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These tiny crustaceans, known as cyamids and nicknamed
'whale lice,' are members of the species Cyamus ovalis.
Cyamids, which range from one-fifths to three-fifths of
an inch in length, depending on the species, live as parasites
on whales. University of Utah biologists studied genes
from various species of whale lice to learn about the
evolution of different species of right whales, some of
which are endangered.
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download high-resolution click here:
Credit: Vicky Rowntree, University of Utah.
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An aerial photograph of two right whales in the Atlantic
Ocean offshore from Argentina shows the distinctive white
markings created by small crustaceans -- known as cyamids
or 'whale lice' -- that attach themselves to callus-like
material on the whales' heads. University of Utah researchers
learned about the evolution of different species of right
whales by studying the genes of the 'whale lice' that ride
the whales.
To
download high-resolution click here:
Credit: Roger Payne, Ocean Alliance/Whale Conservation Institute.
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Callosities, or dark callus-like material, are easily visible
on the head of this right whale because they are covered
by white-colored parasitic crustaceans named cyamids and
nicknamed 'whale lice.'
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download high-resolution click here:
Credit: Mariano Sironi, Institute of Whale Conservation,
Buenos Aires.
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This close-up photograph shows hundreds of tiny, light-colored
cyamids, or 'whale lice,' clinging to dark-colored callus-like
material on the head of a right whale. University of Utah
biologists learned when separate species of right whales
evolved by analyzing genetic material from the whale lice.
To
download high-resolution click here:
Credit: Iain Kerr, Ocean Alliance/Whale Conservation Institute.
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An extreme closeup photograph of a cyamid, or 'whale louse,'
in the process of giving birth to more of the tiny crustaceans,
which live as parasites on whales.
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download high-resolution click here:
Credit: Jon Seger, University of Utah.
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University of Utah biologists Vicky Rowntree, Jon Seger,
Wendy Smith and Zofia "Ada" Kaliszewska studied
the genetics of parasites nicknamed "whale lice"
to learn more about the evolution of endangered right whales,
upon which the parasites ride.
To
download high-resolution click here:
Credit: University of Utah.
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A dead southern right whale is stranded on the beach at
Puerto Madryn, Argentina, after it suffered a fatal blow
when a ship propeller hit the animal behind its blowholes.
The white coloring of the distinctive markings on the animal's
head comes from dense colonies of small parasites known
as cyamids or 'whale lice.' Strandings such as this provide
scientists with their main source of whale lice, which are
studied to provide clues to the evolution of the whales
they ride.
To
download high-resolution click here:
Credit: Romina Pozzi.
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Luciano Valenzuela, a University of Utah graduate student
in biology, watches from his boat as a curious right whale
slowly surfaces in Golfo San Jose, Argentina.
To
download high-resolution click here:
Credit: Mariano Sironi, Institute of Whale Conservation,
Buenos Aires.
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An adult right whale and a calf swim off the coast of Argentina
in this photograph taken from a small plane. The whales
have callus-like material known as callosities on their
heads. The callosities are colored white because tiny parasites
named cyamids or 'whale lice' are attached to the callus-like
material, giving each whale a set of distinctive markings
that allow them to be identified by researchers.
To
download high-resolution click here:
Credit: Roger Payne, Ocean Alliance/Whale Conservation Institute.
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Sept. 14, 2005 – University of Utah biologists studied
the genetics of “whale lice” – small crustaceans
that are parasites on endangered “right whales” –
and showed the giant whales split into three species 5 million
to 6 million years ago, and that all three species probably were
equally abundant before whaling reduced their numbers.
The five-year study, published in the October 2005 issue of the
journal Molecular Ecology, is the first in which the
genes of whale lice were used to track the genetic evolution of
whales. They are not true lice, but instead are tiny crustaceans
-named cyamids. The harmless parasites ride the whales their entire
lives, so their evolution reflects the evolution of the whales.
