蜜蜂的磁場感受之行為與神經反應

Abstract

蜜蜂 (Apis mellifera) 被認為能夠感受磁場的改變，陸生動物磁感受可分為兩種假說：化學磁感受假說及磁鐵礦磁感受假說。前人研究發現蜜蜂腹部脂肪體與營養細胞中存在許多鐵顆粒並認為其具有感受磁場的作用，然而目前缺乏直接證據證明鐵顆粒與磁感受的關係。此外，化學磁感受假說中提出的磁感受器隱色素 (cryptochrome) 在蜜蜂腦內也被發現，其也具有作為蜜蜂磁感受器的潛力。為檢驗蜜蜂是否能由腹部磁鐵接受磁場訊息，本研究首先透過古典制約訓練蜜蜂並藉由觀察其口吻延伸反應 (proboscis extension reflex) 確認蜜蜂的磁感受能力，蜜蜂接受兩天的訓練後得以關連磁場刺激與口吻延伸反應，接著經由手術的方式切斷其腹神經索以阻止腹部與腦的訊息傳遞，手術後的蜜蜂仍能學習氣味與口吻延伸反應的關聯，然而無法再對磁場刺激產生反應。而傳遞磁場訊息的神經反應也在腹神經索被記錄到。本研究說明蜜蜂經訓練後得以關聯磁場刺激與口吻延伸反應，且證實其磁感受訊號確實來自腹部並經由腹神經索傳遞，我們認為蜜蜂將成為磁鐵礦磁感受系統相關研究的理想模式動物並期許未來有更多研究釐清磁感受系統的生理機制。

It has been well known that the honey bees, Apis mellifera, are able to detect the earth’s magnetic field. So far, two hypothesized models are proposed for the magnetoreception of terrestrial animals, i.e. the chemical and the magnetite-based magnetoreception. Previous studies showed that there are some iron granules in the fat body and the trophocytes of the honey bees’ abdomen, suggesting the iron granules are responsible for sensing magnetic changes. However, there is no direct evidence to associate these iron granules with the magnetoreception of honey bee. In addition, the magnetoreceptor of the chemical magnetoreception system, so called cryptochrome, has also been found in the honey bees’ brain which might be the potential magnetoreceptor of the bee. In this study, we first conducted the classical conditioning experiment by monitoring the proboscis extension reflex (PER) to demonstrate the ability of honey bee’s magneticoreception. Honey bees were trained successfully to associate the magnetic stimulus with a sucrose reward after two days of training. Then, the ventral nervous cord was cut to disconnect the signal transmission from the abdomen to the brain. The honey bees could no longer associate the magnetic stimulus with the sucrose reward after the disconnection, but still could learn an olfactory PER task. Moreover, the neural signals transmitted by the VNC have also been recorded at the “neck” of the bees. Our results demonstrate that the bees can be trained to combine the magnetic stimulus and PER through classical conditioning, and reveal that the magnetoreception signals come from the abdomen via the ventral nervous cord to the bee brain and confirm the magnetite-based magnetoreception in honey bee.