Abstract
We used a freshwater amphipod-microsporidian model (Ponto-Caspian hosts: Dikerogammarus villosus and D. haemobaphes, parasite: Cucumispora dikerogammari) to check whether parasites affect biological invasions by modulating behaviour and intra- and interspecific interactions between the invaders. We tested competition for shelter in conspecific and heterospecific male pairs (one or both individuals infected or non-infected). In general, amphipods of both species increased their shelter occupancy time when accompanied by infected rather than non-infected conspecifics and heterospecifics. Infected amphipods faced lower aggression from non-infected conspecifics. Moreover, D. villosus was more aggressive than D. haemobaphes and more aggressive towards conspecifics vs. heterospecifics. In summary, infection reduced the intra- and interspecific competitivity of amphipods, which became less capable of defending their shelters, despite their unchanged need for shelter occupancy. Dikerogammarus haemobaphes, commonly considered as a weaker competitor, displaced by D. villosus from co-occupied locations, was able to compete efficiently for the shelter with D. villosus when microsporidian infections appeared on the scene. This suggests that parasites may be important mediators of biological invasions, facilitating the existence of large intra- and interspecific assemblages of invasive alien amphipods.
Highlights
D. villosus was more aggressive than D. haemobaphes and more aggressive towards conspecifics vs. heterospecifics
To study the potential impact of microsporidiosis on the behaviour and mutual interactions among the Ponto-Caspian amphipods, we focused on two model species: Dikerogammarus villosus (Sowinsky, 1894) and Dikerogammarus haemobaphes (Eichwald, 1841), considered as successful invasive alien species in Europe (Rewicz et al 2015; Jażdżewska et al 2020)
Dikerogammarus haemobaphes spent more time in the shelter than D. villosus when exposed to infected heterospecifics (Fig. 3A), whereas an opposite difference occurred between individuals of these species exposed to non-infected conspecifics (Fig. 1A)
Summary
Animal behaviour is known to be modulated by parasites, by their pathogenicity and inducing defence responses in their hosts (Satinoff 2011; Żbikowska and Cichy 2012), and by increasing parasites’ fitness through host manipulation (Bakker et al 1997; Lagrue et al 2007; Flegr 2015). Parasite-induced changes are usually multidimensional, altering multiple phenotypic traits by a single parasite (Cezilly and PerrotMinnot 2010; Cezilly et al 2013) This includes such aspects as morphology (Bakker et al 1997), habitat selection (Żbikowska and Cichy 2012; Rachalewski et al 2018), mobility (Dezfuli et al 2003), boldness (Flegr 2015), aggression (Thomas et al 2005; Mikheev et al 2010), foraging (Fielding et al 2003; Bącela-Spychalska et al 2014) and reproduction (Hall et al 2007). These changes may further propagate to the impact on ecosystem functioning (Friesen et al 2017; Anaya-Rojas et al 2019) through intra- and interspecific interactions of infected individuals with other organisms through consumption (Fielding et al 2003), predation (Bakker et al 1997; Flegr 2015; Friesen et al 2019) or competition (Anderson and May 1986; Mikheev et al 2010; Reisinger et al 2015; Friesen et al 2018). A more subtle influence of parasites may consist of modifications of the impact imposed by alien species on local communities (Dunn 2009) by changing their behaviour, e.g. food acquisition or preferences (Bącela-Spychalska et al 2014; Iltis et al 2017)
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