リファレンス
Comparison of the Ontogeny of Hunting Behavior in Pharaoh Cuttlefish (Sepia pharaonis) and Oval Squid (Sepioteuthis lessoniana)
https://www.journals.uchicago.edu/doi/full/10.1086/BBLv225n1p50
要旨
生態の異なるイカの捕食行動について、成長に伴う変化を比較した論文
Animals adopt various forms of hunting according to their ecological, morphological, and cognitive features, and their specific hunting skills are acquired ontogenetically in relation to these features. It is noted that cuttlefish and squid hunt prey through the elongation of tentacles used specifically to capture prey. However, these two cephalopods have different lifestyles, leading to questions such as whether hunting skill is acquired similarly after birth and whether tentacle elongation is behaviorally identical. To address these questions, we observed and compared how captive pharaoh cuttlefish (Sepia pharaonis) and oval squid (Sepioteuthis lessoniana) attack prey during their early life stages. Like the adults, S. pharaonis hatchlings used the tentacular lunge attack, whereas S. lessoniana hatchlings used the arm-opening attack. S. lessoniana began to exhibit the tentacular strike attack after 30 days of age. In addition to timing of the emergence of a specific hunting mode, some differences were observed in the physical aspect of hunting behavior. For cuttlefish, maximum tentacle length and maximum speed of tentacle elongation increased from hatching to 30 days of age and then decreased. In contrast, for squid, maximum tentacle length increased from hatching to 30 days of age and then became constant. The distance to prey was positively correlated with maximum length and speed of tentacle elongation in S. pharaonis and with maximum swimming speed in S. lessoniana. These results show that cuttlefish mainly use an ambush strategy and that squid use a pursuit strategy. Possible causes for the ontogenetic differences in hunting behavior are discussed.
コメント
一言：捕食行動を数値含めわかりやすく明文化
いわゆるcuttlefish (コウイカ類) とsquid (ツツイカ類，スルメイカやヤリイカなど) ではどちらも触腕を用いて捕食を行うがその生態は異なるため，捕食行動が成長過程でどのように獲得されるのかを調べ，比較した論文．実験材料はトラフコウイカとアオリイカの2種．トラフコウイカでは孵化後から成体と同様に触腕を瞬時に伸ばして餌を捕獲するが，アオリイカでは孵化直後から孵化後90日までの間に腕全体を広げて餌を捕まえる段階など数段階の変化がみられ，最終的に成体と同様に触腕を伸ばしてつかめるようになるとのことだった．各段階での獲物に攻撃を仕掛ける距離なども調べられており，普段飼育して何となく感じていることが，明確な数値を含めて文章で記載されており，非常にためになった．このような方法でも面白い論文が書けるんやな．考察では，成長に伴う学習によるものではなく，生息環境や体の構造による制限が反映されているのではないかということも述べられていた．眼の構造の違い(コウイカの眼は水平方向に広く見るのに向いているなど)や筋肉構造の違い (筋肉の瞬間的な収縮を可能にするナトリウムチャネルの有無など) まで考察されていて，自分はなかなか勉強しきれていない部分でもあったので参考になったし，まだまだ勉強不足やなぁと痛感した…．
