The Ancestor's Tale : A Pilgrimage to the Dawn of Evolution by Richard Dawkins

Author:Richard Dawkins [Dawkins, Richard]
Language: eng
Format: epub
Tags: Philosophy, General, History, Evolution, Science, Life Sciences, Evolution (Biology), Evolution (Biology) - History, Evolution (Biology) - Philosophy
ISBN: 9780618619160
Publisher: Mariner Books
Published: 2005-09-15T10:18:56.552000+00:00

The Mudskipper's Tale

On an evolutionary pilgrimage it is fitting that some of the tales, though told by surviving pilgrims, should deal with recent re-enactments of ancient evolutionary events. Teleost fish are so variable and so versatile, it is only to be expected that some of them might replay parts of the lobefins" history, and come out onto the land. The mudskipper is just such a fish out of water, and it lives to tell the tale.

A number of teleost fish species live in swampy water, poor in oxygen. Their gills cannot extract enough, and they need help from the air. Familiar aquarium fish from the swamps of South-East Asia, such as the Siamese fighting fish Betta splendens, frequently come to the surface to gulp air, but they still use their gills to extract the oxygen. I suppose, since the gills are wet, you could say the gulping is equivalent to locally oxygenating their gill water, as you might bubble air through your aquarium. It goes further than that, however, because the gill chamber is furnished with an auxiliary air space, richly supplied with blood vessels. This cavity is not a true lung. The true homologue of the lung in teleost fish is the swim bladder which, as the Pike's Tale has shown, they use for keeping their buoyancy neutral.

Those fish that breathe air through their gill chamber have rediscovered air breathing by a completely different route. Perhaps the most advanced exponents

THE MUDSKIPPER'S TALE | 279

of the air-breathing gill chamber are the climbing perches Anabas. These fish also live in poorly oxygenated water and they have the habit of walking over land looking for water when their previous home has dried up. They can survive out of water for days at a time. Anabas is, indeed, a living, breathing example of what Romer was talking about in his (now less fashionable) theory of how fish came out onto the land.

Another group of walking teleost fish are the mudskippers, for example Periophthalmus, whose tale this is. Some mudskippers actually spend more time out of water than in it. They eat insects and spiders, which are not normally found in the sea. It is possible that our Devonian ancestors enjoyed similar benefits when they first left the water, for they were preceded onto the land by both insects and spiders. A mudskipper flaps its body across the mudflats, and it can also crawl using its pectoral (arm) fins, whose muscles are so well developed that they can support the fish's weight. Indeed, mudskipper courtship takes place partly on land, and a male may do push-ups, as some male lizards do, to show off his golden chin and throat to females. The fin skeleton, too, has evolved convergently to resemble that of a tetrapod such as a salamander.

Mudskippers can jump more than half a metre by bending the body to one side and suddenly straightening it — hence some of their many vernacular names, including 'mud-hopper', 'johnny jumper', 'frognsh' and 'kangaroo fish'. Another common name, 'climbing fish', comes from their habit of climbing mangrove trees looking for prey.

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