By Rosslyn Beeby Science and Environment Reporter
A four-year study of a common Australian lizard has proved
hotter incubation temperatures can reverse gender in some
species, turning boys into girls as the weather heats up.
The world-first discovery, made by a team of ecologists
and geneticists from the University of Canberra working
closely with chromosome exvertsfrom the Australian National
University, challenges previous theories of sex determination
and also has profound implications for climate change.
The researchers found temperatures hotter than 34 degrees
during the mid-stages of incubating dragon eggs causes
sex reversals with male western bearded dragon switching
gender to develop and hatch as females, but still retaining
their male chromosomes. The findings are published today
in the international journal Science, and bring evolutionary
biologists a step closer to discovering if there is a specific
sex determination gene.
The study's lead author, University of Canberra geneticist
Alex Quinn said scientists had traditionally regarded the
mechanisms of sex determinationas either genetic or environmental,
and therefore fundamentally different.
"We've found these two mechanisms can co-exist
in one individual," he said.
Using beardeddragons caught in outback Queensland the
research team combined incubation experiments using varying
temperatures with sophisticatedgenetic techniques that
enabled them to colour-code and track the lizards' sex
specific DNA.
Dr Tariq Ezaz and Professor Jennifer Marshall -Graves
from the ANU’s genomicsgroup, taggeddragon DNA with
green and red fluorochrome "flags" to identify
and track gene sequences.
"We were surprised to also be able to pick up small
sex specific differences and very distinct and small chromosomes," Dr
Ezaz said.
Male dragons have two Z chromosomes, and females have
one Z and one W chromosome. In humans, females have two
X chromosomes and males have one X and one Y chromosome.
"What we found is the dragon equivalent of a fully
formed human male with no Y chromosome," Mr Quinn
said.
University of Canberra professor of applied ecology Arthur
Georges is one of Australia’s leading researchers
on how temperatures affect sex determinationin turtles
and lizards.
He said it was previously thought that reptiles had two
modes of sex determination - sex determined at conception
by sex chromosomes (as in humans) and sex determined by
temperatures experienced by embryos during incubation.
"What we've been able to do is demonstrate for
the first time the coexistence of genetic and environmental
influences in one species, which opens up exciting new
avenues for investigating sex determination," he
said.
"We've shown female development in dragons can proceed,under
sex reversal, without a W chromosome and therefore sex
is not determined by a gene on the W chromosome, " Professor
Georges said.
As yet, they don't know if gender bending female dragons
- those boys who turn into girls when the heat is on -
will be fertile.
Mr Quinn said, "That's the big question, whether
any of the sex reversal animals that have hatched will
be able to breed.
"That also had big implications for climate change
as hotter temperatures become the norm, rather than an
occasional or temporary occurrence."
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