First by Land, Then by Sea: Origins of Dietary Adaptations for Whales and Dolphins during Land to Sea Transition

Molecular Biology and Evolution, Nov 2016

Joseph Caspermeyer

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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 - 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)


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Joseph Caspermeyer. First by Land, Then by Sea: Origins of Dietary Adaptations for Whales and Dolphins during Land to Sea Transition, Molecular Biology and Evolution, 2016, pp. 3317-3317, 33/12, DOI: 10.1093/molbev/msw207