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Evolution of Bats Probed in Genetic Study

Evolution of Bats Probed in Genetic Study

(January 12, 2000)

In a study that has implications for the origin of flight in bats and their unique ability to use sonar for navigation, scientists at the University of California, Riverside and Queen's University in Ireland have found genetic evidence that may rearrange a portion of the evolutionary tree.

Writing in the Jan. 13 issue of Nature, they report the analysis of genetic material from 26 different animals that suggests the traditional view of bat evolution may need to be reevaluated.

As a group, bats are one of the most fascinating of mammals. Numbering some 1,000 species in two major divisions - microbats and megabats - bats are the only mammals that fly. And, the microbats have the unique ability to navigate and locate insect prey using echolocation, or sonar, to emit high-frequency sound waves from the larynx and listen for the returning echoes.

The traditional scientific view has held that the evolution of flight in bats can be traced to flying lemurs, nocturnal tree-dwelling mammals about the size of cats that glide from tree to tree thanks to a fold of skin from their neck to tail that is use d like a parachute. But genetic evidence uncovered by the UCR and Queen's University scientists indicates that flying lemurs are not a sister group to bats, said Mark S. Springer, UCR associate professor of biology.

Furthermore, one group of echolocating microbats is more closely related to the megabats, most of which have no echolocation mechanisms, the researchers found. It had been thought that all microbats were each other's closest relatives and that all megabats were each other's closest relatives based on similar body features, called morphology by scientists, Springer said.

"It's all suggestive to me that in evolution of morphological features, there is a lot more flexibility than has ever been previously recognized. Natural selection is very opportunistic," said Springer. "We're seeing more and more cases where different k inds of innovations apparently have evolved independently in different groups, possibly in different geographic regions where you have groups that are facing similar kinds of selective pressures."

Recent advances in DNA technology have given scientists a new tool with which to evaluate evolutionary relationships among animals.

DNA in a sense operates like a molecular clock to help establish when animals diverged from their evolutionary ancestors. By comparing the sequences of chemical bases in particular portions of genetic material in various animals, small differences can be used to establish relationships. In general, the more similar the genetic sequences of two animals, the more closely they are related.

In many cases, genetic evidence has added credence to theories of animal evolution advanced by paleontologists who comb the fossil records for morphological similarities between animals. But sometimes the genetic evidence points to evolutionary relations hips that are different than those established by paleontologists.

Such appears to be the case with bat evolution. And, earlier work by the UCR and Queen's University group helped sort out another contentious issue in evolutionary biology - the ancestral relationships among certain "placental" mammals, animals whose young develop more completely inside the womb. In 1997, the group reported research in Nature that suggested six animals with very dissimilar morphologies - elephants, manatees, elephant shrews, hyraxes, aardvarks and golden moles - evolved from a single anc estor.

For the study on bats, scientists evaluated genetic material representative of a total of 11 groups of microbats, 10 groups of megabats, flying lemurs, humans, mice and carnivores such as cats and dogs.

They found carnivores are more closely related to bats than flying lemurs. "This has certain implications for understanding the origin of flight," Springer said. "Features we see that evolved in conjunction with gliding in the flying lemur appeared to have evolved independently of similar features that evolved in bats."

The genetic evidence also indicated that one group of microbats, including the false vampire bat and the Old World leaf-nosed bat, are related more closely to megabats than they are to other microbats. Springer said that points to two possible scenarios for the evolution of echolocation, either echolocation evolved in the ancestor of all bats and was lost in the megabat group or that the ancestor of all bats did not echolocate and that the feature evolved independently in the different microbats.

Sorting out evolutionary relationships is important to establish the associations between animals, including humans, to one another and to understand how animal life originated and diversified on Earth, Springer said. "Just like new fossil discoveries, evolutionary trees derived from molecular studies are providing us with a new perspective on evolutionary history," he said.

Co-authors of the study along with Springer are: Michael J. Stanhope, a professor of biology and biochemistry at Queen's University; Queen's University graduate students Emma C. Teeling and Mark Scally, who are currently working in Springer's UCR laboratory; and Diana J. Kao and Michael L. Romagnoli, both of whom completed their master's degrees at UCR last June.

The University of California, Riverside ( is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion.

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