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Bat1K's 103-genome family tree points to late-Paleocene Europe as the likeliest birthplace of bats
Bat1K researchers' Nature study of 103 genomes and 44 fossils puts the most likely origin of bats in Europe, 65 to 60 million years ago. The same model places powered flight and echolocation near the root of the tree, before modern bat groups began to split.
The Scientist · Science desk
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What happened
- The 103 genomes cover all 21 recognized bat families, and 42 of them are chromosome-level assemblies generated for this study.
- In the reconstruction, early bats moved from Europe into Africa, and separate lineages later spread into the Americas, Asia and Australia.
- Vielasia, a fossil on the oldest branch of the tree, suggests echolocation was already present close to the beginning of bat evolution.
- Over decades of debate, Africa, Asia and North America had each been proposed as the place where bats first appeared.
- The work involved 137 researchers from 64 countries in the Bat1K consortium, a project to sequence the genomes of every living bat species.
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Why it matters
- constraint Because flight and echolocation were both in place before modern groups split, every living bat inherited both, so the order in which they arose can only be read from early fossils such as Vielasia.
- precedent Rival accounts of where bats began now have to answer a model that places fossils using genomic data, a step Dávalos says other methods cannot take.
- capability Studies of bat disease resistance and longevity can now map those traits onto one tree that covers all 21 families and shows where the fossil bats sit.
Fossils and genomes went into one model. The team modelled fossil and living species together, so the 44 fossil bats were placed on the same tree as the genomes [5][14]. "The approach we used to model the evolution of fossil and living species together can do what other methods cannot -- identify the oldest group of fossil bats while taking the genomic data into account, and uncover when and where bats originated," said senior author Liliana M. Dávalos of Stony Brook University [14].
The genome sampling is wide. Bats make up about one fifth of all living mammals [9]. The new chromosome-level assemblies account for about 41 percent of the 103 genomes [1], and the set averages roughly five genomes per bat family [3].
In my view the tree is the firmest result in the paper. Emma Teeling of University College Dublin, a co-founder of Bat1K and the leading senior author [3], gave it the same weight. "It is extraordinary, after decades of research and conflicting findings, we finally have a robust phylogenetic tree that we can now use to properly understand how and where bats' unique traits evolved," she said [11].
The echolocation inference rests on one fossil, Vielasia [7]. The release does not say which of its features indicate echolocation, or how much more probable a European origin came out than an African, Asian or North American one.
That margin decides whether the old argument over those three continents [2] is finished. The team's own word for Europe is "most likely" [1]. I'd read that as the top entry in a ranking of candidate regions, and Teeling used the same phrase for flight. "As bats are the only mammals known to have evolved true powered flight, our findings point to Europe as the most likely place where mammalian powered flight first evolved," she said [13].
The thing this doesn't tell you is how bats came by their other oddities. Many species are unusually resistant to disease and live far longer than mammals of similar size [10]. Those are questions for the genomes. The team also computationally reconstructed an ancient bat genome, according to the release [15].
What to watch
- Whether the Nature paper's supplementary results give a probability for a European origin set against Africa, Asia and North America.
- A well-dated late-Paleocene bat fossil found outside Europe would test the European origin directly.
- Follow-up papers that use the reconstructed ancient bat genome to trace the genes behind flight, echolocation or disease resistance.