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>> Bill and Esther is their bio engineer biology bio hearing out that I don't. Really agree and this is here I'm not going to give a long introduction but amongst his many awards he is a member of the AAA s. and MacArthur winner so it's a really great.

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Here and I think. That Thanks everybody like I it's just been such a great reception so far I'm kind of astonished because there's really not that many people account tech who. You know could give a rat's ass about what I do so it's I feel a little bit like like like the aging you know rock musician who can't sell any albums back home but finds he's still big in Japan or something.

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So anyway it's it's enjoyable to be here I've never visited Georgia Tech or Emery I've been here a couple times before. In the city but it's just great to be here on campus so I want to talk to you today about some of the research reentering in my laboratory over the last few years that have to do with behavior flies and the aspect of behavior that has you know most interested my group.

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You know for really up to 3 decades now it's flight behavior in flight evolved 4 times we know pretty accurately exactly 4 times in the history of life in birds bats pterosaurs and in sacks and I think it's just worth. Saying a little bit about why Flight is important and why whenever flight evolved it led to this enormous diversification of species and that's still true with with with birds and bats and insects that it was true for pterosaurs before they went extinct so this is a picture of students of comparative physiology will recognise it it's what it is a plot each each point is a measurements made in a given animal that vary across 9 orders of magnitude in body size you know basically from from ants to elephants and what is plotted is a physiological measurement called the cost of transportation the energy required to carry a given amount of body mass a given distance and what's remarkable about the data is that all all the data falls on a single curve on this log log.

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Plot and this is for animals that walk and run if you plot similar data the cost of transport for animals that fly you again quite remarkably find that the data fall on a lot of similar slope it's displaced downward about 10 fold. On the on the ordinance axis which means that similar sized animals can can fly 10 times more cheaply then than walking and this is how profound consequences for the history of life really because it it makes migration a viable thing flying long distances you know across vast landscapes where there's no food available to get to places that where food is available which of course means that all around the planet there's biomass on the move and that biomass on the move has consequences for the animals that rely on that biomass So it's a Porton engine in world ecology just to beef fair to my it theological friends you can plot the same data for swimming and again you get the same line displaced even lower which of course makes sense because the other place where you find migratory animals is in the oceans with with whales and Salmons and so forth.

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But. There's something special particularly I think it gripping about the evolution of insect flight which happened about 400000000 years ago at the transition between the slurry into the Devonian period. And insects as I'm sure you all know at least of macroscopic organisms are the most species rich group on the planet and number of described species outnumber everything else and within insects I've always gravitated towards flies which is the great evolutionary biologist David Grimaldi describes really the most ecologically diverse group of of insects you find them in all on all continents in all different lifestyles.

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And they're just great flyers you know they're called flies for a reason and and just to illustrate this this is a sequence shot in my laboratory at 7 a half 1000 frames a 2nd an infrared lighting that shows 2 flies there on a collision course and both flies can see the other fly in their field of view and they elicit within just a few tens of milliseconds this whole sequence last 200 milliseconds or fraction of a human eye blink the animal see each other perform this beautiful rolled bank term to redirect their dynamic for Specter so that they avoid collision and it's just these sorts of behaviors being studied from the sensory side of the motor side that really really been the you know the the.

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Sub stratum for the research within the laboratory what I'd like to do today is is to really focus on one kind of 2. Specializations that we find in flies and I like to put things in evolutionary perspective and I also like to think about the evolution of organisms particularly flies within sort of clusters of adaptations because I think this is sort of what the the fossil record would suggest one cluster of out of patience that dates back to the origins of insects I call it the Devonian tool kit so fly share these these ancient modules with all insects and then a later a cluster of adaptations that occurred back in the Triassic when one flies a radiated so these would be traits that flies share in common with with other flies and the 2 it's the 2 specific features I want to talk about are navigation.

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Which I think makes sense and. Colloquially and the dip different flight motor which might have to explain a little bit more detail but let's think about navigation if you think about insect it navigates you probably think about you know the monarch butterfly that's famous for these transcontinental. Motor movements from from Canada down down to Mexico the entire loop taking many generations but what you may not appreciate what is emerging over the last 30 years or so is that you know we're aware of monarchs migrating because we're big we can see them but many many many insects migrate or disperse over very very large distances and and my focus really goes back to the work of Theodosius Dobzhansky.

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The famous a geneticist who was working with his proteges back when he was actually a Cal Tech before he kind of got booted out of Caltech but in the early days of being able to identify genetic differences among populations with the Johnson and his proteges recognize is that species of endemic to softball of flies various different species but populations that were at very different locations 100 sometimes thousands of kilometers apart were genetically very very similar and this raised a bit of a paradox because at the time people could imagine how these you know 2 to 3 millimeter size animals could actually fly those distances in order to you know share their genes with with other populations but in the late seventies and early eighty's a prominent population Genesis Jerry Coyne and other folks collaborated on a series of experiments of which I'm just going to talk about one which tried to sort of ask the question maybe we're underestimating what these little flies can do and in one such experiment that was performed in Death Valley National Park they collected from the wild.

