This is Paul Foucher, the Conversion Science Network, talking to Bill Hansen.
Bill organized a conference on evolution of olfaction. We happen to be on Christmas Island.
So Bill, why did you choose olfaction as an entry point into the evolution of sensory systems?
I think it's a cool system.
That's the first thing in general. And I also think it's extremely important
for many of the animals that we have chosen to work on.
So I mainly work on insects and then they are very smelled ribbon as far as I see it.
And this has made their olfactory sense evolve in different ways.
And we find different themes, both peripherally and centrally,
where they have gone in different directions.
And as I also mentioned in my talk, that we also find these systems that exploit
the insect olfactory system in different ways.
And there we have like co-evolution going on, which is also very interesting
how exquisite one system can exploit another one to dupe other organisms to
do what they want them to do.
Right, but now you're jumping ahead of it, right?
Because in your talk, you made this point that actually the way we look at olfactory
systems has sort of changed,
that we have initially taken more of this view of, okay, let's just look at
these receptors, let's see what they tell us about the world,
let's see what they tell us about the stimuli that we're processing,
and now this whole process seems to have reversed, if you want.
So can you say something about this change? change yeah that there was also
a little bit about the methodologies that we use so we have.
We we started off with having a lot of we knew
something about the olfactory system but not very much so
what we knew was more or less that we could we could record a signal and we
could use this signal to tell us something about what insects or other organisms
met so therefore we We used the system as such as a detector for interesting odors.
And we used it to identify the odors. And this way we could see,
for instance, how have pheromone systems evolved.
And then we could identify what one moth smells, and then the closely related
moth smells, and the less closely related moth smells.
And we could draw phylogenetic and evolutionary conclusions.
Now, I think during the last decade, this has turned around a bit.
So now we know a lot of the natural things that insects and other organisms detect.
And now we use that to probe the olfactory system.
So we take the reverse entry in.
So we go in from the chemicals where we know that, for instance,
a fruit fly likes a certain substrate. Okay, then we can use that substrate
by using state-of-the-art chemistry.
We can identify what these compounds are, and then we can go into the olfactory
system, and we can look at what part of the olfactory system is tuned to detect
these different compounds.
So we can sort of dissect the system by odors before we dissect the odors by
the system. Yeah, but this seems almost circular now, because this only seems
to make sense if you really know what these odors are about.
How do you then ground this understanding? I mean, it doesn't mean that you
have a full understanding of the chemical composition of what we call an odor,
and therefore you can interpret this.
That's what's good about insects, because we know a lot of different things.
So the first thing that people started dissecting were the pheromones.
So in 1959, Butanant identified the first silk moth pheromone,
what we call by using half a million females.
Today, we can use more or less one female and one male and get to the chemical
identity of this pheromone.
And by then using that one, we can go into the receptor families and try to
pull out which receptor is tuned to these different compounds.
But also, as I said before, one of my favorites is to use deceptive systems.
Because if you want to deceive someone and you want that to be a stable deception
evolutionarily, you have to be really, really good because it's a constant Red Queen race.
So if you're a flower...
And you don't want to pay your pollinator with nectar, which is pretty expensive.
It's sugar, constant production.
Then you have to smell so good that the other guy, he cannot say no, he will come.
So therefore, in many, many flowers, this has developed.
We think of it sometimes as deception, but I find now the more I look at it,
that if you really go into the literature, one of the biggest families,
for instance, that we have of plants is orchids.
And one third of the orchids are deceptive.
So they have all invented ways
of fooling insects to think that they are something else than they are.
And now also in your own research here, you went through a number of stages, right?
Because I think you were the first who highlighted this deception using,
let's say, the smell of rotting meat.
This was sort of the entry point in this whole issue of deception.
And now that story has advanced quite a bit, also using very different kinds of technologies.
So can you say something about that evolution of your own work in this area of deception?
Well, what we actually started with was orchids. That was when we were still
working on pheromones a lot and trying to understand the olfactory background to pheromones.
And then we found these flowers that are really super mimicking bee pheromones
to dupe bees to pollinate them.
This was the collaboration with our Austrian colleagues. And that system is
just as amazing as anything else.
And it was a good starting point on this whole journey because these flowers,
they do very intelligent insects, intelligent within Cytacean Mark.
But I mean, a male bee of this species, the female will only mate with the male once.
