dynamic population modelling, however, suggested that exotic salmonids may have a very limited influence on the A. tumescens population overall, due to the majority of A. tumescens individuals being maintained by more abundant native hosts. This research highlights the importance of considering both a host's relative density and its competency for parasites when evaluating whether exotic species can modify native host-parasite dynamics.

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

“…When an introduced species is a suitable host for a native parasite, this can seriously impact the exotic hosts, but can also amplify the infection (''spillback'' from exotic to native species) with effects for native species at both the host individual and population level (Daszak et al 2000;Tompkins and Poulin 2006). At the current stage of T. v. verticalis invasion our results provide no evidence of parasite spillback, but it remains a potential risk given the density and reproductive potential of the exotic host, high susceptibility for parasites and the high reproductive potential of parasites, all factors affecting the probability of spillback (Hershberger et al 2010;Paterson et al 2013). We can expect the opposite to the dilution effect hypothesis, which predicts that the introduction of a less competent host species may reduce infection prevalence in the native host (Telfer et al 2005).…”

Pharmacokinetics and residue depletion of praziquantel in rice field eels Monopterus albus

“…Praziquantel (PZQ: 2-cyclohexylcarbonyl-1, 2, 3, 6, 7, 11b-hexahydro-4H-pyrazino [2,1-a] iso-quinoline-4-one) is a broad-spectrum anthelmintic drug used in human and veterinary medicine. In aquaculture, PZQ is mainly used for controlling and killing acanthocephalans (Paterson et al 2013), trematodes (Kim & Cho 2000, Montero et al 2004, Mansell et al 2005, Reimschuessel et al 2011, cestodes (Pool 1985, Kline et al 2009, Iles et al 2012, and other parasites of fish. Although PZQ is applied widely in the treatment of aquatic animals, only a few studies have examined the pharmacokinetics and tissue residues of PZQ in fish (K. Kim et al 2001, C. Kim et al 2003, Tubbs & Tingle 2006a,b, Osman et al 2008, Xie et al 2015.…”

Helpful invaders: Can cane toads reduce the parasite burdens of native frogs?

“…The ‘sink’ mechanism was tested here with a simplistic experimental design; the first anuran was forced into close contact with larvae in a small container and the subsequent anuran was placed in precisely the same location. In nature, the impact of prior residency of a frog or a cane toad will depend on infection dynamics, anuran densities and habitat overlap – as well as a wealth of other variables ( Prenter et al., 2004; Paterson et al., 2013b ). The three anuran species used in this experiment have very similar sizes as metamorphs but adult cane toads and C. australis are much larger than L. convexiusculus .…”

“…The ‘sink’ mechanism has been investigated in only a few invasive systems ( Trejo, 1992; Telfer et al., 2005; Kopp and Jokela, 2007; Thieltges et al., 2009; Paterson et al., 2011, 2013a,b ) but these studies are geographically and taxonomically diverse, meaning the crossover of native parasites to invaders is likely to be common ( Dunn, 2009 ). Thus, it is important to explore the possibility of ‘sink’ mechanisms in other systems, especially involving parasite and host taxa from lineages that have not been the subjects of previous research in this respect.…”