昆虫の空間学習による音響航法行動の変調

Modulation of acoustic navigation behaviour by spatial learning in the echolocating bat Rhinolophus ferrumequinum nippon.

• Yasufumi Yamada
• Yurina Mibe
• Yuya Yamamoto
• Kentaro Ito
• Olga Heim
• Shizuko Hiryu

抄録

コウモリはエコーロケーションを用いて周囲の音響情報を受け取り、複雑な環境を高度にナビゲーションすることができると考えられています。本研究では、コウモリの空間学習と音響センシングを理解するために、障害物コースを繰り返し飛行することで周囲の環境を学習し、飛行とエコーロケーションの制御がどのように変化するかを調べました。これらの実験では、空間学習と飛行環境の相互作用効果を評価するために、鎖とアクリル板を障害物として用いた2つの実験環境（音響透過性と音響反射性）を用意した。その結果、コウモリは蛇行する飛翔の幅とパルスの放出を減少させ、両方の条件で環境学習を行うことでパルスの方向のシフトを減少させているように見えた。このことは、パルスの放出数が各コウモリのエコーロケーション戦術を反映していることを示唆しています。このことから、コウモリは周囲の環境をどれだけ事前に察知できるかで飛行計画を調整していると考えられます。

Using echolocation, bats receive acoustic information on their surroundings, which is assumed to help them sophisticatedly navigate complex environments. In this study, to understand spatial learning and acoustic sensing in bats, we investigated how flight and echolocation control changed in Rhinolophus ferrumequinum nippon as they learnt about their surroundings in an obstacle course that they flew through repeatedly. In these experiments, two testing environments (acoustically permeable and acoustically reflective) were prepared using chains and acrylic boards as obstacles to evaluate the interactive effects of spatial learning and flight environments. We found that bats reduced the meandering width of their flights and pulse emissions, and also seemed to reduce their shifts in pulse direction as they learnt more about their environments in both conditions. Throughout all our experiments, the bats with slower flight speeds tended to emit more pulses, which suggests that the number of pulse emissions reflects the echolocation tactics of each bat. The maximum flight speed was especially increased in the acoustically permeable condition, with frequent emissions of multiple pulses (≧triplets) in the early stages of flight, suggesting that bats adjust their flight plan based on how much of their surroundings they are able to sense in advance.