A female Komodo dragon named Charlie who lives at the Chattanooga Zoo had three hatchlings without ever having mated. Charlie's hatchlings were born last year
but the zoo only recently determined via DNA testing that a male named Kadal who shared her habitat wasn't the father. Indeed, there was no father. Komodo dragons are capable of parthenogenesis, asexual reproduction that's very rare in vertebrates. From CNN
Komodo dragons have evolved to reproduce both sexually and parthenogenetically because they mainly live isolated in the wild and become violent when approached, according to the zoo.
Parthenogenesis happens when another egg, rather than sperm, fertilizes an egg, according to Scientific American. The biological process of making an egg cell, called oogenesis, typically produces a polar body, which contains a duplicate copy of egg DNA.
"Normally, this polar body shrivels up and disappears. In the case of the Komodos, though, polar bodies evidently acted as sperm and turned ova into embryos," Scientific American said in 2006 when the first cases of parthenogenesis in Komodo dragons were reported.
image: Chattanooga Zoo press release
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Back in August 2019, a female komodo dragon named Charlie gave birth to three little dragons at the Chattanooga Zoo. The zookeepers had previously tried to hook her up with a sweet dragon fella named Kadal, but the two never really seemed to hit it off — not that the staff could observe, anyway. And now that they've tested the DNA of young Onyx, Jasper, and Flint, it's finally confirmed: Charlie and Kadal did not hit it off at all, so Charlie took it upon herself to bring the kids into the world. From the Chattanooga Times Free Press:
The DNA results showed the babies were the result of parthenogenesis, which is a type of reproduction where the female produces offspring without male fertilization. […] Female Komodo dragons carry WZ sex chromosomes, while males carry the ZZ type. When parthenogenesis happens, the mother can only create WW or ZZ eggs. Since eggs with the sex chromosomes of WW aren't viable, only ZZ eggs are left to produce all male hatchlings. Parthenogenesis is considered very rare, with the first case of a successful parthenogenesis reproduction in Komodo dragons recorded in 2006.
I was personally fascinated to learn that there are so many different categorizations of asexual reproduction, and that it can indeed occur spontaneously in vertebrates without any fertilization. In 2007, there was apparently a bit of a scandal involving a lab-grown human embryo that was allegedly cloned, but turned it to be a productive parthenogenesis. There are also living human beings with some unique chimeric complications in which they were both fertilized by a male, but also underwent some kind of parthenogenesis at the same time, resulting in a male offspring with Y-chromosomes in his skin, but not in his blood. Read the rest