Adding parasites to the guppy-predation story: insights from field surveys

Abstract

Studies of phenotypic variation in nature often consider only a single potential selective agent. In such cases, it remains an open question as to whether variation attributed to that single measured agent might be influenced by some other unmeasured agent. Previous research has shown that phenotypic variation in the Trinidadian guppy (Poecilia reticulata) is strongly influenced by predation regime, and we here ask whether parasitism might represent an additional important selective agent shaping this variation. We performed a field survey of 26 natural guppy populations of known predation regime in northern Trinidad. We quantified levels of parasitism of guppies by the monogenean ecotoparasite, Gyrodactylus, and examined whether this parasite was associated with guppy body size or male colour. Spatial variation in Gyrodactylus parasitism was consistent between years, and parasite prevalence was generally, but not always, higher at high-predation sites than at low-predation sites. Consistent with previous work, predation regime was related to guppy size and some aspects of male colour, whereas parasitism showed few and only minor associations with the same traits. Moreover, a consideration of parasitism did not alter any interpretations regarding associations between guppy traits and predation regimes. These results suggest that parasitism, at least as quantified in the present study, does not play a major role in shaping variation in guppy body size or colour. Nevertheless, considerable variation in these traits, even within a predation regime, suggests the likely importance of other selective agents beyond just predation regime.

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

“…Although the precise mechanisms will have to be further established, our study adds to the growing body of work that suggests that parasites and predation do not seem to have strong interactive effects on guppies (Gotanda et al, 2013;Pérez-Jvostov et al, 2012;Dargent et al, 2013). We understand the limitations of our lack of replication for any given guppy-Gyrodactylus combination, yet we are confident of our results given that our sympatric infection dynamics closely resemble those of a previous study where strong drainage source effects were also observed (Pérez-Jvostov et al, 2012).…”

Pace of life, predators and parasites: predator-induced life-history evolution in Trinidadian guppies predicts decrease in parasite tolerance

“…Despite clear differences in life history between guppy populations, previous studies have failed to find consistent evidence for the predicted differences in parasite defence, as quantified using parasite infection load as measure of resistance (e.g. [10][11][12]). The inconsistencies between these studies may be because infection loads are easily confounded by differences in exposure to parasites between courses [8].…”

Experimental evolution of parasite resistance in wild guppies: natural and multifarious selection

“…Moreover, the high frequency of an MHC allele [7] that correlates negatively with Gyrodactylus load [8] is retained in these populations. Even more directly, the historic Turure introduction used an ancestral population from the same site as we did (Guanapo source) over 60 years ago, and these fish remain Gyrodactylus-free [6,7]. Similarly, guppies introduced from the Yarra River high-predation site into the previously guppy-free Damier River remained infected in the high-predation reach (prevalence 16%) but not the low-predation reach [6].…”

“…Similarly, guppies introduced from the Yarra River high-predation site into the previously guppy-free Damier River remained infected in the high-predation reach (prevalence 16%) but not the low-predation reach [6]. Finally, the low-predation population of the Guanapo River (upstream from the ancestral source population but downstream from the introduced populations) was Gyrodactylus-free before and during the experiment [6,7]. In short, populations introduced from high-to low-predation sites, either by colonization or by translocation seem to repeatedly evolve increased resistance to Gyrodactylus parasites, a pattern inconsistent with traditional ideas but that we were able to experimentally confirm.…”

“…Even more directly, the historic Turure introduction used an ancestral population from the same site as we did (Guanapo source) over 60 years ago, and these fish remain Gyrodactylus-free [6,7]. Similarly, guppies introduced from the Yarra River high-predation site into the previously guppy-free Damier River remained infected in the high-predation reach (prevalence 16%) but not the low-predation reach [6]. Finally, the low-predation population of the Guanapo River (upstream from the ancestral source population but downstream from the introduced populations) was Gyrodactylus-free before and during the experiment [6,7].…”