Spotted bats using a cave in northern Arizona today belong to the same maternal family line as bats that died in that cave as long as 2,100 years ago. That is the striking finding of a genetic study published Oct. 7 in PLOS One by researchers at Northern Arizona University and the Smithsonian's National Zoo and Conservation Biology Institute.

The team compared DNA from six ancient bats preserved in the cave with samples from living bats caught there. Five of the six ancient specimens shared the most common maternal genetic type found in the region, and so did 14 of 38 bats sampled from the cave in modern times.

The result points to a population that has persisted in the same place for roughly two millennia — an unusually long genetic record for a bat. For a species so elusive that scientists once ranked it among the world's rarest mammals, that long thread of continuity gives conservation planners something rare: a sense of how stable this animal's populations have been over deep time.

A Hard-to-Find Bat with Huge Pink Ears

The spotted bat, Euderma maculatum, is one of North America's most striking mammals, with white spots on a black back and enormous pink ears it uses to hunt moths in desert canyons. It is also one of the hardest to study, because it roosts in high cliff crevices, lives mostly alone, and flies at night.

"Spotted bats are among North America's most mysterious mammals," said lead author Faith Walker of Northern Arizona University, in a statement reported by IFLScience.

Population estimates show how little is known. Published figures for the species range from about 2,500 to 100,000 animals, a spread so wide it reflects uncertainty more than a real count. Only about 95 specimens are held in museum collections worldwide, according to IFLScience.

Reading a Mother's Genetic Signature

The key tool in the study is mitochondrial DNA, a small set of genes kept in the energy-producing structures of cells. Unlike most DNA, which comes half from each parent, mitochondrial DNA passes almost entirely from mother to offspring.

That makes it a kind of maternal surname. If a bat alive today carries the same mitochondrial type as a bat that died 2,000 years ago in the same place, it suggests that female lines have continued there across many generations rather than the site being emptied and later recolonized by unrelated bats.

The researchers paired that maternal marker with nuclear microsatellites, short repeating stretches of DNA inherited from both parents. Together, the two kinds of markers let the team look at both deep maternal history and more recent mixing between populations.

Much of the modern cave sampling came from fieldwork by researchers in the Northern Arizona University bat ecology and genetics lab, who captured 69 bats with mist nets during the summers of 2009 to 2013, including 39 at the cave.

In total, the study analyzed 121 bats. They included modern bats sampled from 1994 to 2025, 65 historical specimens from 15 museums dating back to 1904, and six ancient specimens from the cave that were radiocarbon dated to between about 120 and 2,100 years old.

"By combining DNA from ancient, historical, and modern specimens, we were able to trace their evolutionary history," Walker said.

The Southwest Holds the Most Diversity

Beyond the cave, the study mapped genetic diversity across the species' range in western North America. Bats in the U.S. Southwest carried far more variety than bats farther north, with 26 of the 31 maternal types found in the central region and only two in the northern region.

"Northern populations appear to have lower genetic diversity and may be more vulnerable to future environmental change," Walker said. Lower diversity can leave a population with fewer genetic options for adapting to new conditions such as drought, habitat change or disease.

The two kinds of DNA told different stories. Maternal DNA showed sharp differences between regions, while the DNA inherited from both parents showed only weak differences. That kind of mismatch is often seen when males travel farther than females, though the authors could not pin down the exact cause with their data.

The cave held other surprises. Researchers found two father-son pairs among the bats there and a strongly male-skewed group, 31 males to eight females, which they linked to swarming behavior at the site. The authors say the findings support protecting three kinds of populations: the diverse southwestern core, vulnerable populations at the northern edge of the range, and isolated lineages.

Limits of the Evidence

The study has clear limits — and the authors acknowledge them. The mitochondrial DNA fragment analyzed was short, about 193 to 196 base pairs, and because it is inherited only through mothers, it reveals female lineages and deep history but not the whole population picture.

Sampling was also uneven. Many of the bats came from a single cave, and Mexico and Texas were represented by only three samples combined. Some statistical results, such as estimates of how bats move between regions, changed when sample sizes were balanced, so the authors did not treat them as reliable.

The study is observational genetics, not a population count, and it does not show whether spotted bat numbers are rising or falling today. The authors could not separate the effects of past bottlenecks, founder events, and migration with the data available.

The research was funded by the State of Arizona's Technology and Research Initiative Fund. The authors say they hope land managers will use the genetic map to decide which populations most need protection.

For Arizona residents and visitors, the practical message is simple. Caves and cliffs used by bats are sensitive sites, and disturbing roosting bats can harm them. Hikers who find bats in caves or crevices should leave them alone and follow any closures posted by land managers.

What Readers Want to Know

What did the study find?

Spotted bats using a northern Arizona cave today share the same maternal DNA type as bats that died in the cave up to about 2,100 years ago, suggesting a long, continuous population.

What is maternal DNA?

It is mitochondrial DNA, which passes almost entirely from mother to offspring, so it traces female family lines across generations.

What is a spotted bat?

A western North American bat with white spots on its black back and very large pink ears, used to hunt moths at night.

How many spotted bats are there?

No one knows precisely. Published estimates range from about 2,500 to 100,000.

Which populations are most vulnerable?

Northern populations have lower genetic diversity and may be more vulnerable to environmental change, according to the researchers.

Who did the research?

Scientists from Northern Arizona University, the Smithsonian's National Zoo and Conservation Biology Institute, and Wildlife Conservation Society Canada.