And each female has a unique odor. order. So when the male has mated with this
female, he learns the order of that female and he will not go back to her because
he knows that he will not be allowed to mate once more.
Analogously if every flower that
were mimicking these odors smelled the
same the male would also learn the odor of that
flower and would never go back so what does
the flower do it mimics exactly the variation that
you have between the females within these bees and in
this way dupe the males to to go back
and and to try complex how complex is
this variation chemically but it's a 10 compound found
paramount and and there are three
or four of these that vary in proportions to
to a certain extent and in this way they they get these individual signatures
so that's more or less where we started but then we got into these flowers that
smell that's what we call sexual mimicry right but then we have the the brood
site mimicry and that's where we got more and more
interesting because in the first one you dupe males to
go for sex in the second one you dupe females
to go for a place to lay their eggs and that's
where we started on the the sardinian flowers that smell like rotten meats and
and we first we observed the system and we saw that flesh-eating flies were
attracted and what we found in the end was that these flowers mimic exactly
in the order of rotting flesh to attract flies.
But not only that, but they also mimic the increased temperature of a rotting body.
So the flower increases more than 15 degrees above ambient temperature to actually
attract the flies into itself.
So the odor is a long-range attractant, and then the temperature is the short-range
attractant that makes the fly really go into it.
So it's a multi-sensory deception.
Okay. But then in this case, this is all assessed at the behavioral level.
Well, basically sitting there and looking at this long enough and seeing what
the flies do, what the insects do.
No, we could never have done that without having access to the olfactory system. Okay.
First, we saw the behavior in the field, but then we used the olfactory system
of the bee, of the fly, and so on and so forth, to really pinpoint which odors are the active ones.
So we could never have done that without the biological system as a detector.
So which aspects of the system did you look at at that stage?
This was the first stage, so we only looked at the sound potentials,
which is called an electroantenogram.
So you look up the antenna of an insect, and then you kind of record like an
EKG or an EEG, but here we call it an EEG.
And on the antenna, essentially, you have the receptors that would be sensitive
to different aspects of these molecules. Just like in your nose,
you have thousands and millions of receptors on an insect antenna.
An insect antenna is like an inside-out nose.
So there are the receptors sitting on the outside, constantly exposed to the surrounding.
So how is that work advanced now? Because sometimes also in your presentation,
you try to show that you have now much more also electrophysiological access
to the system, and to also more specifically pinpoint,
let's say, the neuronal correlate, if you want, of the chemical structure of
the specific volatile molecules that you might be interested in.
So what has been the advance there?
So, EAGs have been the methodology of choice for many, and it's something that anyone can do.
So, it's today a general method in any lab working on insect semiochemicals.
But then we have now progressed.
So, now we go in and make recordings from single neurons on the antenna,
and then you gain sensitivity and specificity.
But at the same time of course you lose the wide scope of the EEG because in
the EEG you will get peaks more or less for every compound that the antenna
detects but the question is then,
do you get every compound and that's probably not true but if you go for single
neurons then you increase the sensitivity to such a degree that you really detect
more or less everything that that single neuron detects
but you also gain a lot of information on the system per se because you gain
information exactly on what a specific receptor is tuned to detect it.
But in this case, you're still stuck, if you want, at the level of single receptor neurons.
Yes. So if the encoding of the compound, the overall compound,
would require multiple receptor neurons, how can you access that information?
Information, can you perform multiple recordings simultaneously on this system now?
The first way to get at that is, of course, to make exhaustive studies of the whole antenna.
And that's what we've actually been doing. So you record from hundreds of neurons.
Consecutively, not at the same time, but you probe and you run and you probe and you run.
And in this way, we have actually mapped out more or less the full system of an insect,
like the mosquitoes for instance we have really done very
very exhaustive screenings but what i
guess you're getting at is the next level where we can where
we can open the brain of the insect and we can image the first relay center
in the brain which is the antenna lobe where you have the glomeruli and each
glomerulus represents input from a certain receptor type and there we can and
stimulate the antenna with the output of the gas chromatograph,
and then we can see how different glomeruli light up in the brain of Drosophila, for instance.
And in several species, we have such a good map of the brain,
a constant map that is invariant, that we can map certain receptors to exactly
the specific glomerulus that is activated.
So we know that if this glomerulus lights up, Well, that means that the receptor
69A is activated on the antenna.
But now, let's take Drosophila as our example, right?
So what's the odour space that these insects live in? How complex is this odour space?
