Draft genome of the honey bee ectoparasitic mite, Tropilaelaps mercedesae, is shaped by the parasitic life history

Abstract

The number of managed honey bee colonies has considerably decreased in many developed countries in recent years and ectoparasitic mites are considered as major threats to honey bee colonies and health. However, their general biology remains poorly understood. We sequenced the genome of Tropilaelaps mercedesae, the prevalent ectoparasitic mite infesting honey bees in Asia, and predicted 15 190 protein-coding genes that were well supported by the mite transcriptomes and proteomic data. Although amino acid substitutions have been accelerated within the conserved core genes of two mites, T. mercedesae and Metaseiulus occidentalis, T. mercedesae has undergone the least gene family expansion and contraction between the seven arthropods we tested. The number of sensory system genes has been dramatically reduced, but T. mercedesae contains all gene sets required to detoxify xenobiotics. T. mercedesae is closely associated with a symbiotic bacterium (Rickettsiella grylli-like) and Deformed Wing Virus, the most prevalent honey bee virus. T. mercedesae has a very specialized life history and habitat as the ectoparasitic mite strictly depends on the honey bee inside a stable colony. Thus, comparison of the genome and transcriptome sequences with those of a tick and free-living mites has revealed the specific features of the genome shaped by interaction with the honey bee and colony environment. Genome and transcriptome sequences of T. mercedesae, as well as Varroa destructor (another globally prevalent ectoparasitic mite of honey bee), not only provide insights into the mite biology, but may also help to develop measures to control the most serious pests of the honey bee.

Chemosensing of honeybee parasite, Varroa destructor: Transcriptomic analysis

“…6). A recent analysis of another parasitic mite of honeybees, Tropilaelaps mercedesae , has also revealed the presence of transcripts similar to DmIR25a and DmIR93a, and both genes were highly expressed in the forelegs of the mite 48 .

Figure 6Phylogenetic tree of IR25a homologs of the Acarians: M. occidentalis (Acari, Parasitiformes, Mesostigmata), V. destructor (Acari, Parasitiformes, Mesostigmata), Tetranychus urticae (Acari, Acariformes, Prostigmata) and I. scapularis (Acari, Parasitiformes, Metastigmata). For each sequence the protein’s domains are presented: Ligated ion channel L-glutamate; glycine-binding site (IPR019594) and Ligand-gated ion channel (IPR001320).

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Molecular characterization and expression of vitellogenin genes from the wolf spider Pardosa pseudoannulata (Araneae: Lycosidae)

“…There are several studies available on vitellogenesis and its regulation in arachnid species. Multiple Vg genes are described from Dermacentor variabilis (Acari: Ixodidae) (Thompson et al, 2007;Khalil et al, 2011), Haemaphysalis longicornis (Acari: Ixodidae) (Boldbaatar et al, 2010), Neoseiulus cucumeris (Acari: Phytoseiidae) (Zhao et al, 2014), Varroa destructor (Acari: Varroidae) (Cabrera Cordon et al, 2013), Rhipicephalus microplus (Acari: Ixodidae) (Tirloni et al, 2014), Tetranychus cinnabarinus (Acari: Tetranychidae) (Liu et al, 2016), Rhipicephalus appendiculatus (Acari: Ixodidae) (de Castro et al, 2016), Tropilaelaps mercedesae (Acari, Laelapidae) (Dong et al, 2017) and Tetranychus urticae (Acari: Tetranychidae) (Kawakami et al, 2009). Besides, complete Vg sequences are also described from Ornithodoros moubata (Acari: Argasidae) (Horigane et al, 2010) and Amblyomma hebraeum (Acari: Ixodidae) (Smith & Kaufman, 2014).…”

Varroa chemosensory proteins: some are conserved across Arthropoda but others are arachnid specific

“…Recently, IR genes were reported for several other arachnids, including Tetranychus urticae (Ngoc et al, 2016), G. occidentalis (Hoy et al, 2016), Tropilaelaps mercedesae (Dong et al, 2017) and the spider D. silvatica (Vizueta et al, 2016). However, only 13 of them contained at least two of the essential domains.…”

“…These results delineate this IR subgroup from the other IGRs, and augment its proposed role as a peripheral chemoreceptor, rather than an internal neurotransmitter-receptor. Recently, IR genes were reported for several other arachnids, including Tetranychus urticae (Ngoc et al, 2016), G. occidentalis (Hoy et al, 2016), Tropilaelaps mercedesae (Dong et al, 2017) and the spider D. silvatica (Vizueta et al, 2016). In the last two organisms, some IR transcripts were highly expressed in the first pair of legs.…”

“…Olfactory IRs belonging to the ionotropic glutamate receptor (IGR) superfamily can be found across all protostomes and are implicated as ancient chemoreceptors (Croset et al, 2010;Rytz et al, 2013). Orthologues of the Drosophila melanogaster ionotropic receptor IR25a, which acts as an IR co-receptor, as well as orthologues of glutamate receptors (GRs), have been reported in some Acari, Araneae (Croset et al, 2010;Gulia-Nuss et al, 2016;Hoy et al, 2016;Ngoc et al, 2016;Vizueta et al, 2016;Dong et al, 2017), as well as in Crustacea (Daphnia pulex; Peñalva-Arana et al, 2009;Croset et al, 2010). The ion channel receptor families of ENaCs and TRPs are considered as important receptors for the perception of both outer and inner environments, including chemoperception (Venkatachalam and Montell, 2007;Ben-Shahar, 2011;Zelle et al, 2013;Peng, Shi, et al, 2015).…”