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Pangolins are strange little creatures, with their diet of ants and termites, and the entire outer surface of their bodies covered with armour-like scales (face, belly & the inner surfaces of the limbs are either hairy or naked). When in danger, pangolins are able to roll up in a ball, presenting only that armoured surface to a predator.

Actually, some of them aren't so little: from nose tip to tail tip, they range from 75 cm to more than 1.5 m in length, with their strong tails making up about half of that. Arboreal species tend to be smaller, just a couple of kilos in weight, but apparently the giant pangolin can weigh in at over 30kg. 

Ground Pangolin at Madikwe Game Reserve

Image by David Brossard (Scaly Anteater exits stage left) [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

In taxonomic terms pangolins have their own order (Pholidota), with a single family (Manidae) and genus, Manis; there are 4 species in Africa and 4 in Asia. Like giant anteaters they are toothless (edentate), & indeed, they converge with the giant anteaters in a number of ways and for a while the two groups were thought to be closely related. However, it seems that molecular data (from DNA & amino acids) places the pangolins' order as a sister group to the carnivores. So, the toothless state characteristic of both types of anteater has evolved more than once, as has the heavy musculature and massive claws of their forelimbs. 

I hadn't really thought before about how pangolins manage to digest their diets of termites and ants, after licking them up with those sticky, extrusible tongues. (Here's something else I didn't know: a pangolin's tongue is as long as head & body combined ie half their total body/tail length. It's folded back into a throat pouch when not in use, and the animals produce so much sticky saliva that they have to drink frequently.) It turns out that the stomach is rather like a bird's gizzard: its walls are hardened and it contains sand or very small pebbles, which help to grind up those crunchy meals as the muscles in the stomach wall contract and relax.

It seems that yesterday was World Pangolin Day. It would be nice to think that drawing attention to the plight of these strange little creatures would change the fact that they are currently the most trafficked mammal in the world. After all, they range from vulnerable to critically endangered status and are supposedly protected by both national and international legislation. Sadly I think that greed & stupidity will push them over the edge. 

Why? Because, as this article in The Independent says, pangolins are poached on a huge scale 

for their meat, which is considered a delicacy in China and Vietnam, and their scales, which are used as ingredients in traditional Asian medicine. 

Practitioners believe scales are capable of treating a range of ailments including asthma, rheumatism and arthritis.

That defensive habit of rolling up in a ball is useless against poachers, who can just pick the animals up. So, people are prepared to pay a lot of money for the meat and the scales of these creatures, which is where both greed and stupidity come into it.

Greed: well, money talks. In December 2016, Chinese customs made their largest-ever confiscation of scales - a mind-boggling 3.1 tons from an estimated 7,200 pangolins. Their worth: about $US2 million. Research by TRAFFIC, a network that monitors the international wildlife trade, suggests that around 20 tonnes of pangolins, & pangolin parts, are trafficked each year.

And stupidity, because those hugely expensive scales are made of keratin - nothing more and nothing less than the protein that makes up our own hair and nails. People consuming the pangolin's scales might as well chew their own fingernails, for all the good it would do them. I guess they'll have to, when the pangolins (and rhinos, whose horns are keratin too) are gone from the world.

 

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Polyploidy - the duplication of chromosome sets - is relatively common in plants, and can result in the development of new species. (Many modern food crops are polyploids.) It's much less common in animals, although found in some frogs & salamanders (amphibians) & leeches (annelids). 

So it was with a mix of excitement, surprise, & alarm that I read about a triploid crayfish species: excitement, because I hadn't heard about a polyploid crustacean; surprise, because it's a triploid organism; & alarm, because it's an invasive pest across its range.

File:Procambarus fallax forma virginalis.jpg

Image: Wikimedia commons; photo by Zfaulkes

Procambarus virginalis, the marbled crayfish, was first found in Germany in the mid-1990s but is now widespread in Europe & Africa, including Madagascar. In a paper published this month, Frank Lyko & his colleagues reported on their study of the species' genome (Gutekunst, Andriantsoa, Falckenhayn, Hanna et al., 2017). They found that it has 3 copies of each of its 92 chromosomes (276 chromosomes in total), and that all the chromosomes come from the slough crayfish (Procambarus fallax), but from two individuals that weren't closely related. The team suggested that the marbled crayfish originated from a mating between 2 slough crayfish, where one parent contributed a normal, haploid, gamete (one copy of each chromosome) & the other, a diploid gamete with 2 copies of each chromosome, produced by non-disjunction during meiosis. Their genomic analysis pointed to the aquarium trade in Germany as the source of the new species. 

Now, triploid organisms are usually sterile, because they're not able to produce viable gametes via meiosis. (The same would be true of a pentaploid, with 5 copies of every chromosome.) Yet this crayfish has rapidly become an invasive species, & that means it makes lots of baby crayfish. How does it do this? 

By parthenogenesis. That is, this is a clonal species. (The researchers describe the Madagascan population of P.virginalis as "genetically homogeneous and extremely similar to the oldest known stock of marbled crayfish founded in Germany in 1995.)

Every marbled crayfish is female, producing 'apomictic' eggs by mitosis. No sperm necessary. And because every individual is capable of producing eggs and - in this species, a lot of them - in ideal conditions the species' population can grow much faster than that of a sexually-reproducing species. This gives the marbled crayfish quite an advantage over other, competing, species when it's introduced into a new ecosystem, which is why it has been able to expand quickly across Europe & Africa - having likely arrived in these countries via the aquarium trade. And again, because they are parthenogenetic, you need just a single individual to begin a new invasive population. In Madagascar their spread was enhanced by human activity in terms of moving animals around to establish new food populations, the warmer temperatures (compared to those in Europe), and the ready availability of suitable freshwater habitats, and there's concern that endemic crayfish species, and their unique ecosystems, are threatened by the exotic invader.

But there's much more to this story than a tale of an unusual crayfish. I found it fascinating that that understanding how the marbled crayfish genome evolves over time may have applications to cancer research:

The generation of genetic diversity will be shaped by a complex set of factors, including the intrinsic mutability of the genome, environmental mutagens, genetic drift and selective pressure. All these factors are known to play an important role in the evolution of tumour genomes. The analysis of mutations in marbled crayfish populations provides an opportunity to detect the generation, fixation and elimination of genetic changes with particularly high sensitivity and robustness and could therefore disentangle the specific contributions of individual factors. As such, it will be interesting to further explore marbled crayfish as a model system for clonal genome evolution in cancer.

 

J.Gutekunst, R.Andriantsoa, C.Falckenhayn, K.Hanna, W.Stein, J.Rasamy & F.Lyko (2017) Clonal genome evolution and rapid invasive spread of the marbled crayfish. Nature Ecology & Evolution doi:10.1038/s41559-018-0467-9

 

Interested readers will also enjoy this summary of the paper, with commentary from other scientists. 

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Students often get to look at hydras - tiny, fresh-water members of the group that includes sea anemones, jellyfish, corals, and the Portuguese man'o'war. All these cnidarians have a simple body-plan: two layers of true tissue with a jelly-like layer between them, a sac-like gut with a single opening that acts as both mouth and anus, and the characteristic stinging cells - cnidocytes - that give the taxon its name. And many of them rely on endosymbiotic algae for their survival, using some of the sugars that the algae produce by photosynthesis. The image below shows part of a hydra's tentacle - you can see not only its green algal symbionts, but also a halo of discharged stings.