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Marc Robinson-Rechavi

Frédéric Delsuc: 5 convergent evolutions of ant (or termite) eating among mammals, including one hyena. Focus of his study is on anteaters and pangolins (a bit disappointed not to hear about aardwolf, the termite eating hyena).

Jul 27, 2023, 08:44 AM·Public·Web
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Marc Robinson-Rechavi

F Delsuc: ancestral mammal had many chitinases, consistent with fossil evidence for insectivorous diet, followed by many losses in most mammalian lineages. Anteater has several still expressed digestive system, in pangolin surprisingly most are lost or pseudogenes, with only CHIA5 expressed in digestive system, maybe because of common ancestry with carnivores. biorxiv.org/content/10.1101/20

bioRxivComparative transcriptomics reveals divergent paths of chitinase evolution underlying dietary convergence in ant-eating mammalsAnt-eating mammals represent a textbook example of convergent evolution. Among them, anteaters and pangolins exhibit the most extreme convergent phenotypes with complete tooth loss, elongated skulls, protruding tongues, hypertrophied salivary glands producing large amounts of saliva, and powerful claws for ripping open ant and termite nests. However, comparative genomic analyses have shown that anteaters and pangolins differ in their chitinase gene ( CHIA ) repertoires, which potentially degrade the chitinous exoskeletons of ingested ants and termites. While the southern tamandua ( Tamandua tetradactyla ) harbors four functional CHIA paralogs ( CHIA1 - 4 ), Asian pangolins ( Manis spp.) have only one functional paralog ( CHIA5 ). Here, we performed a comparative transcriptomic analysis of salivary glands in 33 placental species, including 16 novel transcriptomes from ant-eating species and close relatives. Our results suggest that salivary glands play an important role in adaptation to an insect-based diet, as expression of different CHIA paralogs is observed in insectivorous species. Furthermore, convergently-evolved pangolins and anteaters express different chitinases in their digestive tracts. In the Malayan pangolin, CHIA5 is overexpressed in all major digestive organs, whereas in the southern tamandua, all four functional paralogs are expressed, at very high levels for CHIA1 and CHIA2 in the pancreas, and for CHIA3 and CHIA4 in the salivary glands, stomach, liver, and pancreas. Overall, our results demonstrate that divergent molecular mechanisms underlie convergent adaptation to the ant-eating diet in pangolins and anteaters. This study highlights the role of historical contingency and molecular tinkering of the chitin-digestive enzyme toolkit in this classic example of convergent evolution. ### Competing Interest Statement The authors have declared no competing interest.
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Marc Robinson-Rechavi

F Delsuc showing very complete picture of convergence: anatomy, genome/transcriptome, and microbiome

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