I think it is not as complex as ours. We have 200-300 active receptors.
They are playing around with 50-60.
So, I mean, it will be more reduced, but still they can encode an enormous amount of odors.
And, I mean, if you look at all these receptors and the combinatorial coding
that you can get between them and by getting a few or more activated and so
on, still already by having 60,
you can code an immense amount.
So in terms of real, let's say, olfactory objects, how big would that space be for Drosophila?
Dozens, hundreds, thousands?
No, come on. We say that with our receptors, 200, 250 active ones,
we can code an innumerable number of orders.
And so it's more or less the same answer
for drosophila they can more or less
code any odor that they are exposed to yeah the base in theory right if we say
all possible combinations of receptor neurons are being used and that's that
space would be very large but do we know behaviorally that also that that's
that size of of encoding space is really being used or.
Well you're getting into very uh interesting also evolutionary questions there
because i mean of course they have a specific repertoire of behaviorally relevant
odors that mean something to them and that's where that's where we got an instep
into this system by using our latest.
Devious flower as well because we find that this flower is targeting different receptor
populations that mean specific things to the fly to
the fly so which which flower is that that's the
solomon's lily in the north of israel aaron palestina
and this one dupes drosophila to pollinate it without reward and what we found
is that it's really hitting three types of receptors one type is saying that
here is fermentation going on one type says that it's It's fruit going on here. This is fruit.
And then the third one says that this is exactly your type of fruit that you
like. So it's really like a three-step rocket.
And it's probably not mimicking one specific thing.
Uh substrate but it's collecting super attractive
parts of several different stimuli
to build up an image of
something that the fly cannot say no to no because why am i asking why i wanted
us to agree a little bit on on let's say the the magnitude of this of this olfactory
space because this this should constrain a bit our questions around the the
antenna lobe itself Because in the end,
if we go from our receptor neurons through our antenna lobe,
sort of in that interaction,
the encoding of this effective olfactory space should happen, I would assume.
So then what does the antenna lobe really contribute to this process?
Because now you're saying, I can just look at these combinations of receptor
responses and actually with that already I can tell you what I'm sensing out
there in the world. So what's the antenna lobe really adding to this process?
Well, I think the antenna lobe adds balance. So we definitely can tell what
the receptor neurons detect by looking at activations of glomeruli.
But as you know, with rosophila, we have the possibility to encode genetically
our markers at any level.
So we can encode one marker at the input part of the antenna lobe,
and we can encode another marker at the output.
And we can compare these two activations.
And then we see that there are definitely things happening in the antenna lobe.
So if, for instance, we have done a very large screening of synthetic odors that we know are.
Positive for the fly so they will go for them in
a bioassay and then we have other orders that
are that are negative so they will not definitely not
they will go away from them and what we find when
we look at the input only we don't find any
correlation among patterns and the balance of the orders but when we look at
the output of the antenna lobe we found very nice clustering of of of patterns
that are encoding attractivity and patterns that are encoding repulsion.
So there is definitely something going on in there that is sharpening the balance
of the message that is coming. So not the discrimination then?
So in this case you're clustering data from the projection neurons or from the
glomeruli, from optical imaging?
Yes, we are doing optical imaging of both the input, so the receptor neuron
input into the glomeruli, and then we're doing optical imaging of the projection neuron patterns.
So in the same fly, you can do both, but using different kinds of dives.
Or you can do it in different fly circles. Sure, of course. But I mean,
you can clearly separate what is encoded in the input and what is going out of the system.
And then we know that in between there are these large local interneurons that
are shuffling messages between the glomeruli.
So are you saying that then the glomeruli are just performing some transformation
from an odor space into a balance space?
In some way, that's what we're seeing right now, that there seems to be something
going on that gives meaning to these orders.
This is really very interesting, but also a bit, in some sense, counterintuitive, no?
Because we have this projection that's going to the mushroom bodies that many
people have talked about, that have been, let's say, really very much involved
in associative learning and especially also valence-driven learning.
So how should we now compare this interpretation to this more standard view
on this happening at the level of the mushroom bodies?
No, but I think there is an initial sorting, and then this gets refined as they move up the system.
And then you have the two pathways. If you know the insect system,
you know that there is one pathway that goes from the antenna lobe to the mushroom
body, and then it goes out into the lateral protocephalogram.
But then we have one that totally bypasses the mushroom bodies and goes direct
to the lateral horn or the lateral crotocerebral.
