An aquarium in Townsville, Queensland, Australia, reported of an unusual event that happened among their populations of leopard sharks. A female leopard shark reproduced after being separated from a male.
This is the first known case of a shark switching from sexual to asexual reproduction and only the third reported case among vertebrates. Leopard sharks are also known as zebra sharks.
The leopard shark in question is Leonie, was taken into captivity in 1999 and introduced to a male only in 2006, at the Reef HQ Aquarium. She started laying eggs in 2008 and produced several series of offspring before 2012, when the aquarium decided to stop the breeding process and separated her from her mate.
One of Leonie’s offspring, Lolly, has shared a tank with her mother since 2013 and has not been in the presence of a male shark since reaching sexual maturity. However, in 2014, both female sharks laid eggs. Although this behavior seems peculiar, Dr. Christine Dudgeon, biologist at the University of Queensland, declared that it is not unusual for a leopard shark to lay eggs without a male. Even if the eggs are not fertile, a female shark will continue producing them.
The aquarium staff noticed that some of Leonie’s eggs contained embryos, so they tried to incubate them, but none of the eggs hatched. However, next year, both Leonie and Lolly laid eggs that contained embryos. Five offspring emerged from these eggs and two of them, one of each mother, are still to be found at the aquarium.
It is not unusual for female leopard sharks to store sperm for up to four years, but the genetic analysis of the offspring showed that they were the result of asexual reproduction. Dudgeon also stated that the case of Lolly is not unusual. Asexual reproduction starting at the same time with sexual maturity has been found before in other sharks or in reptiles, but the switch from sexual to asexual reproduction is the novelty.
The biologists claimed this is a sort of inbreeding case. Genes are usually mixed in order to create offspring capable to survive and fight all the pathogens and environmental changes. An asexually-produced offspring has only half of the genetic material it needs.
Other cases of asexual reproduction have been reported in an eagle ray and a boa constrictor. The possible explanation for this behavior is that it might be a quick evolutionary response to preserve the species.
Image Source: Wikimedia Commons