Are host–parasite interactions influenced by adaptation to predators? A test with guppies and Gyrodactylus in experimental stream channels

Abstract

Natural populations often face multiple mortality sources. Adaptive responses to one mortality source might also be beneficial with respect to other sources of mortality, resulting in "reinforcing adaptations"; or they might be detrimental with respect to other sources of mortality, resulting in "conflicting adaptations". We explored these possibilities by testing experimentally if the responses of guppies (Poecilia reticulata) to the monogenean ectoparasitic worm Gyrodactylus differed between populations adapted to different predation regimes. In experimental stream channels designed to replicate the natural environment, we exposed eight guppy populations (high-predation and low-predation populations from each of four separate rivers) either to their local Gyrodactylus parasites (infection treatment) or to the absence of those parasites (control). We found that infection dynamics varied dramatically among populations in a repeatable fashion, but that this variation was not related to the predation regime of origin. Consistent with previous work, high-predation guppy females gained more mass, had lower reproductive investment, and had more but smaller embryos than did low-predation females. Relative to control (no parasite) channels, guppies from treatment (infected) channels gained less mass but produced similar numbers and sizes of embryos-and thus had a higher reproductive effort. However, no interaction was evident between infection treatment and predation regime. We conclude that parasitism by Gyrodactylus and predation are both likely selective forces for guppies, but that adaptation to predation does not have an obvious deterministic effect on host-parasite dynamics or on life-history traits of female guppies.

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).…”

“…All fish, regardless of whether or not they were initially infected, were treated with N-cyclopropyl-1,3,5-triazine-2,4,6-triamine (cyromazine; Lice And Anchor Worm Treatment, Ecological Laboratories Inc., U.S.A.) which effectively eliminates Gyrodactylus (Pérez-Jvostov et al, 2012). When no Gyrodactylus were seen on a fish over three consecutive days of visual inspection (as above), the fish was considered parasite-free.…”

“…When no Gyrodactylus were seen on a fish over three consecutive days of visual inspection (as above), the fish was considered parasite-free. Elastomer dyes (Northwest Marine Technology Inc., U.S.A.) were then injected to give each fish a distinct intra-dermic mark, a procedure used effectively in many previous guppy studies (Bassar et al, 2010;Weese et al, 2010;Pérez-Jvostov et al, 2012). The elastomer marks were no longer than 2 mm and no marked fish showed signs of reduced mobility or altered behaviour.…”

“…This natural flow allowed colonisation of the mesocosms by algae and invertebrates, including natural foods for guppies, but excluded any non-experimental guppies. These specific mesocosms have been used in a number guppy studies and are a good mimic of natural conditions (for technical specifications see Palkovacs et al, 2009;Bassar et al, 2010;Pérez-Jvostov et al, 2012).…”

“…In a previous study (Pérez-Jvostov et al, 2012), we used experimental infections in semi-natural mesocosms to test whether adaptation to different predation environments (HP versus LP) influenced Gyrodactylus-guppy interactions. We found strong and repeatable differences in Gyrodactylus infection dynamics between host-parasite assemblages taken from different field locations, but we found that the differences were not related to predation regime.…”