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Roughly. 100000. Which $60000.00 were the commentor software Melanie gaster. Or. A sibling species so they released 60000 fluorescent Li tagged flies and then they had buckets of banana and yeast mash located about 7 kilometers in one direction 15 climbers another direction and the next day at 9 am they looked in those buckets to see if they caught anything and they caught kind of quince then only 17 of these fluorescent Lee tagged flies.

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These very very large large distances across the desert so this would suggest that we really are underestimating the capabilities of these little tiny insects but there's this was like a 3 page paper. It's not there's no data on how long it took the flies to fly it's whether they fanned out across the desert and it's just the flies that happen to fly towards the you know the banana mash where the lucky ones very little detail was known so what my lab has been trying to do in recent years is to replicate these kinds of studies but using.

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Somewhat more modern technology Death Valley where is now a national park you're not allowed to release 100000 of flies but fortunately there is Bureau of Land Management land nearby where you still have to get a permit that causes a little bit of consternation but nevertheless it's possible to do these experiments and these were pioneered by Flora's fund Kate leech in France Cheska Ponce my laboratory and this is what it looks like so it's an old big there's absolutely nothing there so it's a perfect kind of place to do these sorts of experiments and so what we do is we have traps that have a camera system with a computer that is capturing the images of flies arriving on the track and the trap has little mesh funnels that allow the flies to go in if they so care to to debate the bait being treetop apple juice fermented for exactly 24 hours with champagne yeast.

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Which makes e o 2 and ethanol which are the main long distance cues that the flies are using So this is what one of these releases looks like shot by me cowering on the ground because this is sort of what it feels like to release. They get in every orifice and I mean every So I'll just leave it at that.

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And so the experiments we done a lot of different geometries but in the typical experiment we have an array of traps usually 10 traps in a 2 kilometer ring around the released site. At and this is just a kind of a cartoon of what we think is going on I'm not going to show you all the data that justifies that this is actually happening but flies leave the release some flies fly and affix direction they hit the plume that's coming from the trap and then they crawl up and down the plume using a algorithm called Cast and search that I don't have time to talk about but then they get to the trap and that's where we capture them with the cameras that's how they we capture them in the traps some flies are sort of lucky that they fly correctly to the trap and they get there right away because they don't have to crawl up into the plume and some flies I don't know if you say that the lucky ones or the unlucky ones but they had out in the you know they're the tech that just head out into the open landscape so we have a weather system that is telling us the wind magnitude interaction every time we do one of these release experiments and because we've done this a number of times at different times we go out the wind is sort of stronger and stronger and from a different direction and using wind as an independent variable turns out to be rather important so this is sort of plotting some of the data we have all oriented it so the wind the wind direction was down and the important thing I want you to note is that it really depends on how strong the wind is blowing if the wind is relatively.

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Gentle we get a more or less uniform distribution of flies captured at all the traps where the stronger and stronger the wind is we we tend to catch fewer flies and and more of them just downwind traps. And so basically what I'm trying to tell you is the data that's necessary to develop a model of what we think the flies are doing so one critical feature of this model is if you take experiments were done when the wind was relatively gentle and you plot the time course of the flies that are arriving on the trap or inside the trap that we can actually also capture with the camera so it's potted in the green and black trace is is the arrival time of the Flies on the upwind traps and the downwind traps and the remarkable thing is that although more are going downwind but they're arriving at the same time which means the Flies must be regulating their velocity so that flies that are flying into the wind regulating their velocity using the optic flow their visual perception of their own motion are flying at the same speed as the flies that are going with the wind so they must be sort of regulating their speed in order to to have this fixed ground speed so that turns up will be a kind of critical feature model.

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And so. One way to sort of visualize how we can sort of test different hypotheses is. We get these arrivals on the trap and the minimum for the 1st flies we see on the trap sort of represents the minimum flight time probably the flies that were lucky enough to head towards the trap after their release and so for every trap and every experiment we can measure that minimum ground speed that the flies were flying and we can also measure the component of wind velocity in that direction which of course to another to.

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Up you know that parallel wind velocity would be in a slightly different direction so if we plot this estimated ground speed against the parallel wind philosophy we get this distribution of points which has a lot of variability as expected field experiments but there is sort of kind of certain features of it that when the wind speed is low whether it's blowing against the fly or with the fly the flies the estimate of ground speed you know doesn't really change but as as the wind velocity gets stronger and stronger.

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The Flies tend to move at a speed that is best approximated by the wind so they're sort of at vector being at a high wind velocity but they're regulating their their ground speed at low wind velocity and so this is what I'm just going to show this in vector form not mathematical form but this allowed us to develop a model and model is as follows each fly chooses a heading a heading orientation in the world and I'll talk about this later relative to the position of the sun and every fly just sort of randomly choose a slightly different heading it maintains ground speed in the forward direction using its visual system.

