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Biol Invasions (2008) 10:4149 DOI 10.1007/s10530-007-9105-1
ORIGINAL PAPER
Resistance of an invasive gastropod to an indigenous trematode parasite in Lake Malawi
Martin J. Genner Ellinor Michel Jonathan A. Todd
Received: 23 May 2006 / Accepted: 19 February 2007 / Published online: 24 March 2007 Springer Science+Business Media B.V. 2007
Abstract Successful establishment and spread of biological invaders may be promoted by the absence of population-regulating enemies such as pathogens, parasites or predators. This may come about when introduced taxa are missing enemies from their native habitats, or through immunity to enemies within invaded habitats. Here we provide eld evidence that trematode parasites are absent in a highly invasive morph of the gastropod Melanoides tuberculata in Lake Malawi, and that the invasive morph is resistant to indigenous trematodes that castrate and induce gigantism in native M. tuberculata. Since helminth infections can strongly inuence host population abundances in other host-parasite systems, this enemy release may have provided an advantage to the invasive morph in terms of reproductive capacity and survivorship.
Keywords Biological invasion Enemy release
Non-indigenous species Exotic species
Fish parasites African lakes Thiaridae
Introduction
Natural enemies may play a major role in determining success of colonisations of new habitat by invasive lineages. In particular it has been found that colonisers can benet considerably from the release of life history, ecological and tness constraints associated with parasitic infection. Release from the regulatory role of parasites may take two forms. Firstly, invaders may benet by release from parasites that occur within native habitats (Keane and Crawley 2002; Torchin et al. 2003). This is because parasites may not have migrated with host populations, or because parasites are unable to survive in new habitats due to a lack of suitable intermediate or nal hosts. Secondly, invaders may benet through immunity to parasites that are prevalent within the invaded community. Such immunity may occur because parasites are often locally adapted to their hosts (Ebert 1994; 1998), and as a consequence are unable to infect invading taxa (Prenter et al. 2004; Fromme and Dybdahl 2006).
The mollusc-trematode system has been frequently used as a model for investigating the benets, costs and mechanisms of co-evolution between parasites and hosts (Sorensen and Minchella 2001; Lively et al. 2004). Trematodes affect host molluscs through changes...