Research press release


Nature Communications

Zoology: Seahorses go stealth



今回、Brad Gemmellたちは、デジタルインラインホログラフィーを用いて、タツノオトシゴの頭部形状の機能を調べた。この技術を用いることで、3次元画像が得られ、その結果、タツノオトシゴを取り巻く水の動きを追跡観察することができた。この観察で、タツノオトシゴが獲物に近づくとき、タツノオトシゴの鼻を取り巻く水がほとんど動かず、それが、獲物に気付かれずに忍び寄る上で役立つことが分かった。また、ヨウジウオ(タツノオトシゴの近縁種だが、頭部の形状が異なる)によって生じる水の撹乱との比較が行われ、タツノオトシゴの前面に流体力学的に静かな領域が生じる原因が頭部の形状自体であることがさらに実証された。

The shape of the seahorse head has evolved to allow the animals to closely approach their prey while remaining undetected, reports research published in Nature Communications this week. The work suggests that this unique head shape allows for movement with minimal disturbance to the water immediately surrounding it.

Seahorses are very slow swimmers, yet they feed mainly by hunting evasive prey that is able to detect even a slight deformation in the surrounding water. Seahorses’ feeding mechanism relies on their arched necks acting as a spring and allowing the attack to relatively distant prey. This mechanism, and the distance they can capture the prey, is however limited to the actual length of the neck. Thus far it remained unknown as to how the slow swimming seahorses managed to get close enough to their prey while remaining undetected.

Brad Gemmell and colleagues used digital in-line holography to investigate the function of the head morphology of seahorses. This technique allowed for the capture of 3D images and the subsequent tracking of water movement around the seahorses. The authors find that the water around the seahorse snout hardly moves while it approaches prey, helping the seahorse to close in undetected. Comparisons with the water disturbances created by pipefish, close relatives to seahorses but with a different head shape, provided further evidence that it is the head shape itself that produces this hydrodinamically silent region in front of the seahorse.

doi: 10.1038/ncomms3840

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