Scientists uncover the secret of California condors' origins

Recently, while completing the family tree of the California condor, a shocking secret that had been hidden for ten years was revealed.

This secret concerns the origins of the two vultures - when scientists wanted to determine who their parents were, they searched all the adult vultures, but found that none of them was their biological father... Where did these two little guys come from?

A vulture without a father

The California condor (Gymnogyps californianu) is one of the largest birds in North America and has been found all over the continent since about 10,000 years ago. It reaches sexual maturity at 6 to 7 years old and once it finds a mate, it becomes a lifelong couple, building nests and raising children together.

Prior to this, researchers had collected DNA data from every California condor, which allowed them to perform paternity tests on each individual. The two condors whose fathers could not be found were born in 2001 and 2009, respectively, and had died before that. Scientists sequenced the genes of their specimens and compared their genes with the data of all individuals that had been recorded.

However, the test results were unexpected - the researchers only found female birds whose genes matched theirs, and after searching the gene pool of the entire population, they did not find a bird father that matched the genetic data.

Faced with this unprecedented result, the researchers were also puzzled - was there something wrong with the genetic test?

They quickly repeated the test, but the result was still the same. The genes of the two vultures did not match the data of any adult male vulture. A bold idea flashed through the minds of the scientists - could it be that they had no father and were born through parthenogenesis of the vulture mother?

Now it all makes sense.

They have a spouse but choose parthenogenesis

Parthenogenesis is also called parthenogenesis, where the egg cell can produce a new individual without fertilization. In other words, the offspring is completely produced by the mother bird independently, without the participation of the father, and the genes of the baby bird correspond to the mother, without the father in the biological sense.

In vultures, parthenogenesis can only produce male chicks. The sex chromosomes of vultures are different from those of humans - in humans, females have XX chromosomes and males have XY; but in vultures, females have ZW chromosomes and males have ZZ. When the vulture mother's egg cell replicates itself to produce offspring, only ZZ and WW embryos will appear. The WW embryo will not survive, and only the male chicks with ZZ chromosomes will be left.

Unfortunately, the two male vultures produced by parthenogenesis did not live long, living only 2 and 8 years old respectively. Compared with vultures produced by sexual reproduction, their bodies were also weaker and they died without leaving their own offspring.

This is the first case of parthenogenesis in a California condor, but it is not uncommon in other bird species, lizards, snakes and sharks. In 2007, a female tiger shark (Stegostoma fasciatum) was found giving birth to a baby shark at a hotel in Dubai, but she had never seen any male sharks before. In the same year, a virgin female Komodo dragon (Varanus komodoensis) gave birth to a baby shark alone at Chester Zoo in the UK.

Sexual reproduction is the main way of reproduction for animals. Parthenogenesis usually occurs when there are very few males or the entire population is in danger. It can be said to be the last attempt of a species to save itself. This is not the case with these two bird mothers. They are experienced. One has given birth to 11 baby birds, and the other has given birth 23 times, all of which were sexual reproduction. One of the bird mothers also has a partner who has lived with her for more than 20 years.

Even though they have a stable partner, they still choose parthenogenesis - what is the mother bird thinking? Even scientists don't understand this. (However, since they have a partner, can they trick him into hatching eggs?)

After a near-death experience, I finally returned home

Researchers are able to do paternity testing on every California condor because just a few decades ago, the species came within a hair's breadth of becoming history forever.

The California condor has a very low fertility rate. Every February to March, each condor couple will lay an egg, incubate it together, and spend a lot of effort to raise this only child. If they encounter an accident and the egg is lost, they have to start the backup plan - train a new account and lay a new egg. The baby bird will live with its parents until it is about 2 years old and then leave home. At that time, the bird couple will plan to have another child.

Such strict mating habits naturally lead to the low fertility rate of California condors; coupled with illegal hunting, pesticides and habitat destruction, the number of condors has been reduced again and again. Around 1930, there were only about 100 condors in the wild, but humans had not taken any measures to save them. More than 50 years later, there are only 9 wild individuals left in the world. The announcement of extinction seems to be ringing in our ears, and people can no longer ignore their silent calls for help.

It was not until then that the California government urgently formulated a vulture rescue plan and built an artificial breeding center at the San Diego Zoo and Wildlife Park, capturing all the remaining wild individuals and artificially breeding a total of 27 vultures.

In order to make California condors have more babies and avoid jumping back and forth on the edge of extinction, scientists have racked their brains. Fortunately, they have the habit of "making a new one if they lose one". During their breeding season, researchers steal the first egg and incubate it artificially, so the bird couple has to have a second baby. In this way, the fertility rate is improved.

With the careful care of scientists, the number of vultures gradually increased to 52 by 1992. A wild reintroduction program was also launched, and artificially bred young vultures were regularly released back to their true home. In 2020, there are 504 California condors, of which 329 live in the wild, all of whom are descendants of the original 27 vultures. Compared with other birds, their numbers are still small, but fortunately they have escaped the fate of extinction.

Over the past 30 years, scientists have recorded the DNA data of every California condor. For every newborn condor, they can identify its parents by analyzing its DNA. With the genealogy, inbreeding can be avoided during artificial breeding - the offspring of inbreeding are prone to atrophy and die before birth.

In this study, scientists were just doing routine work to identify the parents of two vultures, but they did not expect to find such a rare phenomenon of parthenogenesis. It was really a surprise. However, this discovery was all due to the perfect gene pool of California condors. If it were another species, this mystery of their origin might never be solved. This makes people wonder, is parthenogenesis more common in nature than everyone thinks? What is the reason that makes bird mothers choose to produce offspring alone when they have a partner?

While these new questions are being studied, efforts to protect the California condor will continue, so that one day their majestic feathers may once again fill the skies above the American continent.

References

[1]Critically endangered condor chicks are species' 1st known 'virgin births' | Live Science

[2]https://www.nytimes.com/2021/10/30/science/san-diego-zoo-condor-virgin-births.html

[3]California condors: Virgin births discovered in critically endangered birds - BBC News

[4]https://www.allaboutbirds.org/cams/california-condor/

[5] Xiao Shu. Endangered bird: California condor[J]. Man and Nature, 2004(3):2.

[6]The Zebra Sharks of Burj Al Arab - YouTube

Virgin Birth Expected at Christmas—By Komodo Dragon (nationalgeographic.com)

Clone alone: ​​Who needs sex? | New Scientists

Author: White Stork on the Shore

Editor: Mai Mai

Source: Species Calendar