Abiotic environmental variation drives virulence evolution in a fish host–parasite geographic mosaic

Abstract

Parasite virulence varies greatly. Theory predicts that this arises from parasites optimising a trade‐off between the mortality they inflict on current hosts, and their transmission to future hosts. The effect of the environment on this co‐evolution is rarely considered. Geographic mosaics are fertile systems for studying co‐evolution, but again, the diversity of outcomes is often assumed to result from co‐evolutionary dynamism, rather than being moulded by the environment. Here, we quantify variation in virulence among lakes in a geographic mosaic of co‐evolution between a trematode ectoparasite (Gyrodactylus arcuatus) and its three‐spined stickleback (Gasterosteus aculeatus) host. Virulence varies greatly in this system, and parasites are generally locally adapted to their hosts. Parasites are also locally adapted to the water in their own lake, and virulence is strongly related to lake pH, the dominant axis of abiotic environmental variation in this system. These results suggest that the evolution of virulence can be substantially affected by the abiotic environment, which has important implications for understanding co‐evolution. There are also implications for the evolutionary management of disease, e.g. ectoparasites in aquaculture, the impacts of which might be expected to reduce given ongoing acidification of aquatic ecosystems. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12921/suppinfo is available for this article.

Genotypic variation in an ecologically important parasite is associated with host species, lake and spore size

“…Morrison et al ., 2010 ; Hawley et al ., 2013 ; Audebert et al ., 2020 ), and other important traits, such as the ability to survive and disperse in the environment (e.g. Tack et al ., 2014 ; Mahmud et al ., 2017 ; Rogalski and Duffy, 2020 ). Thus, not only is genetic variation within parasites common, it is also important to the ecology and evolution of host-parasite systems.…”

Ecology directs host–parasite coevolutionary trajectories across Daphnia–microparasite populations

“…These findings are consistent with the idea that ecological interactions above and beyond parasitism can select on hosts, but do not act on the host insulated parasites; shifts in host genotype frequencies instead drive parasite genetic change via coevolution. Whereas, for ectoparasites, which live on the host exterior, wider ecological conditions are known to shape the evolution of virulence 17,18 .…”

Transmission dynamics of ectoparasitic gyrodactylids (Platyhelminthes, Monogenea): An integrative review

“…Despite abiotic factors being the first tested factors in gyrodactylid dynamics, today these receive less research attention than biotic factors. We stress the need to conduct more studies of abiotic factors such as: water pH, since studies point a strong relationship between gyrodactylid virulence and water pH (Mahmud et al ., 2017); salinity, taking into consideration that some species like G. salaris shows wide salinity tolerance, and dark light conditions, which could trigger host-seeking behaviour. Collectively, these abiotic factors can potentially alter dynamics of gyrodactylid–host interactions and may determine transmission rates.…”