Mosquitofish can leap with “skill and purpose.”
How did animals move from water to land? The answer may have just got a little murkier. A study published this month in the Journal of Experimental Zoology found that two distantly related fish share a similar method for jumping about on land, suggesting that a common ancestor evolved this ability long ago. But unlike amphibious fish such as the mudskipper, which has pectoral fins adapted to “walking” on land, these fish have no specialized equipment for leaping, and would therefore leave no evidence of their talent behind in the fossil record.
In the lab scientists placed fish on a moist surface and filmed their leaps using a high-speed camera (see video below). In this study researchers compared the western mosquitofish, which is known to hop onto land when pursued by predators, and the zebrafish, which doesn’t leave the water in its natural habitat. And yet in the lab both fish can jump with “skill and purpose,” and in very similar way. This led researchers to hypothesize that a common ancestor of the two fish evolved the capacity to jump on land, more than 150 million years ago. The researchers are currently filming the jumping behavior of every fish species they can get their hands on to conclusively determine whether jumping did in fact evolve once or whether it cropped up multiple times in different lineages.
Here’s a video of the western mosquitofish, or Gambusia affinis. Its trajectory, at about 45 degrees from the ground, makes it a “better” jumper than the zebrafish, giving it more distance per unit of effort. This makes sense, given that zebrafish don’t naturally leave the water:
Now for the zebrafish (Danio rerio). Notice how it bring its head toward its tail before leaping, the opposite of the the mudskipper’s technique:
Here’s the proficient jumper Kryptolebias marmoratus, a killifish that spends some of its time out of water while evading predators:
Finally, here’s a convict cichlid (Amatitlania nigrofasciata). Researchers analyzed this fish since it’s not known to display a jumping behavior outside of water. Scientists hypothesize this fish has lost the ability to leap on land, although it’s also possible that it never possessed that ability. Further study of related fish will help them find out.
Reference: Alice C. Gibb, Miriam A. Ashley-Ross, Cinnamon M. Pace, John H. Long. Fish out of water: terrestrial jumping by fully aquatic fishes. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2011; DOI: 10.1002/jez.711
Image and video credit: Northern Arizona University.