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.
Citation
Stephen
P. De Lisle, Locke Rowe. Independent evolution of the sexes promotes
amphibian diversification. Proceedings of the Royal Society B, February
2015 DOI: 10.1098/rspb.2014.2213