Parasites in sympatric populations of native and invasive freshwater bivalves

Jouni Taskinen,Fabio Ercoli,Binglin Deng,Małgorzata Ożgo,Nicoletta Riccardi,Jocelyn M Choo,Wojciech Andrzejewski,Maria Urbańska

doi:10.1007/s10750-020-04284-0

Abstract

An increasing threat to local, native freshwater mussels (Unionida)—an ecologically important but globally alarmingly declining group—is the invasion by exotic bivalves. The Enemy Release Hypothesis predicts that introduced species should benefit from enemy-mediated competition because they are less likely to be harmed by natural enemies, such as parasites, than their native competitors. We investigated within-site differences in parasitism between sympatric native (tot. five spp.) and invasive (tot. three spp.) bivalves in eight northern European waterbodies, which harboured totally 15 parasite taxa. In paired comparisons using within-site averages, the mean number of parasite species in the native bivalves was 2.3 times higher, and the sum of parasite prevalences 2.4 times higher, than in the invasive bivalves. This may lead to enemy-mediated competitive release of invaders and contribute to the success of invasive freshwater bivalves, in general. However, while the invasive clam Corbicula fluminea was completely free from parasites, parasite parameters of the other invader, Sinanodonta woodiana, were relatively high, indicating that the role of parasites can be invader-specific and urges further research. Understanding the factors affecting success of freshwater bivalve invasions, such as parasitism, can aid invasion control and conservation of local, native (endangered) bivalves.

Highlights

Biological invasions threaten biodiversity and cause drastic changes in the invaded ecosystems, leading to local extirpation of native species, biogenic homogenization and extensive economic costs (e.g. Olden et al, 2004; Pimentel et al, 2005; Keller et al, 2011; Lockwood et al, 2013)
One prediction of the Enemy Release Hypothesis is that introduced species should benefit from enemymediated competition because they are less likely to be affected by natural enemies than their native competitors (Elton, 1958; Keane and Crawley, 2002)
Enemy Release Hypothesis (Elton, 1958) suggests that invasive species should lose parasites during the invasion process, which should lead to a lower parasite load in the new, introduced range, benefitting the invaders in competition against the local, native competitors

Summary

Introduction

Biological invasions threaten biodiversity and cause drastic changes in the invaded ecosystems, leading to local extirpation of native species, biogenic homogenization and extensive economic costs (e.g. Olden et al, 2004; Pimentel et al, 2005; Keller et al, 2011; Lockwood et al, 2013). Blakeslee et al, 2013) for the success of invasive species (when they have colonized the new, invaded area) is provided by the Enemy Release Hypothesis that invaders benefit from lower pressure of natural enemies when compared to native species (Elton, 1958). As (3) invaders usually do not bring their own enemies with them to the new area during the colonization process, it (4) results in a situation where the pressure by the natural enemies in the invaded area can be remarkably lower for the invaders than for the local, native species (as well as when compared to the parasite pressure of the invader in its original range). The introduced animal populations were less heavily parasitized and had only half of the parasite species as compared to their

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