A female zebra shark (Stegostoma fasciatum) gave birth by fertilizing her own eggs despite sharing the same tank with two healthy males who might possibly be willing to help, a new study reports. Journal of Fish Biology (opens in new tab). This unusual scenario challenges previous assumptions about the risks and benefits of parthenogenesis, a form of asexual reproduction sometimes nicknamed “virgin birth,” according to the study’s authors.
“This is the second case in which we know where sharks are born through parthenogenesis, even when there are healthy mates,” the study author said. Kevin Feldheim (opens in new tab) One from the Field Museum of Natural History in Chicago expression (opens in new tab). “This latest article is just another step in learning why these ‘virgin births’ happen.”
A number of bird, reptile, amphibian and fish species use parthenogenesis as a biological backup plan for reproduction when mates are difficult to find. But the process can be risky; animals born through parthenogenesis usually have a shorter lifespan and are generally sterile; this may explain why asexually reproducing vertebrate species rarely choose to use it unless they have a choice.
Related: Hail Mary! 9 surprising stories about virgin births in the animal kingdom
While performing routine genetic testing on two shark pups at Chicago’s Shedd Aquarium, Feldheim and colleagues discovered a strange exception to the usual rules of parthenogenesis.
This DNA the results were surprising. The pups did not mate with any of the male sharks in the tank. And while their DNA matched that of the female shark, some of those matches were too close for comfort. The few gene pairs that should have reflected a father’s contribution were instead identical copies of the mother’s genes—a finding that is highly suggestive of parthenogenesis.
Beyond genetics, there were other questionable signs. Although the fry normally hatched on their own, the aquarium staff had to cut the fry’s eggs; both cubs ultimately survived for only a few months.
The offspring may have died due to deleterious recessive alleles – dysfunctional or defective copies of the mother shark’s genes would be compensated for by a normally functioning dominant gene from the other parent in the offspring produced by sexual reproduction. Instead, these baby sharks may have inherited multiple copies of the defective gene variants from the mother.
One of the disadvantages of asexual reproduction is that both copies of a gene come from the same parent and leave no room for error; If the mother is a carrier of an autosomal recessive disorder, meaning it takes two copies of the gene to show the disease, the offspring will have it. While the study’s authors could not confirm that deleterious recessive alleles were responsible for the death of these particular offspring, they said this would be typical of parthenogenesis.
The findings may have implications for zebra shark conservation. Because these sharks are an endangered species, learning more about how they reproduce can help aquarists breed them in captivity. Actually, the only other reported case (opens in new tab) The proportion of female zebra sharks choosing parthenogenesis over a suitable male was part of a larger study investigating the use of reproductive technologies to support conservation-based breeding programs.
“This study is just the beginning of our understanding of the occurrence of this genetic phenomenon in zebra sharks,” said the study author. high school watson (opens in new tab), deputy director of animal operations and habitats at Shedd Aquarium on air. “Zoos and aquariums like the Shedd have a key role in protecting endangered species such as zebra sharks in some parts of the world. Knowing more about parthenogenesis and verifying the genetic makeup of our populations in zoos and aquariums is crucial. Making informed decisions that fuel this work. for.”