Jumping fish could give clue to evolution

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The phrase 'fish out of water' conjures up an image of helplessness, but a fish jumping around on land may not be just aimlessly flopping about, according to a new study.

In the study, to be published in a forthcoming issue of the Journal of Experimental Zoology Part A, Alice Gibbs and coauthors examined the way fishes jump around when stranded on land, focusing on the Mosquitofish (Gambusia affinis) and the Zebra danio (Danio rerio).

Mosquitofish are known to voluntarily strand themselves on land in order to escape predators, while Zebra danios are very distantly related to Mosquitofish and are not known to voluntarily leave the water.  

Jumping Mosquitfofish are known to use a tail flip to drive their locomotion out of the water, and the authors were testing the hypothesis that this tail flip is present in distantly-related fish and is a modified version of an aquatic fast start escape response.

This hypothesis was mooted because of the similarities in both forms of locomotion: both involve a large sideways curvature of the body, followed by the body flexing in the opposite direction.

The authors used high-speed digital video cameras to record five Mosquitofish and five Zebra danios utilising an aquatic fast start escape response induced with a visual or mechanical stimulus. They then recorded another five Mosquitofish and five Zebra danios leaping on land before analysing their results.

The authors found that the tail flip used by the fishes to jump around on land is indeed similar to the aquatic fast start escape response, differing only in the increased time the fish spent flexing its body in the tail flip (to allow it to store more elastic energy to generate lift for jumping).  

The authors also noted that the Mosquitofish appeared to be better jumpers on land than the Zebra danios, as they jumped further and displayed better stability and control during the jumps.

The results of the study imply that morphological adaptations may not be a necessary prerequisite for terrestrial locomotion (all that is needed being the evolution of new behaviours) and that the vertebrate invasion of land may have occurred more frequently than previously thought.

For more information, see the paper: Gibb, A. C., Ashley-Ross, M. A., Pace, C. M. and Long, J. H. (2011), Fish out of water: terrestrial jumping by fully aquatic fishes. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology. doi: 10.1002/jez.711

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