When it comes to the evolutionary tree, bats have some unique close relatives.

04.10.24

By Dr. Karin Akre

Pop quiz!

Which of the following animals is LEAST closely related to bats?

a. Whales

b. Pumas

b. Cows

d. Flying squirrels

    Did you guess whales because they are enormous and live underwater? Or pumas because of their bulging muscles and silent stalking paws? Or perhaps the cow, an animal that would need a jetpack to get off the ground? If you guessed any of these, you were wrong. The answer is “d. Flying squirrels.”

    In fact, whales, pumas, and cows are all part of the group of animals thought to make up bats’ closest living relatives. This group is large and diverse! It includes even-toed ungulates (like camels, pigs, and cows), cetaceans (like whales), carnivores (like lions and pumas), odd-toed ungulates (like horses, rhinos, and tapirs), and pangolins. This group of closest relatives does NOT include flying squirrels, or any other rodents! 

    How can a small furry mammal that glides between trees using a skin membrane be more distantly related to bats than whales are? 

    Let’s unpack. 

    Extended family

    https://www.science.org/doi/10.1126/science.abn3943

    Many people can relate to the idea of odd relationships with distant relatives. But our quiz explores evolutionary relationships, not kin relationships like aunts or cousins. Evolutionary relationships are defined by which types of animals share ancestors that lived millions of years ago. 

    Bats, whales, pumas, cows, and flying squirrels (and people!) are all related as placental mammals. The most recent ancestor shared by all placental mammals had hair, produced milk, and gave birth to live young. Scientists suspect it looked like a tiny shrew, and lived around the end of the Cretaceous period. Over generations, offspring accumulated changes, leading to populations with differences, then to distinct species. This process repeated over and over, branching into new species and leading to today’s diverse mammals. 

    Within these branches, there is an ancient most recent common ancestor shared by bats and flying squirrels. There is also a most recent common ancestor shared by bats and the group including whales, pumas, and cows; and this ancestor lived more recently than the one shared with flying squirrels. The ancestor to bats and this diverse group did not have wings or echolocate. Only after branching from this ancestor did animals evolve longer fingers and membranes for wings, becoming bats. 

    Parallel Lives 

    Are you skeptical because flying squirrels look and behave more like bats than whales, pumas, and cows do?

    Broadly, looking at shared traits does give clues about relatedness. All mammals have hair and make milk, so it’s easy to see that they are more closely related to each other than they are to fish. Within mammals, plenty of features, like skulls, are valuable for understanding evolutionary history. But comparing anatomy or behavior across species can be tricky because sometimes, similar body parts and behaviors look alike not because they were inherited from the same ancestor, but because they emerged twice, along separate paths of convergent evolution. 

    https://www.science.org/doi/10.1126/science.abl8189

    Flying squirrels benefit from moving between trees quickly, which may help them forage efficiently and avoid predators. The evolution of skin membranes for gliding reflects a benefit to airborne movement which bats also experience—not a shared evolutionary history. In fact, skin membranes for gliding have also evolved in frogs, reptiles, and fish, and none of these animals are closely related to bats, or to flying squirrels.

    Echolocation in whales and bats is another example of parallel evolutionary pathways. If echolocation were inherited from their shared ancestor, we’d expect some pumas, rhinos, and pangolins to also echolocate. Instead, bats and whales evolved echolocation separately in response to similar ecological needs. Both nocturnal flight and swimming involve 3-D movement through poor visibility environments to hunt or navigate. Acoustic information is far more reliable than visual perception in these environments.

    Evidence

    How do scientists know all this? Comparative anatomy, embryo development, the fossil record, and genetics all contribute to our understanding of evolutionary history. In genetic studies, DNA sequences tell dramatic stories that have played out over millions of years. More sequence variation between sections of species’ DNA or whole genomes indicates a more distant relationship. Scientists have even used DNA sequence differences as a molecular clock that estimates the time since two species branched apart. Multiple genetic studies indicate that bats’ closest relatives are the diverse group that includes whales, pumas, and cows.

    DNA sequences can also demonstrate convergent evolution. Scientists have identified several genes that are involved in echolocation. By comparing the DNA of these genes in bats and whales, they found that many of the same genes inherited from a common ancestor have evolved in similar ways to support echolocation. These genes are more alike in echolocating whales and bats than they are in echolocating and non-echolocating whales. 

    Genetic Treasures 

    https://www.nature.com/articles/s41586-020-2486-3/figures/2

    Studying bat evolutionary relationships and genetics reveals even more reasons to conserve bats: bat genes hold secrets that could fuel medical advances for people! As fellow placental mammals, our distant relationship is important even though we aren’t as closely related to bats as whales, pumas, or cows are. All placental mammals function with a similar set of biological processes due to our shared genetic architecture, inherited from our common ancestor. Evolution has changed each taxonomic group differently, altering gene sequences to solve similar problems in new ways. For example, bat immune systems don’t react to pathogens the same way ours do. Understanding bats’ immune response may reveal novel therapeutic approaches for treating human immune system function. Scientists are also interested in studying bat aging, hibernation, and hearing to generate innovative ideas for human health. By protecting bat species, we preserve their priceless DNA sequences and rich evolutionary stories.

    Karin Akre, Ph.D.

    Science Writer

    Dr. Karin Akre joined Bat Conservation International as our Science Writer in September 2023. She supports scientific research to inform conservation actions for bats by creating engaging and informative content for diverse audiences. She contributes to scientific articles, grant proposals, and outreach materials.

    Karin has over 20 years of experience in science writing and research. She has published scientific articles on the evolution of behavior, and she taught animal behavior and conservation courses at the University of Texas, Austin and Hunter College. Prior to working for BCI, she wrote and edited K-12 science textbooks, encyclopedia articles, and science-based television scripts. Her writing translates complex scientific information into language that can educate and inspire audiences to increase their awareness of conservation topics.

    Karin received her Ph.D. in ecology, evolution, and behavior from the University of Texas, Austin and a bachelor’s degree from Harvard University in psychology and biology.

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