Scientists have recorded a rare case of a female zebra shark reproducing asexually, despite the presence of healthy males.
A baby zebra shark was born at the Shedd Aquarium in Chicago, although its mother did not mate with any males in the tank, Newsweek reported on December 17. This discovery was published in a new study in the Journal of Fish Biology.
An adult zebra shark (left) and its pup (right). (Photo: Shedd Aquarium/Brenna Hernandez).
Asexual reproduction – producing offspring genetically identical to the parent without mating – is common among many invertebrates but is rarely observed in vertebrates like sharks, except when no mate is available for sexual reproduction.
The research team discovered that the zebra shark in Chicago reproduced asexually after analyzing the genes of the pups. The testing aimed to aid in the breeding of this threatened species. However, one pup puzzled the scientists because it contained genetic information from only one adult shark, not two.
“The pup did not match with any of the adult males in the tank, but it did match with the female that laid the eggs,” said Kevin Feldheim, a researcher at the Field Museum and the lead author of the study.
Many reptiles, including whiptail lizards, geckos, rock lizards, and snakes, sometimes reproduce asexually. Some species, such as the New Mexico whiptail lizard, reproduce entirely asexually, meaning there have been no males for millions of years. Despite the absence of males, female lizards still engage in mating behaviors to stimulate their hormonal cycles, promoting egg-laying.
This phenomenon has been observed in sharks, but it is extremely rare. The case of the zebra shark in Chicago is even rarer because there are suitable males available for mating.
“This is only the second case we know of a shark reproducing asexually even when healthy mates are available. This finding challenges our understanding of how and why asexual reproduction occurs, and it highlights an important aspect of science: We will never stop learning,” Feldheim stated.
