Abstract
Reduced parasite species diversity and infection intensity on invasive populations can facilitate establishment and spread of invasive species. We investigated the parasite diversity of invasive populations of tilapia Oreochromis mossambicus from published literature and necropsies conducted on 72 fish captured in the Ross River, north Queensland, Australia. The parasite diversity of invasive O. mossambicus from 13 countries was compared to published reports on endemic populations in African river systems and tributaries to determine parasite species that had likely been co-introduced. In total, four parasite species were shared between native and invasive tilapia. We propose that these parasites (three monogeneans, Cichlidogyrus tilapiae Paperna, 1960, Cichlidogyrus sclerosus Paperna and Thurston, 1969, Cichlidogyrus halli (Price and Kirk, 1967) and one trichodinid Trichodina heterodentata Duncan, 1977) have likely been co-introduced with invasive Oreochromis mossambicus populations. Invasive Australian O. mossambicus had substantially reduced parasite diversity (five species) compared to cumulative parasite species diversity documented from the native region (23 species). Australian O. mossambicus were infected by two co-introduced parasites and three additional parasite species that have not been recorded previously on this species in Africa indicating possible parasite spillback from Australian natives or alternatively, acquisition from other introduced fauna. The substantially reduced parasite diversity on invasive Australian O. mossambicus could contribute to the ability of this species to become a serious fish pest.
Highlights
The enemy release hypothesis proposes that invaders lose their co-evolved parasites in the process of invasion, which might give them a competitive advantage over native species (Torchin et al 2003)
The competitive advantage conferred by the enemy release hypothesis may be reduced over time as more parasite species are co-introduced with repeat incursions or as parasite species from the invaded habitat/location infect the invader population (Colautti et al 2004; Goedknegt et al 2016)
A potential consequence of this interaction is “parasite spillback”, whereby the invasive fish species can act as a reservoir of infectious native parasites that can negatively impact native fish populations already pressured from other factors, such as competition (Kelly et al 2009a)
Summary
The enemy release hypothesis proposes that invaders lose their co-evolved parasites in the process of invasion, which might give them a competitive advantage over native species (Torchin et al 2003). The competitive advantage conferred by the enemy release hypothesis may be reduced over time as more parasite species are co-introduced with repeat incursions or as parasite species from the invaded habitat/location infect the invader population (Colautti et al 2004; Goedknegt et al 2016). Those parasite species that survive the invasion period tend to exhibit direct life cycles and/or low host-specificity and are more likely to establish populations in the new location, either on the invasive host or new native hosts (= co-invasion; Bauer 1991; Lymbery et al 2014). The complex interaction between the invasive host, parasites and the environment has the potential to modify population regulatory processes and have consequent flow-on effects to ecosystem dynamics
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