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Scientists suggest several new species of orcas, including
in the Antarctic
By Peter Rejcek, Antarctic Sun Editor
New technology in gene sequencing confirmed what scientists
have long suspected about Orcinus orca: The large marine
mammal commonly referred to as a killer whale actually
represents several genetically distinct species, including
at least two new ones that swim in the Southern Ocean
around Antarctica.
Scientists analyzed tissue samples from more than 100
killer whales from the North Pacific, the North Atlantic
and the Southern Ocean. As a result of the study, published
last month in the journal Genome Research, the scientists
suggest there are two types of killer whales in the Antarctic
and a mammal-eating “transient” killer whale
in the North Pacific, in addition to the “standard”
black-and-white orca of SeaWorld fame.
Pitman said he was aware of previous scientific literature
by Soviet-era scientists in 1979 and 1980 that there were
killer whales in the Antarctic that appeared dissimilar
enough to be different species. He first traveled down
to McMurdo Station with help from the National Science
Foundation in 2001-02.
During the trip, he spotted three distinct types of killer
whales, and collected tissue samples from all three. Pitman
made two subsequent trips to McMurdo and several expeditions
to the Antarctic Peninsula for additional observations
and sampling.
“After we published papers about our observations,
and I collected a series of tissue samples, I was able
to interest a number of my co-authors [on the Genome Research
paper] into looking into species-level differences among
killer whales worldwide, including the very distinctive
Antarctic forms,” he wrote via e-mail while in the
field tagging killer whales off the coast of California.
The two additional types of killer whales in the Antarctic
are not only genetically different. One (Type C) dines
on fish while the second (Type B) prefers a diet of seals.
“Dietary specialization seems to spur speciation
in killer whales, even among populations with overlapping
distributions, because of the behavioral and ecological
divergences involved with taking different kinds of prey,”
Pitman explained.
For example, fish-eating orcas use echolocation almost
continuously to communicate among group members and to
locate their prey while those that prey on mammals rely
on silence and stealth because their prey has acute hearing
abilities.
“Our information on dietary specialization in Antarctica
comes mainly from observations, but elsewhere, in the
North Pacific for example, these differences in diet are
reflected in chemical signals in the skin and blubber
of the different ecotypes,” he said.
Differences in behavior, feeding preferences and physical
features among killer whales around the world made it
likely there were several species. However, DNA analysis
had been inconclusive because of scientists’ inability
to map the entire genetic picture, or genome, of the whales’
mitochondria, an organelle within the cell inherited from
the mother.
“The genetic makeup of mitochondria in killer whales,
like other cetaceans, changes very little over time, which
makes it difficult to detect any differentiation in recently
evolved species without looking at the entire genome,”
said Phillip Morin , lead author and geneticist at NOAA’s
Southwest Fisheries Science Center in a press release
from NOAA.
The researchers used a relatively new method called highly
parallel sequencing to map the entire genome of the cell’s
mitochondria from the worldwide sample of killer whales.
Highly parallel sequencing of DNA is far faster and less
costly than historical methods of analysis, according
to NOAA. For instance, the examination of mitochondrial
DNA genome in one sample can take several months. The
new technique allows researchers to analyze 50 or more
samples in just a few weeks.
While the paper suggests three new species, the authors
say more species may emerge upon further analysis. Pitman
said there may be at least a half dozen new species, including
a fourth killer whale (Type D) in the Southern Ocean that
he believes will prove to be a different species.
The authors of the study also say that determining how
many species of killer whales there are is “critically
important for resource managers to establish conservation
priorities and to better understand the ecological role
of this large and widespread predator in the world’s
oceans.”
For instance, Pitman noted that Type C killer whales
that feed on fish in the Ross Sea may be under stress
from commercial toothfish longlining operations. “This
need for data to make management decisions should make
it likely that someone should be looking at how the fishery
may be impacting this species,” he said.
The NOAA biologist also said that the killer whale study
highlights how far science still has to go in understanding
the vast array of life on the planet and its oceans.
“The killer whale is arguably the most universally
recognizable animal that swims in the ocean,” he
said. “It has been studied intensively for decades,
and we still don’t even know how many species there
are out there. I think it is a clear indication about
how little we know about what swims in our oceans.”
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Antarctic
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