Convergent evolution of the surface micro and nano structures in coronavirus and annual fish embryo. Thoughts while under “enhanced community quarantine” in Miag-ao (Iloilo Province, Panay Island, Philippines).
Jonathan R. Matias
April 2, 2020
The COVID-19 pandemic has finally reached my town of Miag-ao on March 27, 2020 with the announcement of the first person testing positive. Considering that the first death outside of Wuhan, China happened in the Philippines on February 1, COVID-19 has taken its time to show up in my town, arriving via an infected person who left Manila before the city went into total quarantine. All of the provinces in this island of Panay had been on quarantine since March 17, 2020.
Life in quarantine is difficult for most of us. It is something we have never been used to in a free society. To keep mentally and physically busy, people find their own ways within the confines of their own realities. For me, it is about traveling backwards in time 40 + years ago in the mid 1970’s and 80’s when I was young and very much interested in understanding the biology of a particular rare fish from East Africa – the annual killifish. The word “kill” was derived from the Dutch word meaning small stream. An annual fish population can exist even in pools of water created by elephant hoof prints during the rainy season.
This fish lives in transient, temporary streams that dry up seasonally in Africa and South America. During the summer, all the adults and juveniles die when the fresh water of the shallow pools starts evaporating. The population survives in the form of drought resistant embryos buried in the dry soil. These embryos undergo an extreme form of suspended animation called diapause occurring at three stages of their development. With his evolutionary feat, they can survive at least 10 years (maybe more) in dry soil until the rains return. They share the same habitat as mosquitoes and annual fish had been proposed as a tool for biological control of mosquitoes [See: https://poseidonsciences.scienceblog.com/104/rip-van-winkle-hibernating-fish-and-malaria-control/]. There are many similar states of suspended animation in other organisms, such as microbes, insects and tardigrades and even in mammals, but this is one of the two instances of diapause occurring in fish [http://en.wikipedia.org/wiki/Embryonic_diapause].
I started my life in science trying to unravel the mystery surrounding the biological basis of diapause while an intern (1975-1977) with Jules Markofsky at the Orentreich Foundation in New York City during my undergraduate years. We published a series of papers in the Journal of Experimental Zoology by 1977 and continued the studies, though on a somewhat sporadic nature (see references below). In the mid-1980’s I asked my friend, Eugene Hull, who at that time was a graduate student in New York University, to run a scanning electron microscopy (SEM) of the N. guentheri embryonic surface. The results of the SEM were never published. It simply was not a priority at the time. My life got busy with other pursuits, both scientific, business and personal.
Fig.1. Figure 1. Adult male and female Nothobranchius guentheri, native to the island of Zanzibar, Tanzania. Males are about 5 cm in length while the colorless females are much smaller at 3.5 cm.
However, I still retain the interest up to present time and continued to maintain a population of the annual killifish, Nothobranchius guentheri, as part of the Poseidon Sciences R&D program in Tanzania where the species is endemic. Long before the COVID-19 pandemic, I had the labs send embryos of N. guentheri in suspended animation to Miag-ao for research and also entertainment. After all, this species of fish is really colorful but short-lived; hence, the word ‘annual’ since they live about a year. In comparison, tilapia and gold fish, for example, can live up to seven years.
Having more free time while this quarantine is going on, I started looking at old photographs of the annual fish embryo and accidentally found a few of the old SEM records. What struck me was the similarity of the surface architecture on both the annual fish embryo and the coronavirus.
Figure 2. Comparison of the surface architecture of the embryo of the annual fish, N. guentheri, and the coronavirus as seen by electron microscopy. Fish embryo surface architecture seen using scanning electron microscopy; Coronavirus surface structure by electron microscopy described in https://en.wikipedia.org/wiki/Coronavirus.
Both organisms create spikes on the surface as seen in Fig. 2. The coronavirus needs this surface modification to enable attachment to the surface of human lung cells and other cells of the respiratory system. These spikes are made up of glycoproteins protruding from the capsid (capsule) that protects the RNA (ribonucleic acid) inside; hence the look of a crown, circular ornament with precious stones and jewels that kings and queens wear during official ceremonies. In Italian and in Spanish, crown is translated as 'corona' which gave rise to the name of the virus. I don't think the Portuguese 'coroa,' the Finnish 'kruunu,' or the Ukrainian 'kropoha' would have given the virus a more dramatic aura. Dont even ask how the Chinese [王冠 ] or Vietnamese [vương miện] translations of
crown would have sounded. See other translations of crown in other languages in this link: https://www.collinsdictionary.com/dictionary/english-italian/crown
The annual fish embryo need the same spikes (composition of the spikes still unknown, but likely also proteinaceous) to attach to the muddy bottom substrate of the freshwater pool. Presumably, this is an adaptation so that the fertilized egg can anchor itself with decaying vegetation to prevent being washed away by turbulence created by animals crossing the pond or drinking the water. Many other species of fish create elaborate microstructures on the surface of fertilized egg depending on the environment they live on. However, none that I have seen in other studies can compare to these spikes found in annual killifish that also resemble a crown or corona as in coronaviruses. Other non-annual killifish --those species that do not exhibit suspended animation or diapause in the embryonic stages-- do not exhibit this extreme form of surface architecture [Scheel, JJ. 1990. Atlas of Killifishes of the Old World, pp 38.]
Figure 3. Comparison of annual fish embryos and coronavirus.
