Parasite Transmission in Social Interacting Hosts: Monogenean Epidemics in Guppies

Abstract

BackgroundInfection incidence increases with the average number of contacts between susceptible and infected individuals. Contact rates are normally assumed to increase linearly with host density. However, social species seek out each other at low density and saturate their contact rates at high densities. Although predicting epidemic behaviour requires knowing how contact rates scale with host density, few empirical studies have investigated the effect of host density. Also, most theory assumes each host has an equal probability of transmitting parasites, even though individual parasite load and infection duration can vary. To our knowledge, the relative importance of characteristics of the primary infected host vs. the susceptible population has never been tested experimentally.Methodology/Principal FindingsHere, we examine epidemics using a common ectoparasite, Gyrodactylus turnbulli infecting its guppy host (Poecilia reticulata). Hosts were maintained at different densities (3, 6, 12 and 24 fish in 40 L aquaria), and we monitored gyrodactylids both at a population and individual host level. Although parasite population size increased with host density, the probability of an epidemic did not. Epidemics were more likely when the primary infected fish had a high mean intensity and duration of infection. Epidemics only occurred if the primary infected host experienced more than 23 worm days. Female guppies contracted infections sooner than males, probably because females have a higher propensity for shoaling.Conclusions/SignificanceThese findings suggest that in social hosts like guppies, the frequency of social contact largely governs disease epidemics independent of host density.

Testing for local host–parasite adaptation: an experiment with Gyrodactylus ectoparasites and guppy hosts

“…Predators and predator cues are certainly known to have very strong plastic effects on guppy behaviour and growth Evans et al, 2007;Gosline and Rodd, 2007;Brown et al, 2013), and these guppy traits are known to influence infection (Johnson et al, 2011;Richards et al, 2010). Thus, perhaps we would have found very different results had we exposed guppies to predators or predator cues.…”

Parasites of Trinidadian guppies: evidence for sex‐ and age‐specific trait‐mediated indirect effects of predators

“…Differences in predation level, on the other hand, are consistent both spatially and temporally and drive adaptive evolutionary responses in the host, such as shoaling (Houde 1997, Reznick et al 1997, Magurran 2005. Additionally, the rate of Gyrodactylus transmission is not density dependent, but is governed by the frequency of social contacts, i.e., shoaling (Johnson et al 2011). The consistent differences in parasite prevalence between populations that experience different predation pressure are thus more likely to be trait-than densitymediated.…”

“…The dominant guppy parasites, which include Gyrodactylus turnbulli and G. bullatarudis (hereafter Gyrodactylus) are directly transmitted ectoparasitic monogeneans that impact guppy swimming ability (Cable and Harris 2002), reproductive fitness (e.g., Kennedy et al 1987), and survival (van Oosterhout et al 2007). Shoaling is an important anti-predator behavioral trait in guppies that facilitates Gyrodactylus transmission (Richards et al 2010, Croft et al 2011, Johnson et al 2011, and females are more likely to become infected than males because of their higher shoaling tendency (Richards et al 2010, Johnson et al 2011. Notably, Johnson et al (2011) found that Gyrodactylus transmission remained high in aquaria with reduced guppy density, indicating that social interactions were more important than density in maintaining transmission rates.…”

The prevalence of parasites in ornamental fish from fish market in Medan

“…however it still became threatened for diseases outbreak because the epidemic study on monogenea infection in guppy result showed that in social hosts like guppies. the frequency of social contact largely rules disease epidemics independent of host density [17].…”