World's first hybrid sharks in Australian waters
by Amy Coopes
Scientists said that they had discovered the world's first hybrid
sharks in Australian waters, a potential sign the predators were
adapting to cope with climate change.
The mating of the local Australian black-tip shark with its global
counterpart, the common black-tip, was an unprecedented discovery with
implications for the entire shark world, said lead researcher Jess
Morgan.
"It's very surprising because no one's ever seen shark hybrids
before, this is not a common occurrence by any stretch of the
imagination," Morgan, from the University of Queensland, told AFP. "This
is evolution in action."
Colin Simpfendorfer, a partner in Morgan's research from James Cook
University, said initial studies suggested the hybrid species was
relatively robust, with a number of generations discovered across 57
specimens.
The find was made during cataloguing work off Australia's east coast
when Morgan said genetic testing showed certain sharks to be one species
when physically they looked to be another.
The Australian black-tip is slightly smaller than its common cousin
and can only live in tropical waters, but its hybrid offspring have been
found 2,000 kilometres down the coast, in cooler seas.
It means the Australian black-tip could be adapting to ensure its
survival as sea temperatures change because of global warming. "If it
hybridises with the common species it can effectively shift its range
further south into cooler waters, so the effect of this hybridising is a
range expansion," Morgan said. "It's enabled a species restricted to the
tropics to move into temperate waters."
Climate change and human fishing are some of the potential triggers
being investigated by the team, with further genetic mapping also
planned to examine whether it was an ancient process just discovered or
a more recent phenomenon.
If the hybrid was found to be stronger than its parent species - a
literal survival of the fittest - Simpfendorfer said it may eventually
outlast its so-called pure-bred predecessors.
"We don't know whether that's the case here, but certainly we know
that they are viable, they reproduce and that there are multiple
generations of hybrids now that we can see from the genetic roadmap that
we've generated from these animals," he said. "Certainly it appears that
they are fairly fit individuals."
The hybrids were extraordinarily abundant, accounting for up to 20
percent of black-tip populations in some areas, but Morgan said that
didn't appear to be at the expense of their single-breed parents, adding
to the mystery. Simpfendorfer said the study, in Conservation Genetics,
could challenge traditional ideas of how sharks had and were continuing
to evolve.
"We thought we understood how species of sharks have separated, but
what this is telling us is that in reality we probably don't fully
understand the mechanisms that keep species of shark separate," he said.
"And in fact, this may be happening in more species than these two."
AFP
|