Geneticists map the rhinoceros family tree

Date:
August 24, 2021
Source:
Cell Press
Summary:
There's been an age-old question going back to Darwin's time
about the relationships among the world's five living rhinoceros
species. One reason answers have been hard to come by is that most
rhinos went extinct before the Pleistocene. Now, researchers have
helped to fill the gaps in the rhino evolutionary family tree by
analyzing genomes of all five living species together with the
genomes of three ancient and extinct species.



FULL STORY ========================================================================== There's been an age-old question going back to Darwin's time about the relationships among the world's five living rhinoceros species. One reason answers have been hard to come by is that most rhinos went extinct before
the Pleistocene. Now, researchers reporting in the journal Cellon August
24 have helped to fill the gaps in the rhino evolutionary family tree by analyzing genomes of all five living species together with the genomes
of three ancient and extinct species.


==========================================================================
The findings show that the oldest split separated African and Eurasian
lineages about 16 million year ago. They also find that -- while
dwindling populations of rhinos today have lower genetic diversity
and more inbreeding than they did in the past -- rhinoceroses have
historically had low levels of genetic diversity.

"We can now show that the main branch in the rhinoceroses' tree of life
is among geographic regions, Africa versus Eurasia, and not between the
rhinos that have one versus two horns," says Love Dale'n (@love_dalen)
of the Centre for Palaeogenetics and the Swedish Museum of Natural
History. "The second important finding is that all rhinoceroses, even the extinct ones, have comparatively low genetic diversity. To some extent,
this means that the low genetic diversity we see in present-day rhinos,
which are all endangered, is partly a consequence of their biology.

"All eight species generally displayed either a continual but slow
decrease in population size over the last 2 million years, or continuously small population sizes over extended time periods," said Mick Westbury (@Mick2474) of the University of Copenhagen, Denmark. "Continuously
low population sizes may indicate that rhinoceroses in general are
adapted to low levels of diversity." This notion is consistent with an apparent lack of accumulated deleterious mutations in rhinos in recent
decades. Westbury says that rhinos may have purged deleterious mutations
in the last 100 years, allowing them to remain relatively healthy,
despite low genetic diversity.

The new study was inspired at a scientific meeting. Dale'n and Tom
Gilbert, University of Copenhagen, had been working separately on
different rhino species. They realized that if they joined forces,
along with colleagues around the world, they could do a comparative
study of all living rhinos together with the three species that went
extinct during the last Ice Age.



========================================================================== There were some challenges to overcome, says Shanlin Liu, China
Agricultural University, Beijing. "When we decided to put together
all the rhinoceroses' data and conduct a comparative genomics study,
we also confronted the 'big data' problem," Liu explained.

The genome data represented different data types, in part due to the
inclusion of both modern and ancient DNA. The team had to develop
new analysis tools to take those differences into account. The new
approaches and tools they developed can now be applied to studies in
other taxonomic groups.

Dale'n says that the findings are "partly good news, and partly not." It appears that low levels of genetic diversity in rhinos is part of their
long- term history and hasn't led to an increase in health problems
related to inbreeding and disease-causing mutations.

"However, we also find that present-day rhinos have lower genetic
diversity, and higher levels of inbreeding, compared to our historical
and prehistoric rhinoceros genomes," he says. "This suggests that recent population declines caused by hunting and habitat destruction have had
an impact on the genomes.

This is not good, since low genetic diversity and high inbreeding
may increase the risk of extinction in the present-day species."
The findings do have some practical implications for rhino conservation,
the re-searchers say.

"Now we know that the low diversity we see in contemporary individuals
may not be indicative of an inability to recover, but instead a natural
state of rhinoceros," Westbury says. "We can better guide recovery
programs to focus on increasing population size rather than individual
genetic diversity." The team hopes that the new findings will be useful
for continued study of rhinoceroses and their conservation. Dale'n
reports that his team is now working on a more in-depth study of the
extinct woolly rhinoceros. Meanwhile, Westbury is involved in comparing
the genomes of African black rhinoceros sampled from before the recent
decrease in population size to those of contemporary individuals.

"We hope that this will provide a framework to better understand where translocated populations may have arisen from, direct changes in genetic diversity, and whether any populations may have been lost forever because
of humans," Westbury said.

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


========================================================================== Journal Reference:
1. Shanlin Liu, Michael V. Westbury, Nicolas Dussex, Kieren
J. Mitchell,
Mikkel-Holger S. Sinding, Peter D. Heintzman, David A. Duche^ne,
Joshua D. Kapp, Johanna von Seth, Holly Heiniger, Fa'tima
Sa'nchez-Barreiro, Ashot Margaryan, Remi Andre'-Olsen, Binia De
Cahsan, Guanliang Meng, Chentao Yang, Lei Chen, Tom van der Valk,
Yoshan Moodley, Kees Rookmaaker, Michael W. Bruford, Oliver Ryder,
Cynthia Steiner, Linda G.R.

Bruins-van Sonsbeek, Sergey Vartanyan, Chunxue Guo, Alan
Cooper, Pavel Kosintsev, Irina Kirillova, Adrian M. Lister,
Tomas Marques-Bonet, Shyam Gopalakrishnan, Robert R. Dunn, Eline
D. Lorenzen, Beth Shapiro, Guojie Zhang, Pierre-Olivier Antoine,
Love Dale'n, M. Thomas P. Gilbert. Ancient and modern genomes
unravel the evolutionary history of the rhinoceros family. Cell,
2021; DOI: 10.1016/j.cell.2021.07.032 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210824121037.htm

--- up 15 weeks, 4 days, 22 hours, 45 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)