A female zebra shark (Stegostoma fasciatum) in Australia has learned to live, and reproduce, without a male counterpart. The shark, which lives in an aquarium, is one of only three animals documented that once reproduced sexually – she had a male partner for around 13 years – and then switched to reproducing asexually. Now scientists are now wondering if this phenomenon is more common than we thought.
Leonie the zebra shark had a male partner from 1999 to 2012 at a Townsville, Australia aquarium, and they had over two dozen babies. When her partner was moved to a different tank, Leonie spent around four years by herself, until she gave birth to three surprise baby sharks in 2016. She’d lacked contact with any males for those four years. Scientists initially thought perhaps she’d saved sperm from the former male partner, but genetic testing revealed the three babies only had DNA from their mother.
Sharks can reproduce asexually when an adjacent cell called a polar body fertilizes an egg, and it could be that is what happened with Leonie. The mechanism isn’t optimal, as it can lead to inbreeding, but could be employed by sharks when there aren’t any males around. Lead author on a study published by Scientific Reports, Christine Dudgeon of The University of Queensland, told New Scientist, “It’s not a strategy for surviving many generations because it reduces genetic diversity and adaptability. It might be a holding-on mechanism. Mum’s genes get passed down from female to female until there are males available to mate with.”
Some species such as other sharks, snakes, rays, turkeys, and Komodo dragons are capable of reproducing both asexually and sexually, but asexual reproduction usually happens in females that have never reproduced sexually. The only other female animals recorded switching from sexual to asexual reproduction are a boa constrictor and an eagle ray; both lived in captivity. But it could be this anomaly actually occurs more frequently than we realized. Dudgeon said perhaps we just haven’t been looking.
Via New Scientist