Aquarium staff in Italy were recently surprised by the birth of a baby shark in a tank that’s home to just two females.
The smooth-hound shark (Mustelus mustelus) was born earlier this month at the Cala Gonone Aquarium in Sardinia, according to a post by the aquarium. The mother has lived in a large pelagic tank at the aquarium for over 10 years in the company of just one other female of the same species, raising some questions about the parental setup of the newborn.
Could this be the second coming of a smooth-hound messiah? Or perhaps the work of a mysterious lothario shark that snuck into the tank late one night? Not likely, say scientists at the aquarium. They suspect this “virgin birth" is the result of an unusual reproduction strategy known as parthenogenesis.
Parthenogenesis – a term derived from the Greek words for “virgin birth” – is a form of asexual reproduction where an egg can develop into an embryo without being fertilized by a sperm. Different species pull off this feat using a variety of different mechanisms, but one of the more common mechanisms in vertebrates involves the egg becoming fertilized by a polar body, a small cell that contains genetic material leftover from egg cell formation.
The resulting offspring only has genetic material from the mother. However, they are not genetically identical clones and feature roughly half the genetic diversity of their mother. This shaky genetic foundation means the offspring are often malformed or die early. Despite these shortcomings, parthenogenesis can be a useful last-ditch strategy for females to reproduce and pass on some genetic material if they fail to find a male during the mating season.
This form of reproduction is most often seen in plants and insects, but has been documented in a bunch of different animals before – including anacondas, komodo dragons, rays, sharks, and even birds. There are, however, no known naturally occurring cases in wild mammals.
The newborn was named Ispera, which means “hope” in Sardinian. The aquarium believes they may be the first case of parthenogenesis observed in this species. They hope to confirm this by carrying out DNA analysis of the newborn, which should reveal whether they are a true half-clone of the mother.
"It would therefore be a scientific discovery of considerable interest since it could pave the way for research aimed at verifying how parthenogenesis is a process that the [species] use even in nature," Cala Gonone Aquarium said in a Facebook post.