Genomic signatures of hybridization between Ixodes ricinus and Ixodes
persulcatus
Abstract
Identifying hybridization between common pathogen vectors is essential
due to the major public health implications through risks associated
with hybrid’s enhanced pathogen transmission potential. These hard-ticks
Ixodes ricinus and Ixodes persulcatus are the two most common vectors of
tick-borne pathogens that affect human and animal health in Europe. I.
ricinus is a known native species in Finland with a well-known
distribution. Over the past 60 years, I. persulcatus has expanded in
range making the species appear in areas previously not found in
Finland. Here we used double-digest restriction site-associated DNA
(ddRAD) sequencing on 92 ticks (morphologically identified as 46 I.
ricinus, and 46 I. persulcatus) collected across Finland to investigate
whether RAD generated single nucleotide polymorphisms (SNPs)
discriminate tick species and identify hybridization events. Two
different clustering methods were used to infer the specific species
based on how they clustered and identified hybrids among them. We were
able to discriminate between the two tick species and identified five
putative hybrids with admixed genomic proportions ranging from
approximately 25 to 75 percent. Four of these hybrids were
morphologically identified as I. ricinus and the other as I.
persulcatus. Our results suggest that RAD SNPs are robust for
identifying both species of the ticks as well as their hybrid
individuals. These results suggest ongoing hybridization between I.
ricinus and I. persulcatus in their natural populations in Finland. This
study is a significant step in understanding the formation of
hybridization zones due to range expansion potentially associated with
climate change. Despite our findings, our data are insufficient for
resolving the factors that affect population genetic structure within
species.