![]() The pufferfish was the sole exception-like the platypus, it has kept a single pepsinogen gene, which it uses for non-digestive purposes. They’ve also lost many of the genes for pepsinogens-digestive enzymes that break down proteins. They scoured the full genomes of these species and showed that they’re all missing the genes for the gastric proton pump-the enzyme that acidifies the stomach. Now, Filipe Castro and Jonathan Wilson from the University of Porto have found the same pattern in other stomach-less vertebrates, like the zebrafish, pufferfish, medaka, platyfish, and Australian ghostshark. Xose Puente from the University of Oviedo first discovered that the platypus has lost its main stomach genes, back in 2008. And we now know that several of these losses were accompanied by disappearing genes. On at least 18 separate occasions, vertebrates have abandoned their stomachs. (It’s commonly said that pufferfish puff by expanding their stomachs, but while they have a sac in the right place, it’s not a glandular, acid-secreting one, so it doesn’t really count.) Of the almost 30,000 species, it seems that around a quarter have abandoned their stomachs, including groups like wrasse, carp, cowfish, pufferfish, zebrafish and more. Lungfish, a group of slender freshwater fish that can breathe in air, don’t have stomachs nor do the chimeras, bizarre-looking relatives of sharks and rays.Īnd the teleosts-the group that includes most living fishes-have taken stomach loss to extremes. The platypus doesn’t have one, nor do its closest relatives, the spiny echidnas. It allowed our ancestors to digest bigger proteins, since acidic environments deform these large molecules and boost the actions of enzymes that break them apart.īut over the last 200 years, scientists have shown that many vertebrates have lost their stomachs. ![]() The stomach, defined as an acid-producing part of the gut, first evolved around 450 million years ago, and it’s unique to back-boned animals (vertebrates). In other words, the platypus has no stomach. There’s no sac in the middle that secrete powerful acids and digestive enzymes. And if you look inside a platypus, you’ll find another weird feature: its gullet connects directly to its intestines. ![]() ![]() The males have a venomous claw on their hind feet, and the females lay eggs. It has a leathery duck-like bill, a flattened tail and webbed feet. The platypus is an anthology of weirdness. ![]()
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