Size of egg influences lizard sex

June 5th, 2009 - 4:23 pm ICT by IANS  

Sydney, June 5 (IANS) A lizard’s egg size shows whether it’s going to be a boy or girl, says a new study.
“We were astonished,” said Richard Shine of the University of Sydney (U-S). “Our studies on small alpine lizards have revealed another influence on lizard sex: the size of the egg.

Big eggs tend to give girls, and small eggs tend to give boys. And if you remove some of the yolk just after the egg is laid, it’s likely to switch to being a boy, even if it has female sex chromosomes; and if you inject a bit of extra yolk, the egg will produce a girl, even if it has male sex chromosomes.”

In many animals, the sex of offspring depends on specialized sex chromosomes. In mammals and many reptiles, for instance, males carry one X and one Y chromosome, while females have a pair of X chromosomes.

Conversely, animals like alligators depend on environmental cues like temperature to set the sex of future generations.

The new findings add to evidence that when it comes to genetic versus environmental factors influencing sex determination, it doesn’t have to be an either/or proposition.

Shine’s group also noticed something else: large lizard eggs were more likely to produce daughters and small eggs were likely to produce sons, said a U-S release.

Despite the correlation, Shine said he had assumed that the association was indirect. In fact, his colleague R Radder conducted studies in which he removed some yolk from larger eggs, more likely to produce daughters, to confirm that assumption.

“We were confident that there would be no effect on hatchling sex whatsoever,” Shine said. “When those baby boy lizards started hatching out, we were gob-smacked.”

These findings were published online in the Thursday edition of Current Biology.

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