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Yet. The wind it allows the wind to push itself sideways so it doesn't regulate the sideslip that it experiences it only regulates the influence of the wind along its launch a to nobody axis and so the result velocity vector would look like this of the Flies or are not necessarily flying along their their lawns you to know body position so in cheesy Powerpoint animation this is sort of what the behavior would look like so all the flies each one chooses an orientation relative to the sun and the flies move away with a vase the vector that's determined by this forward ground speed regulation but also this unregulated sideslip generated by the wind so when we implement our models via simulation with just a few free parameters their preferred ground speed there's some sort of saturation they you know they can't generate infinite airspeed so they have a maximum airspeed in a minimum airspeed and we do you know using computer thousands and thousands of simulations using the wind speeds that we measure in the field we get a distribution of within the model simulation that you know matches the measured values from the field pretty well and I don't really want to go into this lies like way too complicated but just to give you some sense you were trying to approach some rigor this is testing the model that I just described to you about against a whole bunch of other models that are in the literature on migratory insects that don't involve regulating groundspeed don't involve the this phenomenon with the animals maintaining a fixed heading.

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As they move and so far you know our model sort of fits the data we measure in the field better than any of the the other models that are out there now what we're trying to do is to go back in the laboratory and test this model more rigorously using something we call a virtual desert where we have an animal that's tethered to a fine pen that can rotate itself by changing its direction we can present it with with ground flow through an electronic display and the animal is sort of sitting inside a wind tunnel that we can position at arbitrary orientations with respect to to the flies so we you know we have a way of sort of more specifically testing the predictions of our model but I want to rather than talking about preliminary data from this I want to sort of move more towards the neural biological perspective and talk about this one critical feature of a model that has to do with the animal using the sun to orient its body position and the fact that each fly somewhat counterintuitive Lee will choose a different orientation in which to maintain during the migratory flight so I want to make a clear distinction between 2 behaviors.

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Photo taxes would be a behavior in which an animal flies directly towards a source of light or directly away from a source of light if it was a negative photo taxes but the behaviors I'm talking about are described as Mino Taxus where what the animal does is maintain its or it's some fixed orientation some angular orientation relative to a sun that then maintains over time and so the way we study this in the laboratory and this is the work of Rado who's still in the lab but she's about to start her own research group at University of California Riverside we have flight simulators where we tether flies to find little pens we use a camera system to measure the motion of the wings and from that camera system we can infer whether the Flies trying to steer left or right and we can allow it to play a little video game where it can control with its wing motion the angular velocity of this one small bright spot which we consider the sun and we're making the assumption that the animal is responding to it.

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As it would a son so in a typical experiment what you see if you plot the heading of the animal over time is that for a couple minutes it sort of spins the sun all different orientations and then it locks in on a particular angle that is not necessarily putting the sun right in front of it in this particular case the animal actually chose an angle of about 90 degrees and so if you you can plot these data as it is often done in the orientation literature by plotting the vector strength which is sort of the sum over the whole experiments of all of the instantaneous orientation vectors the length of that vector goes from 0 to $1.00 and the closer it is the one the greater fidelity to a particular orientation and then that you orientation is plotted by sort of allowing like like the hands of a clock and so what these data show is if you do this to a bunch of flies.

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Each fly will sort of choose its own orientation and very interesting if you stop the fly after it's started in the arena you give it a rest up to 2 hours and you test it again the heading to in the 1st experiment is the same the correlate to the heading The 2nd experiment so they're remembering this orientation angle over long periods of time which raises interesting neuro biological consequences so now.

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I need to tell you about something especially if you're not interested off of a person that is really kind of revolutionize the world maybe that's you know overstating it because not that many people care about flies but. A super a breakthrough if you will in the study of navigation and spatial organization place memory in flies through the work of several laboratories most notably a vivid cameraman at you know a farm in a former post-doc of mine who says Rockefeller there's a region in the brain of the fly called the central complex because it's complex and it's central.

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And it's a region of near a pill. That has 2 very important structures that I'm going to talk about one called The Apprentice Reaper bridge which is the sort of bicycle handlebar region and then the ellipsoid body that literally is a Taurus it's a it's a donut in the brain of the fly you know just like Homer Simpson mapped in the brain and these regions of the brains contain a set of neurons called the e.p. Gene Iran's that in this region of the brain the dent writes like little slices of pizza around the pizza.

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And what those regions in code is the as a method orientation of the animal so you literally have a circle that encodes 360 degrees of spatial orientation and then the terminals actually represent that 360 degree orientation twice so if what happens when the animal is either walking or flying is that there is a spot of of high activity that rotates around that circle depending upon what orientation the animal is in space and a lot of interest in this because it represents it represents a neural structure called a ring a tractor of that is sort of was sort of a hypothetical thing and it seems to be a manifestation or ring attractor you sort of have a whole bunch of different modules that only one got 1111 module can be active at any given moment and it hits all the other ones around it and so let me just give you a sense of what it looks like so this blob of green activity that's circling around this region this is a fly in a flight simulator recorded in our laboratory as the fly is sort of steering around it's its representation of where it's heading is.

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Is causing this bump to move around inside this circular region in the brain so here's another such movie imaging the pattern of activity the prisoners who were Bridge where you sort of see 2 windshield wipers of activity moving back and forth because as a mental heading is encoded twice a so we can actually have the animal performing this a sun orientation while we're recording the activity from this region of the brain and what you can see is the position of this bump you know around the circle is tracking the position of the sun around the animal.

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And what Isabel and Kate have done in the laboratory these imaging experience with the Eros and these are techniques that are available for software there are very very very specific driver lines for the cells in these cells only. So it's possible to silence these neurons by expressing an inward rectifying potassium conductance and when you do that you get a rather interesting result So here's the control data.

