What gives the seahorse its equine look? The way it eats, according to a reecent study. Check out the video below.
The study by scientists from Belgium and the USA is published in a recent issue of the journal Nature Communications.
Seahorses are distinctly unlike most fishes in shape, with a horse-like head, s-shaped body and a prehensile tail. The unusual shape of seahorses has fascinated humans since the time of Ancient Greece, but the significance of its unusual body shape remained a puzzle until research by Sam Van Wassenbergh and his colleagues suggests that the bent head of the seahorse enables it to move its head further and strike at more distant prey.
Seahorses and other members of the Syngnathidae (including the closely related pipefishes and sea dragons) feed on small marine invertebrates, snapping their heads upwards toward the prey and using suction to draw the meal into their mouths. Utilising a process known as pivot feeding, the tendons of the rotational muscles at the base of the skull of the fish act like elastic bands that snap the head upward remarkably quickly (no more than five milliseconds) as the prey swims by. Recent studies have shown that the ancestors of seahorses were very much like pipefishes in having a trunk that is in line with the head, implying that seahorses have evolved an S-shaped body.
Using high-speed videos and mathematical model simulations of prey capture in three seahorse species and four pipefish species, the authors analysed the effects of head and trunk posture on prey-capture performance via cranial rotation.
They found that the range of movements for the head is severely restricted for pipefishes (that have their heads in line with their trunk).
The decreased head strike range is not a problem for actively swimming hunters such as pipefishes, because they compensate for this by moving themselves forward. However, seahorses are ambush predators that sit and wait for their food to swim by. Therefore, any increase in the head strike range, however small, will confer an evolutionary advantage.
The authors’ models predicted that strike distance would increase by about 28% when the angle of the head relative to the trunk increased as a result of gradually transforming the pipefish model into a more seahorse-like shape. The extremely quick rotation of the head towards the prey results in additional forward motion that increased the head strike range in the seahorse model. This was borne out by the results from the high-speed videos taken of prey capture.
For more information, see the paper: Van Wassenbergh, S, G Roos & L Ferry (2011) An adaptive explanation for the horse-like shape of seahorses. Nature Communications 2, 164.