And there we think that these two pathways are mediating different things.
One is taking the road over the conscious center of the insect brain and then
going out to maybe the executive center.
But one path is going directly to the executive.
And i think our feeling is that maybe
this maybe this is extremely important especially for
this reflexive pathway so that you need a
sorting already here to tell the reflexive pathway
what is going on yeah it would still be strange i mean i'm a bit confused now
because in some sense it would mean that if if my output from my from my antenna
load processing is just if you want good or bad um the balance of of the stimuli
i'm dealing with and i lose my discrimination determination abilities i cannot
say anymore whether it was an apple or an orange.
You would expect that also for let's say your
behavior this might be rather unspecific yeah but
i don't i that's going too far i think because because it yeah it seems like
you have clusters so so within each cluster of of there might be 15 glomeruli
so one saying apple one saying orange one saying pineapple one saying banana
and and i mean but but it seems like what
we're finding is that these that say something good,
and sort of take part in the combinatorial coding of something that is good.
They seem to be in some way clustered and have become clustered during evolution.
And the glomeruli, maybe also 10 or 15, that are saying that something is bad,
they have also become clustered in another way.
And this makes it possible for us by principal component analysis to say, to predict.
Was this pattern, was this activation pattern in the antenna lobe,
for a an attractive odor or was
it for a repulsive all right so you're saying
it's like a multidimensional code it's something like on the
one hand it will tell you what it is like this is a banana and it's good yeah
or this is some acid and it's bad so it will tell you both yeah all right so
but why at the level of the antenna also from an evolutionary and behavioral
perspective it seems counterintuitive that already at this early processing stage we start to label.
Stimuli with respect to valence or not do you
find this intuitive i i don't find
it so counterintuitive because if we we
think that the system has evolved by by glomeruli splitting and forming new
ones you know you have the evolution of a receptor by a mutation of a previous
existing one and this adds a new glomerulus in in the antenna so this means that
maybe you had one detecting something,
a good fruit of some kind, but then you got a refinement that was evolutionarily
advantageous, that they could detect another kind of fruit,
that might be good to separate from the ones they knew already before.
So then you got the glomerulus added, and these glomerulus will very likely
be added close to the one that it was split off from.
And in this way, I see that these clusters have formed.
I don't see that they really, they might not really form a functionally important cluster.
Functionally important character, but I find that it's evolutionarily interesting,
because these clusters have been built maybe from some proto-glomerulus that they all stem from.
So there has been a few bad ones,
a few good ones, but then these have evolved and become more and more,
If the way it's derived now sounds a bit like I can keep on adding glomeruli
until my skull is filled up or my exoskeleton explodes because I have no more
space if I look at the mouse the mouse has 1200,
but they are much much smaller so you can I think you can keep on adding glomeruli
but I think there is also an end to when you need more,
that was the whole issue of the effective stimulus space but then in Drosophila
to what extent is this really genetically predefined or to what extent and isn't
really open to the stimuli the animal is exposed to.
What is predefined? The number of glomeruli that they will express.
I think it is definitely predefined in the drosophila that we work on today.
I mean, we can go from individual to individual to individual, and it will be constant.
And we know that glomerulus D, it's always there.
We can find it. right so so that
that one is is pretty fine but then i'm also sure that
there can be during evolution a mutation that is
advantageous enough to be become fixed in
the population that creates a new a new receptor but
then we also know that receptors can pseudogenize and they
become inactive so so i'm i mean the
over evolutionary over evolutionary time the
the system can change it can go backwards it
can go forwards it can go left or right so
so i'm sure i'm sure that things are happening there but
but they take a little too long for us to observe them right what we can do
is to go and compare species and that's what we're doing so we can for instance
look at all the 12 species of the melanogaster group and and see okay did we
have for instance looked at what does diet change mean?
So we have one species that have started eating only one single fruit out on the Seychelles.
And this fruit smells very, very strongly of a pineapple odor,
ethyl hexanoate, and of acids.
And the acids make the other species more or less die when they eat it.
And here we find a very, very strong effect on the olfactory system of the fly.
So this fly has more or less sacrificed three or four other cells that are active in detecting the.
