The repetitive genome of theIxodes ricinustick reveals transposable elements have driven genome evolution in ticks

Abstract

Ticks are obligate blood-feeding parasites associated with a huge diversity of diseases globally. The hard tickIxodes ricinusis the key vector of Lyme borreliosis and tick-borne encephalitis in Western Eurasia.Ixodesticks have large and repetitive genomes that are not yet well characterized. Here we generate two high-qualityI.ricinusgenome assemblies, with haploid genome sizes of approximately 2.15 Gbp. We find transposable elements comprise at least 69% of the twoI.ricinusgenomes, amongst the highest proportions found in animals. The transposable elements in ticks are highly diverse and novel, so we constructed a repeat library for ticks using ourI.ricinusgenomes and the genome ofI.scapularis, another major tick vector of Lyme borreliosis. To understand the impact of transposable elements on tick genomes we compared their accumulation in the twoIxodessister species. We find transposable elements in these two species to be drivers of genome evolution in ticks. TheI.ricinusgenome assemblies and our tick repeat library will be valuable resources for biological insights into this important ectoparasite. Our findings highlight that further research into the impact of transposable elements on the genomes of blood-feeding parasites is required.