“These are the original whale riders,” says Jon Seger,
a University of Utah biology professor and the study’s principal
author. “It’s a case of the whale riders telling us
what the whales did.”
[“Whale Rider” was a 2002 Oscar-nominated film about
the legend of an ancient Maori chief who crossed the sea on the
backs of whales, and a modern Maori girl in New Zealand who aspired
to become the new chief.]
“Whale researchers have dreamed for years of being able
to ride with the whales and see the world they experience,”
says study co-author Vicky Rowntree, a University of Utah research
professor of biology and senior scientist at the Ocean Alliance/Whale
Conservation Institute in Lincoln, Mass. “Whale lice have
been doing it for millions of years, and can tell us things about
the whales we can’t learn any other way.”
By studying certain genes in the whale lice, the researchers showed:
- A single right whale species diverged into three species
– North Atlantic, North Pacific and southern ocean right
whales – 5 million to 6 million years ago when movements
of Earth’s tectonic plates formed the Isthmus of Panama,
separating the Pacific and Atlantic. That set up warm equatorial
currents that kept most blubber-laden right whales from crossing
the equator because they could not tolerate the warm waters.
- One southern right whale crossed the equator 1 million to
2 million years ago, leaving evidence of the trip when its whale
lice bred with those on North Pacific right whales.
- The highly endangered North Atlantic and North Pacific right
whales once may have been as abundant as southern right whales,
suggesting their reduced genetic diversity is due to whaling
in recent centuries, not some longer-term, deadlier cause. That
raises hope for the ultimate recovery of the North Atlantic
and North Pacific species.
Seger and Rowntree, who are spouses, conducted the study with
Zofia “Ada” Kaliszewska, who graduated the University
of Utah and now is a Harvard University graduate student; Wendy
Smith, a Utah biology graduate student; and 14 co-authors who
collected whale lice or whale genetic material from beached whales
around the world.
How Whale-Riding ‘Lice’ Tell Tales about
Whales
Cyamids were nicknamed “whale lice” by early whalers,
who often were infested with real head and body lice. Whale lice
are related to crabs and shrimp, and cling to the whales’
raised, callus-like patches of skin – named callosities
– the grooves and pits between callosities, and also to
skin in slits that cover mammary glands and genitals. The white
whale lice covering the callosities create distinct markings that
stand out against the whales’ dark skin, making it possible
for scientists to distinguish individual whales.
“Their lifestyle is analogous to that of lice in that they
live on the skin of the host and they eat sloughed skin,”
Seger says. Each whale louse looks vaguely like a miniature crab,
ranges from one-fifth to three-fifths of an inch in length, and
has five pairs of sharp, hooked claws. About 7,500 whale lice
live on a single whale.
Whale lice infest only whales, just as bird lice infest only birds
and human lice infest only people. Recent genetic studies of head
and body lice have revealed details of human evolution. Whale
lice hang onto the whales throughout their lives, so they share
a common ecological and evolutionary history with the whales.
Genes from whale lice actually may reveal more about the whales
than the whales’ own genes do, because the parasites are
much more abundant and reproduce more often than whales. As a
result, the parasites have much greater genetic diversity and
scientists have more mutations to track.
The Utah research focused on genes found in mitochondria –
the power plants of cells – and that mutate at a high rate,
acting like a clock to reveal when evolutionary events happened.
The scientists calibrated the clock by comparing genes from whale
lice with related snapping shrimp.
The Utah biologists extracted DNA from whale lice, determined
the sequence of the genetic components in a particular mitochondrial
gene, and then built family trees to show the relationships among
whale lice.
The same three whale louse species – Cyamus ovalis,
Cyamus gracilis and Cyamus erraticus –
were thought to infest each of the three different species of
right whales. But the new study revealed that like the whales,
each whale louse species also split into three species, so North
Pacific, North Atlantic and southern ocean species of right whales
each are infested by three distinct species of cyamid. That tripled
– from three to nine – the number of cyamid species
infesting right whales.
The Right Whale – for Extinction?
