February 21, 2025

Inside the front section of Monday’s newspaper was a USA Today article on the birth of a baby swell shark (Cephaloscyllium ventriosum).  The swell shark pup hatched on January 3rd after an egg was spotted by the Shreveport aquarium’s animal husbandry team eight months ago.  The birth could be from rare form of asexual reproduction (parthenogenesis), or from delayed fertilization.  The two female sharks present in the tank had not been in contact with a male for more than three years.  A DNA analysis once the pup is big enough for a blood sample to be taken will determine how the birth occurred, but it will take months before the test can be performed.  “This situation is incredible and shows the resilience of this species,” said Greg Barrick, the curator of live animals at Shreveport aquarium. “We are very excited in the coming months to confirm whether this was indeed a case of parthenogenesis or if it was delayed fertilization.”

When I looked online, I found parthenogenesis (Greek parthénos, “virgin” and “génesis, “creation”) is a natural form of asexual reproduction in which the embryo develops directly from an egg without need for fertilization.  In animals, parthenogenesis means the development of an embryo from an unfertilized egg cell.  Parthenogenesis occurs naturally in some plants, algae, invertebrate animal species, and a few vertebrates (some fish, amphibians, and reptiles) and has been induced artificially in animal species that naturally reproduce through sex (fish, amphibians, and mice).  Normal egg cells form in the process of meiosis (division) and have half as many chromosomes as their mother’s body cells (haploid).  Such individuals are usually non-viable, and parthenogenetic offspring usually have a complete number of chromosomes (diploid).  In parthenogenesis, the offspring having all of the mother’s genetic material are called full clones and those having only half are called half clones.

The baby shark has been named Yoko, after the Native American Chumash people’s word for shark (onyoko) and is said to be thriving, although sharks born by such reproduction face significant challenges.  The aquarium staff said she will leave an “unforgettable legacy” to the study of shark reproduction and conservation.  If Yoko was born via parthenogenesis, she would join a small number of invertebrate animals capable of “virgin births”.  Laying eggs without mating is much rarer in vertebrates, but it has been seen in zebra sharks (Stegostoma tigrinum), sawfish (Pristis zijsron) and a handful of reptiles.  This type of birth was first documented in Komodo dragons (Varanus komodoensis) in 2006 in two separate British zoos.  Charlotte, a stingray (Hypanus americanus) in an aquarium in North Carolina, was found to be pregnant in 2024 despite not having been in contact with a male for eight years.  While scientists assume vertebrates turn to parthenogenesis when no mates are present, it is unknown why they occur and what triggers birth. 

THOUGHTS: Whether Yoko was born from delayed reproduction or parthenogenesis, she is an extraordinary birth. The aquarium staff said she will leave an “unforgettable legacy” to the study of shark reproduction and conservation.   While the behavior of domesticated animals has long been studied (ethology) attention has only focused on animals in the wild during the last century.  What we have found is they are far more complex and diversified than we previously believed.  The study has even forced us to reconsider what “makes us human”.  It seems we are not so different after all.  Act for all.  Change is coming and it starts with you.