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Where it's basically all the genetics are the same except that the sequence of this potassium channel is missing and then you see the typical experiment that you know each fly chooses a heading holds that heading over time if you get rid of these compass neurons what you end up with this photo taxes the animals can maintain the sun in a given position but they can only fly directly towards it and so this is sort of a cartoon the result that with a compass system intact the animal can perform enough taxes without the compass system you end up with just photo taxes and the reason why we think we think the the foetid tactic circuitry I don't have time to go into the evidence for this is sort of a completely different parallel pathway so you you take away Mina taxes and the system sort of collapses to just flying towards the bright object and what we're trying to do now in the laboratory and what Isabel wants to do in her future research is get down to the.

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Other elements of this circuitry to really understand how. The animal can use this compass signal and compare it to some representation of the heading that it's trying to maintain and how that discrepancy between like where I'm trying to hold the sun where the sun is causes a you know an error signal that makes the animal steer so that's sort of where things are going what I want to do instead because I think it's kind of more interesting from the perspective of of animal evolution is.

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Just mentioned that thing that fascinates many of us about the center complex it is incredibly conservative across species you find almost identical structure and grasshoppers cockroaches wasp dung beetles moths full of flaws bees and so forth and the work that's most personally done by by Stanley Hinds there is a emerging picture about how this this ancestral.

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Compass system has has been tweaked in a bunch of different crown tax to do different things so you for example in modern butterflies they also perform a solar meta taxes to do their migration but in that case and set of picking a random heading they pick a heading that will either send them south or north at the right time of year in the case of of bees they use this compass setting in order to go back and forth from the hive to the flowers that they're forging and so forth so you know it's just a very very interesting system not only to think about a complicated copy Taishan like where I am in space where my heading but also to think about the evolution of nervous systems because this core hardware this Devonian tool kit has been tweaked to get it to do different things and I just want to mention one story.

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Where that is just going to be a behavioral level but has to do with the role of this compass in tress real locomotion so. The cataclysm is an ant is a is a desert ant lives in Tunisia and has an amazing behavior they live in a place where it's so hot that they can't lay down chemical cues so every aunt has to leave the nest it goes on a Securitas route finds food and they go straight back to the to the nest right distance right angle because it is performing a computation known as path integration and or do a path and Gratian you need a compass and so it's using exactly the same we believed.

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Is using exactly the same compass in the central complex you need some sort of metric some sort of measurement stick and you need it you need a form of memory and rigor Vainer and his proteges including with her have done a lot of fantastic experiments to determine that the sun is the compass largely just as it is in fruit flies and the measurement stick appears to be mostly counting with your how far you walk with your legs and these experiments were done by picking up the ant when it found the food and gluing stilts to its legs so when the animal would walk they would move further a purse tried then they would without the stilts so they would just overshoot the nest and then the easier experiment is to chop the legs in half and you get these little stumpy and these guys get halfway to the nest and they start looking for the nest so these are really classic experiments showing that the flies have a step or so what I would like to tell you is that as exotic as this behavior of path integration is we have very strong evidence that flies exhibit this behavior as well and I think it's actually something that probably all insects can do and it's a slightly different context so Vincent a tear was a famous insect physiologist who described the behavior back in the fifty's that he called dances.

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And what that dance was is is a hungry fly if it finds food it starts to do these sort of loopy behaviors around the food going away and coming back going away coming back and what's the purpose of this with the idea is if you find food food tends to be patchy in the environment so you find food but don't stuff yourself because you know there might be a better breed nearby you just do a little local search and you might find better food and so Irene can when she was working and laboratory we developed a system so there's a fly walking around little chamber in the middle where the red dot is a yummy drop of yeast this is a hungry fly yeast is like the flies favorite food it has like the protein that this female fly needs to lay eggs and so forth and the fly searching all around it's paying no attention to these because it hasn't discovered it yet and then it finds the yeast and then immediately after it it eats the least little bit its behavior changes and it exhibits this behavior I showed last slide it kind of walks away from the food goes back to the food it performs these this behavior we call the dances and another experiment that Irene did to show that the fly must have a spatial memory of where the food is in this experiment the food was originally in the arena but I quickly moved it to the edge of the arena so the food is not there anymore so all the chemical if there is any chemical cues or visual cues you know they're over on the side of the arena with the red dot but the fly keep circling and going back to the place where the food used to be this is also done in complete darkness it could be done in animals that have their factory capabilities.

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Compromise So we know. And I'll give you further evidence that this is done like the ants if you thought of even the compass senses that you thought of because they have no access to the sun they're keeping track of their orientation they're keeping track of how far they go back so.

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The methodological breakthrough that simplifies our analysis of the system which is easy and flies was implemented by Roman in the laboratory so we can even get rid of the food instead of give the animals food we can give them the up to genetic sense of food so we take sugar receptors and we can express Chatterer Dobson in those sugar receptors so in this case the fly gets a little sugar reward if you will only when it goes to the center of the arena and so even without the food we can get this sort of beautiful rich Anetta.

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Dense behavior I'm sort of talking to you guys and I realize there are guys over here so maybe I should I should come over here occasionally so that the problem is this is a mess of spaghetti like what the hell is going on and this giant mess of spaghetti So what we do is work with with with simplified geometry saw.