Convergent evolution is a process wherein two unrelated organisms independently develop the same traits or characteristics to address a similar environmental problem. An example of convergent evolution is the adaptations to flight. Different animals developed wings independently of each other to enable flight, such as bats, butterflies, pterosaurs and birds [https://www.sciencedaily.com/terms/convergent_evolution.htm]. The spikes that coronaviruses and annual fish embryos possess were developed independently to solve each of their own ecological situations. It is interesting that the annual fish embryo is 1 mm in diameter while the diameter of a coronavirus is 60 to 140 nm or about 1/100,000th of the fish embryo https://www.britannica.com/science/coronavirus-virus-group. So far away from each other as species goes, yet they created the same evolutionary solution to a similar problem. Although the coronavirus is technically not a life form, but simply a single strand of RNA (ribonucleic acid) particle, it does mutate often and is evolving faster than animals or plants do.
Figure 4. Size of the coronavirus particle.
There are many theories about how coronavirus evolved. One of them is that the “most recent common ancestor” (MRCA) of coronavirus co-evolved with bats 55 million years ago. The more recent variants dated back 8000 BCE and the human coronavirus was first detected in the 1950’s [See: https://en.wikipedia.org/wiki/Coronavirus#Evolution]. In the case of annual fishes, they had existed likely during the period when Africa and South America were connected as part of the super continent (Pangea) about 330 million years ago [https://en.wikipedia.org/wiki/Pangaea]. When the supercontinent broke apart, separating South America from Africa 175 million years ago, annual fishes evolved into many diverse species over the millennia from the original Pangean life forms.
Figure 5. Chemical composition of the coronavirus
Vaccine development against the coronavirus that cause the COVID-19 pandemic targets the spike proteins because it is the most accessible for recognition by our immune system. The spike proteins are designated as S proteins and group themselves into 3 proteins per spike. One of the proteins on this spike extends further outward to enable it to attach to the ACE2 protein in the cell of human airway, thus enabling it to invade the cell and multiply. Recently, the New York Times published a highly informative article that summarizes what we know today about these proteins found in SARS-Cov2 that causes COVID-19. [see https://www.nytimes.com/interactive/2020/04/03/science/coronavirus-genome-bad-news-wrapped-in-protein.html?fbclid=IwAR2VTcRSIa7bum0TXwAsqZsTXjitKCMsayIr1-QEPF_GpgakMyCkghneIEg]
Figure 6. Computer graphics of the Spike proteins in SARS-Cov2. From The New York Times article cited above.
All experiments start with questions, sometimes seemingly outlandish. So, here is my list:
- 1. If the annual fish embryonic spikes are also proteinaceous, could it be similar to the coronavirus spike? Do they both synthesize the spike in a similar process?
2. If they are identical or at best close enough in chemical composition, can the embryonic spike of annual fish be useful to study the formation of the coronavirus spike? Or, maybe even be of help in vaccine development?
For now, back to gardening and playing with fish to keep my time occupied during this pandemic.
Stay safe everyone!
This article is dedicated to the memory of:
Long Island Killifish Association, New York
a friend, a jazz music man, an accomplished saxophone player and a lover of aquarium fish.
A man of many ‘worlds’
A victim of COVID-19 on April, 2020
For any comments, please email me at: email@example.com
References on annual killifish biology:
Markofsky J and Matias JR (1977a). The effects of temperature and season of collection on the onset of diapause in embryos of the annual fish Nothobranchius guentheri. Journal of Experimental Zoology
Markofsky J and Matias JR (1977b). Effects of light-dark cycles and temperature on embryonicdiapause in the East African annual fish Nothobranchius guentheri. Chronobiologia
Matias JR and Markofsky J (1978). Waterborne vectors of Disease in tropical and subtropical
areas and novel approach to mosquito control using annual fish. Proceedings of the Columbia University Seminars on Pollution and Water Resources
Matias JR and Markofsky J (1978). The survival of the embryos of the annual fish Nothobranchius guentheri exposed to temperature extremes and the subsequent effects on embryonic diapause
. Journal of Experimental Zoology. 204:219-227.
Markofsky J, Matias JR, Inglima K. Vogelman JH and Orentreich N. (1979). The variable effect of ambient and artificial light: dark cycles on embryonic diapause in a laboratory population of the annual fish Nothobranchius guentheri.
Journal of Experimental Biology 83:203-215.
Markofsky J and Matias JR (1982). The effects of Photoperiod and temperature on embryonic diapause
. Proceedings of the Third International Conference of the International Society of Chronobiology, pp.269-275.
Brind JL, Alani E, Matias JR, Markofsky J and Rizer RL (1982). Composition of the lipid droplet in embryos of the annual fish Nothobranchius guentheri
. Comparative Biochemistry and Physiology 73B:915-917.
Matias JR (1982). Embryonic diapause in annual fishes:Evaporative water loss and survival
. Experentia 38:1315-1317.
Matias JR (1984). The strategy for survival in annual fishes
. Proceedings of the 150th
National Meeting of the American Association for the Advancement of Science, 24-29 May 1984, p. 146.
Matias JR (1984). The stage-dependent resistance of the Chorion to external chemical damage and its relationship to embryonic diapause in the annual fish, Nothobranchius guentheri.
Matias JR (1984). Cryptobiosis in annual fishes: relative tolerance of various embryonic stages to environmental extremes
. American Zoologists 24:100A.
Matias JR, Adrias AQ (2010). The use of the annual killifish in the control of the aquatic stages of mosquitoes in temporary bodies of freshwater. A potential new tool in vector control
. Parasites and Vectors,