You may think that this title is a mistake. How can an amoeba, an organism without a brain, be social? Amoebas aren’t more than a cell, yet certain species can work together to survive.

Let’s discuss sociality: what defines a social relationship and how did it evolve? Well for an organism to evolve physically or behaviorally, the change has to benefit the organism’s fitness. The reason for parents to work together to raise their young is one simple example. If the only advantage two parents rearing a child had was that they could collect twice as much food would not increase fitness and be a drastic enough effect of working together. However if with two parents one collected food and one stayed back at the nest to protect the baby at all times, this would increase fitness because the baby has a much reduced chance of dying. So basically 1+1=2 will not create evolution, but 1+1=5 will. (I hope this analogy makes sense.)

Thy type of sociality in these dictyostelium discoideum amoebas is not regular sociality but eusociality. The defining factors of eusocial relationships are that organisms live in big colonies with a caste system. This system allows for cooperative brood care (when individuals take care of offspring from other individuals), overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups.

So now that you understand the why, now we can talk more about the what. The what is the dictyostelium discoideum amoeba. They feed on bacteria and as they grow they get together in large groups that form a slug shaped body.

(not actually purple, just the lighting)

This slug shaped body actually has the ability to move towards the light. There are castes in this slug body, the front 20% are the ones that die, and the back 80% are the ones who live. You would think that the ones that die for the others would be in the back of the slug and get less food. However, the ones at the front who get the most food are actually the most well-fed. Some of the ones in the back of the slug are more starved and act as the signal for when the slug should turn into a stalk with a bulb on the end. So let me explain. The way the life cycle of these amoeba work is that they make stalks (made out of the dead 20%) with bulbs at the top filled with the living amoeba.

These amoeba feed on the bacteria on the forest floor mostly found on animal feces. When flies land on the feces, they land on the amoeba as well, eat them, and transfer them somewhere else where the life cycle is repeated. If the amoeba did not work together, they would have to hope a fly would land on their tiny, tiny single-celled selves. But if they act together, it is much easier for them to be dispersed.

The mechanisms behind how the amoeba do this are complicated to explain but I will try to tell you what I think I know about them. If certain alleles are different in a specific gene, the amoeba can actually differentiate who is the same and who is different. The amoeba slugs will deform and reform, picking up random amoeba until they are made up of enough of the genetically-same (clones) amoeba.

This is super cool to me. These little amoeba, basically the simplest organisms one can find, are interacting socially on such a high level. Studying this behavior can give us major insight into how and why other organisms interact the way they do. By studying simple examples, scientists can hope to better understand what is the intensely complex system of animal, and even human behavior.

Even though this wasn’t about ants, I hope you enjoyed it. I think it gives perspective on why we study ant behavior in the first place.

picture 1 from https://photoeditor61.wordpress.com/2014/03/11/slime-mold-race/

picture 2 from http://biology.stackexchange.com/questions/7145/how-selfish-is-dictyostelium-slug-formation