How the pangolin got its scales – a genetic just-so story (2024)

How the pangolin got its scales – a genetic just-so story (1)

Everyone loves animal oddities. Darwin and Lamarck pondered the advantages of the giraffe's long legs and neck, while a few decades later Rudyard Kipling explained how the leopard got its spots. Today genome sequencing is fleshing out what we thought we knew about some distinctive animal adaptations, from the giraffe to the leopard.

Adaptations are inherited traits that increase the likelihood of an individual surviving to reproduce. A zebra's stripes rendering it invisible when it runs and the fennec fox's giant ears that dissipate heat and hear distant predators are adaptations.

A report in this month's Genome Research provides the basis for a "just-so story" about how the pangolin – aka the scaly anteater—got its scales. They protect, but in a way beyond the obvious. According to the genome, the armor of the pangolin replaced part of its immune response.

Endangered!

The eight modern species of pangolins began to diverge from their shared ancestor about 60 million years ago, which diverged from insectivores that preceded the placental mammals about 100 million years ago, when hairy animals were just beginning to replace the reigning reptilian giants.

Four of the modern species of pangolins live in Asia and four in Africa. The International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species considers them "critically endangered" and they also make the Evolutionarily Distinct and Globally Endangered (EDGE) mammals and amphibians list.

Pangolins are the the most trafficked and poached mammal. They are a delicacy in Vietnamese and Chinese cuisine, and their ground-up scales are used in Chinese medicine to treat cancer, various skin conditions, and poor circulation. In African folklore, a captured pangolin was brought to the chief, observed for a time, then sacrificed and served as relish for the meal of the chief and his senior wife.

Agriculture and deforestation have steadily shrunk the pangolins' habitats, and the animals are extremely difficult to maintain in captivity.

Meet the pangolin

The pangolin's trademark armor is actually a coating of hairs (keratin) glommed together into large, overlapping scales that cover all but the soft belly. "Pangolin" is from the Malay word 'pengguling,' for rolling up, which is what they do when they feel threatened, protecting their soft middles and the organs within.

The animal is toothless and nearly jawless, it's pointy snout and strong tongue ideal for hoovering up meals of ants and termites. Pangolins live in trees and underground. Seven of the eight species are fairly small, like a cat, but the giant pangolin Manis gigantean approaches 6 feet in length. It resides in burrows left by regular anteaters, which are only very distant relatives.

How the pangolin got its scales – a genetic just-so story (3)

Pangolin vision is very poor, yet the sense of smell acute.

Pseudogenes and contracting gene families

Because the pangolin was the only placental mammal who hadn't had its genome sequenced, Siew Woh Choo, from the University of Malaysia and colleagues did so, for two females. One is a Malayan pangolin of species Manis javanica, which sounds like a Starbucks drink, and the other a Chinese pangolin, M. pentadactyla. The Malayan's genome is 23,446 genes and the Chinese one is 20,298—same ballpark as us.

Evolutionary geneticists probe genomes for signs of positive and negative natural selection. Genes that don't vary much in DNA sequence from individual to individual indicate positive selection, because whatever the sequence is, the encoded protein is working: an if-it-ain't-broke scenario. In contrast, a gene that's no longer functional can be riddled with mutations, varying greatly among individuals – if it's protein isn't useful or even produced, it doesn't much matter what the underlying DNA sequence is. (Note to The New York Times and other media outlets: avoid "to evolve". Change driven by mutation and natural selection is not a desire or choice. It just happens. Giraffes didn't yearn to reach the treetops and alter their DNA accordingly.)

Genes that have diverged in sequence so greatly from the ancestral one that they no longer function are called pseudogenes. They may arise from a gene duplication – having an extra copy allows one gene to go on functioning while the partner accumulates mutations. In this way genomes come to harbor pseudogenes, the ghosts and echoes of functional counterparts from the past. The best-studied pseudogenes are in the beta globin cluster in human genomes.

Several pangolin genes have been "pseudogenized" into "loss of function" – what isn't needed accumulates glitches. And in those deactivated genes lies a genetic just-so story:

How the pangolin got its scales – a genetic just-so story (4)
  • A gene called ENAM, which encodes the largest tooth enamel protein, is full of premature stop codons, duplications, and deletions. Ditto the genes for the enamel proteins ameloblastin and amelogenin. Other toothless creatures, including baleen whales, birds, and turtles, also have mutations in these genes.
  • Several vision genes have been mutated into silence.
  • The interferon epsilon gene is so altered that it doesn't work in both pangolin species, as well as in their African counterparts. Yet it is fully functional in 71 other species of placental mammals, where it provides a "first line of defense" against skin infections. Several other interferon genes, which deal with infection, inflammation, and skin healing, are missing too. The Malayan pangolin has three, the Chinese pangolin two, yet other mammals a full set of ten. Use it or lose it.
  • Pangolin genomes have fewer heat shock genes, perhaps explaining their sensitivity to stress and their poor fate in zoos.