The sort of normal drosophila melanogaster odors and
instead into those and see like it has put cells that only
detect this new type of fruit so so
it has zoomed in it has totally zoomed
in its its peripheral system towards this
fruit and at the same time it has increased the
center of the brain the glomeruli that takes care
of this input by 200 percent so so
it's it's really the first example we know this from
sex detection in moths that the
male has increased the number of detecting units enormously
and at the same time expanded his brain area taking care of female input enormously
but this was the first time we see such a thing happening with when it comes
to food and diet but then is it is it really the case that for these insects
just allocating more real
estate to the processing of the signal increases their discrimination ability?
Is that all it takes? I would say that it increases their detection ability.
Because these flies, they're a bit weak, and they have one competitor.
And if they are not there first, they will be out-competed by the other guy.
So they're very dependent on detecting the fruit at an early stage of ripeness.
At least that what i told you of the of this
amplification by numbers is not the only thing because
they have also boosted the sensitivity of each neuron
by about a thousand times so so they have they have maybe 200 more neurons and
then each neuron is a thousand times more sensitive so we get down to a detection
limit that very very clearly competes with moth pheromone detection,
which is among the most sensitive we know before.
So we're down to picogram, nanogram of compound being detected.
In terms of these detection thresholds, what's the sensitivity for drosophila
at the periphery for these kinds of stimuli?
And is that sensitivity also boosted by the processing that happens in these
glomeruli in some way? Or you don't know?
What we know is that we go down to levels of moth pheromone communication,
where we can be playing with 10 molecules, which is really homeopathic concentrations.
Then what we have observed in our investigations before is that we sometimes
see a boost in amplification at the next level.
And this boost we still cannot explain. And we see sometimes a similar thing in Drosophila.
So there is something going on after the receptor neuron has detected with its sensitivity.
And then to the output levels of the antenna load, we see an augmentation of
sensitivity that we still cannot really explain.
Okay. So if we talk about things that cannot be explained, so would you claim
that to a large extent you understand the system now?
Could you really make that claim?
Oh, no. Okay. Okay, so where are we with respect to our understanding of this system?
Despite the very big investigations, both from our lab,
but even more from other labs that have come out lately on these local interneurons,
we still don't understand what they do that shuffle the message between glomeruli. Secondly...
We lack one very basic thing, and that is how things are hooked up.
And that's why we're now entering into very, very detailed electron microscopic
investigations of single neurons,
of single glomeruli, and trying to understand how are really receptor neurons
hooked up to local neurons,
how are hooked up to projection neurons.
Are there things feeding back in the system?
Why do you need to know this? Well, you can never understand the system unless you know how it's wired.
We don't even know the basics. No one has ever taken the trouble of looking
at the very, very basics.
There's one study of cockroaches 10 years, 15 years ago, where Dagmar Malun
in Jürgen Birch's lab actually took the trouble of looking at some of the connectivity
of the antenna load. Okay.
But, I mean, you have neurons that are coming in, and you don't even know what they hook up to.
We hypothesize that they might hook up to this neuron or they might hook up
to that neuron, but we still don't know.
Yeah, but look, on the other hand, you do have a lot of electrophysiology of this system.
You know what these projection neurons that are reading out the glomeruli,
how they are responding to different kinds of stimuli.
Yeah, but why do they respond like that? No, but you also know the dynamics of the glomeruli.
So that means apparently something is missing from the pure physiological perspective.
So what is missing there?
And what's the ambiguity exactly you're trying to resolve now?
But there are still different schools.
There is the Nobel Prize winner, Richard Axel School, who say that nothing is happening.
Things are coming in and things are going out. And it's the same.
And then there is the more Gilles Laurent school that says that things are coming
in, then they are modified, and then they go out.
And here, in this case, I more agree with the Laurent school.
I think more and more are doing that.
Of course, things are happening in the antenna lobe. It's not just a relay station.
Why would we have hundreds and sometimes thousands of local neurons shuffling the message,
if you wouldn't need a modification in there
well you could have as i say a simple interpretation i will
need some gain control because concentrations can vary and
i should sort of regulate now the amplitude of my responses and that's it but
that's nothing to do with encoding this olfactory space itself of course you
could have but we don't see that that's not what we observe as i told you we
We see sharpening of images.
We see what we think is contrast enhancement, where one odor can more or less
turn off all the other glomeruli.
It increases the response in one glomerulus enormously, and it depresses the
response in all other glomeruli in the whole antenna lobe.
Okay. So there are definitely things similar to the visual system going on in there.
All right. So in terms of how we encode this olfactory world.
