Genetic basis of host switch by Varroa mites on the Western honeybee

Maeva and Sasha

The domestication of the Western honey bee and globalization have facilitated the arrival and spread of new parasites and pathogens including the Varroa mites. Since Varroa destructor successfully switched host from the Asian honeybee (Apis cerana) to the Western honeybee (Apis mellifera) in multiple independent events, it has spread almost worldwide. Not only the ectoparasite induce direct damages via spoiling haemolymph but it is also a virus vector leading to its consideration as one of the main driver of honeybee global decline. Concerns rise as the sister species V. jacobsoni has emerged as an additional threat with the recent jump reported 10 years ago in Papua New Guinea.

How did those specialized organisms repeatedly “jump” and adapt onto a new host? What are the potential genetic and population key factors enabling such events?

The two vilains of the story: V. jacobsoni and V. destructor (magnified 6x)

Our project aims to tackle some of these questions using next-generation sequencing technology and genetic analysis of mite populations from their original and new hosts. We sequenced and assembled de novo the genome of both V. destructor and V. jacobosoni mite in order to quantify the structure of the parasite genomes and to identify which genes have evolved due to recent selection. The comparison of whole mite genome collected from their native range will allow to i) identify genetic mechanisms associated with the host switches by the mites, ii) detect historical signatures of selection after the host switch, iii) determine if gene flow has or still occured among populations and between mites species.

Since V. destructor has spread globally, it offers the opportunity to reconstruct a novel parasite spread and population evolution at large scale. For that we have started to build a world mite collection with the help of numerous collabotors to retrace the history of V. destructor populations using IM and ABC demographic models. From where did the invasive Varroa came from? What could be the size of the source population(s)? Are the invasive populations genetically connected? So many questions that we hope to answered, to be continued… :honeybee: :honeybee: