This Lady Lizard Can Reproduce Without a Mate

Self-fertilization may help the world’s largest lizard survive.

This story appears in the November 2017 issue of National Geographic magazine.

The Komodo dragon, the largest species of lizard now alive, can grow to 10 feet long and nearly 200 pounds. A muscular carnivore armed with sharp teeth, Varanus komodoensis dines on prey as large as deer, wild boar, and water buffalo.

As formidable as the Komodo dragon seems, it’s very much at risk. On seven Indonesian islands that are the only places the species lives in the wild, humans burn its habitat to clear land and poach animals on which it preys. Even on land protected as Komodo National Park, officials reported just 3,013 Komodo dragons in 2016, down from 3,222 in 2013.

When her species needs replenishing, what’s a mother dragon to do? She can reproduce the old-fashioned way, by mating with a male and laying eggs. Or she can lay eggs without having mated, through a sort of virgin birth process called parthenogenesis.

In 2006 at England’s Chester Zoo, a female named Flora, who’d had no male contact, laid a clutch of viable eggs that tests showed had only her DNA. That was the first confirmation of parthenogenesis in captive Komodo dragons; scientists now believe it “happens very often,” says Gerardo Garcia, Chester Zoo’s curator of lower vertebrates and invertebrates.

How does it work? In humans, males have both male and female sex chromosomes. In Komodo dragons, females do—so Flora had within her the genetic materials needed for embryos to develop. This self-fertilization yields offspring that are “absolutely healthy,” Garcia says—but every one is male.

Being able to reproduce both sexually and asexually gives the dragons an evolutionary edge, Garcia says. If no mate is handy, a female can bear sons parthenogenetically—and when they’re older, they can be her mates. “It’s not ideal” for keeping the gene pool diverse, he says. But it’s a way for the species to continue.

VARANUS KOMODOENSIS

Habitat/range: Tropical-forest edge and grasslands of seven Indonesian islands

Conservation status: IUCN assesses it as vulnerable.

Other facts: One of about 80 species of monitor lizards, Komodo dragons have existed for perhaps 3.8 million years, fossils suggest.

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