Family tree: New study illuminates bats' murky origins

Bats are cryptic creatures. They inhabit the dark, roosting in hidden, inaccessible places, and possess rare skills that seem almost supernatural: exceptional longevity, advanced echolocation, and powered flight unique among mammals.

Yet their genes have been difficult to decipher and their fossils hard to find, leaving scientists puzzled about how these traits evolved or when and where bats first emerged.

A major study — the largest analysis of bat genomes and fossils to date — sheds new light on the origins of these mysterious mammals. Published in the journal Nature, the study suggests that the first bats emerged in Europe roughly 65 million years ago and that echolocation developed early, before bats diversified into today's families. It presents a new evolutionary tree, upending long-held assumptions about relationships between different bat families.

The findings are “rewriting” the biological history of bats, said Ariadna Morales, an evolutionary biologist at the American Museum of Natural History and co-author of the paper. “The evolutionary tree of bats changed.”

The study — the first phase of the Bat1K project to sequence and analyse the genomes of all living bat species — lays the foundation for research into their remarkable abilities.

“Bats are the most extraordinary of all our mammalian lineages,” said Emma Teeling, a zoologist at University College Dublin and Bat1K co-director. “This is a springboard.”

There are roughly 1,500 living bat species, accounting for over one-fifth of all mammal species, living on every continent except Antarctica. Researchers collected and sequenced genomes from 103 species across all 21 living bat families, comparing full genomes as well as specific chromosomes.

“Different parts of the genome tell different stories,” said Morales, incoming assistant professor at the City University of New York.

Several lines of evidence converged, allowing researchers to map evolutionary relationships. The resulting phylogenetic tree differed significantly from earlier models. For instance, the sucker-footed bats of Madagascar were previously grouped with neotropical families; the new tree places them in the superfamily containing vesper bats, the most common bats on Earth. This group was also found to be closely related to sac-winged bats, previously thought to be distant relatives.

By analysing fossils alongside genomic data, researchers estimated when lineages diverged. While Africa, Asia, and North America were all candidate birthplaces, the analysis pointed firmly to Europe, from where bats expanded into Africa and across the globe.

The study also suggests echolocation appeared before modern bat lineages arose. Scientists have long debated whether echolocation or flight came first. A 2008 study favoured flight, but this larger dataset reopens the question.

“It looks pretty clear that echolocation evolved before the diversification of all living families,” said Nancy Simmons, curator emerita at the American Museum of Natural History. “We’re back where we were years ago: flight and echolocation seem to have evolved at the base of the tree. We still don’t know which came first.”

Researchers hope the tree will help pinpoint genes underpinning flight, echolocation, and disease resistance. “To uncover evolutionary history is extraordinary,” Teeling said. “But there’s so much more we can do with this.”