Transcript Social Insects - Frederick H. Willeboordse

Nature’s Monte Carlo Bakery:
The Story of Life as a Complex System
GEK1530
Frederick H. Willeboordse
[email protected]
1
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.
2
GEK1530
Social Insects & Amoebae
Ants
Dictyostelium Amoebae
3
GEK1530
Ants
What are ants?
Fascinating!
Camponotus japonicus
The Messor aciculatus
ant makes the deepest
nest in the world. The
depth is about 4 m.
4
GEK1530
Ants
What are ants?
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)
5
GEK1530
Ants
Ecological Success
Ants are hugely successful ecologically
speaking and are common in almost all
terrestrial habitats.
In some rainforests, the dry weight of ants
and termites is about four times the dry
weight of all the other land animals
combined!
There are about 10,000 known species which is more than twice
the total number of mammal species.
6
GEK1530
Ants
Individual Abilities
Generally, single ants behave in a simple
way. Indeed, alone, an ant is perhaps not
really an ant at all!
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!
7
GEK1530
Ants
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.
Life cycle, the
manga way
8
GEK1530
Ants
The Life Cycle of an Ant Colony
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.
A female that has returned to the ground and
whose wings have fallen off
2) An egg changes to a larva within about
25 days. After some 10 days, the larva
forms a white cocoon.
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!
The first worker is born inside the
nest of Camponotus japonicus.
9
GEK1530
Ants
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.
The nest size increases once
sufficiently many workers are
born.
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 mating
10
GEK1530
Brain
Not an insect of course … 
Brains are basically extensions of the spinal cord and
started developing around 500 million years ago.
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 …
Long evolutionary
history
Short evolutionary
history
11
GEK1530
Brain
Building Blocks
A neuron consists of three
main parts:
Dendrites: For incoming signals
Hair-like structure surrounding the
nucleus. There are many dendrites
and they are usually 10s of microns
in length.
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.
Axons: For outgoing signal
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.
Body: Where the nucleus resides
12
GEK1530
Brain
Large scale structures
The brain has roughly three parts:
Forebrain
Frontal Lobes (decisions and
judgments)
Cortex (voluntary motor control)
Limbic system
Midbrain
Basically alike in all mammals
Brain stem
Thalamus (information relay)
Basically inherited from reptiles
Hypothalamus (regulates drives
and actions)
Cerebellum (controlling things
like muscle movement)
Hippocampus (memory formation)
Amygdala (information processing for
long term memory)
Medulla (controlling things like
breathing and hart rate)
Between brackets: major functions but there can be other functions as well.
13
GEK1530
Comparison
Ants - Brains
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.
The colony/network IS the organism.
14
GEK1530
Comparison
Ants - Brains
Number of Units
Robustness
Connectivity
Memory
Stability of Connections
Global Interactions
Complex Dynamics
Ant Colonies
Neural Networks
High
High
Local
Short-term
Weak
Trails
Exist
High
High
Local
Short- & long-term
High
Brain waves
Common
15
GEK1530
Comparison
Ants - Brains
The main and most essential difference lies in the connectivity.
Contact between ants => short/transient
Synaptic connections => long-term
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).
16
GEK1530
Colony Behaviour
Emergent dynamics
Interaction with nearby ants
Interaction with the global
chemical field
The behavior of the colony emerges form the local interactions
of the ants with a global chemical field!
17
GEK1530
Colony Behaviour
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.
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.
18
GEK1530
Colony Behaviour
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.
19
GEK1530
Amoebae
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.
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.
20
GEK1530
Dictyostelium
Professor Cornelis Weijer
Professor of Developmental Physiology
University of Dundee
From his website
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.
Darkfield Waves
21
GEK1530
Dictyostelium
Lifecycle of
Dictyostelium
22
GEK1530
Dictyostelium
Migrating Slug
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, 761769
23
GEK1530
Dictyostelium
Culminating Slug
Lifecycle
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
Time-lapse video showing
slug formation, migration
and culmination. From R.
Chisholm, Northwestern
University
24
GEK1530
Wrapping up
Give it some thought
Key Points of the Day
Is an ant farm similar to a
neuron farm?
Social organization displays
interesting similarities to multicellular organiztion
Ant hill = Brain?
References
Brief course of the brain
Dictybase
Social Insects
Gakken’s photo encyclopedia of ants
25