Are you also there looking more at, let's say, the Laurent interpretation,
like we have some kind of possible temporal coding coming out of the system?
Or do you think you see a more spatial kind of coding or rate kind of coding?
So where are you going there?
Because in the end, of course, for the rest of the brain, what matters is not
what the glomeruli do, it's what the projection errors are telling the rest of the system, right?
I think we have to look in both ways all the time.
I definitely think there is a spatial code of some kind, but what that really
means in the readout, I mean, what really means something is which projection
neuron will get activated.
It and and i mean is this
is the spatial code just a product of
of that we we have glomeruli in there and it's parcel
in this way so that what what we
what we choose to see as as a spatial map is is a product of of the connectivity
of the antenna lobe i i don't think that's so important i think the main thing
is that certain receptor neurons come into one location and the message of those
receptor neurons are mainly picked up by projection neurons at the same location.
So in that way, you could say that you have some kind of spatial map.
But then at the same time, I think it's really important to not forget the temporal
aspects, but you also have to choose the way that you look at it.
I get very confused by some of the studies that have been done,
and I still struggle to understand them really.
For what reason? I mean, what's the confusing bit?
Took,
I mean, you get very, very intricate analysis going on of the oscillations going
on, for instance, in the antenna lobe and the mushroom body and so on.
And I'm still not, I still haven't got my brain all ready with that.
Right. It also has been fairly, it's not that this is all clear cut,
right? There's still quite some debate.
Oh, there's a lot of debate. This is the right way to look at it, yeah. Yeah.
But I also have this feeling that we have more to learn about,
for instance, coincidence detection.
I think that is one way that you could augment the sensitivity of the system
in the way that we don't understand right now, so that we see the higher sensitivity
at the second level that we could explain by theory from just a mere convergence.
And this higher increase could be explained by, for instance,
cells going into synchrony on
the antenna, and then this synchrony being detected in the antenna lobe.
And that's exactly what we're trying to get at now by doing multiple recordings
from neurons on the antenna. So have you seen this kind of synchrony?
The analysis, we did it a few months back.
But the analysis to get at, to get really, to get, okay, here the stimulus reaches
both of these neurons exactly at this millisecond, and then go into the analysis
and say that, okay, after 10 milliseconds, they start spiking together.
Right. That takes some time. Okay. So now, we'll talk about the evolution here,
right, certainly in this meeting.
And it was sort of interesting, maybe also ironic, that you said,
well, olfaction is a bit like a visual system. But from an evolutionary perspective,
you could also make the argument that actually the visual system is like the olfactory system.
And so where do you stand on that issue?
Do you see really that the olfactory system is like a proto-sensory system?
Whose principles have been generalized towards other modalities,
or what's your take on that?
I think all these sensory systems are created from cilia.
And cilia were there from the beginning. We have cilia in different forms on all organisms.
And as Heather Eisen was saying in her talk here at the conference,
for instance, probably chemoreception and mechanoreception were the two first sensory systems.
And if we then compare, probably the cilia of the visual system might have occurred
from the mechanosensories and cilia in some way.
And you have got the rhodopsin integrated and so on.
So I think it's very hard to talk about the proto-sense of some way.
I find the old theory... That is interesting because you're sidestepping the
issue a bit by focusing so much at the sensory periphery, right?
You could still argue that the processing that has been performed,
is being performed by the antenna lobe, combined with their projection neurons,
and maybe a little bit downstream from that, that provides, let's say,
the proto-processing principles of any sensory modality,
irrespective of how the periphery gets you the specific signals.
Would you buy that? Also that you would not buy necessarily.
I mean, you can compare it. If you look at audition hearing,
then you have this, that you have certain frequencies being taken care of in
certain barrels in our auditory cortex and so on.
So I think that this parcellation definitely occurs in different sensory systems. On the other hand,
The glomerulus formation we see all over the place.
We see some organisms that have an agglomerular input from receptor neurons,
but I see them as the exception.
I don't agree with some of what we heard earlier here at the conference,
that there are many, many.
I think there are a few where we don't see this.
But take an antenna and move it to the place of a leg of a fly,
and glomeruli will be formed where the nerves hit the nervous system.
So I mean, olfactory receptor neurons have the capability of forming glomeruli
where they hit the olfactory system in more or less any organism.
So this seems to be a general principle that has evolved probably independently
in several different lineages during evolutionary time.
So I think that is a very basic way of organizing chemo detection.
