Asian water dragons have been added to the list of animals that can reproduce without male assistance. An individual being kept at the Smithsonian's National Zoo has produced offspring without encountering a male since well before she was sexually mature. Although parthenogenesis has been observed among more than 20 reptile species, this is the first report of it in a member of the Agamidae family.
A female water dragon known as WD-10 in the zoo's Reptile Discovery Center started laying eggs in 2009. WD-10 has been caged alone or with other females since the age of four months, and didn't become sexually mature for more than a year thereafter.
Many species don't require males for egg-laying (think chickens), but need them if the eggs are ever to hatch. In 2015, however, keeper Kyle Miller “took a chance” and put the water dragon's eggs in an incubator. The first incubated clutch produced two hatchlings that died in their shells, which was enough to keep Miller trying. One healthy daughter hatched from the next clutch in 2016. Two years later, a second hatchling was initially healthy but died from trying to eat something that blocked its digestive system, truly a warning about eyes bigger than one's stomach.
Acknowledging a remote possibility WD-10 had stored sperm from a male or had received an unrecorded male in the cage, the keepers conducted DNA analysis. In PLOS One, they announced that the genetic matches between mother, daughter, and unhatched offspring were too perfect for offspring born with two parents.
So far, the Smithsonian has resisted the temptation to change WD-10's name to Mary.
There are obvious advantages to parthenogenesis, particularly in recovering after disasters. In this light, it seems odd it is not more common. However, WD-10's story may hint at an explanation. The keepers incubated 64 eggs, but she only had two healthy offspring. Some of the other eggs were never fertile, and even among those that were, the success rate was poor.
The researchers acknowledge the possibility their incubation may have differed in temperature or humidity from the water dragon's ideal. However, it's more likely that parthenogenesis isn't a reliable method of reproduction for water dragons, although some other species do make it work better.
The team are keen to see whether WD-10's surviving daughter also reproduces in this manner, which would suggest this was not a one-off accident. “Somewhere in their evolutionary history, they [could] have this trait where they can repopulate ... completely in the absence of mates,” Miller told Smithsonian.com.
Reproduction without males (at least initially) has been a useful plot device for films from Jurassic Park to Godzilla, which raises the question: If water dragons can reproduce on their own, what about fire dragons?