title: Co-invaders: The effects of alien parasites on native hosts.
abstract: We define co-introduced parasites as those which have been transported with an alien host to a new locality, outside of their natural range, and co-invading parasites as those which have been co-introduced and then spread to new, native hosts. Of 98 published studies of co-introductions, over 50% of hosts were freshwater fishes and 49% of parasites were helminths. Although we would expect parasites with simple, direct life cycles to be much more likely to be introduced and establish in a new locality, a substantial proportion (36%) of co-introductions were of parasites with an indirect life cycle. Seventy-eight per cent of co-introduced parasites were found in native host species and can therefore be classed as co-invaders. Host switching was equally common among parasites with direct and indirect life cycles. The magnitude of the threat posed to native species by co-invaders will depend, among other things, on parasite virulence. In 16 cases where co-introduced parasites have switched to native hosts and information was available on relative virulence, 14 (85%) were more virulent in native hosts than in the co-introduced alien host. We argue that this does not necessarily support the naïve host theory that co-invading parasites will have greater pathogenic effects in native hosts with which they have no coevolutionary history, but may instead be a consequence of the greater likelihood for parasites with lower virulence in their natural host to be co-introduced.
authors.affiliation: Freshwater Fish Group and Fish Health Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch 6150, Western Australia, Australia.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Lymbery
authors.affiliation: Freshwater Fish Group and Fish Health Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch 6150, Western Australia, Australia.
authors.forename: Mikayla
authors.initials: M
authors.lastname: Morine
authors.affiliation: Freshwater Fish Group and Fish Health Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch 6150, Western Australia, Australia ; Fisheries Department, Faculty of Agriculture, Gonbad Kavous University, Iran.
authors.forename: Hosna Gholipour
authors.initials: HG
authors.lastname: Kanani
authors.affiliation: Freshwater Fish Group and Fish Health Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch 6150, Western Australia, Australia.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Beatty
authors.affiliation: Freshwater Fish Group and Fish Health Unit, School of Veterinary and Life Sciences, Murdoch University, Murdoch 6150, Western Australia, Australia.
authors.forename: David L
authors.initials: DL
authors.lastname: Morgan
keywords: Co-introduction; Co-invasion; Host-switching; Invasive species; Virulence