Abstract
Many freshwater habitats are subject to change through time. Specifically, natural flow regimes are substantially modified by not only seasonal climatic change, but also anthropogenic activity. Consequently, freshwater organisms are exposed to variable flow, potentially altering their behaviour and subsequently parasite transmission amongst social hosts. Here, we investigate the effects of flow conditions on the shoaling behaviour of Trinidadian guppies (Poecilia reticulata), and the resulting transmission of a directly transmitted ectoparasite, Gyrodactylus turnbulli. Shoals exposed to continuous flow exhibited significantly greater G. turnbulli peak intensities and abundance when compared to fish subjected to interrupted, but not no-flow conditions. Parasite transmission rate was greater in shoals exposed to interrupted flow, resulting in parasites becoming more distributed amongst shoal members and thus reducing mean intensity in comparison to continuous flow shoals. Furthermore, as prevalence increased, the distance between shoaling conspecifics increased at greater rates in interrupted and no-flow conditions compared to continuous flow: indicating that in the absence of flowing water, parasitism has a greater effect on shoaling decisions. This data highlights how fish behaviourally respond to variable flow conditions and the implications for parasite transmission.
Highlights
Natural variations in precipitation and the seasonal melting of mountainous snowpack can substantially modify freshwater habitats through time
The current study investigated Gyrodactylus turnbulli transmission dynamics within a social host, the Trinidadian guppy, under prolonged exposure to continuous, interrupted and no-flow conditions
Our results highlight how flow alteration substantially modifies parasite transmission dynamics, whereby parasitism was more prevalent in shoals exposed to interrupted flow conditions due to greater transmission rates
Summary
Natural variations in precipitation and the seasonal melting of mountainous snowpack can substantially modify freshwater habitats through time. Whilst there are further benefits to group formation, including enhanced predator detection (Magurran, 1990) and increased foraging efficiency (Pitcher & Parrish, 1993), such behaviour can promote parasite transmission between individuals (Barber et al, 2000). Population-based modeling categorized transmission as either density- or frequency dependent, it is recognised that both transmission modes simultaneously promote disease persistence within populations (Ryder et al, 2007; Ferrari et al, 2011; Hu et al, 2013; McCallum et al, 2017). For social species, including shoaling fish, parasite transmission between individuals may be affected by population density, but the frequency of contacts between infected and susceptible hosts, allowing parasite persistence even at low-host densities (Johnson & Paull, 2011)
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