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The honey in a laboratory has a paradigm where the fly performs these behaviors but it only has this linear circular track and just walk around the circle and so here's a little movie of The Fly moving back and forth but we can all again have these sites where it gets the opposite genetic reward so we can basically perform dance in one dimension so the way we analyze these data is to sort of mathematically wrap them out so we're plotting the angular position of the fly over time and here's what a long sequence looks like so before the op genetic Ward is activated the flies are just walking all the way around the arena and then when the up to generic reward is activated every time the fly goes past the spot it gets a 2nd of.

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Sugar sense and then it's refractory for 9 seconds so in order to get more it has to like you know go away and come back and the flight the flight does as it goes away from the reward site goes back so it's performing these sort of one dimensional dances Ok so the most interesting part of this whole experiment is what happens when we turn the reward away and you notice that the animal continues to go back and forth around where the food was the virtual food but there is no food there there's no cue to food because there was never food there to begin with and.

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So what we do this analysis we carefully kind of keep track of this behavior right after the food activation is over when you know everything that the flies doing must be depending upon its It's its memory of where the food was and in particular I'm going to just do a really you know kind of ridiculous and boring drill down into just the 1st couple of movements the fly does the distance between the last food sensed and the 1st time it turned around we'll call our not for the sort of 1st order you know 0 order run and then the 1st run between that turnaround point and the next turnaround point we call our.

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R one so if you plot those against one another you plot the distance from the food to the 1st turn point and then the 1st turn point to the 2nd term point you get a very strong leader relationship with a slope that's not significantly different then then one and so the model just to spill the beans what we think the animal is doing is it's how it's measuring how far it goes from the food and it's using that distance to determine how far it walks back to the other direction so it's doing path integration in this very simplified one dimensional fashion Ok so you could say Well but wait you could get this relationship just because some flies walk a little bit and other flies walk a lot that has nothing to do with what an individual flies remembering and so you can test for that at least partially by testing the same fly again and again and again on the same task and what you find is that the you know this trend of this linear relationship between 0 order run and the next run you find within each individual fly for all the flaws so it's not just a trend that emerges because different flies are different it seems to be true friend of the emerges because the you know the flies are experiencing something different when they walk further versus when they walk.

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Shorter. So you could ask an interesting question kind of flies remember 2 locations where you have 2 sites of food. And you do the same experiment you look at what happens after the food's no longer available and if use for example look at the distribution of these turnaround points after the food is no longer available they you know that they're a pull apart when the food sites were further apart so this might make you think of how they must be able to remember to locations but I don't think that necessarily is the case and in fact if you plot this 1st run versus the 2nd run for the one food case for the 2 food case and for another 2 food case but where the iter food distance was larger you find exactly the same relationship same slope but but but the offsets of the curves are different the y. intercept are different so you know what we're proposing is that you know there's sort of one thing the fly is remembering is the distance from the food to the 1st time it turned around but then there's this sort of like offset distance which is basically the overshoot how fast it walks past the food when it's going back.

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If you plot that overshoot as a function of the distance between the food during the experiment you've found another relationship so it suggests that the fly is performing and remembering another spatial inner Grohl it's measuring the distance between the food over time and storing that value so that what you end up with is that the entire run length is sort of the sum of 2 you know remembered integral spatial integrals the distance between the food and the distance from the food before it turns around and so we can crunch this into a model and see if it can predict this sort of distribution of where the fly is reversing after the experiments that it's kind of consistent with her so this model can predict it doesn't mean it's right but this model has no spatial really memory it's not like the animal knows a specific location it just has to know these 2 spatial scales and so what I think is going on here which is kind of this is more for sort of if you think about ecology or optimal far reaching.

[00:38:24]
What this algorithm would do is that when a fly is searching in a dense patch of food. It will actually make sort of short. Run distances run lengths that scale with food density whereas if it's if it's forging in a patch of food that. You know sparser its run length will will increase because you know that the distance between food that had previously sampled also increases so this might be one sort of.

[00:38:57]
You know evolutionary ecological. Explanation for. What's going on Ok thank you for that indulging I know it didn't have anything to do with flight flight which was my promise but the important thing that you know I think is interesting is how this region of the brain that's very very very ancient you know can be used for for different tasks that involve spatial orientation and memory and to be fair based on the sort of.

[00:39:29]
Comparative neuro neuro anatomical record and work of Nick Strauss father and others it's likely that the central complex evolved in walking animals before insects evolve flight and then it got co-opted for for for flight behaviors that we see and Crown taxa so in and last 15 minutes what I want to talk about is another specialisation we find in flies that is unique to flies that has to do to the distribution.

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The organization of the muscles with which they fly so flies. Flap their wings back they power their wings using a set of muscles we call power muscles for good reason so when a fly hits your windshield This is what you're looking at a fly is about 50 percent of these muscles they fill the thorax they have amazing molecular and functional specializations that they don't have to time to go into.

