Local, but not long-distance dispersal of penguin ticks between two sub-Antarctic islands

Advances in high throughput genomic approaches are enabling the accurate appraisal of movements of diverse species, previously considered intractable. The impact of long-distance dispersal and distribution changes on species interactions (such as host-parasite interactions) is of particular importance as attempts are made to project how ecosystems will shift under environmental change. The sub-Antarctic region, comprising isolated islands separated by hundreds to thousands of kilometres of open ocean, presents an ideal model system for studying long-distance dispersal, distribution, and ecosystem change. Here we used genomic methods to determine the extent of movement of penguin ticks (Ixodes uriae) among different host species, and among penguin colonies at small (within an island) and large (among islands separated by >6000 km) scales, in the sub-Antarctic region. Our results suggest that I. uriae ticks may be readily shared between distantly related penguin species with similar phenology, but indicate that-as inferred by previous research-ticks are less likely to be shared between flighted and non-flighted seabirds. We also find evidence for small-scale movements of penguin ticks with their hosts, but no evidence for movements between islands separated by thousands of kilometers of open ocean. These inferred limitations to penguin tick movement could be the result of restricted host movements or the inability of penguin ticks to survive extended trips at sea. Our findings help elucidate parasite-host dynamics, with implications for host health and persistence in a region experiencing rapid environmental change.