Woolly mammoths evolved smaller ears and woolier coats over the 700,000
years that they roamed the Siberian steppes

Date:
April 7, 2023
Source:
Cell Press
Summary:
A team of researchers compared the genomes of woolly mammoths
with modern day elephants to find out what made woolly mammoths
unique, both as individuals and as a species. The investigators
report that many of the woolly mammoth's trademark features --
including their woolly coats and large fat deposits -- were already
genetically encoded in the earliest woolly mammoths, but these and
other traits became more defined over the species' 700,000+ year
existence. They also identified a gene with several mutations that
may have been responsible for the woolly mammoth's miniscule ears.


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FULL STORY ==========================================================================
A team of researchers compared the genomes of woolly mammoths with modern
day elephants to find out what made woolly mammoths unique, both as
individuals and as a species. The investigators report April 7 in the
journal Current Biology that many of the woolly mammoth's trademark
features -- including their woolly coats and large fat deposits --
were already genetically encoded in the earliest woolly mammoths, but
these and other traits became more defined over the species' 700,000+
year existence. They also identified a gene with several mutations that
may have been responsible for the woolly mammoth's miniscule ears.


==========================================================================
"We wanted to know what makes a mammoth a woolly mammoth," says
paleogeneticist and first author David Di'ez-del-Molino of the Centre
for Palaeogenetics in Stockholm. "Woolly mammoths have some very
characteristic morphological features, like their thick fur and small
ears, that you obviously expect based on what frozen specimens look
like, but there are also many other adaptations like fat metabolism and
cold perception that are not so evident because they're at the molecular level." To identify genes that were "highly evolved" in woolly mammoths
-- meaning they had accrued a large number of mutations -- the team
compared the genomes of 23 Siberian woolly mammoth with 28 modern-day
Asian and African elephant genomes.

Twenty-two of these woolly mammoths were relatively modern, having
lived within the past 100,000 years, and sixteen of the genomes had
not been previously sequenced. The twenty-third woolly mammoth genome
belonged to one of the oldest known woolly mammoths, Chukochya, who
lived approximately 700,000 years ago.

"Having the Chukochya genome allowed us to identify a number of genes
that evolved during the lifespan of the woolly mammoth as a species,"
says senior author Love Dale'n, professor of evolutionary genomics at
the Centre for Palaeogenetics in Stockholm. "This allows us to study
evolution in real time, and we can say these specific mutations are
unique to woolly mammoths, and they didn't exist in its ancestors."
Not surprisingly, many genes that were adaptive for woolly mammoths are
related to living in cold environments. Some of these genes are shared
by unrelated modern-day Arctic mammals. "We found some highly evolved
genes related to fat metabolism and storage that are also found in
other Arctic species like reindeer and polar bears, which means there's probably convergent evolution for these genes in cold-adapted mammals,"
says Di'ez-del-Molino.

While previous studies have looked at the genomes of one or two woolly mammoths, this is the first comparison of a large number of mammoth
genomes.

This large sample size enabled the team to identify genes that were
common among all woolly mammoths, and therefore likely adaptive, as
opposed to genetic mutations that might only have been present in a
single individual.

"We found that some of the genes that were previously thought to be
special for woolly mammoths are actually variable between mammoths,
which means they probably weren't as important," says Di'ez-del-Molino.

Overall, the 700,000-year-old Chukochya genome shared approximately 91.7%
of the mutations that caused protein-coding changes in the more modern
woolly mammoths. This means that many of the woolly mammoth's defining
traits - - including thick fur, fat metabolism, and cold-perception
abilities -- were probably already present when the woolly mammoth first diverged from its ancestor, the steppe mammoth.

However, these traits developed further in Chukochya's descendants. "The
very earliest woolly mammoths weren't fully evolved," says Dale'n "They possibly had larger ears, and their wool was different -- perhaps less insulating and fluffy compared to later woolly mammoths." More modern
woolly mammoths also had several immune mutations in T cell antigens
that were not seen in their ancestor. The authors speculate that these mutations may have conferred enhanced cell-mediated immunity in response
to emerging viral pathogens.

Working with ancient mammoth DNA comes with a slew of hurdles. "Every
step of the way, things are a bit more difficult, from fieldwork, to
lab work, to bioinformatics," says Di'ez-del-Molino.

"Apart from the field work, where we have to battle both polar bears and mosquitos, another aspect that makes this much more difficult is that
you have to work in an ancient DNA laboratory, and that means that you
have to dress up in this full-body suit with a hood and face mask and
visor and double gloves, so doing the lab work is rather uncomfortable
to put it mildly," says Dale'n.

"I would like to highlight Marianne Dehasque, the second author of this
paper, who did the herculean effort of performing lab work on most of
these samples." All the mammoths whose genomes were included in this
study were collected in Siberia, but the researchers hope to branch out
and compare North American woolly mammoths in the future. "We showed a
couple of years ago that there was gene flow between woolly mammoths
and the ancestors of Colombian mammoths, so that's something that we
will need to account for because North American woolly mammoths might
have been carrying non-woolly mammoth genes as well," says Dale'n.

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========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. David Di'ez-del-Molino, Marianne Dehasque, J. Camilo Chaco'n-Duque,
Patri'cia Pečnerova', Alexei Tikhonov, Albert Protopopov,
Valeri Plotnikov, Foteini Kanellidou, Pavel Nikolskiy, Peter
Mortensen, Gleb K.

Danilov, Sergey Vartanyan, M. Thomas P. Gilbert, Adrian M. Lister,
Peter D. Heintzman, Tom van der Valk, Love Dale'n. Genomics of
adaptive evolution in the woolly mammoth. Current Biology, 2023;
DOI: 10.1016/ j.cub.2023.03.084 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/04/230407110720.htm

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