Africa’s deepest freshwater lake holds a dizzying array of animals, including hundreds of species of cichlid fish found nowhere else in the world. They crowd the waters of Lake Tanganyika, with scales and stripes in most colors of the rainbow. One kind of cichlid there measures just over an inch; others are 2 to 3 feet long. “When you’re snorkeling in the water with these fish, it’s just incredibly striking how different they are,” said Catherine Wagner, an assistant professor of botany at the University of Wyoming. Throughout history, local fishermen have pulled up the cichlids in nets for food, but for several decades researchers from around the globe have collected these fish as well in their quest to understand that lush diversity.
A recently published study in Nature offers a new wealth of data on Lake Tanganyika’s cichlids and uses it to outline the wild ebb and flow of evolution for these fish, which diversified from one common ancestor to an astonishing 240 or so cichlid species in less than 10 million years.
That’s a very small amount of time for so many species to evolve, said Walter Salzburger, an associate professor at the University of Basel’s Zoological Institute and senior author on the study. And this process wasn’t gradual or random — the data reveals that these cichlids evolved predominantly in bursts. “It’s still surprising how clear and distinct these pulses of accelerated evolution are,” Salzburger said.
Mapping out the emergence of all these species took Salzburger’s team several years. The researchers compiled a list of the lake’s cichlid species after they tracked down descriptions in scientific records as well as in books and magazines written about cichlids (which are so visually striking that they have become popular aquarium fish). In between encounters with crocodiles and hippos during their months in Africa, the researchers snorkeled and dived to gather examples of every cichlid they could. Fishermen on the lake provided specimens that live deeper than divers can reach. “Whenever we saw a boat, we would ask, ‘What do you have?’” said Fabrizia Ronco, a postdoctoral researcher at the University of Basel and first author on the study. Eventually, they amassed a collection of almost every one of Lake Tanganyika’s 240 cichlid species, including dozens that had not been described previously.
Back on land, the researchers scanned the fish to examine their skeletal structures, studied the differences in their genes, and analyzed their chemical composition for clues to the ecological niche each occupied. The team accumulated enough details to reveal how all the species are related and when they diverged from one another.
“It’s just a fantastic amount of data,” Wagner said. “This was just a dream, a sparkle in our eyes 10 years ago, that we would be able to sequence this many genomes.”
One finding was that all but a handful of the species have a common ancestor that lived only about 9.7 million years ago. That corresponds to shortly after Lake Tanganyika is believed to have formed, which strongly implies that the species evolved within the lake from that one ancestral species, and not from multiple colonization events over the millennia.
This fact confirmed for the researchers that Tanganyika’s cichlids were ideal subjects for testing ideas about adaptive radiation — an evolutionary event in which many diverse species emerge rapidly and adapt to new environmental niches. Evolutionary theorists have two models for how adaptive radiation might play out. In one, rapid diversification in some aspect of body morphology produces a burst of new species at first, and then speciation slows as the available niches fill up. In the other model, differences in species emerge in stages as a lineage cracks open opportunities available to it, which means that the rate of speciation can both rise and fall over time. Evolutionary biologists have turned up only limited evidence to bolster either of these theories.
The Link LonkDecember 01, 2020 at 11:11PM
https://ift.tt/39vAL3X
New Fish Data Reveal How Evolutionary Bursts Create Species - Quanta Magazine
https://ift.tt/35JkYuc
Fish
No comments:
Post a Comment