Nature
PUBLISHED
When the spotted bat was first described in 1891 it was considered to be one of the rarest mammals in the world. Even by 1965 there were only 35 specimens known to science, a number that has since crept up to a still surprisingly low 95 individuals found in museum collections around the world.
Despite these low numbers, the bat is no longer considered quite so rare, although estimates of its population vary wildly from 2,500 to 100,000. An attractive little member of the vesper family, it is thought to have the largest ears of any bat species in North America.
But it's by diving into their genetics that researchers recently found something surprising.
The team sampled over 120 individual bats, ranging from ancient bones found in a cave to recent specimens collected in 2025. Amazingly, they found that some bats alive today carried the same maternal DNA as individuals that died 2,100 years ago, suggesting they maintained a continuous population.
From this work, the researchers were able to map the genetic diversity of the species from across their range in the western US.
“Spotted bats are among North America's most mysterious mammals,” said Faith M. Walker at Northern Arizona University, in a statement.
“By combining DNA from ancient, historical, and modern specimens, we were able to trace their evolutionary history across space and time and identify the populations that may be most important to conserve for the future.”
A charismatic creature
The spotted bat is one of the most distinctive bats in the world.
It has long, silky fur with a snow-white belly transitioning to jet black on its back, where it is further adorned with two white spots over each shoulder and third that covers its rump.
As if that wasn’t striking enough, the little mammal, which weighs no more than 15 grams (0.5 ounces), sports a pair of extraordinarily large, pink ears that swoop backwards.
Even though bats make up around 20 percent of all known mammals, researchers still know relatively little about the group as a whole. This is for a number of reasons, but largely it comes down to their nocturnal nature and small size.
When it comes to the spotted bat, things are further compounded by the fact that, unlike some other species of bat, they don't gather in large colonies and instead live relatively solitary lives.
This explains why they were initially thought to be so rare, and why there are still so few specimens in museum collections today.
Cryptic bats
To try to learn more about this charismatic little mammal, the researchers turned to their genetics. By sampling 121 individuals taken from across their range, they could study patterns of connectivity, isolation, and success that wouldn’t be possible from just taking location data alone.
In one particular cave where researchers were able to sample the bones of spotted bats that died 2,100 years ago, they found the bats still living there carried the same genetic markers, suggesting a significant long-term continuity of the population.
This work also revealed a significant difference between the northern and southern bat populations.
“One of the most important findings of our study is that spotted bats in the southwestern United States harbor the greatest genetic diversity across the species' range, making this region a critical reservoir of evolutionary potential for the species,” said Walker.
“In contrast, northern populations appear to have lower genetic diversity and may be more vulnerable to future environmental change.”
It is hoped that by better understanding the population dynamics of this cryptic mammal, conservationists will be able to create more instructive management plans to help the species survive into the future.
The research has been published in the journal PLOS One.
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