1. 1 GEK1530 Frederick H. Willeboordse frederik@chaos.nus.edu.sg Nature’s Monte Carlo Bakery: The Story of Life as a Complex System

2. 2 Social Insects Lecture 11 Complex organisms consist of many cells and many cell types. Another way to form a kind of a complex organism is through social organization. Here we look at social insects like bees and the dictyostelium amoebae.

3. GEK1530 3 Social Insects & Amoebae Dictyostelium Amoebae Ants

4. GEK1530 4 Ants What are ants? Camponotus japonicus The Messor aciculatus ant makes the deepest nest in the world. The depth is about 4 m.Messor aciculatus Fascinating!

5. GEK1530 5 Any of various social insects of the family Formicidae, characteristically having wings only in the males and fertile females and living in colonies that have a complex social organization. (Source American Heritage Dictionary) \Ant\, n. [OE. ante, amete, emete, AS. [ae]mete akin to G. ameise. Cf. Emmet.] (Zo["o]l.) A hymenopterous insect of the Linn[ae]an genus Formica, which is now made a family of several genera; an emmet; a pismire. Note: Among ants, as among bees, there are neuter or working ants, besides the males and females; the former are without wings. Ants live together in swarms, usually raising hillocks of earth, variously chambered within, where they maintain a perfect system of order, store their provisions, and nurture their young. There are many species, with diverse habits, as agricultural ants, carpenter ants, honey ants, foraging ants, amazon ants, etc. The white ants or Termites belong to the Neuroptera. (Source Webster’s Revised Unabridged Dictionary)EmmetFormica What are ants? Ants

6. GEK1530 6 Ants are hugely successful ecologically speaking and are common in almost all terrestrial habitats. There are about 10,000 known species which is more than twice the total number of mammal species. In some rainforests, the dry weight of ants and termites is about four times the dry weight of all the other land animals combined! Ecological Success Ants

7. GEK1530 7 Even though ant brains are always small, between species, the sizes can differ several orders of magnitude. The number of neurons can be as little as 10,000! Individual Abilities Generally, single ants behave in a simple way. Indeed, alone, an ant is perhaps not really an ant at all! Ants

8. GEK1530 8 Collective Abilities High level of self organization. Collective ‘intelligence’. E.g. in army ants, the swarm behaves like a single entity even though there is no central control. Ants Life cycle, the manga way

9. GEK1530 9 Since the queen is all alone, she has to take care of feeding the larvae and herself and any other tasks that might be necessary (like defending the larvae). Talk about being treated like a queen! A female that has returned to the ground and whose wings have fallen off 1) The (inseminated) female creeps under a stone or wood to make the initial nest. If the situation allows, the entrance is closed off. She then lays about one egg every day. 2) An egg changes to a larva within about 25 days. After some 10 days, the larva forms a white cocoon. The first worker is born inside the nest of Camponotus japonicus.Camponotus japonicus The Life Cycle of an Ant Colony Ants

10. GEK1530 10 5) After the growing period (usually several years) the first sexuals are born. In a given region, the sexuals of the colonies in that region often fly out at the same time so that there is a high probability for a male to meet a female during her nuptial flight. 6) When the queen dies the colony will usually not survive since workers do not reproduce. A young Camponotus japonicus (female) flying up for matingCamponotus japonicus 3) About 60 days after the eggs are laid, the first worker is born. Sooner or later, the number of workers increases to around 10. At this stage, the queen starts to receive food from the workers and makes them take care of the larvae. 4) With a gradual increase in the number of workers, the nest grows. About 2,000 ants live in a single nest of the Camponotus japonicus ant.Camponotus japonicus The nest size increases once sufficiently many workers are born. Ants

11. GEK1530 11 Not an insect of course … The current size of the human brain is likely less than 100,000 years old. Interestingly enough, many things that we find easy to do but are (currently) very difficult to program are associated with processing done in the older parts of the brain – vision, movement coordination … Similarly, things that we find difficult to do but are easy to program are associated with the newer parts of the brain – math, logic … Brains are basically extensions of the spinal cord and started developing around 500 million years ago. Long evolutionary history Short evolutionary history Brain

12. GEK1530 12 Building Blocks The fundamental elements of the brain are the neurons. A human brain contains about 100 billion neurons. One neuron can connect to up to 10,000 other neurons. The point of contact (with a bit of space in between) between the axon of one neuron and the dendrite of another is called a synapse. A neuron consists of three main parts: Body: Where the nucleus resides Axons: For outgoing signal Dendrites: For incoming signals Hair-like structure surrounding the nucleus. There are many dendrites and they are usually 10s of microns in length. Also called nerve fibers. Typically a neuron has only one axon but it can be quite long 1mm or more. At the end it branches out to connect to other neurons. Brain

