Additive effects of temperature and infection with an acanthocephalan parasite on the shredding activity of Gammarus fossarum (Crustacea: Amphipoda): the importance of aggregative behavior

Abstract

Climate change can have critical impacts on the ecological role of keystone species, leading to subsequent alterations within ecosystems. The consequences of climate change may be best predicted by understanding its interaction with the cumulative effects of other stressors, although this approach is rarely adopted. However, whether this interaction is additive or interactive can hardly be predicted from studies examining a single factor at a time. In particular, biotic interactions are known to induce modifications in the functional role of many species. Here, we explored the effect of temperature on leaf consumption by a keystone freshwater shredder, the amphipod Gammarus fossarum. This species is found at high densities in the wild and relies on aggregation as an antipredator behavior. In addition, gammarids regularly harbor acanthocephalan parasites that are known to induce multiple effects on their hosts, including modifications on their functional role. We thus assessed the cumulative effect of both intraspecific interactions and parasitism. Consumption tests were conducted on gammarids, either naturally infected with Pomphorhynchus tereticollis or uninfected, feeding alone or in groups. Our results show that increased temperatures induced a significant increase in consumption, but only to a certain extent. Interestingly, consumption at the highest temperature depended on amphipod density: Whereas a decrease was observed for single individuals, no such effect on feeding was observed for individuals in groups. In addition, infection by acanthocephalan parasites per se significantly negatively impacted the shredding role of gammarids. Overall, the combined effects of parasitism and temperature appeared to be additive. Thus, future studies focusing on the impact of climate change on the functional role of keystone species may benefit from a multimodal approach under realistic conditions to derive accurate predictions.

Origin of the natural variation in the storage of dietary carotenoids in freshwater amphipod crustaceans

“…For instance, parasitized Gammarus roeseli exhibited a strong depletion of circulating carotenoids and enhanced level of lipoperoxidation damages when exposed to pollutants [52,53]. Similar states of stress might be possible from environmental temperature changes when combined with pathogenic challenges [54]. Our results therefore appear consistent, at both the within and between cryptic species levels, with the hypothesis that evolving greater capacity of carotenoid storage in response to the necessity of increasing immune activity to deal with higher parasitic threat could be adaptive [11].…”

Consequences of divergent temperature optima in a host–parasite system

“…We included up to two‐way interactions to every model on host/parasite response variables and added tank as a random factor to control for potential tank effects. We added the quadratic term of temperature (temperature × temperature) since previous studies illustrated that responses of host parasites systems to temperature variation can be described with quadratic terms (Paull et al , Mordecai et al , Labaude et al ). Accordingly, we expected that data of the response variables in the present study might follow quadratic curves when split up by temperature (Supplementary material Appendix 1 Table A1).…”

Magnitude and direction of parasite‐induced phenotypic alterations: a meta‐analysis in acanthocephalans

“…For instance, temperature recently has been shown to affect the extent of manipulation of phototaxis in amphipods infected by acanthocephalans, but not that of geotaxis or refuge use (Labaude, Cezilly, & Rigaud, ). Environmental influences and infection with manipulative parasites may thus have interactive or additive effects on the phenotype of infected hosts (see Labaude, Rigaud, & Cézilly, ) and, therefore contribute directly to the observed variation in the magnitude of manipulation within and among host–parasite associations, with potential consequences at the level of ecosystems.…”