Mu­tated frog gene re­pels preda­tors

Saskatoon StarPhoenix - - CITY+REGION - FEDERICA GIANNELLI

The in­cred­i­ble colour pat­terns of Colom­bian dart frogs have long been a mys­tery, but now Univer­sity of Saskatchewan re­searchers have iden­ti­fied the gene re­spon­si­ble for the black blobs and stripes that make the colours stand out.

Post-doc­toral re­searcher Andres Posso-Ter­ra­nova and his former su­per­vi­sor Jose Andrés have found ev­i­dence that a sin­gle gene called MC1R con­trols the deep black colour on the skin of these poi­sonous frogs. The re­searchers have found that the dis­rup­tion of the gene is re­spon­si­ble for the black blobs and stripes. Their re­sults have been pub­lished this week in the in­ter­na­tional jour­nal Evo­lu­tion.

“We knew the same gene stim­u­lates the pro­duc­tion of black pig­ment in other an­i­mals, but it’s also re­spon­si­ble for cam­ou­flage in mice and red hair in hu­mans,” said Andrés, a U of S bi­ol­ogy pro­fes­sor. “There was no ev­i­dence of a cor­re­la­tion with col­oration of frogs un­til now.”

The black pat­terns pro­vide a sharp con­trast to the dart frogs’ bright colours — red, yel­low and orange — to send a highly de­tectable warn­ing sig­nal to preda­tors such as snakes that the frogs are toxic, much like the colour­ing of wasps and bum­ble­bees.

“These warn­ing pat­terns are very ef­fec­tive and they are eas­ily learned by preda­tors,” said Posso Ter­ra­nova.

Dart frogs, tra­di­tion­ally used by Colom­bian Indige­nous hunters to ob­tain poi­son for blow­gun darts, make their pow­er­ful poi­son by eat­ing toxic bugs. The poi­son is only dan­ger­ous to hu­mans if it en­ters their blood­stream.

Deep in one of the wettest jun­gles of the Colom­bian Choco prov­ince, the re­searchers pho­tographed more than 300 frogs to clas­sify them and col­lected ge­netic sam­ples from more than 90. Back at the U of S, they used state-ofthe-art DNA tech­nol­ogy to screen more than 15,000 genes that could be as­so­ci­ated with col­oration.

The re­searchers’ sur­pris­ing dis­cov­ery was that un­re­lated species of frogs in the north and the south of the prov­ince show mu­ta­tions of the MC1R gene in the same DNA re­gion, ex­plain­ing why the frogs share sim­i­lar black pat­terns even if they are not close rel­a­tives and live hun­dreds of kilo­me­tres apart.

“These mu­ta­tions as­so­ci­ated with black colour show the foot­prints of nat­u­ral se­lec­tion,” Andrés said. “It con­firms that dark pat­terns are ben­e­fi­cial for frogs’ sur­vival, so it has been passed down through gen­er­a­tions.”

As a child grow­ing up in Colom­bia, Posso-Ter­ra­nova said there were so many frogs in his back­yard but he has wit­nessed how fast they are dis­ap­pear­ing due to global warm­ing and a chang­ing en­vi­ron­ment.

He cau­tions more re­search is needed, but hopes his project may help the Colom­bian gov­ern­ment de­velop strate­gies to pro­tect en­dan­gered frogs.

The frog study, funded by the fed­eral agency NSERC and a Col­cien­cias grant from the Colom­bian gov­ern­ment, also found ev­i­dence that there are at least three en­dan­gered species, in­stead of the two iden­ti­fied in a 1976 study.

Con­duct­ing re­search in a coun­try with an un­sta­ble so­cio-po­lit­i­cal sit­u­a­tion wasn’t easy.

“Only thanks to re­cent peace ne­go­ti­a­tions be­tween guer­rilla groups and the Colom­bian gov­ern­ment is it pos­si­ble for sci­en­tists to ac­cess ar­eas once off-lim­its,” said Posso-Ter­ra­nova.

Federica Giannelli is a grad­u­ate stu­dent in­tern in the U of S re­search pro­file and im­pact unit. This con­tent from the Univer­sity of Saskatchewan runs through a part­ner­ship with The Star Phoenix.

JOSÉ ANDRES

Andres Posso-Ter­ra­nova’s quest was to find evo­lu­tion­ary se­crets of Colom­bian dart frogs.

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