13. GEK1530 13 Large scale structures The brain has roughly three parts: Brain stem Medulla (controlling things like breathing and hart rate) Cerebellum (controlling things like muscle movement) Basically inherited from reptiles Midbrain Thalamus (information relay) Hypothalamus (regulates drives and actions) Hippocampus (memory formation) Amygdala (information processing for long term memory) Between brackets: major functions but there can be other functions as well. Limbic system Basically alike in all mammals Forebrain Cortex (voluntary motor control) Frontal Lobes (decisions and judgments) Brain

14. GEK1530 14 In both cases, individual units do not gather, store or process information to a great extent. Information is dealt with at the collective level due to an interaction between the units. Ants - Brains The colony/network IS the organism. Comparison

15. GEK1530 15 Ants - Brains Ant ColoniesNeural Networks Number of Units Robustness Connectivity Memory Stability of Connections Global Interactions Complex Dynamics High Local Short-term Weak Trails Exist High Local Short- & long-term High Brain waves Common Comparison

16. GEK1530 16 Ants - Brains The main and most essential difference lies in the connectivity. As a consequence, memory in ant colonies is limited (chemicals can lead to longer-term type memories but this strategy seems to reduce the possible number of memories that can be stored). Contact between ants => short/transient Synaptic connections => long-term Comparison

17. GEK1530 17 Emergent dynamics The behavior of the colony emerges form the local interactions of the ants with a global chemical field! Interaction with the global chemical field Interaction with nearby ants Colony Behaviour

18. GEK1530 18 Chaos in Ant colonies Let us have a look at some interesting behavior of the ant species Leptothorax. Their colonies are usually rather small 50~300 and can hence be studied quite easily in the lab. When investigating the activity level of these ants, it turns out that they are periodically all active or inactive with 3-4 activity peaks an hour. Colony Behaviour Since the periodic activity is one by the collective, it is interesting to see what an isolated ant’s activity level would be. Interestingly enough, this is chaotic! Consequently, the periodic activity is an emergent complex phenomenon.

19. GEK1530 19 Swarming Instead of nests, army ants form so-called bivouacs where up to half a million ants can be packed together during the night. When the light exceeds a certain level a swarm will form that has a clear direction even though locally the ants can seem to run around randomly. The foraging trails can be linear but also fractal like. Colony Behaviour

20. GEK1530 20 In ants as well as in the brain, we clearly see how simple units combine to a complex whole that is qualitatively completely different for its elements. Now let us have a look at another (less well-known) social life form. The amoeba Dictyostelium which displays dynamics that are kind of between those of ants and brains. Amoebae Oxford English Dictionary: A microscopic animalcule (class Protozoa) consisting of a single cell of gelatinous sarcode, the outer layer of which is highly extensile and contractile, and the inner fluid and mobile, so that the shape of the animal is perpetually changing.

21. GEK1530 21 Darkfield Waves The coordinated chemotactic movement of cells can be seen as propagating darkfield waves in aggregates, where the waves propagate mostly as spirals, in streaming mounds where the waves appear as multiarmed spirals in the mound transforming into single waves fronts in the aggregation streams. In slugs waves can be seen to propagate from the tip towards the end of the prespore zone. Professor Cornelis Weijer Professor of Developmental Physiology University of Dundee From his website Dictyostelium

22. GEK1530 22 Lifecycle of Dictyostelium Dictyostelium

23. GEK1530 23 Side view of an older Dictyostelium discoideum slug stained with neutral red. The migration of older slugs (48 h and more) is characterised by a strong periodic up- and downward movement of the whole prestalk region. This is accompanied by the repeated aggregation of anterior-like cells at the prestalk-prespore boundary, where they stop, while at the same time the unstained prespore cells continue to move over the pile. The tip of the slug is lifted from the substrate into the air until it becomes unstable and falls back onto the agar surface. Time between successive images: 20 seconds. Scale bar: 100 µm, (see Dormann D., Siegert F. & C.J.Weijer (1996), Development, 122, 761- 769 Migrating Slug Dictyostelium

24. GEK1530 24 Side view of a culminating Dictyostelium discoideum slug stained with neutral red. During early culmination all cells in the prestalk zone rotate. Later during stalk tube formation the prestalk cells rotate most vigorous at the prestalk-prespore boundary. Time between successive images: 5 seconds. Scale bar: 50 µm, (see Dormann D., Siegert F. & C.J.Weijer (1996), Development, 122, 761-769 Culminating Slug Dictyostelium Time-lapse video showing slug formation, migration and culmination. From R. Chisholm, Northwestern University Lifecycle

25. GEK1530 25 Wrapping up Give it some thought References Gakken’s photo encyclopedia of ants Social Insects Brief course of the brain Dictybase Is an ant farm similar to a neuron farm? Ant hill = Brain? Key Points of the Day Social organization displays interesting similarities to multi- cellular organiztion