First by Land, Then by Sea: Origins of Dietary Adaptations for Whales and Dolphins during Land to Sea Transition
Advance Access publication October
Ancient DNA Traces Extinct Caribbean “Island Murderer” Back to the Dawn of Mammals
Joseph Caspermeyer
MBE Press Office
Wang Z, Xu S, Du K, Huang F, Chen Z, Zhou K, Ren R, Yang G. 2016. Evolution of digestive enzymes and RNASE1 provides insights into dietary switch of cetaceans. Mol Biol Evol. 33:3144-3157. The Author 2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: s reb 8 , 2 0 1 6
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The cetaceans, including whales, dolphins and purpoises, are
thought to be among the most successful animals to have
ever transitioned from land back to the sea, beginning about
50–55 Ma. Over eons, along with losing limbs and hair,
growing tails, and gaining blubber, the remarkable evolutionary
changes also included a dramatic dietary change, from
herbivorous to carnivorous.
Now, they are content munching on a diet of fish, squid,
shrimp or plankton. They are among many mammals that
have fascinated scientists with their dramatic shifts in their
diet, including giant pandas (carnivores to herbivores), dogs
(carnivores to omnivores) and colobine monkeys (omnivores
to herbivores).
And like their even-toed land-dwelling ruminants (the
order Artiodactyla, including cattle, pigs, sheep and deer) for
which they share skeletal features, they have also maintained
a multi-chambered foregut.
Now, researchers Wang et al. (2016) have performed the
first survey to understand the genetic patterns of the dietary
changes for ocean mammals to turn from herbivores to
carnivores during their evolution.
To do so, they built separate mammalian and cetacean
datasets. Next, they analyzed both datasets using various tools
to test for positive selection along specific lineages within the
10 digestive enzymes genes studied, along with a total of 77
RNASE1 gene sequences (important in foregut plant
digestion) from 43 mammalian species. These were chosen
because they represent the four main kinds of digestive
enzymes that breakdown the types of food animals eat: fats
(lipases), proteins (proteinases), carbohydrates (glucosidases),
and plants (RNASE1).
They found evidences of adaptive evolution within
cetaceans for some proteinases (i.e., CTRC, PRSS1, and
TMPRSS15) and lipases (i.e., CYP7A1, LIPF, and PNLIP),
suggesting that cetaceans have evolved an enhanced digestion
capacity for protein and lipid, the major nutritional
components in their prey of fishes and invertebrates.
They also present evidence to support their conclusion
that modern cetaceans have lost the pancreatic RNASE1
copy with digestive function, which is congruent with
their dietary change from herbivorous to carnivorous
(pancreatic RNASE1 is thought to be responsible for
digesting plants).
The study provides original insights into the evolutionary
mechanism of dietary switch from herbivorous to carnivorous
in cetaceans, and the broad tools can be applied to other
studies investigating dietary changes.
From skeletal remains found among ancient owl pellets, a
team of scientists has recovered the first ancient DNA of
the extinct West Indian mammal Nesophontes, meaning
“island murder.” They traced its evolutionary history back to the
dawn of mammals 70 Ma.
The authors, including Brace et al. published their findings
in the advanced online edition of Molecular Biology and
Evolution.
The insect-eating creature existed in the Caribbean islands
until the 16th century when, perhaps, they were
outcompeted as the first Spanish ships arrived—
introducing rats as stowaways. “Nesophontes was just one
of the dozens of mammals that went extinct in the
Caribbean during recent times,” said Professor Ian Barnes,
Research Leader at London’s Natural History Museum.
Scientists used a 750-year-old specimen to generate many
thousands of base pairs of DNA sequence data. This allowed
the research team to uncover its evolutionary origins and
finally resolve the relationships between its closest relatives,
the insectivores, a group including shrews, hedgehogs and (...truncated)