[00:40:28]
But they're each contraction is not controlled by an electrical impulse from the nervous system rather they stretch activate each other so it's like a magnet mechanical resonator that can pump energy strain energy into the thorax which makes the wings go back and forth. Flight control the ability to to steer is performed by a set of little tiny muscles that are good twitch muscles each action potential the motor neuron causes a a change in by mechanical properties and they insert on the inside of the wing henge in a very very complicated way and through the action of these little muscles that function as little controllable Springs the animal is able to distort its wing motion into different configurations which then caused changes in air Demick forces moments and now the animal to steer so so steering is really the you know the function of this tiny set of muscles and that's what I want to talk about.

[00:41:31]
There are 4 groups of these muscles there are exactly 12 of them are organized in 4 groups depending upon what little tiny. Skeletal bits called Square rights that are right in the armpit of the fly and I'm not going to worry about the names especially you know the details of the of this arcane infrastructure but each one muscles pull on one of these 4 little elements in the wing hinge the wing gets distorted in a particular way each muscle is regulated by one and only one motor neuron each so there are 12 motor neurons there are 12 muscles for the fist you're not as in the crowd like each muscle is just a single motor unit.

[00:42:11]
And it's these are tiny muscles they're kind of tendons with an attitude so through the years we've developed some techniques for putting a little tiny electrodes in these little muscles but it's pretty damn hard and there's only a couple of muscles that are large enough for electrophysiological recordings but in recent years what we've been able to do using genetic techniques and this was pioneered by Lindsay in the laboratory is we can express the calcium indicator g. camp in the steering muscles and visualize their activity through the cuticle of the fly in flies flying in a flight simulator playing a little video game and what you see sort of see here is a movie of the activity measured with the dynamics of the calcium indicator and I don't know if you can see it in this lighting but what you should see is there are certain muscles that arc are sort of bright all the time and there are other muscles that are kind of turning on going blinky blinky occasionally.

[00:43:08]
And this is a pattern that is very consistent so if you look across all the muscle groups there are certain muscles whose activity is always on with sort of you know modulations over time and we call these the tonic muscles and then also associated with with each muscle group there are muscles that are usually off and are only occasionally recruited and if you do an expanded.

[00:43:34]
Time scale what you see is that these phases of muscle in particular are recruited only when the animal is exhibiting rapid steering maneuvers as indicated by the fast changes in wing motion that are plotted at at the top so there's the stratification of these muscles in 2 phase of muscles that are all that are only recruited occasionally and tonic muscles that are on all the time that we believe are sort of setting that you know the basic trim of the system.

[00:44:06]
And. Just to sort of. Give a little more details into this when an animal performs a really fast rapid maneuver like like like like that it turns out that that's generated by actually rather subtle changes in wing motion but we motion that is. Elicited very very very quickly and so.

[00:44:29]
This is you know one thing the animal needs to steer is to make subtle changes and we motion that are very very very fast Another Thing and Animal has to do however especially if it say encountered wind damage so here's a fly flying along where we deliberately cut one of the wings in half a nasty people that we are and if you then plot the changes in wing motion that allows us fly to fly stable compared to a normal pattern of wing motion the both the damage wings and intact wings are flapping in a very very very different way consistently in a different way precisely you know the different way that's necessary to make sure that the animal is not spinning out of control and is flying straight so sort of in summary what you have with these tonic muscles is a slow guidance system that can allow the animal to sort of maintain a constant heading maintain a basic trim as it flies along and then you have a rapid maneuvering system with these phasing muscles that can exert elicit.

[00:45:32]
Quick changes in flight trajectory said to get away from a looming presence predator so that's just the basic background of these steering steering muscles and in the last little bit I want to. Dive down into. An important aspect of their physiology. If you record from these muscles particularly the tonic muscles so this is a high speed video combined with an electrophysiological recording from one of the muscles the b one muscle you know if you remember the name except it's the muscle that got me tenure so I'm very fond of it.

[00:46:09]
This muscle fires a single spike every single wing beat at roughly the same phase. By mechanical work on this muscle years ago showed that if you vary that phase of activity that suddenly changes the mechanical properties of the muscle particularly effectively the stiffness that dynamic stiffness so what we think is going on with these muscles and this is similar to work in other systems in the work of and on and others and cockroach is that this muscle is being used by the animal like a little controllable spring and the way the nervous system can regulate the stiffness of the spring is by either making the muscle fire a little bit early in each flapping cycle or a little bit later so so so it's by regulating phase that's regulating the function of the muscle which raises the question what's determining the phase what's the time or what's the clock it's not a central pattern generator it turns out.

[00:47:08]
For reasons I won't describe. For lack of time won't go into that evidence but the you know the the information is actually coming from mechanics receptor that are on the wings that are firing at specific phases that type those timing signals are going into the nervous system activating the motor neurons which then make the muscles active at the right time in the stroke but if you build a system like this where the the sensors were on the wings themselves that would run into certain problems because the wings are of course aerodynamic structure so if the animal performs a maneuver the the loading on the wing changes and that would change.

[00:47:52]
The feedback coming from the wing so it would sort of compromise the role of McCann receptor is on the wing as well as a little clock that the motor system can use so how would you solve this problem well one solution would be to say hey let's take one wing and say you don't get to make aerodynamic forces you're just a metronome you're just a clock you know I'm just going to turn you into like a little nubbin and your job is going to be to oscillate up and down and provide little timing cues that the the central nervous system can use and so I'm going to argue that this is exactly what has happened in flies so if you're a fly fish you're not you know that flies are unique among insects in that they have turned their hind wing into this drumstick structure called a halt here.