Right whales – which can reach 60 feet and 70 tons –
were named because “they were the ‘right’ whale
to kill, the first whale to be commercially hunted” 1,000
years ago off Spain; their blubber made their carcasses float
for easy recovery, Rowntree says.
Two of the three species of right whales are in danger of extinction.
A recent study estimated only 350 remain in the North Atlantic.
Rowntree says about 200 survive in the North Pacific, while the
Southern Hemisphere population of 8,000 to 10,000 whales is growing
7 percent per year and recovering from whaling.
When whaling began in the Southern Hemisphere in the 1700s, there
were an estimated 40,000 to 150,000 right whales there, Rowntree
says.
North Atlantic right whales have lower genetic diversity than
southern ocean right whales. But the new study showed “the
genetic diversity of whale lice is virtually as great for the
North Atlantic right whale as for the southern right whale, suggesting
that historically (but before whaling) the North Atlantic right
whale population was comparable in size to that in the Southern
Hemisphere,” Seger says. “This suggests that the reduced
genetic diversity of North Atlantic right whales happened recently,
possibly due to whaling, not because the whale population was
small even before whaling.”
Whale louse populations correlate with population sizes of right
whales, so if North Atlantic right whales had small populations
before whaling, the diversity of their whale lice would not be
as great as those on the southern right whales.
Limited data from North Pacific whale lice suggest right whales
also were abundant there before whaling began, in line with early
whaling records, Rowntree says.
Small population size can be harmful because it is impossible
to avoid inbreeding and an increased risk of genetic disease.
The study raises hope for endangered Northern Hemisphere right
whales by suggesting that their reduced genetic diversity is a
relatively recent phenomenon and perhaps not as severe overall
as it appears to be in the particular genes that were studied,
Seger says.
One Whale Species Became Three as Oceans Separated
Some 20 million years ago, North and South America were separated
by deep seas, but 18 million years ago, undersea volcanism slowly
began forming a volcanic island chain. By 3 million years ago,
the chain formed solid land, the Isthmus of Panama, linking the
two continents. By 5 million or 6 million years ago, the sea between
the two continents was so shallow that whales could not swim between
the North Pacific and North Atlantic, Rowntree says. Changing
circulation patterns established warm currents that discouraged
right whales from moving between southern and northern oceans.
“Right whales have such thick blubber they can’t cross
the equator,” Rowntree says. “The waters are too warm.
They can’t shed heat.”
Seger says: “The genetics of whale lice show conclusively
that the three species of right whales have been isolated in the
North Pacific, North Atlantic and Southern Hemisphere for about
5 million to 6 million years,” with a possible range of
error from 3.6 million to 9.9 million years.
That is consistent with previous studies of the right whales’
genes. One limited study suggested North Atlantic right whales
(Eubalaena glacialis) and southern (Eubalaena australis)
right whales became distinct species 3 million to 12 million years
ago. A more complete study suggested North Pacific right whales
(Eubalaena japonica) diverged from southern right whales
4.4 million years ago, give or take 2.5 million years.
The new study revealed a fascinating detail. About 1 million to
2 million years ago, at least one southern right whale –
and no more than a few – managed to cross the equator and
join other right whales in the North Pacific. The biologists reached
that conclusion because they found that Cyamus ovalis
whale lice in the North Pacific are much more closely related
genetically to southern Cyamus ovalis than either population
is to those in the North Atlantic. Another species, Cyamus
erraticus, does not show such a pattern; those whale lice
in all three oceans are all more distantly related.
The simplest explanation is that a single southern right whale
crossed the equator and mingled with North Pacific right whales.
Some of the abundant Cyamus ovalis whale lice jumped
from the southern whale to northern whales, but the less common
Cyamus erraticus, which lives mainly in genital areas,
did not.
Despite the barrier posed by warm water, climate has changed over
the ages and “probably there were times when the equatorial
waters weren’t as hot as they usually are, and some adventurous
juvenile male crossed the equator,” Rowntree says.
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