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Listen closely. Scientists propose that echolocation in bats evolved twice.

Batting Around Echolocation

For years, researchers have debated how to classify the world's bats. Although the majority of those that use echolocation--emitting sound waves that bounce off objects--to hunt are usually lumped into one group, a new study suggests that some belong in a separate category. But evolutionary biologists are quick to note that the work will likely fuel an already fierce classification controversy in the bat world.

Originally, bats were classified based on similarities in their appearance and behavior. But in the mid 1990s, several evolutionary biologists began to assess kinship by analyzing degrees of genetic difference among species. Microbats, the group of bats that emit echolocation signals from the larynx, came under close scrutiny because, surprisingly, some molecular studies divided them into two groups that diverged long ago, suggesting that echolocation evolved twice. Meanwhile, longstanding questions remained about where bats fit in the larger scheme of mammalian evolution.

Evolutionary biologists Emma Teeling and Mark Springer from the University of California, Riverside, and their colleagues sought to resolve this controversy by studying a broad range of bats and examining more genes in each than did previous studies. Their genetic analysis encompassed 20 species of bats and nine other mammals. In each animal, the team studied 7100 bases, the letters that define genes.

The study showed that microbats fall into two separate categories, reaffirming that throat-derived echolocation evolved twice, the researchers report in the 22 January early edition of Proceedings of the National Academy of Sciences. In addition, the analysis ran counter to the hypothesis that bats belong to a larger group that includes primates, lemurs, and tree shrews. Instead, Springer notes, all bats are more closely related to the group encompassing moles, anteaters, and even carnivores.

Bat specialist Michael Miyamoto from the University of Florida in Gainesville calls the work "excellent and significant." But Scott Pedersen, an evolutionary biologist at South Dakota State University in Brookings, criticizes the research for including too few species of bats, given that roughly a thousand exist.

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