A first of its kind: a female zebra shark might have become the first shark ever to give birth to babies without mating or s*x.
Leonie could be the first shark ever observed to make the switch from sexual to asexual reproduction.
Sure, she used to have a mate at the Reef HQ Aquarium in Townsville,
Australia. The pair even had several litters before they were separated
in 2012.
But Leonie had been living apart from males for the past few years, so
her keepers were surprised when she laid eggs that produced three baby
sharks in April 2016. Leonie could be the first shark ever observed to
make the switch from sexual to asexual reproduction.
"We thought she could be storing sperm; but when we tested the pups
and the possible parent sharks using DNA fingerprinting, we found they
only had cells from Leonie," said University of Queensland
biologist Christine Dudgeon, who described the case in the journal
Scientific Reports Monday (Jan. 16).
Parthenogenesis occurs when embryos develop and mature without
fertilization by a male's sperm. Rather, an egg progenitor cell that
usually gets absorbed by the female's body acts as a surrogate sperm to
"fertilize" her egg. This reproduction strategy is more common in plants
and invertebrate organisms. However, scientists have been documenting
an increasing number of vertebrate species that can have virgin births
even when their species normally reproduces sexually. For example,
Komodo dragons, the world's largest lizards, have given birth by
parthenogenesis. So have wild pit vipers, blacktip sharks, chickens and
turkeys.
In most of these previous parthenogenesis cases, the females were from
captive environments and never had any exposure to male mates during
their reproductive prime, Dudgeon and her colleagues wrote. That makes
Leonie one of the rare individuals known to have had babies by sexual
reproduction only to switch to asexual reproduction later on.
The little babies given birth to by the shark
"Leonie adapted to her circumstances, and we believe she switched because she lost her mate," Dudgeon said in a statement. "What
we want to know now is, 'Could this occur in the wild?' and, if so,
'How often does it?' One reason why we haven't seen it before could be
because we haven't been looking for it. It might be happening in the
wild, but it's never been recorded in this species before."
If parthenogenesis is indeed an evolutionary adaptation to a lack of
suitable mates, that could have implications for the survival of zebra
sharks. The species, which is found in the western Pacific and Indian
oceans, is listed as endangered on the International Union for
Conservation of Nature's (IUCN) Red List of Threatened Species.
Dudgeon plans to monitor Leonie's pups to find out if these asexually
produced sharks can have pups of their own with a male partner.
"You lose genetic diversity with generations of asexual
reproduction, so we'll be seeing if these offspring can mate sexually
themselves," Dudgeon said.
Posted by 9ija daily news, Published at Thursday, January 19, 2017 and have
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