Data from: Resist globally, infect locally: a transcontinental test of adaptation by stickleback and their tapeworm parasite

Parasite infections are a product of both ecological processes affecting
host-parasite encounter rates and evolutionary dynamics affecting host
susceptibility. However, few studies examine natural infection variation
from both ecological and evolutionary perspectives. Here, we describe the
ecological and evolutionary factors generating variation in infection
rates by a tapeworm (Schistocephalus solidus) in a vertebrate host, the
threespine stickleback (Gasterosteus aculeatus). To explore ecological
aspects of infection, we measured tapeworm prevalence in Canadian
stickleback inhabiting two distinct environments: marine and freshwater.
Consistent with ecological control of infection, the tapeworm is very rare
in marine environments, even though marine fish are highly susceptible.
Conversely, commonly infected freshwater stickleback exhibit substantial
resistance in controlled laboratory trials, suggesting that high exposure
risk overwhelms their recently evolved resistance. We also tested for
parasite adaptation to its host by performing transcontinental reciprocal
infections, using stickleback and tapeworm populations from Europe and
western Canada. More infections occurred in same-continent host-parasite
combinations, indicating parasite “local” adaptation, at least on the
scale of continents. However, the recently evolved immunity of freshwater
hosts applies to both local and foreign parasites. The pattern of
adaptation described here is not wholly compatible with either of the
common models of host-parasite coevolution (i.e., matching infection or
targeted recognition). Instead, we propose a hybrid, eco-evolutionary
model to explain the remarkable pattern of global host resistance and
local parasite infectivity.