| 研究実績の概要 |
Since 2016, we initiated a Varroa world collection that was large of 878 samples from 31 countries. During the fellowship, we succeeded in increasing its size and coverage by developing new international collaborations with now 1659 samples from 60 countries. We unearthed i) 106 historical samples collected during V. destructor early spread between 1989 to 2000 and ii) all Varroa species, including undescribed ones. Using our reference genome of V. destructor (Vdes3.0) and state-of-the-art genomic tools, we successfully sequenced the whole genome of 1760 samples worldwide.
By focusing on the native range, where the parasites exist in sympatry on a novel and original host, we found that host switches put the parasites on the path to speciation but that each switch requires considerable genetic diversity to take hold. We were able to reconstruct the origin of host switches and pin-point new ones with congruent and independent analysis. This is in stark contrast to the long-held view that Varroa is quasi-clonal on the novel host and explains its remarkable adaptability to different host races and human countermeasures.
We then studied the world biogeography of the invasive V. destructor using spatial and temporal population genomics. We were able to show that key elements to Varroa’s success were due to unreported host switch events and multiple invasion pathways which promoted hybridization. By looking at different population levels (from host colony to continents), we further elucidate the origin and evolution of V. destructor on its new host.
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