Worm your way through this! What makes worms stick together?

Can one tiny worm make a difference?

Biologists have been working on understanding animal behaviour for a long time, and one of the big questions that we’re still trying to answer is “how do animals stay together?”(1)

Scientists know quite well how this works on a large scale, such as herding in zebra, but they don’t really know how it works on the mesoscale (the stuff you can only ‘just’ see with the naked eye).

Enter the realm of the Nematode! (This is where worms come into the story)

This article is all about fun! In the form of Science and puns! (I’m sorry…) Twitter user: @ArfMeasures

Caenorhabditis elegans, or C. elegans, for short, is all the rage in Behavioral Biology. Able to aggregate and swarm in the hundreds – these tiny collective feeders are the perfect organism to study to understand mesoscale behaviour (1).

Much smaller than your typical garden worm, Caenorhabditis elegans is one of the most studied mesoscale organisms around (Sibelius Natural Products 2019).

The three worm commandments

So, what exactly causes worms to swarm and aggregate? How does it all work? Serena Ding and her team recently did a study to find out exactly how these guys move (1).

Commandment 1: “Thou shalt come back to the horde”

If a worm leaves its group, it stops moving, and reverses back to rejoin its neighbours (called ‘cluster edge reversals’) (1).

Worms just keep coming back to their group. Could batman have something to do with it? Probably not, but this page needed more batman. (imgflip.com, Meme Generator, Shannon Kaiser 2020)

They may return due to encountering harmful amounts of oxygen as they go away from the group (Correspondence with Serena Ding 2020).

Commandment 2: “Thou shalt obey the speed limit”

Worms slow down when they’re surrounded by other worms (called ‘density-dependent switch) (1).

Commandment 3: “Thou shalt follow thy brethren”

Worms move towards areas that have more neighbors (called ‘taxis towards neighboring worms’) (1).

So basically, when we get lots of worms together, they move slower, they stick together, and they draw more individuals. 

Look at this! You can see how they move to a new spot to consume food. (Their last spot is a dashed circle) (Ding et al. 2019).
Get a big enough group, and they swarm across the food source like a tidal wave. Watch them consume their food from left to right (of the dotted red line) (Ding et al. 2019).

Why is this study important?

Why should anyone look at worm behaviour?

Well, mainly because we know how stuff behaves under a microscope and macro scale , but not at the mesoscale, which may be different (1). Understanding how behavior works at all scales is important to understand why animals behave differently (1). Additionally, Serena’s conclusions can also help geneticists; their data can be used to help discover what genes control these behaviors (1).  

Behaviour occurs in response to nervous system function. So if an animal is behaving oddly, we can find out if certain chemicals (2) or mutations are responsible (3).

For example, in the wild, worms aggregate over food, but over multiple generations in the lab, they become solitary! Perhaps their diet of E. coli is responsible for this? (correspondence with Serena Ding 2020).

Plenty of things hurt worms, like bacteria or fungi, which can either kill them or cause disease symptoms (4), and scientists know that E. coli harms it.

Bacterial metabolites (the stuff that E. coli produces), changes how long worms live (5). When we decrease the amount of folate in E. coli, for example, C. elegans lives longer than it did before (5). This happens with other metabolites too (5).

So why feed an animal something that is bad for them?

The answer is: E. coli has been fed to them for decades of experiments (6), if we fed them a different bacterium, we would get conflicting results between studies.

You’ve got to use them proper science methods, bro. (imgflip.com, Meme Generator, Shannon Kaiser 2020)

To avoid introducing experimental errors, we need to prevent C. elegans from becoming solitary.

So, we freeze them!

This may seem cruel, but worms cope well this, and they stay alive for a long time, like this. We can then copy them as needed, creating a new population of clones, and refreeze them. No errors here – thanks freezer!

This meme speaks for itself. (imgflip.com, Meme Generator, Shannon Kaiser 2020)

More fun facts for you to ‘worm’ your way through.

  • One individual can clone itself up to 300 times! (correspondence with Serena Ding 2020).
  • They can eat the amoebae of slime mold! (6).
  • 5 new species were discovered only recently (7).
  • Juvenile worms (called dauer worms) associate with other animals for phoresy or necromeny (look both of those up) (8).
What coud be more fun than learning about nematodes? (imgflip.com, Meme Generator, Shannon Kaiser 2020)

References

  1. Ding, S.S., Schumacher, L.J., Javer, A.E., Endres, R.G. and Brown, A.E., 2019. Shared behavioral mechanisms underlie C. elegans aggregation and swarming, eLife, 8, p.e43318.
  2. Brown, A.E., Yemini, E.I., Grundy, L.J., Jucikas, T. and Schafer, W.R., 2013. A dictionary of behavioral motifs reveals clusters of genes affecting Caenorhabditis elegans locomotion, Proceedings of the National Academy of Sciences, 110(2), pp. 791-796.
  3. Javer, A., Ripoll-Sánchez, L. and Brown, A.E., 2018. Powerful and interpretable behavioural features for quantitative phenotyping of Caenorhabditis elegans. Philosophical Transactions of the Royal Society B: Biological Sciences, 373(1758), p.20170375.
  4. Darby, C., 2005. Interactions with microbial pathogens. In WormBook: The Online Review of C. elegans Biology [Internet]. WormBook.
  5. Zhang, J., Holdorf, A.D. and Walhout, A.J., 2017. C. elegans and its bacterial diet as a model for systems-level understanding of host–microbiota interactions. Current opinion in biotechnology, 46, pp.74-80.
  6. Grewal, P.S., 1991. Influence of bacteria and temperature on the reproduction of Caenorhabditis elegans (Nematoda: Rhabditidae) infesting mushrooms (Agaricus bisporus). Nematologica 37, 72–82.
  7. Kiontke, K. and Sudhaus, W., 2006. Ecology of Caenorhabditis species. WormBook, ed. The C. elegans Research Community, Wormbook.  doi/10.1895/wormbook.1.37.1
  8. Karp, X., 2018. Working with dauer larvae. WormBook: the online review of C. elegans biology, 2018, pp.1-19.

Published by shannonwkaiser

Shannon is an excitable Biology student, currently studying a Masters of Research at Macquarie University. Intent on going into research, he plans on understanding how bushfires impact Cane toads (Rhinella marina).

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