[lit-ideas] Global Warming -- Lizard sex 101
- From: "JimKandJulieB@xxxxxxx Krueger" <juliereneb@xxxxxxxxx>
- To: lit-ideas@xxxxxxxxxxxxx
- Date: Sun, 22 Apr 2007 10:50:52 -0500
Ok -- this one is just plain bizarre. And I never knew marine turtles &
alligators are temperature-driven re. the sex of offspring. Fascinating
article. My youngest daughter spent the weekend here (she's been floating
alot -- age 13 does that to a person). Over the course of the weekend, I've
experienced her adopting of 2 African Hissing Cockroaches (roughly 2" long,
exoskeletal, whose previous owner purchased them at the pet shop only to
learn that said owner's Mother was allergic to them. My immediate reaction
was, me too! I'm not exactly endeared to them, but researching their care &
feeding they're pretty amazing creatures.), a box turtle the Sheltie was
harassing which Elena is taking to a friend's house which she believes to be
a safer environment for it, a wild mouse one of the cats chased into a floor
vent in her bedroom where it became stuck at the waist w/ its little head
sticking up which the cat thought fun to bat around (Elena rescued the
mouse, scolded the cat, and released the mouse outside), the grooming of
cats, changing of mouse cages & bedding (tame mice), care of doves, and a
partridge in a pear tree. Well, not yet on the partridge but I'm not
promising anything. I feel like I'm zoology class.
Julie Krueger
http://www.livescience.com/animalworld/070419_lizard_sex.html
Warming Climate Reverses Sex of Lizards
*by Jeanna Bryner <http://www.space.com/php/contactus/feedback.php?r=jbr>*
LiveScience Staff Writer
posted: 19 April 2007
02:23 pm ET
High temperatures can reverse the sex of dragon lizards before they hatch,
turning males into females.
The finding, detailed in the April 20 issue of the journal *Science*, could
have implications for the development of life as the planet's climate warms.
The research reveals that extreme temperatures could inactivate a gene on
the male sex chromosomes of dragon
lizards<http://www.livescience.com/reptiles/>and thus turn male
embryos into females. The sex-reversed lizards look
female and have female organs but genetically they are male, said lead
author Alexander Quinn of the University of Canberra in Australia.
*Sex 101*
Until now, scientists have assumed that the sex of mammalian and reptilian
offspring is determined by either genes on sex chromosomes or external
factors such as temperature, but not both at once. Genetics was thought to
direct the sex of Australian central bearded dragon lizards (*Pogona
vitticeps*).
Sexual reproduction involves the joining of sex cells, sperm and egg, each
of which carries a set of chromosomes, including a sex-determining
chromosome.
In most mammals, including humans, females have two X (sex)
chromosomes<http://www.livescience.com/humanbiology/ap_050316_chromosomes.html>,
while males have one X and one Y. For the dragon lizard, the sex
chromosomes are labeled as Z or W and females have dissimilar chromosomes
(ZW), and males have matching ones (ZZ).
So it was thought that the female determined the sex of the offspring, the
opposite of the case in humans. Here's why: If a dragon lizard egg cell
containing a W chromosome is fertilized, the resulting zygote will be ZW (or
female) while if a Z egg cell gets
fertilized<http://www.livescience.com/reproduction/>, the result will
be ZZ (or male). What the egg cell brings to the table
determines the sex outcome.
To test this, Quinn and his colleagues from the Australian National
University incubated *Pogona vitticeps* eggs at constant temperatures,
ranging from 68 to 99 degrees Fahrenheit (20 to 37 degrees Celsius).
No embryos survived at the coldest temperature. In ideal conditions, between
72 to 90 degrees Fahrenheit (22 and 32 degrees Celsius), an equal mix of
male and female lizards developed. However, when the mercury soared to
between 93 and 99 degrees Fahrenheit (34 and 37 degrees Celsius),
significantly more females resulted, indicating that temperature trumped
gene-controlled sex determination.
*It's a girl*
The scientists examined the baby lizards' physical features, including their
sex organs, to label each as being outwardly, or "phenotypically," female or
male. They also analyzed the lizards' DNA for female-specific markers linked
to the W chromosome.
Nearly 100 percent of the eggs incubated at intermediate temperatures
developed into lizards with genes that matched their physical features.
However, about half of the lizards from high-temperature incubators had a
mismatched make-up, in which genetic males "looked like" females.
"High temperature during the development of the embryos prevented the male
DNA triggering testis development," Quinn told LiveScience. "By default,
they developed instead as females with ovaries."
The scientists hypothesize that a gene on the Z chromosome—not the female W
chromosome—triggers male development. They suggest a protein expressed by
this gene is sensitive to temperature. "At most temperatures the protein is
working at its best, but high temperatures make it less effective, making it
unable to trigger male development," Quinn said.
*Climate change*
The results suggest that an interaction between temperature and genetics
steers sex development in central bearded lizards.
Before now, scientists have been concerned about how global warming will
affect sex
ratios<http://www.livescience.com/animalworld/061127_male_crocs.html>in
species such as alligators and marine turtles, where temperature alone
drives the sex of offspring.
"But now our study opens up the possibility that many [genetically
sex-determined] reptiles might face the same risk as well, if they show
reversal to 100 percent of one sex at high temperatures, like the bearded
dragon," Quinn said.
How these animals will adapt to global warming is a complex and open
question. "Obviously, reptiles with temperature influences in their sex
determination must have persisted through many climatic fluctuations
throughout their evolutionary history," he said, "but a concern is that the
current rate of climate warming might be too fast for these animals to adapt
to it."
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