An eight-year study of Komodo dragons (Varanus komodoensis) has revealed some interesting differences between the genders in the world's largest lizard species. Male Komodo dragons grow much bigger than and live nearly twice as long as females, who apparently spend so much time reproducing and doing the equivalent of housework that it sends them to an early grave.

No, the female dragons aren't donning aprons and doing laundry, but they do spend six months or more at a time defending eggs in their nests from potential predators. During that time, the females don't eat and lose much of their body weight. Males, meanwhile, spend their days hunting, fighting and, one presumes, drinking beer and bowling.

The females' defensive behavior alone doesn't account for the size and weight differences, according to research published September 19 in the journal PLoS One. The researchers—a team from Indonesia, Australia and Italy—tracked 400 komodo dragons on four Indonesian islands from 2002 to 2010 and found that males and females grew at about the same rate until they reached sexual maturity in about their seventh year. After that males kept growing, reaching an average length of 160 centimeters (excluding tails). But the females' growth plateaued at an average of 120 centimeters. The researchers concluded that males kept expending energy for growth, allowing them to compete against one another for mates, whereas the females stopped growing, redirecting all of their energy into building and maintaining nests, reproducing and guarding eggs.

The differences didn't end at size. The researchers found that male Komodo dragons lived an average of 60 years; female life expectancy topped out at 32. In the eight years of tracking and testing the animals, the researchers were never able to find a female 33 years or older. Although Komodo dragons are cannibalistic (one reason why females have to defend their nests), the researchers found that after the lizards grew large enough to defend themselves the primary cause of death was natural aging.

The researchers say the growth and death rates could be related. Because females die so young, the males might need to keep growing so they can fight one another for the few remaining females or for territory.

This research might also serve to explain why there is such a huge gender gap in Komodo dragon populations. Out of the 2,500 or so wild dragons in Indonesia, only around 350 are breeding females. As the authors wrote in the paper, this new understanding of female mortality and gender-based growth rates could help inform future conservation efforts by allowing scientists to model future population demographics.

Previously in Extinction Countdown:

Komodo dragons? Not in my backyard–Nor Yours

Photo: Adhi Rachdian via Flickr. Used under Creative Commons license