Friskier frogs: en­dan­gered species gets a sex ap­peal boost

The Guardian Australia - - News - Calla Wahlquist

Aus­tralian re­searchers are ap­ply­ing a sex hor­mone to the skin of the crit­i­cally en­dan­gered north­ern cor­ro­boree frog in a world-first treat­ment to en­cour­age fe­males to ac­cept less de­sir­able mates in cap­tiv­ity.

A trial con­ducted by the Univer­sity of Wol­lon­gong and Taronga zoo found that, by ad­min­is­ter­ing the hor­mone to both a male and fe­male frog be­fore pair­ing them off, re­searchers could in­crease the chance that they would ac­cept their al­lo­cated part­ner from about 22% to 100%.

In a world-first, the re­searchers put a few drops of the syn­thetic go­nadotrophin-re­leas­ing hor­mone on the frog’s stom­ach in­stead of us­ing the ac­cepted tech­nique of in­ject­ing the hor­mone un­der the skin.

It is the same type of hor­mone used in IVF.

“Be­cause frogs have highly per­me­able skin, the hor­mone gets ab­sorbed straight in,” lead re­searcher Dr Aimee Silla said. “It’s ex­tremely safe to use and we are re­ally pleased with the out­come of these tri­als be­cause we’re hop­ing that this method of ap­pli­ca­tion will be adopted by other am­phib­ian breed­ing pro­grams glob­ally.”

Taronga zoo’s north­ern cor­ro­boree frog pop­u­la­tion is drawn from a ge­net­i­cally iso­lated wild pop­u­la­tion in the north­ern Brind­abella Range, on the bor­der of New South Wales and the Aus­tralian Cap­i­tal Ter­ri­tory.

Pro­tect­ing the ge­netic in­tegrity of the wild pop­u­la­tion is a key aim of the cap­tive breed­ing pro­gram.

Frogs bred in the zoo are re­leased into the ranges to boost the wild pop­u­la­tion, which cur­rently stands at around 200. It is the larger of the three known wild pop­u­la­tions of north­ern cor­ro­boree frog.

Since the hor­mone ther­apy pro­gram be­gan in 2014, about 800 off­spring – a mix of eggs, tad­poles and ju­ve­nile frogs – have been re­leased.

With­out hor­mone ther­apy, the frogs usu­ally re­jected paired part­ners and were in­stead in­tro­duced to prospec­tive mates in large groups, al­low­ing them to pair off on their own.

Un­for­tu­nately, Silla said, only about one third of the males were cho­sen to mate.

“The fe­males are given that op­por­tu­nity to choose the mate that they think is most de­sir­able, and that’s where we are see­ing those mat­ing bi­ases and only a cou­ple of in­di­vid­u­als get­ting those mat­ings,” she said.

“From a ge­netic man­age­ment per­spec­tive, we would re­ally like to iden­tify par­tic­u­lar males that are ge­net­i­cally im­por­tant and be able to have a larger rep­re­sen­ta­tion of those genes in the off­spring be­ing pro­duced.”

Ap­ply­ing the hor­mone, she said, just makes the frogs more amenable to zookeeper match­mak­ing.

“If we sup­ply both the male and the fe­male with these re­pro­duc­tive hor­mones, it just en­cour­ages them to breed with the mate that we have given them and their mate be­comes more at­trac­tive be­cause they’re more re­cep­tive to breed­ing,” she said.

Taronga Con­ser­va­tion So­ci­ety Aus­tralia her­peto­fauna su­per­viser Dr Michael McFad­den said the hor­mone trial also had ben­e­fits for frog health be­cause it re­duced the num­ber of fe­male frogs that re-ab­sorbed their eggs af­ter an un­suc­cess­ful breed­ing sea­son.

He said he hoped the pro­gram would be ex­panded to other threat­ened am­phib­ian species.

Among them is the south­ern cor­ro­boree frog, which lives in tiny pock­ets of Kosciuszko na­tional park and is cur­rently fac­ing in­creased threats due to a New South Wales gov­ern­ment plan to pro­tect feral horses.

Pho­to­graph: Zoos Vic­to­ria

Re­searchers ap­ply a sex hor­mone to the skin of the north­ern cor­ro­boree frog to stim­u­late de­sire.

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