The first case of “virgin birth“, a form of reproduction without the need for male fertilisation of egg in a vulnerable shark species was reported in Italy.
Italian researchers findings published in Scientific reports this week, shows the first recorded occurrence of this biological process in the common the smooth-hound shark, scientifically known as Mustelus mustelus, a species at risk due to unlawful fishing practices, found in the Mediterranean and other temperate waters.
According to the research team from the Experimental Zooprophylactic Institute of Piedmont, Liguria and the Aosta Valley, two 18-year-old female M. mustelus sharks under observation in captivity have displayed parthenogenesis each year since 2020, in this reproductive mechanism, females can reproduce without the need for male egg.
“Remarkably, 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 authors said.
What is parthenogenesis
Cycling parthenogenesis, a form of reproduction where offspring can be produced from either fertilized or unfertilized eggs, is a phenomenon that occurs in more than 15,000 species. Despite its prevalence, its not yet fully comprehended.
While parthenogenesis is more frequently observed in invertebrates, it has not been documented in mammals to date. However, certain reptiles, sharks, rays, and skates are able to “modify their adaptive strategy according to the surrounding circumstances”, the authors wrote.
“Although the mechanisms driving parthenogenesis remain unclear, it is suggested that male population reduction could be a pivotal factor,” they added.
Where are they found
Researchers conducted a 13-year study on these two 18-year-old female sharks housed in the Cala Gonone Aquarium in Sardinia since 2010, in an effort to better understand the reproductive capabilities of M. mustelus.
Studying sharks in their natural habitats presents difficulties in comprehending the occurrence, but captive environments provide optimal settings for extended observation, as highlighted by the researchers. Over the past twenty years, aquariums located in the United States, United Arab Emirates, and Australia have recorded this phenomenon in various shark species.
According to the study, the M. mustelus, is facing a dire future, as this medium-sized species, which inhabits shallow waters and has a potential lifespan of up to 25 years and is now classified as endangered, with estimates showing that the population of these sharks could decrease by up to 50% over the next few decades.
Production of young ones in absence of males
Despite the absence of male sharks in their environment, the females continued to produce offspring on a nearly annual basis. “Nonetheless, a nearly annual production of young was observed in the absence of males,” the authors wrote.
This finding sheds new light on the reproductive strategies employed by these endangered sharks and raises questions about the factors contributing to their population decline.
The researchers mentioned that among the sharks conceived through parthenogenesis at the aquarium, only a single individual continues to thrive. “The two adults ‘are in good health’,” the authors stated, adding that these sharks share their large exhibition tank with other Mediterranean marine species.
(With inputs from agencies)
Italian researchers findings published in Scientific reports this week, shows the first recorded occurrence of this biological process in the common the smooth-hound shark, scientifically known as Mustelus mustelus, a species at risk due to unlawful fishing practices, found in the Mediterranean and other temperate waters.
According to the research team from the Experimental Zooprophylactic Institute of Piedmont, Liguria and the Aosta Valley, two 18-year-old female M. mustelus sharks under observation in captivity have displayed parthenogenesis each year since 2020, in this reproductive mechanism, females can reproduce without the need for male egg.
“Remarkably, 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 authors said.
What is parthenogenesis
Cycling parthenogenesis, a form of reproduction where offspring can be produced from either fertilized or unfertilized eggs, is a phenomenon that occurs in more than 15,000 species. Despite its prevalence, its not yet fully comprehended.
While parthenogenesis is more frequently observed in invertebrates, it has not been documented in mammals to date. However, certain reptiles, sharks, rays, and skates are able to “modify their adaptive strategy according to the surrounding circumstances”, the authors wrote.
“Although the mechanisms driving parthenogenesis remain unclear, it is suggested that male population reduction could be a pivotal factor,” they added.
Where are they found
Researchers conducted a 13-year study on these two 18-year-old female sharks housed in the Cala Gonone Aquarium in Sardinia since 2010, in an effort to better understand the reproductive capabilities of M. mustelus.
Studying sharks in their natural habitats presents difficulties in comprehending the occurrence, but captive environments provide optimal settings for extended observation, as highlighted by the researchers. Over the past twenty years, aquariums located in the United States, United Arab Emirates, and Australia have recorded this phenomenon in various shark species.
According to the study, the M. mustelus, is facing a dire future, as this medium-sized species, which inhabits shallow waters and has a potential lifespan of up to 25 years and is now classified as endangered, with estimates showing that the population of these sharks could decrease by up to 50% over the next few decades.
Production of young ones in absence of males
Despite the absence of male sharks in their environment, the females continued to produce offspring on a nearly annual basis. “Nonetheless, a nearly annual production of young was observed in the absence of males,” the authors wrote.
This finding sheds new light on the reproductive strategies employed by these endangered sharks and raises questions about the factors contributing to their population decline.
The researchers mentioned that among the sharks conceived through parthenogenesis at the aquarium, only a single individual continues to thrive. “The two adults ‘are in good health’,” the authors stated, adding that these sharks share their large exhibition tank with other Mediterranean marine species.
(With inputs from agencies)
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