Varroa, Oudemans, 1904

Gudin, Filipe Macedo, 2023, Ophirion lenkoi Gudin 2023, sp. nov., Zoological Studies 62 (11), pp. 1-12 : 9

Hybridization in Varroa mites

Two independent host-shift events occurred in both the Russian Far East and Japan. The possible occurrence of R–J hybrids has been proposed because they have been observed to be sympatric in Brazil, Japan, Thailand, and the United States (de Guzman et al. 1999; Carneiro et al. 2007; Dietemann et al. 2019). A worldwide sampling analysis based on microsatellite markers revealed the occurrence of hybrid events and did not point to the presence of asymmetrical introgression between the J and R types, although many hybrids involving J alleles in the genetic background of the R type have been reported ( Solignac et al. 2005; Dietemann et al. 2019). A postzygotic barrier has been proposed to serve as a mechanism for selection against type J, possibly explaining why type R replaced type J and coexisted with it in sympatric areas ( Solignac et al. 2005). Examining the genetic content of R–J hybrids in sympatric areas would provide additional information on the selection fitness of the highly virulent type R relative to the less virulent type J.

Gene expression levels are key factors that can help elucidate why type R but not type J is highly virulent for A. mellifera . Allozyme patterns used to examine genetic differentiation furnished no recognizable differences for populations of V. destructor in Brazil, China and Europe ( Issa 1989; Biasiolo 1992). Zhang et al. (2010) reported that V. destructor exhibited differences in expression of genes related to metabolic functions and nerve transmission signature of A. mellifera versus A. cerana . Oldroyd (1999) indicated that bees have been exposed to type R for the longest period in eastern Russia; thus, tolerance to Varroa is most common in that region, although many naturally resistant populations of A. mellifera have been found ( Locke 2016). Moreover, on the basis of genome-wide analyses, Techer et al. (2019) found that divergent selection regimes existed between V. destructor and V. jacobsoni . In this study, network analysis indicated that type T was linked to the most common types R and J. The mechanism underlying the tolerance or virulence difference between the R and J types in A. mellifera could be elucidated using the available genomic sequences of the J, R, and T types.

Hybridization events between V. jacobsoni and V. destructor might be also possible. Spillbacks of V. destructor to A. cerana and spillovers of V. jacobsoni to A. mellifera have been found in sympatric populations in Thailand, where reciprocal genetic admixture has occurred between V. destructor and V. jacobsoni ( Dietemann et al. 2019) . The ITS sequence (EF025470) of V. jacobsoni was obtained from Java, Indonesia, where coinfestation of the two mites has commonly occurred ( Anderson and Morgan 2007; Anderson and Fuchs 1998). Therefore, the identical ITS sequence in V. jacobsoni and V. destructor may have resulted from hybridization events. However, the fact that V. destructor and V. jacobsoni have identical ITS patterns may also have resulted from the ancestral retention of an ITS region.