Italian researchers have reported the first birth by parthenogenesis, that is, without fertilization, of a baby shark of an endangered species, the Mustelus mustelus, also called the common greyhound shark.
“This study reports the first case of facultative parthenogenesis” in this shark classified by the International Union for Conservation of Nature (IUCN) as endangered, the researchers write in their study published this week in the online journal Scientific Reports.
Researchers from several specialized institutes in Piedmont, Liguria and Valle d’Aosta have observed parthenogenesis every year since 2020 in two female greyhound sharks, aged 18 and living since 2010 in a huge aquarium in Sardinia.
“It is remarkable that this finding reveals that parthenogenesis can occur annually in these sharks, alternating between two females, and conclusively excludes long-term sperm storage as a cause,” the researchers note.
An almost annual production of young was thus observed in the absence of males.
Three births occurred in 2020, 2021 and 2023, but only one specimen, the one born in 2021, is still alive today.
Population in decline
The greyhound shark, also called the dogfish or smooth shark, with an average size of 1.50 to 2 m, is mainly threatened by illegal fishing in the Mediterranean and other warm seas. According to estimates cited by the researchers, the population of this species of the fish family “could decrease by up to 50% in the coming decades”.
Parthenogenesis, more common in invertebrates than in vertebrates, has not yet been observed in mammals.
Some reptiles and sharks or rays “can modify their adaptive strategy” of reproduction “according to the surrounding circumstances”, underlines the report.
“Although the mechanisms underlying parthenogenesis remain unclear, it is suggested that the reduction of the male population could be a determining factor,” the researchers estimate.
They also note the difficulty of understanding parthenogenesis in free-ranging sharks, stressing that long-term study of those in captivity is the ideal solution.
Aquariums in the United States, the United Arab Emirates and Australia have documented the phenomenon in other shark species over the past two decades.