Parthenogenesis, or “virgin birth” , has been described in all vertebrate taxa except mammals. Some vertebrate species adopt obligate parthenogenesis due to the absence of males in the population (e.g., the desert lizard Cnemidophorus uniparens ). However, in species that normally reproduce sexually, ticopartenogenesis occurs exceptionally. Most vertebrates, such as varanids, elasmobranchs, and some snakes, implement facultative parthenogenesis, changing their adaptive strategy according to circumstances. However, the triggers for parthenogenesis are still unclear, but the lack of male specimens is thought to play an important role.
Parthenogenesis in elasmobranchs has been described in captive animals, given the difficulty of documenting it in wild . Specifically, cases of parthenogenesis have been documented for viviparous species such as the Bonnethead Sphyrna tiburo (2001), the Blacktip shark Carcharhinus limbatus (2007) , and the Whitetip reef shark Triaenodon obesus (2012) . This reproductive phenomenon has also been observed in oviparous species. Between 2002 and 2005, it was documented for the Whitespotted bamboo shark Chiloscyllium plagiosum . Subsequently, for the Zebra shark Stegostoma tigrinum (2008; 2017) , and i n 2014, multiple parthenogenesis was documented for the Swellshark Cephaloscyllium ventriosum.
In this study, the c ommon Smooth−hound were reared for 13 years in a public aquarium (Cala Gonone Aquarium; Sardinia, Italy) in absence of conspecific males. However, a quite annual young production was precisely observed in absence of males. The storage of sperm in the female reproductive tract has been documented in several species of female elasmobranchs, from weeks up to 45 months. Using 13 species−specific microsatellite loci, the alternate hypothesis was tested here that the offspring were the result of long−term sperm storage or parthenogenesis. Moreover, each offspring was reconducted to its proper mother.