| 研究実績の概要 |
Host switches allow parasites to expand their niches. However, successful switches may require suites of adaptations and may decrease performance on the old host. As a result, reduction in gene flow accompanying many host switches drives speciation. Because host switches tend to be rapid, it is difficult to study them in real time and their demographic parameters remain poorly understood. As a result, fundamental aspects that control subsequent parasite evolution, such as the size of the switching population or the extent of immigration from the original host, remain largely unknown. To shed light on the host switch process, we explored how host switches take place in independent host shifts by two ectoparasitic honey bee mites (Varroa destructor and V. jacobsoni). Both switched to the western honey bee (Apis mellifera) after it was brought into contact with their ancestral host (Apis cerana), ~70 and ~10 years ago, respectively. V. destructor subsequently caused worldwide bee collapses. Using mite species collected in their native ranges from both the ancestral and novel hosts, we were able to correctly reconstruct the (known) temporal dynamics of the switch. We further found that hundreds of haplotypes were involved in the initial host switch, and, while greatly reduced, some gene flow between mites adapted to different hosts remains. Our findings suggest that while reproductive isolation may facilitate the fixation of traits beneficial for the exploitation of the new host, ongoing genetic exchange may allow genetic amelioration of inbreeding effects.
|
| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Through our collaboration with Australia’s CSIRO we were able to acquire all the specimens necessary for this work quickly and without additional costs, in time or expenditure funds. Genomic sequencing libraries were straightforward to make and we could obtain the sequencing data quickly. As a result, we were able to obtain data for Objective 1 and 3 already. In addition, we finished the demographic modeling for Objective 1 and analysis for Objective 3. We are working on Objective 2, which has proven to be intractable using the samples used in the other two objectives, but we solved all of the technical difficulties and have acquired additional samples to work on.
|
| 今後の研究の推進方策 |
In the next few months we will finish sequencing the DNA for all the Varroa mites collected (over 1000), and ~300 RNA libraries. The rest of the time will be spent analyzing the data and preparing manuscripts for publication. The DNA libraries will be used for tracing Varroa’s spread worldwide, and to understand how it evolves in response to different honey bee populations and human selection pressures. The RNA libraries will be used to trace the spread and evolution of viruses, the proximal causes of honey bee declines.We are working on two manuscripts: (1) Understanding the demographics associated with host switches in honey bee parasites. (2) A toolkit for studying Varroa genomics and transcriptomics: preservation, extraction and sequencing library preparation. The former is a major scientific paper, while the latter will be a widely useful methodological paper for other workers in the field.
|
