Testing for local adaptation in the Gasterosteus–Gyrodactylus host–parasite system

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 adaptation? Hypothesis: Parasites have higher infection success on sympatric than on allopatric host populations. 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.status: publishe

Testing for local adaptation in the Gasterosteus-Gyrodactylus host-parasite system

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 adaptation? Hypothesis: Parasites have higher infection success on sympatric than on allopatric host populations. 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