Abstract
Background Varroa mites are widely considered the biggest honey bee health problem worldwide. Until recently, Varroa jacobsoni has been found to live and reproduce only in Asian honey bee (Apis cerana) colonies, while V. destructor successfully reproduces in both A. cerana and A. mellifera colonies. However, we have identified an island population of V. jacobsoni that is highly destructive to A. mellifera, the primary species used for pollination and honey production. The ability of these populations of mites to cross the host species boundary potentially represents an enormous threat to apiculture, and is presumably due to genetic variation that exists among populations of V. jacobsoni that influences gene expression and reproductive status. In this work, we investigate differences in gene expression between populations of V. jacobsoni reproducing on A. cerana and those either reproducing or not capable of reproducing on A. mellifera, in order to gain insight into differences that allow V. jacobsoni to overcome its normal species tropism.ResultsWe sequenced and assembled a de novo transcriptome of V. jacobsoni. We also performed a differential gene expression analysis contrasting biological replicates of V. jacobsoni populations that differ in their ability to reproduce on A. mellifera. Using the edgeR, EBSeq and DESeq R packages for differential gene expression analysis, we found 287 differentially expressed genes (FDR ≤ 0.05), of which 91% were up regulated in mites reproducing on A. mellifera. In addition, mites found reproducing on A. mellifera showed substantially more variation in expression among replicates. We searched for orthologous genes in public databases and were able to associate 100 of these 287 differentially expressed genes with a functional description.ConclusionsThere is differential gene expression between the two mite groups, with more variation in gene expression among mites that were able to reproduce on A. mellifera. A small set of genes showed reduced expression in mites on the A. mellifera host, including putative transcription factors and digestive tract developmental genes. The vast majority of differentially expressed genes were up-regulated in this host. This gene set showed enrichment for genes associated with mitochondrial respiratory function and apoptosis, suggesting that mites on this host may be experiencing higher stress, and may be less optimally adapted to parasitize it. Some genes involved in reproduction and oogenesis were also overexpressed, which should be further studied in regards to this host shift.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3130-3) contains supplementary material, which is available to authorized users.
Highlights
Varroa mites are widely considered the biggest honey bee health problem worldwide
To understand the evolutionary host shift of Varroa mites to a new host, we have studied the transcriptome profile of V. jacobsoni reproducing on A. mellifera and compared it to that of V. jacobsoni restricted to reproducing on A. cerana
Varroa jacobsoni assembled transcriptome V. jacobsoni mite samples were collected from two different honey bee hosts, A. cerana and A. mellifera, and from two different geographic locations, the Solomon Islands and Papua New Guinea (PNG), respectively (Table 1)
Summary
Varroa mites are widely considered the biggest honey bee health problem worldwide. Until recently, Varroa jacobsoni has been found to live and reproduce only in Asian honey bee (Apis cerana) colonies, while V. destructor successfully reproduces in both A. cerana and A. mellifera colonies. We have identified an island population of V. jacobsoni that is highly destructive to A. mellifera, the primary species used for pollination and honey production The ability of these populations of mites to cross the host species boundary potentially represents an enormous threat to apiculture, and is presumably due to genetic variation that exists among populations of V. jacobsoni that influences gene expression and reproductive status. Varroa destructor is widely considered the most serious risk factor for honey bee colony mortality worldwide [7,8,9,10] These large ectoparasitic mites are associated with a condition known as parasitic mite syndrome (PMS), or “Varroosis”. The incidence of DWV is closely associated with mite infestation and colony mortality, but other bee-pathogenic viruses such as acute bee paralysis virus have been identified as part of the “Varroosis” [15, 16]. Failure to treat infested colonies with miticides typically results in colony death within 1–3 years
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