Flying squirrels, sugar gliders and bats haven't had a common ancestor in 160 million years, but they form their wing flaps using some of the same genetic ingredients.
That's the intriguing finding from a Princeton-led team of biologists, detailed recently in the journal Science Advances. In other words, when the seven known flying mammals evolved flight - a phenomenon ecologists call "convergent evolution" - they recycled some of the same genetic parts that had been in their DNA since dinosaurs roamed the Earth.
A sugar glider (left) and a microbat (right) are about as distantly related as any two mammals on Earth, but their wing flaps share some genetic ingredients.
The researchers investigated how wing flaps develop in two tiny mammals, the marsupial sugar glider (Petaurus breviceps) and a microbat: Seba's short-tailed bat (Carollia perspicillata). The biologists discovered a network of genes driving the formation of this flap in sugar gliders and bats, and likely other flying mammals as well.
"Among flying mammals, sugar gliders and bats are just about as distantly related as you can get," said Charles Feigin, first author on the new paper and a former postdoc in Ricardo Mallarino's lab at Princeton University. "They also have very different mechanisms of flying, plus all the other flying mammals are more closely related to one or the other, so we have pretty good reason to suspect that similar mechanisms are at play in all of them."
A sugar glider (left) and a micobat (right) in flight.
Mallarino's lab focuses on the origins of diversity. "If you go back to the to the days of Darwin, he was fascinated by how and why we have biodiversity," said Mallarino, an assistant professor of molecular biology who is associated faculty in ecology and evolutionary biology.
"Over the past decades, the biological community has done a good job understanding why: There's a very close relationship between the features of an animal or a plant and its environment. So, for example, natural selection drives the evolution of a beak of a certain size that allows a bird to crush a seed. But how does a bird actually get a larger beak or a smaller beak? Our lab approaches diversity from this other perspective: At the molecular level, how do these things happen?"
Sugar gliders, small nocturnal flying marsupials native to New Guinea and Australia, are more closely related to kangaroos than to their lookalike, distant cousins the flying squirrels. Like kangaroos, sugar gliders give birth to joeys that are still early in their development, presenting an extraordinary opportunity to watch development, said Feigin, who is now a research fellow specializing in marsupial development at the University of Melbourne. The Princeton-led team combined many techniques in their study, including DNA and RNA sequencing.
"Even 10 years ago, you couldn't easily sequence a species like this; that was restricted to humans or mice, or else it cost a fortune," said Mallarino. "Now, because these tools have advanced so much, we can sequence a genome - even a mammalian genome, which tends to be very large - pretty easily."
They found that a key gene in growing the patagium - Wnt5a - is also linked to skin thickening in mouse ears, suggesting that this genetic toolkit may have served other roles before being adapted for flight.
"Evolution is economical; it uses what it has," said Mallarino. "Instead of evolving an entirely different pathway to make a flight structure, it uses the molecules that are at hand and are found across all mammals living on this planet. I think this is why we keep seeing what we call convergent evolution: the same genes keep coming again and again. They work in different ways, and they're integrated with other genes in different ways - the patagium in bats is quite different than the patagium in gliders - but you use the same gene because it's what is at hand. I think this is the beauty of evolution."
Other Princeton members of the research team were graduate student Jorge Moreno; research specialist Sarah Mereby; then-undergraduate Ares Alivisatos of the Class of 2021; and Wei Wang, director of the high throughput sequencing and microarray facility at the Lewis-Sigler Institute for Integrative Genomics.
"Convergent deployment of ancestral functions during the evolution of mammalian flight membranes" by Charles Y. Feigin, Jorge A. Moreno, Raul Ramos, Sarah A. Mereby, Ares Alivisatos, Wei Wang, Renée Van Amerongen, Jasmin Camacho, John J. Rasweiler IV, Richard R. Behringer, Bruce Ostrow, Maksim V. Plikus and Ricardo Mallarino was published in the March 2023 issue of Science Advances (DOI: 10.1126/sciadv.ade7511). The research was supported by the National Institutes of Health (R35GM133758, F32 GM139240-01, U01-AR073159, R01-AR079150, and P30-AR075047), the LEO Foundation (LF-AW-RAM-19-400008 and LF-OC-20-000611), the W.M. Keck Foundation (WMKF-5634988) and the National Science Foundation (DMS1951144)
