Changes in parasite species distributions could be driven by host range expansions: the case of hybridisation between two Australian reptile ticks

Anthropogenic stressors such as climate change and diminishing habitats cause widespread disturbances in species distributions for a variety of taxa. Range shifts and hybridisation following secondary contact become of particular importance when it comes to parasites such as ticks, as they are dependent on their host distributions and can carry numerous harmful pathogens. We aimed to determine if two parapatric reptile tick species, Amblyomma albolimbatum and A. limbatum, hybridise at their parapatric boundary by comparing morphological and genomic variation using single nucleotide polymorphisms. Our results show that both tick species were genomically distinct, but hybridisation has occurred. We found a hybrid and an A. limbatum outside of their previously known range, suggesting there could have been a shift in tick distribution. What were thought to be hybrids due to intermediate morphological traits were not hybrids but morphological variants of the parental species. This information suggests more distinctive morphological features are needed for identifying these tick species and that novel environmental conditions and a broadening of tick niche due to hybridisation could increase host exposure to different pathogens.