Expanding gene families

A look at gene families that have more members in pangolin genomes compared to those of other placental mammals provides the complementary positive view of evolution. These include genes that encode:

  • proteins that build the cytoskeleton, form cell-to-cell junctions, and promote nervous system function and signal transduction – traits necessary for scale formation
  • cathepsins and septins, which squelch bacterial infections
  • odorant receptor genes that underlie the pangolin's superior sense of smell.

So the clues in the pangolin genomes – which gene families have contracted and which expanded—suggest strongly that the armor has replaced part of the immune response. The tightly-knit, tough scales deter not only predators, but keep the animal free of infection.

Although it is intriguing to imagine reasons why animals are as they are – from the giraffe's neck to the leopard's spots to the pangolin's armor – clues in DNA sequences can provide a broader and less biased view of adaptive traits, from those that have stood the test of evolutionary time to those relegated to the genomic junkyard.

More information:Siew Woh Choo et al. Pangolin genomes and the evolution of mammalian scales and immunity, Genome Research (2016). DOI: 10.1101/gr.203521.115

Journal information:Genome Research

Provided byPLOS Blogs

This story is republished courtesy of PLOS Blogs: blogs.plos.org.

Citation:How the pangolin got its scales – a genetic just-so story (2016, October 21)retrieved 7 September 2024from https://phys.org/news/2016-10-pangolin-scales-genetic-just-so-story.html

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How the pangolin got its scales – a genetic just-so story (2024)

FAQs

How the pangolin got its scales – a genetic just-so story? ›

EXPANDING GENE FAMILIES

How did the pangolin get its scales? ›

We further postulate that genetic changes during the evolution of hair-derived pangolin scales likely involved genes related to hair formation in general, and particularly keratins, which are essential components of scales and hair (Meyer et al. 2013).

What could be the central cause for why the Chinese pangolin is on the verge of extinction? ›

These little guardians have survived thousands of years of natural changes, but now they are on the verge of extinction due to habitat loss and illegal poaching. More than one million pangolins were brutally murdered for black-market trade in the past 10 years; that is 11 pangolins every hour.

Is pangolin illegal? ›

All eight species of pangolin are protected under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the highest level of international law.

What is a paragraph about a pangolin? ›

OvervIEW. Pangolins are uniquely covered in tough, overlapping scales. These mammals eat ants and termites using an extraordinarily long, sticky tongue, and are able to quickly roll themselves up into a tight ball when they feel threatened. Eight different pangolin species can be found across Asia and Africa.

Is pangolin the only mammal with scales? ›

They are the only mammals wholly-covered in scales and they use those scales to protect themselves from predators in the wild. If under threat, a pangolin will immediately curl into a tight ball and will use their sharp-scaled tails to defend themselves.

Why is pangolin scales so expensive? ›

Demand is particularly high for their scales, but whole animals are also sold either living or dead for the production of other products with purported medicinal properties or for consumption as exotic food.

What is the fine for killing a pangolin? ›

In DR Congo, anyone found guilty of killing, hurting, capturing or possessing a fully protected animal, including the pangolin, faces one to 10 years in prison and/or a fine of five to 10 million Congolese francs (US $5,500-11,000).

Do pangolins mate for life? ›

Pangolins do not mate for life. Male pangolins will fight over females, though the winning male will enjoy a fleeting 3-5 day 'relationship' with a female before moving on. The females will only have up to 1-2 offspring per year.

Is it legal to have a pet pangolin? ›

Pangolins make terrible pets, and it is illegal to own them. They are not well-suited to living in any environment outside of their natural habitat. In fact, many zoos that have tried to house pangolins have found that most die within their first year out of the wild due to stress or dietary issues.

Is pangolin a dinosaur? ›

Pangolins have been described as 'walking pinecones', 'artichokes with tails' and 'modern-day dinosaurs'. While at first glance you might presume they are related to other ant-eating species, scientists now know one of their closest relatives is actually the mongoose.

How many pangolins are left? ›

How many pangolins are left in the world? The honest answer is, we don't know. Because pangolins live such secretive, secluded lives, no population studies have been able to successfully estimate how many pangolins live in the wild.

How long do pangolins live? ›

Life span in the wild is unknown; however, some captive animals have lived as long as 20 years. All pangolin species have been hunted for their meat, and the organs, skin, scales, and other parts of the body are valued for their use in traditional medicine.

What did pangolins evolve from? ›

The eight modern species of pangolins began to diverge from their shared ancestor about 60 million years ago, which diverged from insectivores that preceded the placental mammals about 100 million years ago, when hairy animals were just beginning to replace the reigning reptilian giants.

Can pangolins regrow their scales? ›

Pangolins are born with a set amount of scales which they have for the rest of their life. They cannot regrow them. Temminck's ground pangolins have between 11 and 13 rows of scales on their back and the same amount on their tail.

What are pangolin scales good for? ›

Practitioners have cited using pangolin scales to cure mammary gland blockages in breastfeeding women, treat rheumatism, stimulate blood flow, reduce swelling, promote the discharge of pus from wounds, and more.

How many pangolins are left in the world? ›

How many pangolins are left in the world? The honest answer is, we don't know. Because pangolins live such secretive, secluded lives, no population studies have been able to successfully estimate how many pangolins live in the wild.

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