In 2018 and 2020, Michael Pauers traveled 8,500 miles to fish Lake Malawi, but not with a pole and lure. He and his research partner, Titus Phiri, collect and describe cichlids—best known as popular aquarium fish—with the goal of discovering new species in the wild.
As Pauers, an associate professor in the UWM College of General Studies, was sifting and sifting through the lake water, a blue specimen with a red dorsal fin caught his eye. Some cichlids sport color combinations, he said, but this one is unique.
“It’s amazing. I can’t believe how bright and saturated the colors are,” Pauers said. It is one of six new species of cichlid in the genus Labeotropheus that he and Phiri, with the help of professional divers, found during the trips. They named it rubidorsalis.
Cichlids represent the most diverse adaptations of vertebrates in the world, and most of them—about 2,000 species and possibly more—live in the freshwater of the African Great Lakes. There are so many species that categorize them, a field called taxonomy, is constantly changing.
Pauers and Phiri, a research scientist at the Malawi Department of Fisheries, are interested in why there are so many species and why new ones appear all the time. But they are also interested in listing its entire spectrum, which is spread over 73 genera. The cichlid genus that Pauers studied, Labeotropheus, is found only in Lake Malawi, along with 600 other species that are exclusive to the lake.
Filling a genus
When Powers graduated from UWM, there were only two known species of Labeotropheus. By the time he described three freshmen in 2016–17, he was already on the faculty at his alma mater. His discoveries mark the first time in 60 years that species have been added to the genus.
Then, he and Phiri described six more species they collected during the 2020 expedition. They published their findings in the journal Ichthyology and Herpetology in May. The Pauers are now involved in the identification of nine of the 11 known species of this genus.
And scientists who discover a new species must name them—within scientific guidelines, of course.
After examining one of his first specimens of a new species, he had trouble naming it, finally deciding on Labeotropheus simoneae in honor of his daughter, Simone. “Someone at my daughter’s school said she had very rosy cheeks,” she said. “And that’s one of the distinguishing features of that fish.”
Labeotropheus is unique because the fish eats algae that it scrapes off rocks with its lower jaw. To do this, it rests its bulbous nose on a rock while feeding. The mouth is very straight in this genus, forming the shape of “half a rectangle,” Pauers said.
The great lake’s diverse habitats are responsible for the unparalleled diversity of cichlids, Phiri said. Cichlids live in both shallow and deep water and have a wide range of diets, made possible by a second set of jaws placed at the back of his throat, he said.
“My theory is that the lake is very old, and its formation was gradual, creating different habitats over time,” Phiri said. “The cichlid is adapted to different niches, forming different species that are very close to each other.”
What makes a species evolve?
Many of the differences in the new species Pauers and Phiri found are in color, but they also found differences in body shape, and the number of teeth and scales. The couple also put the cichlids under a microscope and measured their physical features, a difficult task that few scientists do.
In many cases, the differences are so small, they can be a feature that separates one species from another. Complicating matters is the fact that females and males of the same species look different.
But taxonomy is complex, and adaptations don’t necessarily lead to a new species, Powers said.
Scientists examine whether physical adaptations are linked to behavior, when defining a new species. And the differences in color patterns in the newly discovered species are related to mating, Pauers said.
If females prefer to mate with members of their own species, the males’ color pattern is a sign to females that a potential mate is suitable. In addition, males are more likely to be aggressive toward males of their own species because they perceive them as rivals, he said.
“So, they’ve specialized anatomically,” he said. “And that accounts for its behavioral diversity as well.”
With a new species, differences can also be found in their genes. “We looked at the ‘whole genome’ of our findings—not looking at genes for any particular trait—and we have evidence for very distinct genetic separation among the new species. ,” Powers said.
There is no substitute for the real thing
To maintain the classification of cichlids, scientists have transferred some species from one genus to another or from the former large genus Haplochromis to a new genus over the decades. After studying Labeotropheus with specimens for nearly 20 years, Powers was convinced that there were many species, and determined to see them around.
One aspect of the research that survives human experience, he said, is how cichlid ecology informs their adaptability. For example, the team found three new species of Labeotropheus very close to each other. “I thought, ‘how do we keep these species separate if there are no physical barriers?'” Turns out, habitat depth plays a role.
Powers contributed about 500 cichlid specimens to the Milwaukee Public Museum after his trips. He and Phiri also deposited specimens at the Field Museum in Chicago and the South African Institute of Aquatic Biodiversity in Makhanda, South Africa.
The specimens are important in logging the changing taxonomy of cichlids, he said.
“These are the benchmarks against which other scientists compare their specimens, when they think they’ve found something that hasn’t been discovered before.”
Michael J. Pauers et al, Six New Species of Labeotropheus (Cichliformes: Cichlidae) from the Malayan Shore of Lake Malachi, Africa, Ichthyology and Herpetology (2023). DOI: 10.1643/i2021055
Provided by the University of Wisconsin – Milwaukee
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