Host introductions and the geography of parasite taxonomic diversity

Abstract

Aim Geographical variation in parasite diversity is examined among populations of fish in their original heartland and in areas where they have been introduced. The diversity in heartland and introduced populations is contrasted, and also compared with the expectations of a null model.Location Data on the parasite communities of two salmonid fish species were obtained: the rainbow trout Oncorhynchus mykiss in its British Columbia heartland and in introduced populations in North America, Great Britain, South America and New Zealand; and the brown trout Salmo trutta in heartland populations from Great Britain, and in introduced populations in North America, South America and New Zealand.Methods The average taxonomic distinctness and its variance were computed for each parasite community, and used as measures of the taxonomic diversity of parasite species in each fish population. Observed values of taxonomic distinctness were also compared with those expected if each community was a random selection from the world list of parasite species known for each of the two host species.Results Few parasite communities departed from the expectations of the null model, i.e. few had a taxonomic diversity of parasites greater or lower than that expected from a random selection of parasite species. However, these departures were not more or less likely among heartland fish populations than among introduced ones. In both fish species, parasite communities in introduced populations tended to be a little more taxonomically diverse than in the heartland populations.Main conclusions Overall, the results suggest that the accumulation of parasite species in introduced hosts over short (ecological) periods of time can result in parasite assemblages that are just as, or even more, taxonomically diverse than those developed over much longer (evolutionary) time frames in the host species geographical heartland. This finding highlights the importance of ecological factors in parasite biodiversity in addition to coevolutionary processes.

Higher parasite richness, abundance and impact in native versus introduced cichlid fishes

“…While parasite species are expected to be lost from the native range, new species are generally acquired in the introduced habitat (Cornell and Hawkins, 1993;Poulin and Mouillot, 2003;Torchin et al, 2003). Yet, the consequences of this acquisition are difficult to predict, and can range from benign to severe disease, since new parasites do not share a co-evolutionary history with the introduced host (Shea and Chesson, 2002;Taraschewski, 2006;Dunn, 2009).…”

Use of the introduced bivalve,Musculista senhousia, by generalist parasites of native New Zealand bivalves

“…The success of many introduced species is often explained by the Enemy Release Hypothesis (ERH), which states that non-native species escape their natural enemies, including parasites, upon introduction to a novel environment (Torchin et al 2001(Torchin et al , 2002Keane & Crawley 2002). A different scenario is that non-native species are "empty habitats" when they arrive in a new area, awaiting colonisation by local parasites (Poulin & Mouillot 2003). Non-native species often acquire a new parasite assemblage from native organisms in the new environment over short periods of time (Bauer 1991;Barton 1997;Poulin & Mouillot 2003;Torchin & Mitchell 2004).…”

“…A different scenario is that non-native species are "empty habitats" when they arrive in a new area, awaiting colonisation by local parasites (Poulin & Mouillot 2003). Non-native species often acquire a new parasite assemblage from native organisms in the new environment over short periods of time (Bauer 1991;Barton 1997;Poulin & Mouillot 2003;Torchin & Mitchell 2004). The longer the non-native species is present, the more likely it is to accumulate enemies (Torchin & Mitchell 2004).…”

“…Because many parasites are specialists, often requiring multiple and sometimes specific intermediate hosts to complete their complex life cycles (Bauer 1991;Ruppert& Barnes 1994;Poulin & Mouillot 2003), specialist parasites present in native species are unlikely to switch host and establish in a non-native species (Torchin et al 2002;Poulin & Mouillot 2003). In contrast, a native generalist parasite that can make use of any one of several host species is more likely to adopt an introduced species as an alternative host (Bauer 1991;Barton 1997;Poulin & Mouillot 2003), which can result in an introduced species accumulating a modest assemblage of parasites in their new environment (Poulin & Mouillot 2003).…”

“…In contrast, a native generalist parasite that can make use of any one of several host species is more likely to adopt an introduced species as an alternative host (Bauer 1991;Barton 1997;Poulin & Mouillot 2003), which can result in an introduced species accumulating a modest assemblage of parasites in their new environment (Poulin & Mouillot 2003).…”