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Size matters in the battle to adapt to diverse environments and avoid extinction

February 20, 2015

TORONTO , ON — A new Uni­ver­si­ty of Toron­to study may force sci­en­tists to rethink what is behind the mass extinc­tion of amphib­ians occur­ring world­wide in the face of cli­mate change, dis­ease and habi­tat loss.

The old cliché “size mat­ters” is in fact the gist of the find­ings by grad­u­ate stu­dent Stephen De Lisle and Pro­fes­sor Locke Rowe of U of T’s Depart­ment of Ecol­o­gy & Evo­lu­tion­ary Biol­o­gy in a paper pub­lished today in Pro­ceed­ings of the Roy­al Soci­ety B.

By exam­in­ing research on glob­al pat­terns of amphib­ian diver­si­fi­ca­tion over hun­dreds of mil­lions of years, De Lisle and Rowe dis­cov­ered that “sex­u­al­ly dimor­phic” species – those in which males and females dif­fer in size, for exam­ple – are at low­er risk of extinc­tion and bet­ter able to adapt to diverse envi­ron­ments.

Their work sug­gests the abil­i­ty of males and females in sex­u­al­ly dimor­phic amphib­ian species to inde­pen­dent­ly evolve dif­fer­ent traits – such as size – helps them sur­vive extinc­tion threats that kill off oth­ers, says De Lisle.

He says clas­sic eco­log­i­cal the­o­ry would not have pre­dict­ed that about amphib­ians, a class of ver­te­brates that includes frogs, toads, sala­man­ders, newts and cae­cil­ians.

The con­ven­tion­al school of thought believes dif­fer­ent-sized sex­es of the same species take up more resources and are less able to adapt and diver­si­fy than species where eco­log­i­cal­ly rel­e­vant traits like size are basi­cal­ly the same between males and females.

“I think if our results bear on mass extinc­tion at all, it sug­gests we maybe should start look­ing more close­ly at the traits of some of the species that are going extinct,” says De Lisle.

“Sci­en­tists might start think­ing in a new way about how oth­er traits, like sex dif­fer­ences in habi­tat use or diet, might play a role.”

While pea­cock feath­ers or deer antlers are under­stood to help males of those species suc­cess­ful­ly mate, less is under­stood about amphib­ians, which are being wiped out so fast many are going extinct before sci­en­tists can iden­ti­fy them.

Some esti­mate between 30 and 40 per cent of the world’s approx­i­mate­ly 7,000 species of amphib­ians are cur­rent­ly in dan­ger of extinc­tion – more than any oth­er ani­mals on earth – and their decline is a crit­i­cal threat to glob­al bio­di­ver­si­ty.

Many sci­en­tists believe amphib­ians serve as “canaries in a coal mine,” and declines in their pop­u­la­tions indi­cate oth­er groups of ani­mals and plants will soon be at risk.

Amphib­ians are not only an impor­tant part of the food chain and bio­di­ver­si­ty. Some have chem­i­cals in their skins that can be devel­oped into med­i­cines to fight dis­eases such as can­cer and per­haps even AIDS.

Because their skins are high­ly per­me­able and they have a two-staged life cycle that starts in water and then moves to land, amphib­ians may be more sus­cep­ti­ble to tem­per­a­ture changes, water and air pol­lu­tion than oth­er ani­mals.

The new study by De Lisle and Rowe adds anoth­er piece to the puz­zle about why some species are doing well while oth­ers are in decline or dis­ap­pear­ing.

For exam­ple, both the gold­en toad and the har­le­quin frog of Cos­ta Rica’s Mon­teverde Cloud For­est Pre­serve dis­ap­peared com­plete­ly in the late 1980s despite liv­ing in what was con­sid­ered a pris­tine habi­tat.

“Our work sug­gests we still maybe don’t have the best under­stand­ing of what traits might be influ­enc­ing these extinc­tions, although now we have the under­stand­ing that sex­u­al dimor­phism is an impor­tant trait,” says De Lisle.



Steven De Lisle
Ecol­o­gy & Evo­lu­tion­ary Biol­o­gy
Uni­ver­si­ty of Toron­to

Kim Luke
Com­mu­ni­ca­tions, Arts & Sci­ence
Uni­ver­si­ty of Toron­to