[00:48:38]
So the halter I kept saying I was going to do this and in this so the halt here you can see that little stick like thing behind the wing it beats in and the phase with the wing. And a fruit fly about $220.00 times a 2nd and if you look at the structure of the whole tier it's the base of the whole tier is covered with the kind of sensory fields it has around between 250 to 400 neurons arranged in about 5 different fields depending upon species and these are incredibly sensitive structures called compound of forms and Cilla that encode the motion of the halt here as it beats back and forth so most of these fields are firing just as a halt here is going back and forth and of course because it's.

[00:49:23]
Synchronous with wing motion they prove they would provide these nice timing cues effectively in Wing time now I think if you google halt here. You'll actually get a lot of pictures of dumbbells that's what they're named after dumbbells but if you go to the wicket Pedia page hall tears will lead to the Flies what you'll read is that the flies are supposedly up in the hall tears are scope's they function as gyroscopes because and this is true at least one of this set of sense on the base of the halt here are sensitive not to the up and back motion of the back and forth motion of the hood here but lateral deflection of the halt here caused by the Coriolis forces that occur when the body of the animal rotates during flight so the whole tier is effectively a functioning system basically functioning as a metronome to provide timing cues and a gyroscope to tell the fly.

[00:50:19]
That it's rotating and there's a lot of interesting stories on the on the gyroscopic function that I don't have time to go into but there's a lot the main thing I want to say is Ok. Regardless of the role of the whole tier. If you have this beautiful mana synoptic system of mechanic receptors on the whole here controlling the steering muscles of the wing How do you change the activity of the steering muscles in the wing How can you get the fly to do anything active.

[00:50:48]
And with this sort of hardwired system and the solution at least part of the solution that we think is that not only does the wing have little tiny steering muscles the halt here has little tiny steering muscles so. At the base of the whole tear there is a set of steering muscles that are the serial homologs of the steering muscles at the base of the wing.

[00:51:13]
And these are extremely tiny structures. But it turns out we can record from them using the same optical methods that were used for the. Muscles at the base of the wing and these are experiments done by Brad Dickerson who now has his own group at University of North Carolina so you can image the activity of the hall to your muscles when you present the animal with visual motion so the animals being presented with with visual motion and we get changes and the animal steers in response that visual motion and the pattern of these halts your muscles.

[00:51:48]
Changes over time and another set of experiments that are similar you can record using to photon my cross could be from the terminals of the hall to your sensory neurons in the brain of the fly while the flies flying under the 2 photon microscope again present the animal visual motion and there's a change in the activity of the halter afferent as recorded with the calcium indicator So in summary.

[00:52:17]
We have evidence from these experiments that that descending input coming from the visual system changes the pattern of activity of the hall to your muscles and presumably that's that's what changes the feedback coming from the hall tears so you change the way the whole tears are beating or or the set or something subtly about the sensitivity of the hall to your sensory cells that changes the activity from the sensory cells so.

[00:52:45]
It sort of raises the question Can Can these changes actually be responsible for changing the activity of wing muscles and to do that experiment what we need to do is sort of measure this the changes and wing muscle phase that occur when this is all going on so to test this and this your experiments done by Lucia D'Souza in the laboratory we give up that you netiquette activation of the motor neurons of the hall to your muscles unfortunately and while we record from the steering muscles of the wing this is possible and flies through the effort collaborative effort with Erica Earhart and others that you know you and he who did my laboratory we've identified a series of driver lines in flies specific for steering muscles of the whole tier and we can then use these driver lines to express the c.s. crimsoned channel just as we use in those.

[00:53:38]
Experiments on feeding but in this case what we're doing is we're activating the motor neurons of these whole tear muscles while we're recording the spikes in the steering muscles in the wing and lo and behold we found one driver line that labeled 2 motor neurons and when we activated these motor neurons we got a phase advance in the firing of this steering motor neuron which was consistent across flies and we also got a recruitment of one of the face it muscles that is new usually silent and these muscles are agonists of one another so this makes sense and coincidentally 2 other motor neurons when we activate them cause the phase De Lay in the firing of this muscle so there's like a push in the pool that's available in the nervous system that would presumably allow the animal to steer by you know increasing the stiffness or decreasing the stiffness of the steering muscles therefore making their wings beat a different way changing the air Demick forces or moments allowing the animal.

[00:54:38]
To change its flight course so this is just a hypothesis for what we think sort of happened in evolution that originally flies evolved from 4 wing insects relying on account of sensory feedback from the sensors of the wing but what happened in flies is they build a more precise system by by sacrificing one of those wings into a hall tear that has has very very precise timing signals that are not contaminated by the production of aerodynamic forces and yet still the activity can be regulated by descending commands that act through the motor system of the halt here maybe simultaneously maybe subsequently the system was co-opted as a gyroscope by allowing some of those sensory cells at the base of the halt here to be specialized to detect lateral deflections that occur when the when the animal's body rotates during during flight so that's sort of the the end of my little example of these are 2 features of what you know what it means to be a fly having a navigational sense and valving this fascinating structure called the central complex and then this very unique flight motor that involves this you know wonderful structure of the whole tier.