But then if you look at how visual, then you don't see this kind of architecture.
Well, but still you would have some patterns of convergence and divergence that
are especially convergence initially that are regulated in some form.
So you might speculate to say, well, the formation of the glomerulus is like
your proto-receptive field.
And other sensory modalities that's thrown in, let's say, a thalamus,
an intermediate processing stage, just developed a more complicated form of a glomerulus.
But now it really became a mechanism to define more complex receptive fields.
I mean, I'm just sucking this out of my thumb right now, but you could tell
a story along these lines that you could try to defend.
But that's not necessarily one you would buy right now. You would really see
it as separate principles for separate modalities.
Yes, basically. But at the same time, I agree that you can definitely have receptive
fields and that it gets organized, of course.
Organization is needed for sensory detection.
Right. But I don't see direct parallels when I look at the olfactory system
and the visual system, for instance.
So I think more and more science is needed.
But before we can say that, there has been a lot of evolution going on since they were born.
Yeah that that's what you guys tell me so now
um so another thing you're
doing here on the island is to look at specific species of crabs or specific
particular one the rubber crab right so so why is that really how is this helping
us to understand your factory system well here we are really interested in understanding
how does the sensory system adapt during evolutionary time
to go from detection in water to detection in air and this has happened during
the last five million years it's a pretty fast process and we know also interesting
new facts about different kinds of
receptors detecting different kinds of stimuli we know that this the old.
Evolutionarily, probably old ionopropyl receptors are very active in detecting
waterborne compounds and so on.
So what we're trying to look at is basically all the way from the antenna into
the brain, what has happened to these guys.
And it's not only in this species, but then we're comparing to other species.
And what we find really interesting is that different species of crustaceans
have taken totally different evolutionary pathways.
Pathways so out of the five lineages that went down to land we have chosen mainly
two to look at and that's the the hermit crabs and the isopods the woodlice and they have taken,
diametrically different pathways so the the
hermit crabs they have expanded the brain area that take care of olfactory input
to occupy almost 50 percent of their brain while isopods have totally decreased
almost to zero the part of their brain that takes care of olfactory input.
So I find this very interesting. Why do two different types of the same type
of animal, crustacean basically, when they go on to land.
Go in so diametrically different evolutionary directions?
And that's what we're trying to understand. To understand it, we do,
do we have we are studying the antenna we're studying all the receptors set
up so far we have only found gustatory receptors and ionotropic receptors we
cannot find our type of olfactory or the insect type right and at the same time
we're doing the brain anatomy we're looking at
how it's built how things project how the different centers are constructed
comparing comparing between isopods and crustaceans and the hermits and so on.
We were in the middle of that project, but evolutionarily I find it extremely
interesting because we have sort of an experiment that has been going on during
the last five million years.
Right. But now it seems a bit counterintuitive, right? Because aren't you sort
of swimming against the current now?
Because, you know, we have preparations like Drosophila, like the mouse,
which are in some sense becoming now the standard preparation because we know so much about them.
And what we have is molecular access to them that they can become highly controlled
experimental preparations.
And now you come and you find some really very odd crab species to start to
look at, about which we know very little.
So isn't it a high-risk operation?
Of course, but at the same time, I think it's highly dangerous to get stuck
only in the model species.
So we should use the model species to the utmost, and I really like working
on Drosophila, But at the same time, of course, we need a comparison with other systems.
Otherwise, we get extremely narrow in our view of the world.
And we get totally Drosophila-centric or Musa-centric or whatever you would say.
And I mean, we need comparison. And to understand evolution specifically,
you can never understand evolution only by looking at Drosophila melanogaster,
an animal that has been totally associated with humans during the last 15,000 or 25,000 years.
So it's really, really needy that we also keep our eyes open,
and that's what I really like to do.
I like to use the model system, but I also really like to go outside of that
and to try to understand what has really gone on in nature.
Right. So then how many years will it take for us to understand this crab now?
Oh they you know when you start that
on a new system like this one first you have
to nail down the the ecology of the
species to try to understand what they are doing and what
you should basically do is just to sit down in your ass for one year and watch
the crab but we don't have time to do that most of us so are you good in this
we i now have one postdoc on the island and she's doing massive marking of the
crabs and we're really trying to get the impression of what's going on.
And we're marking them with GPS loggers and so on to try to understand their
movements and basically how they interact.
But all of this is supposed to form the base for...