Evolutionary Ecology Research vol:15 issue:4 pages:489-502
Background: Parasites are often assumed to be locally adapted to their hosts, while a growing
body of literature shows this is not a fixed rule. We used the threespine stickleback (Gasterosteus
aculeatus) and its host-specific parasitic flatworm Gyrodactylus gasterostei of the Belgian
lowland–upland system to test for local adaptation and assess whether findings are consistent
over different life stages.
Question: Is the Gasterosteus–Gyrodactylus host–parasite model system an example of local
Hypothesis: Parasites have higher infection success on sympatric than on allopatric host
Methods: F1 laboratory-bred stickleback originating from a lowland and upland population
were infected with parasites of lowland and upland origin. We monitored parasite numbers per
individual for 6 weeks and for two life stages and calculated the effect size of local adaptation.
Results: Infection success of parasites was not higher on sympatric than on allopatric
host populations. Instead, total worm load differed among sub-adult host populations, but
not among adult host populations. This suggests immune competence differs among host
populations at a specific life stage, rather than local adaptation of the parasite.