Repeat shark parthenogenesis report adds to smooth-hound case

Researchers reporting in Animals describe another case of facultative parthenogenesis, or reproduction without fertilization, in the common smooth-hound shark (Mustelus mustelus) at Cala Gonone Aquarium in Sardinia. The new report builds on a 2024 Scientific Reports paper from the same group, which said two adult females housed without males for 13 years produced pups in multiple years, with DNA testing showing no paternal contribution and offspring genetics consistent with terminal fusion automixis. In the earlier study, births were documented in 2020, 2021, and 2023, with a presumed earlier event in 2016; the new Animals paper adds an April 2024 event involving two offspring from a single parthenogenetic episode. The species is considered threatened, and the authors argue the repeated pattern may reflect more than a one-off anomaly. (nature.com)

Why it matters: For veterinary professionals, especially those in aquariums, zoos, and aquatic animal medicine, the case is a reminder that unexpected pregnancies in long-term all-female groups may not be explained by sperm storage alone. Genetic workup matters, because confirming parthenogenesis requires excluding paternal alleles, and the reproductive outcome may still be poor: in the 2024 report, only one parthenogenetic offspring was alive three years later, while others died after birth or had deformities or traumatic injuries. The findings also add to a growing body of evidence that parthenogenesis in sharks may be more common in managed care than previously recognized, even if its fitness value remains uncertain. (nature.com)

What to watch: Watch for follow-up data on offspring survival, any additional 2025 or 2026 cases, and whether other institutions begin routine genetic testing of unexplained shark births. (nature.com)