Team pins down where bats originated

The largest study ever of bat genome research combined with bat fossils reveals that bats originated in Europe some 65 million years ago, not in Africa, Asia, or North America as scientists have long thought.

The research also shows that echolocation, like flight, evolved near the dawn of bat evolution.

Overall, the work in Nature helps to resolve scientific debates about bat evolution and rewrites the bat family tree.

Bats are the only mammals that are capable of powered flight. After their European origins, they quickly spread to Africa and then worldwide. There are more than 1,500 species of bats globally, and they account for more than one-fifth of Earth’s mammals. Bats play a key role in maintaining healthy ecosystems in most areas of the world by pollinating plants, dispersing seeds, and consuming vast numbers of insect pests.

The research provides the first-ever reconstruction of the genome of the ancestor of all living bats. This reconstruction shows what the ancestral genome of a mammal capable of flight would have looked like. Data from genomes of a total of 103 species and traits from 44 fossil species were generated and analyzed by 137 researchers from 64 countries to complete the study. The international team makes up the Bat1K consortium. This initiative works to generate and analyze reference-quality genome assemblies for all living bat species.

“The approach we used to model the evolution of fossil and living bat 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,” says Liliana M. Dávalos, a professor in the ecology and evolution department at Stony Brook University, one of the lead investigators for the global research team and a co-corresponding author.

By using state-of-the-art DNA sequencing and computational methods to generate genomes and combining these with observations from dozens of ancient species, the consortium was able to gather the largest set of bat genome assemblies and fossil samples to date. Then, they applied models of evolution that account for changes in both morphology and genomes of the bats, as well as how continents change over time.

This enabled the team to overturn previous hypotheses proposing Asian, African, or North American bat origins in favor of a European one. The earliest descendants dispersed to Africa, and then they established a Europe-Africa hub from which bats then expanded into Asia, the Americas, and Australia, explain the authors.

Building the dataset was a tall task. The investigators collaborated by collecting bat samples worldwide over decades. This included representatives of some of the rarest and unusual bat families found in remote locations.

Among those are tiny bumblebee bats of Thailand and Myanmar, one of Earth’s smallest mammals, and the sucker-footed bats of Madagascar, which have suction cups on their wrists and ankles that they use to cling to small leaves.

The fossil evidence from the large sample also provided important clues about another long-standing mystery: when bats first evolved echolocation.

Key to this work was the placement of the fossil bat Vielasia within the oldest branch of the bat family tree. This bat had features that point to the ability to echolocate and therefore indicates that echolocation predates the diversification of modern bats. The finding suggests that two of the defining characteristics of bat biology, powered flight and echolocation, evolved near the origin of the group itself.

The authors say that these early abilities of flight and echolocation also explain the extraordinary evolutionary success of bats over the subsequent 65 million years.

“For decades there has been a question as to which came first in bats—flight or echolocation—and this is because bats cannot fly at night without some change in perception to enable flight in the dark,” explained Dávalos.

“Our analysis, here at Stony Brook, shows that the oldest branch of bats already had species that unambiguously echolocated. Therefore, based on the tree with these fossils, bat echolocation evolved shortly after mammalian flight did,” she adds.

The research into powered flight and other evolutionary characteristics of bats gives scientists not only a genomic map for how the bat lineage evolved powered flight and advanced biosonar but also lays the foundation for understanding other extraordinary bat characteristics.

These characteristics include the fact that many bat species show remarkable resistance to disease and live exceptionally long lives for small mammals. Some species can live close to 40 years. The authors contend that the genomic resource built for this latest study, along with findings on the origins and evolution of bats, will give scientists the first robust evolutionary framework to investigate the genes behind traits leading to bat disease resistance and longevity.

Taking this a step further, such research may help define genes implicated in health and longevity and could eventually inform human research on aging, immunity, and disease resistance.

Source: Stony Brook University