[00:55:57]
And. You know I want to thank everybody in my laboratory but before I go and this is a little bit of a downer I apologize but I'm ending this to like all of my talks now. I've studied flying insects for 30 years starting at about the time that a group in Germany started monitoring the population.

[00:56:23]
Density of of of insects in 97 sites around CERM any which they did to flee for the next 27 years measuring you know how many insects flying insects there are they are capturing traps so this is exactly my career Well my career as well some people would say my career has gone beyond 2015 met of debate but nevertheless you know so this represents 75 percent drop in insect biomass where they used to be 8 insects they're now 2.

[00:56:57]
Over exactly same time period in North America there's been a collapse of 3 roughly 3000000000 births. The 3000000000 birds the ones that are hardest hit are the insectivorous birds so you know there's this emerging story. A lot of the world is running out of food. And it's not visible as sort of how to tat loss because you don't see the insects disappearing.

[00:57:24]
But. You know this is very disturbing I think we should all be disturbed by these trends So what's causing it it's very complicated probably the most likely. Culprit is the use of. Pesticides that are very important and agriculture but I think is sort of a case where we you know we normally think about you know we're losing the polar bears we're losing qualities and I have nothing against polar bears but these are usually described as like you know canaries in the coal mine that give us a sense of things going bad this is not a case of canaries in the coal mines because the whole damn coal mine collapsing if we lose you know these these insect population densities so this is sort of all the more reason why.

[00:58:05]
You know you should think before you swat next time. And I hope. You know appreciation because I think you know as a research scientist I think we also have you know responsibility is kind of think more broadly about you know the world and how we should be expending energy in the world and it's actually.

[00:58:26]
It isn't just flippant I think the reason that I've started moving into the field and studying how animals move over large distances in the field is really to sort of perhaps tweak my research towards something that can be a little more helpful in understanding the implications of these global changes that we're seeing so anyway sorry for that bit but.

[00:58:49]
I promised my daughter I do this from now on I really appreciate the invitation to come here. You know Georgia Tech Emory the whole area is just you know it's just a really important. You know node of scientific research and I'm happy to be able to visit for the 1st time so thanks a lot.

[00:59:19]
The. Question. For you. Yeah. Sort of I mean I get to be more specific like if if the animal sort of sampling food and I should say this is like the work that really nice work by Carlos Ribeiro in Portugal you know if you give a fly a buff a it doesn't just go up to like the you know the lobster bisque and stuff itself it samples you know from one food spot to the other it goes around all the time there's good reason for that because it's probably trying to maintain the carbohydrate to 2 protein ratio so the idea of sort of sampling and then for some reason it's sort of like it it leaves the patch then the idea is that like the like the you know the that it remembers that distance so the runs that it would do would be scaled to you know the density of food that it's been previously sampling.

[01:00:36]
But. Right. Right no no it's interesting yeah. Physics behind. No I don't you know. I thought about this a lot mostly in the context of the chemical cues that they could be using to find the food but you know flies live in like super advection like the clay numbers are astronomical so you know diffusion plays absolutely no you know no role in this.

[01:01:16]
I could have more conversation with that but thanks for the question so this. Means that they're rocking this. Right it can be so flies how they do have a little bit of a blind spot but it's about like 40 degrees so you know they have basically panoramic vision which is typical of most flying insects so you know being able to I mean it's true that there's definitely a little bit of a bias towards forward minute tactic angles but you know we find them behind and we're not sure about you know the forward angle is cases where the flies doing mean attacks or maybe these are cases where the kind of photo tactic behavior is taking over but yeah no flight absolutely physically possible you.

[01:02:04]
Yeah that's why flies are hard to swallow for me. Specially. When. You know yeah. Yeah absolutely excellent question so in Monarch butterflies and bees they do what physiology is called Time compensation so they exactly compensate for the you know the as a myth of motion of the sun during the day so that like the bee will will change its media tactic angle such that it's always going towards the hive or or back towards or towards the flowers even though now the sun is in a different position so these are classic experiments and.

[01:02:50]
But migratory butterflies do the same thing so we've tested this in fruit flies and we haven't found any evidence for time compensation and in other animals that like dung beetles that use the sun you know again to just to sort of be able to hold Of course there isn't any evidence for time compensation but it kind of makes sense so if an animal has about 2 a fully fed fruit fly has about 2 hours of flight time in terms of gas effectively and over 2 hours the like the difference in the trajectory that would be caused by the as in both the motion of the sun is like trivial like it's so I don't think there would have been like really looked strong selection for time compensation when you're using the sun compass just for you know these like 2 hour dispersal distances so that this kind of the rationalization but it's a great question and in other insect species there's very very strong evidence that they do do time compensation.

[01:03:51]
In Cataclysm. Yeah and cataclysm Well the thing about how to live his soul different is that like every time the animal Farge is it's like resetting its compass. So it doesn't really have to do time compensation because it's only forging for a given amount of time if they don't find the food they get the hell back to the nest because they would dry up and people crispy guys Yeah Ok On that note I think.

[01:04:17]
Like lunch with the students.