This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: They can't fly or swim, so why do their closest relatives appear on different continents? Grey Gustafson, an associate professor in the Department of Biological Sciences, discovered through DNA sequencing that the ancestors of some of today's tiger beetles existed in South America and Africa before the two continents separated.
What's more, North America's largest tiger beetles are related to these ancestral South American giant tiger beetles. Gustafson and his colleagues recently published their findings in Proceedings of the Royal Society B. Gustafson's research began with two groups of tiger beetles found in the western U.S.: the genus Amblycheila, called the giant tiger beetles, and the genus Omus, the night-stalking tiger beetles.
The previous hypothesis was that both groups belong to the tribe Manticorini—named for the mythical chimeric monster—which also contains large-bodied, flightless tiger beetles found in the Southern Hemisphere. If that were true, Gustafson said, it would raise the question: How and why did tiger beetles end up in North America when most species of the tribe live in sub-Saharan Africa, with the only other close relative being found in South America? "We wanted to know how a large-bodied, flightless beetle could get across the ocean to South America and then, better yet, how our North American beetles fit into this tribe," Gustafson said.
Scientists have done substantial research to better understand the biology, classification, life history and conservation of tiger beetles, but they've done comparatively little to understand the evolutionary history of these insects. So, Gustafson spent three years generating data that could reveal more about the evolutionary history of North American manticorine tiger beetles. With help from colleagues, Gustafson collected and compared DNA sequences from across their entire genomes.
"We assembled genomic sequences from freshly collected material in the western U.S., ethanol-preserved frozen material from colleagues and specimens held in natural history collections in the U.S. and Europe," Gustafson said. The research team then used the data to produce a family tree to understand the most recent common ancestors. With this information, researchers were able to trace when the lineages diverged from one another.
"The exciting thing we found was that the group is actually older than when the continents were separated, so they didn't actually get across the oceans," Gustafson said. "They originated before an ocean separated South America from Africa on a supercontinent called Gondwana." Gustafson and his colleagues found that not only are the giant tiger beetles of North America most closely related to the South American tiger beetle, but together these tiger beetles are most closely related to those found in southern Africa. The family tree produced by DNA sequencing revealed the Manticorini tribe evolved at a time when South America and Africa were part of a landmass known as Gondwana, which later separated into the distinct continents we know today.
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