Behavior is written in the genes.
All of us have innate behaviors;
all animals are born with behaviors.
Behaviors which through evolution have become more complex.
In many aspects,
behavior in males and females of the same species is different.
These differences in behavior
are due to differences in the wiring of the nervous system.
At the same time, these differences in wiring are established genetically.
Aggression is a behavior that in general is specific to males.
We see it in species that are very different,
evolutionarily apart from each other.
The way each one of these species fights is different
but the mechanisms are similar
and the reasons are almost always the same.
Males fight for females, for food, or for territory.
I study aggression in flies.
You are about to see an attack.
One animal is going to stand up
and is going to hurl its body-weight at his opponent.
The other one, meanwhile, is going to try to escape.
Why do I study aggression in flies?
Because the behavior, that I'm interested in understanding,
is the same, and the system is much simpler.
It's like studying a model.
Sometimes it happens that the other animal,
instead of escaping, stays and starts to fight,
and then something we call "boxing" occurs.
Something crucial about attacking is that only the males do it.
The one who attacks first is much more likely to win.
And males only attack other males.
Females never attack.
So, why study behavior in flies?
Because their behaviors are the same as ours:
Flies sleep, eat, court, fight, learn, and remember.
The nervous system is much simpler;
and the genes that play a role in this behavior are very similar.
So, studying aggression in flies allows us to understand
how this behavior develops in other species.
A key element when deciding whether to court or attack
is determining the sex of the other animal.
All males are programmed to decide between courtship or aggression,
but the sensory signals they use
to see if what is in front of them is a male or a female are different;
for example, in our species visual signals are very important.
This is what a fly has in front of itself.
So, how does it decide?
Evidently, it somehow makes a decision
because what it is going to do is very different in each case.
When there is a male entering its territory,
it is going to start attacking
and to chase him everywhere until the other one decides to escape.
When there is a female, he extends his wing for her.
As you can see, he literally courts her.
He chases her everywhere,
he sings to her until he has finally won her over.
So the question is, how does it know?
How does it decide?
What are the key signals that it uses to decide if it has to court or attack?
If we can identify these signals, can we change them?
Can we invert this decision?
In insects, like in many species,
chemical signals called pheromones are very important.
These signals are produced by one animal and detected by another.
So, then something we decided to do
was to switch the pheromones, change the scent.
To make it happen,
we manipulated the expression of one gene, called "transformer".
"Transformer" is turned on in females and turned off in males.
So, something that we can do is to mute the "transformer" in females
and force its acquisition in males.
In doing so, we masculinize females and feminize males.
But not all over, we aren't going to manipulate the entire animal.
We are going to choose certain parts,
in particular the cells which produce pheromones.
What we can achieve are females that have masculine pheromones
or males that have feminine pheromones;
then we are going to see what is going to happen
when a normal male, unmanipulated,
meets a female that has masculine pheromones.
This is what happens, it attacks her.
When she enters his territory, he does something
that he would never do in front of a normal female,
which is start attacking her.
When we carried out the reciprocal experiment,
what we found was that males with feminine pheromones were courted.
What does this mean?
That males are genetically programmed to court
when they find feminine pheromones
and to attack when they find masculine pheromones.
But, this behavior,
this innate behavior that is wired in the brain --
court if there are feminine pheromones, attack if there are masculine pheromones --
can it be changed?
Could it be that an animal as simple as a fly
could learn from its experience and modify a behavior which is innate,
something which is wired in its nervous system?
To respond to this question, we did a similar experiment.
Again, we manipulated the "transformer",
but this time, in the females' brains.
These females still have feminine pheromones
but they act like males.
We muted their "transformer" in the brain to turn them into aggressive females.
They not only dislike courtship completely but they also attack.
We then asked ourselves,
what is a male going to do when it meets a female
that has female pheromones but is aggressive?
The first thing it's going to do is court her as much as possible.
It chases and chases her, extends its wing, sings to her,
but the moment comes when he decides to change his behavior.
The moment comes after so much ineffective courting
and in addition to being attacked by her;
he says, "enough is enough" and ends up attacking her.
This means that even an animal as simple as a fly
can learn from its experience and modify its behavior.
And not only that.
When there are fights between two males, there is always a winner and a loser.
After a male loses many times
what happens is that he suppresses this behavior.
He stops fighting.
This means that even in an animal as simple as a fly
not only behavior is in the genes,
but the ability to learn from experience and modify it is there, too.
Thank you very much.
(Applause)