Impacts of crustacean invasions on parasite dynamics in aquatic ecosystems: A plea for parasite-focused studies

Abstract

While there is considerable interest in, and good evidence for, the role that parasites play in biological invasions, the potential parallel effects of species introduction on parasite dynamics have clearly received less attention. Indeed, much effort has been focused on how parasites can facilitate or limit invasions, and positively or negatively impact native host species and recipient communities. Contrastingly, the potential consequences of biological invasions for the diversity and dynamics of both native and introduced parasites have been and are still mainly overlooked, although successful invasion by non-native host species may have large, contrasting and unpredictable effects on parasites. This review looks at the links between biological invasions and pathogens, and particularly at crustacean invasions in aquatic ecosystems and their potential effects on native and invasive parasites, and discusses what often remains unknown even from well-documented systems. Aquatic crustaceans are hosts to many parasites and are often invasive. Published studies show that crustacean invasion can have highly contrasting effects on parasite dynamics, even when invasive host and parasite species are phylogenetically close to their native counterparts. These effects seem to be dependent on multiple factors such as host suitability, parasite life-cycle or host-specific resistance to parasitic manipulation. Furthermore, introduced hosts can have drastically contrasting effects on parasite standing crop and transmission, two parameters that should be independently assessed before drawing any conclusion on the potential effects of novel hosts on parasites and the key processes influencing disease dynamics following biological invasions. I conclude by calling for greater recognition of biological invasions’ effects on parasite dynamics, more parasite-focused studies and suggest some potential ways to assess these effects.

The Ecological Importance of Amphipod–Parasite Associations for Aquatic Ecosystems

“…In the context of biological invasions, parasitism often provides a competitive advantage to the non-native amphipods but there are also cases in which parasites limit the success of invaders avoiding the replacement of the native amphipod species [172]. When parasitized by the acanthocephalan Pomphorhynchus laevis, the immune system of the native Gammarus pulex is impaired and resource storage is decreased whilst the invader G. roeseli, infected with the same parasite, is not affected [149].…”

Do behavioural defence mechanisms explain different levels of trematode infections in congeneric hosts?

“…At the ecosystem level, this could lead to a reduction in the number of infective stages in the habitat, and to a parasite ‘dilution effect’, in which increased species diversity, including non- or low-competency hosts, leads to reduced risk of disease (Keesing et al ., 2006). Dilution effects have been observed and described for diverse ecological communities that can mediate infection levels (Morand & Guégan, 2008; Johnson & Thieltges, 2010), as well as in the context of biological invasions, in which introduced species can lead to reduced parasite transmission in a system (reviewed in Poulin et al , 2011; Goedknegt et al , 2016; Lagrue, 2017). In our case the dilution effect would be a result of an endemic species being a low-competency or dead-end host, and could therefore play an important role in the transmission dynamics of trematodes in the ecosystem.…”

Invasion ecology meets parasitology: Advances and challenges

“…Second, the contributions in this issue explore the often neglected impact of invasive free-living species on the dynamics of native parasites. Lagrue (2017) reviews the many ways in which invasive crustaceans can alter the transmission success of native parasites, or the infection risk faced by native hosts, in freshwater ecosystems. These issues are explored using field data by Galipaud et al.…”