Plate tectonics helped seahorses to stand upright

Mutation favored by formation of shallow seas

Seahorses © NOAA
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Why do seahorses swim upright? All other fish prefer the horizontal. A German-Australian researcher duo has now clarified this question: Shifts in the continental plates gave rise to large shallow seas with seagrass beds 25 million years ago. In these, a mutated - upright - form of the seahorse ancestors could hide better, as the scientists in the journal "Biology Letters" report.

Together with his colleague Luciano Beheregaray, the German marine biologist Peter Teske hired genetic research between seahorses and the Australian "Pygmy Pipehorses" as part of a research project at the Australian Macquarie University. These belong to a group of fish that are considered the closest relatives of seahorses. The English name of these animals is a combination of pipefish (pipefish) and seahorse (seahorse), which suggests that they combine characteristics of both groups. The Pipehorses do not swim upright, but fish typically horizontally in the water.

"Seahorses and Pygmy Pipehorses are very similar, " explains Teske. "Both have a tail that is not used for swimming, but to hold on to plants and other objects. In both groups, the males hatch the eggs in a gross pocket. The only major difference is in principle the upright posture. "In fact, the parallels are so strong that even Teske the Pipehorses initially considered seahorses, which had given up their upright posture for some reason.

Plate tectonics promotes upright mutation

However, the genetic studies of the researchers revealed the opposite: about 25 million years ago, genetic mutations in some Pygmy Pipehorses apparently caused an upright posture: the first seahorses had developed. What happened then is a fascinating example of how natural selection can promote the development of new species.

At the same time, plate tectonics was causing major changes in the area north of what is now Australia: the continents were widening, and extensive shallow water areas were developing between Australia and Indonesia, where seagrass was spreading rapidly. display

Upright pose optimal camouflage in new seagrass fields

This new habitat was ideal for new seahorses, as the upright leaves of sea grass offered their upright bodies excellent camouflage. Not only were they better protected from predators, they were also able to sneak up far more unnoticed to their own prey, small crustaceans and fish. The upright swimming position had become a biological advantage under these conditions.

From their new habitat, the seahorses spread over the whole world over the millions of years. The Pygmy Pipehorses, from which they have developed, still live on their Australian algae reefs.

(Macquarie University, 08.06.2009 - NPO)