According to new research, climate change may leave some lizards in a gender lurch. The Australian bearded dragon's sex is determined by both its chromosomes and the environment its egg is incubated in, so warmer temperatures could be skewing wild populations to have more females.
"This is the first time we have proved that sex reversal happens in the wild in any reptile at all," lead study author Clare Holleley of the University of Canberra told the Associated Press. The study, she said, is an example of how climate extremes can put animals at risk on the most basic biological level.
It's normal for some of these lizards to hatch as females when they have the chromosomal makeup of males. That's because the species doesn't rely solely on chromosomes to determine their sex. The lizards are also influenced by the temperature at which their eggs are incubated. Some species use just chromosomes or just egg temperature to determine their sex (and no one is really sure why), but the bearded dragon uses a combination of both.
With temperatures warming, however, this mechanism may end up putting the lizards at a disadvantage.
In the new study, Holleley and her colleagues combined controlled breeding experiments with field data collected from observations of 131 adult lizards.
In warmer areas, 11 of the wild lizards were found to be females with male chromosomes -- indicating that temperature had determined their fate.
Eleven isn't a lot, and the researchers plan on continuing their research with larger sample sizes. But here's the potential problem: When those females reproduced -- which they did at nearly twice the rate of chromosomal females -- their offspring all lacked sex chromosomes, meaning that their sex was determined entirely by temperature.
So in a warming climate, it's possible that the species could see a snowball effect of females primed to produce female offspring, spurring a growing sex imbalance. Sure enough, the researchers saw the percentage of heat-determined females going up each year of their study. Eventually, there could be so few males that the species would lack the genetic diversity needed to stay strong in the face of their warming world.
It wouldn't be impossible for the male sex chromosome to disappear entirely, according to the researchers.
Scientists will have to keep a close eye on this and other species to see how their fare in Australia's ever-warming climate.