Study re­veals frogs flour­ished af­ter di­nosaurs croaked

Kuwait Times - - HEALTH & SCIENCE -

A mas­sive as­ter­oid strike that wiped out the di­nosaurs mil­lions of years ago cre­ated room for frogs to col­o­nize the Earth, said a study Mon­day that shows how frogs be­came among the most di­verse ver­te­brates in the world. As many as 10 types of frogs are be­lieved to have sur­vived the mass ex­tinc­tion some 66 mil­lion years ago, which erased three­quar­ters of life on Earth, said the re­port in the Pro­ceed­ings of the Na­tional Academy of Sciences.

Of th­ese sur­vivors, just three ma­jor kinds of frogs went on to di­ver­sify and pop­u­late the planet. Some 6,700 known frog species ex­ist to­day. Nearly nine in 10 — 88 per­cent-of mod­ern frogs can trace their roots back to th­ese three lin­eages of hardy an­ces­tors. “Frogs have been around for well over 200 mil­lion years, but this study shows it wasn’t un­til the ex­tinc­tion of the di­nosaurs that we had this burst of frog di­ver­sity that re­sulted in the vast ma­jor­ity of frogs we see to­day,” said study co-au­thor David Black­burn, as­so­ciate cu­ra­tor of am­phib­ians and rep­tiles at the Florida Mu­seum of Nat­u­ral His­tory.

“This find­ing was to­tally un­ex­pected.” Un­til now, sci­en­tists be­lieved that most mod­ern frog species emerged at a steady pace be­tween 66 mil­lion and 150 mil­lion years ago. But the lat­est re­search shows frogs burst onto the scene more like an “ex­plo­sion,” as the tiny am­phib­ians swept into habi­tats left va­cant by other crea­tures.

Largest ge­netic study to date

For the study, re­searchers in China and the United States com­piled the largest set of frog ge­netic data ever eval­u­ated. Ge­netic sam­ples were taken from 156 frog species and com­bined with pre­vi­ously pub­lished data on 145 more species. Past stud­ies looked at five to 12 genes, while the cur­rent one ex­am­ined vari­a­tions in 95 genes, of­fer­ing a much more de­tailed look at how in­di­vid­ual species re­late to one an­other.

Re­searchers also stud­ied fos­sil records to de­ter­mine when dif­fer­ent kinds of frogs likely di­verged from one an­other. Re­searchers found “ev­i­dence of not one but three ex­plo­sions of new frog species, on dif­fer­ent con­ti­nents, and all con­cen­trated in the af­ter­math of the mass die­off of most di­nosaurs and many other species about 66 mil­lion years ago,” said the re­port. Two of the three sur­viv­ing lin­eages-Mi­cro­hyl­i­dae and Natata­nu­ra­came out of Africa. The third, Hy­loidea, spread through­out what be­came South Amer­ica.“Th­ese frogs made it through on luck, per­haps be­cause they were ei­ther un­der­ground or could stay un­der­ground for long pe­ri­ods of time,” said co-au­thor David Wake of the Uni­ver­sity of Cal­i­for­nia. “This cer­tainly draws re­newed at­ten­tion to the pos­i­tive as­pects of mass ex­tinc­tions: They pro­vide eco­log­i­cal op­por­tu­nity for new things.” Sim­i­lar evo­lu­tion­ary events hap­pened with birds, said co-au­thor David Hil­lis, pro­fes­sor of in­te­gra­tive bi­ol­ogy at Uni­ver­sity of Texas, Austin. “We know that the mass ex­tinc­tion event wiped out most of the di­nosaurs, ex­cept for a few bird species, which then ex­ploded in di­ver­sity and be­came one of the dom­i­nant groups of land an­i­mals,” he said. “As we look at more and more groups of life, we see the same pat­tern, and that turns out to be the case for frogs as well.”

Find­ing new habi­tats

In par­tic­u­lar, the demise of di­nosaurs and most birds cre­ated new niches for frogs in the late Cre­ta­ceous Pe­riod. Some climbed into trees for shel­ter, lead­ing to the evo­lu­tion of the now ubiq­ui­tous tree frogs. “We think there were mas­sive al­ter­ations of ecosys­tems at that time, in­clud­ing wide­spread de­struc­tion of forests,” said Black­burn. “But frogs are pretty good at ek­ing out a liv­ing in mi­cro­hab­i­tats, and as forests and trop­i­cal ecosys­tems re­bounded, they quickly took ad­van­tage of those new eco­log­i­cal op­por­tu­ni­ties.”

Some frogs also adapted by pro­duc­ing young with­out a tad­pole stage-to­day the stan­dard for about half of all frog species. Mod­ern frogs face a host of threats to their sur­vival, in­clud­ing habi­tat de­struc­tion, hu­man en­croach­ment and cli­mate change. “I think the most ex­cit­ing thing about our study is that we show that frogs are such a strong an­i­mal group,” said lead au­thor Peng Zhang, a re­searcher at Sun Yat-sen Uni­ver­sity in Guangzhou, China. “They sur­vived from the mass ex­tinc­tion that com­pletely erased di­nosaurs and boomed back quickly.”—AFP

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