Kategorie: News
How the pygmy seahorse has adapted perfectly to its coral environment
Genetic research reveals why this small marine animal with a short snout is so astonishingly well camouflaged: The pygmy seahorse (Hippocampus bargibanti) is one of the most fascinating sea creatures living in the coral reefs of the western Pacific.
A German-Chinese research group led by evolutionary biologist Axel Meyer from Konstanz has now uncovered the secret of their adaptation. The aim of their study was to find out why these animals, with their shortened snout and textured skin, fit so perfectly into the coral world.
Their findings show that the dwarf seahorse's unusual appearance is the result of evolutionary adaptation to corals. Over the course of around 18 million years of evolution, the animals have lost a large number of genes, including those responsible for the elongation of the snout in other seahorses. As a result, their mouths remain short, enabling the animals to hide in the polyps of the coral day and night, effectively deceiving their predators.
Unlike their relatives, which have long, horse-like snouts, pygmy seahorses have genetically specialised in a short snout as part of their adaptation. Axel Meyer explains: "Normally, the snout of seahorses grows longer over time. But in pygmy seahorses, growth is suppressed by the loss of the hoxa2b gene. This keeps the animal small and short-snouted – perfect camouflage in the coral world." CRISPR-Cas9 experiments on zebrafish confirmed this theory. The result: the head of the pygmy seahorse remains stuck in the early stages of development, which significantly improves its ability to camouflage itself.
Many lost genes
But it is not only the shape of the head that is specially adapted to the environment. The skin colour, the formation of skin nodules that mimic coral polyps, and the immune system were also genetically examined. It was found that dwarf seahorses have the smallest known immune system compared to other vertebrates.
"This is probably due to the fact that coral toxins can be tolerated by dwarf seahorses and even offer protection against microbes. Their immune system therefore no longer needs the genes necessary for this. Furthermore, the gender roles have been reversed in seahorses, as males incubate the eggs in their brood pouch. However, because the eggs are not genetically identical to the cells in the males' bodies, they would normally be rejected. Therefore, the immune response is weakened and the genes responsible for it have been lost," says Meyer.
These genetic compromises are by no means a disadvantage, but rather an example of ecological adaptation. ‘The enormous genetic losses in pygmy seahorses are a prime example of how evolutionary pressure renders certain genes superfluous or even eliminates them altogether,’ summarises Axel Meyer. The animal shows how a combination of losses and specific adaptation can create an extraordinary biological niche in which camouflage and survival go hand in hand.
See also: Original publication ( www.pnas.org/doi/10.1073/pnas.2423818122 )