As It Happens

It turns out female condors can reproduce on their own, without help from males

Two female condors in the San Diego Zoo Wildlife Alliance’s managed breeding program laid eggs and hatched chicks — on their own. It's the first report of asexual reproduction, or parthenogenesis, in the endangered birds.

2 female condors conceived offspring from unfertilized eggs — but the chicks didn't fare so well

Two California condors reproduced on their own — asexually — while they were part of a breeding program at the San Diego Zoo Wildlife Alliance. (San Diego Zoo Wildlife Alliance)

Two female condors in a California breeding program laid and hatched chicks without any fertilization help from males.

A new study published last week in the Journal of Heredity reported asexual reproduction, or parthenogenesis, occurring in the endangered birds for the first time, according to the San Diego Zoo Wildlife Alliance.

Scientists there were performing routine analysis of old DNA samples when they realized that two male chicks that hatched in 2001 and 2009 were conceived from unfertilized eggs. They checked their records and found that the chicks were related to their mothers, but both were biologically fatherless.

"I was very surprised, to be honest," Cynthia Steiner, associate director of conservation genetics at the San Diego Zoo Wildlife Alliance, told As It Happens host Carol Off.

During a routine analysis of DNA samples from two California condors, geneticists discovered the birds were related to their mothers, but were biologically fatherless. (San Diego Zoo Wildlife Alliance)

Parthenogenesis can occur in other species such as honey bees, sharks and Komodo dragons. In birds, it usually only happens when females don't have access to males. 

These mother condors previously mated with males in the San Diego managed breeding program and produced 34 chicks, and both mothers were living with fertile males when they produced the eggs asexually.

"It was actually kind of like any spontaneous phenomenon," Steiner said. "These females were producing eggs that were fertilized by males in the past, but they were also able to reproduce in this asexual way at some point in their lives."

Cynthia Steiner is the associate director of conservation genetics at the San Diego Zoo Wildlife Alliance. (San Diego Zoo Global © 2015)

Unlike sexual reproduction, parthenogenesis does not need sperm to fertilize an egg. Instead, the female contributes twice as much genetic information to create an embryo.

However, there appear to be some downsides. Both of the male chicks that were born asexually appear to have been physically unfit, Steiner said. 

Scientists released one of them back into the wild, where that chick spent two years trying to integrate with the population.

"This individual was a little bit unfed," Steiner said. "He died because he was underweight.... We don't know if that was something related to the parthenogenesis by itself, or [if] it was just an ecological phenomenon."

The other chick stayed in captivity and lived about eight years. California condors can live up to 60 years.

"[He] was showing some physical traits that were pretty much unique. Some malformations in the back. This individual was underweight as well," she said.

This chick also behaved differently than other captive male condors that were born through sexual reproduction. 

"It was a male, but it was not behaving as a male in terms of the regular courtship," she said. "It was ... with some females, but he never actually mated."

California condors are a rare and endangered species. Scientists started breeding them in captivity in the 1980s, when there were just 23 condors left around the world. Now, there are more than 500 condors. (San Diego Zoo Wildlife Alliance )

With three-metre wingspans, condors are the largest flying birds in North America. They once ranged throughout the West Coast, but were driven to the brink of extinction due to habitat loss, poaching, and lead poisoning, according to the San Diego Zoo.

There were only about 20 of them left in the 1980s when the U.S. government captured them and placed them in zoos for captive breeding. 

There are now more than 500 California condors, including more than 300 that have been released into the wild in California, Arizona, Utah and Mexico.

The San Diego Zoo Wildlife Alliance has been collecting the genetic data of all the condors born in captivity and in the wild ever since the breeding program began.

Of all the condors they've collected data on, only these two male chicks were born through parthenogenesis.

According to Steiner, some scientists believe that the condors responded to their low population numbers in the early 2000s by producing the two male chicks asexually.

"Now that the population of California condors is bigger ... the question is whether this phenomenon is going to happen again in individuals of the living population, since now we know that the population is doing much better in expanding," he said.


Written by Mehek Mazhar with files from Associated Press. Interview with Cynthia Steiner produced by Katie Geleff.

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