On August 23, Brookfield Zoo in Illinois unexpectedly welcomed a new baby epaulette shark (Hemiscyllium ocellatum). This species is already an intriguing one because it is one of the nine members of a group called "walking sharks." What made this birth unusual was the fact that the pup's mother had never mated with a male.
Rare Virgin Birth
The mother shark arrived at the facility in 2019, and it has never shared a tank with a male. This means that the newborn shark was developed through asexual reproduction.
The embryo developed in parthenogenesis, which allowed it to grow without male genetic material. Epaulette sharks typically reach sexual maturity when they are around seven years old, but the mother shark was only three years old when this happened.
According to zoo staff, the female shark began laying eggs every month since last year. Most of her eggs were infertile, except one. After five months of incubation, this egg surprisingly hatched and is now two months old. It currently measures approximately five to six inches (12.7 - 15.24 cm) long, and it can grow to be as long as three feet (91 cm).
Specialists are now monitoring the newborn shark to make sure that it develops properly and remains healthy. They feed it with minced squid tentacles, finely chopped capelin, and other seafood.
This case is believed to be the second time an epaulette shark was produced parthenogenetically in a U.S. zoo. The other known instance of the same species born this way came from the New England Aquarium, where the female sharks at Brookfield Zoo also came from.
According to Brookfield Zoo lead animal care specialist Mike Masellis, their colleagues at New England Aquarium have been a great resource as baby sharks produced asexually can be very delicate.
The same case was also reported in an aquarium in Italy, where a baby shark was born asexually back in 2021. In Acquario Cala Gonone in Sardinia, a smoothhound shark pup was born in a tank where only females are kept.
Parthenogenesis in Sharks
Parthenogenesis results from the ability of females to self-fertilize their eggs in extreme scenarios. This ability has been observed in over 80 vertebrate species and is well-documented in insects, birds, fish, and reptiles. It was until fairly recently that this ability was confirmed in sharks.
The specific type of asexual reproduction observed in sharks is called automictic parthenogenesis. Instead of combining an egg with sperm, this mode of reproduction uses a polar body, which is a byproduct of germ cells that undergo meiosis to produce eggs. Polar bodies contain chromosomes that are usually absorbed into the female body.
When a shark undergoes parthenogenesis, one of the polar bodies that should have been absorbed under normal sexual reproduction conditions does not get reabsorbed. Instead, they act like sperm and fuse with the cell that will become an egg. This results in a fertilized egg containing a normal set of chromosomes, but does not have all the genetic diversity observed in sexual reproduction.
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