What Our Ancestor, the Platypus, Can Tell Us About Our Evolution

Author: Isabel Zhang

From: Chicago, IL, US

By JJ Harrison (https://www.jjharrison.com.au/) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12151746


Introduction


When British zoologist George Shaw first saw a platypus in 1799, he was so perplexed that he checked for stitches, thinking that it was some Franken-style creature. I don’t blame him though; what kind of animal would have a rubbery bill, ankle spikes full of venom, luxurious fur that glows under black light, and a tendency to lay eggs?


To this day, researchers are still trying to better understand the platypus. Recently though, they’ve made a huge breakthrough on the platypus and its family, the Monotreme species. Their discovery has led scientists to ask: Is the platypus actually normal, and are humans the creatures that turned out strange?


But before we dive into the breakthrough, let’s talk about what monotremes are.


What Are Monotremes?


The monotremes are a group that consists of the platypus and four echidna species, all native to Australia. They have a mix of mammalian and reptilian features. However, what makes them the most odd is their unique reproductive strategy as mammals: they lay eggs despite having fur, being warm blooded, and nursing their young with milk.


Unsurprisingly, monotremes form the most distantly related and least understood group of living mammals.


Monotremes’ Contribution to Our Understanding of Evolution


Now, back to the recent breakthrough about monotremes, which has been brought to you by an international collaboration of 40 researchers from Australia, China, Japan, USA and Denmark. The breakthrough they’ve made on monotremes are (drum roll, please)... their genetic blueprint!


Okay, maybe that doesn’t sound too exciting to you, but for researchers, studying monotremes’ genome is providing fundamental insights into their unique biology and the evolution of all mammals. Indeed— as monotremes split from other mammals roughly 187 million years ago, their strange traits may have actually been present in the ancestor we all share.

Having such a comprehensive map enables comparisons between the genomes of monotremes and other mammals, helping to fill gaps in the step-by-step story of how mammals appeared and then diverged. These comparisons date many evolutionary innovations. For instance, co-first author of the new research, Dr Linda Shearwin-Whyatt, says, “The system for safe removal of the oxygen carrier, hemoglobin from blood was thought to be common to all mammals. We were surprised when we discovered the system was missing from monotremes, implying that it arose quite recently in the ancestor of all other mammals.”

The comparisons also reveal that other traits took other paths. For example, monotremes, which are toothless, have lost genes associated with dental development that are present in other mammals. In addition, platypuses have venom-producing genes that other mammals lack but are similar to those found in some reptiles (this might explain their toxic foot spikes). Less visible, albeit equally perplexing, is that while other mammals generally have one pair of sex chromosomes, monotremes have five pairs.

With regards to monotremes’ anomalous egg-laying, the newly-mapped genomes reveal that they have one copy of a gene called vitellogenin, which is involved in the production of egg yolks. Many birds and insects have multiple copies of vitellogenin, but most mammals don't have the vitellogenin gene. This suggests that this gene (and perhaps the reproductive strategy itself) may have been something the rest of us lost, rather than an innovation of the monotremes. Meanwhile, they also have milk-producing genes similar to ours and those of other mammals, allowing them to nourish their young.

Conclusion: Further Contributions


The fact that the new genetic blueprint can tell us a lot about our 187-million-year-evolution from our common ancestors, the platypus and echidna, is pretty cool. But the research is relevant even beyond expanding our understanding of mammalian evolution.

University of Sydney’s Professor Katherine Belov says, “The new genome sequences also provide a roadmap for genetic management of threatened echidna populations and exciting new leads for drug development via the discovery of novel peptides in platypus venom.” So, now we have leads for protecting the echidna species and biomedical applications— double cool, if I say so myself.

Monotremes are much loved by people in Australia and around the world. I hope their newly-mapped genomes that have brought novel insights into their biology, a foundation for a deeper understanding of mammalian biology, and a basis for conservation of these iconic animals for future generations, has excited you- as well as made you fall in love with them.

 

About the Author: Isabel Zhang

Isabel is a senior in high school, and is interested in biology and engineering. In her free time, she loves to bake, sketch, and hang out with her family.

 

References

  1. Fox, A. (2021, January 12). Platypus Genes Are Just as Odd as the Creature Itself. Retrieved from https://www.smithsonianmag.com/smart-news/platypus-genome-shows-looks-may-not-always-deceive-180976735/

  2. U. (2021, January 12). Genomes reveal new insights into iconic Aussie animals. Retrieved from https://www.newswise.com/articles/genomes-reveal-new-insights-into-iconic-aussie-animals

  3. Henderson, E. (2021, January 08). Genetic blueprint provides insights into unique biology of egg-laying monotreme mammals. Retrieved from https://www.news-medical.net/news/20210108/Genetic-blueprint-provides-insights-into-unique-biology-of-egg-laying-monotreme-mammals.aspx

  4. T. (2021, January 10). Platypus proving key in evolution study. Retrieved from https://www.nwaonline.com/news/2021/jan/10/platypus-proving-key-in-evolution-study/




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