Navigation in Insects

Question 1

What two kinds of movement does the brain control?

Answer 1

Motor control = moving body parts with respect to each other

Navigation = moving around in the environment (usually across distances much greater than one’s body size)

Question 2

Is movement evolutionary?

Answer 2

Yes = it is the most evolutionary old function of the nervous system

Question 3

What is navigation?

Answer 3

The ability of animals to move through their environment in a planned manner without maps or instruments

Question 4

What are two types of navigation?

Answer 4

1. Moving around randomly - can eventually bring you to nutrients
2. Chemotaxis - sensing chemical gradients and moving up or down them

Question 5

What are some examples of animals using chemotaxis?

Answer 5

Dogs following the scent of an animal
Ants following pheromones

Question 6

What behaviours are similar to chemotaxis?

Answer 6

Phototaxis - moving along a gradient of light (illumination)

Thermotaxis - moving along a temperature gradient

Question 7

What is beaconing?

Answer 7

Moving towards a directly perceptible sensory cue

A beacon is an intentionally conspicuous device designed to attract attention to a specific location

Question 8

What are examples of beaconing?

Answer 8

Phototaxis
Thermotaxis
Phonotaxis - e.g., mating calls
Visual beaconing
Chemotaxis

Question 9

How small are insects brains?

Answer 9

A fly brain is similar in size to one neuron in a mammalian brain, but their tiny brain contains 100,000 neurons

It is a simple brain

Question 10

What mechanisms do insects use for navigation?

Answer 10

1. Visual beaconing/ view memory
2. Path integration
3. Vector memory

Question 11

What is visual beaconing?

Answer 11

Moving towards a visually perceived target

Question 12

What type of ants are used to test visual beaconing and why?

Answer 12

Desert ants cannot rely on pheromones as pheromones left on the sand are easily blown away, therefore, desert ants can be used to test visual beaconing

Question 13

What is the main finding of Graham and Cheng (2009)?

Answer 13

Ants use the panoramic skyline as a visual cue during navigation

Question 14

Explain the methods of Graham and Cheng (2009)

Answer 14

Open access feeder located 5m from nest

The retinal elevation of the panoramic skyline from the feeder location was measured at 15 degree azimuthal intervals

A test arena, 1m in radius, was created using black plastic sheeting, the height of the sheeting was varied so that from the centre of the arena the retinal evaluation of the artificial skyline matched that of the natural panorama viewed from the feeder

Goniometer placed in the centre of artificial panorama used to measure the departure bearing of ants released in the arena

Ants taken back to the feeder location and then released

Question 15

What did Graham and Cheng (2009) find when they released the ants?

Answer 15

The ants showed an accurate homeward departure direction, demonstrating their familiarity with the visual environment in the actual panorama

In the first test, the artificial panorama was aligned with the natural panorama, relative to a global compass heading

In this case, the ants headed in a direction very close to the bearing taken by the ants from the normal training position

Question 16

What did Graham and Cheng (2009) find when the arena was turned relative to the compost area?

Answer 16

The movement of the ants back to the location of the feeder may have been because the ants follow a global compass direction which they recall when they recognise a location or because they derive directional information from the skyline

To distinguish this ants were also tested with a rotated artificial skyline - in this condition, ants also followed the directional information given by the rotated skyline

This is behavioural evidence of visual beaconing

Question 17

Why do animals use visual beaconing?

Answer 17

By going from one visually recognised location to the next, complex routes can be traversed

However, returning straight to the nest is highly more efficient

Ants know how far and in which direction their nest is so when they find food they can return straight back to their nest rather than the same route they travelled to find the food

Question 18

What is required for insects to be able to return straight back to their nest without returning to each visual beacon?

Answer 18

Path integration

Question 19

How do ants estimate how far they have walked?

Answer 19

They use optic flow to estimate distance
In the absence of optic flow cues and of pheromone/chemical trails (desert ants), ants estimate the distance walked not by the energy expended but by counting or integrating the number of steps they have taken

Question 20

What is optic flow?

Answer 20

Optic flow is a form of visual streaming which occurs as we are moving continuously in one direction
It occurs because the image of the same objects are constantly changing with regards to which area of the retina they stimulate

Question 21

What is path integration?

Answer 21

A continuous and automatic process that animals use to determine their position that includes both distance from and direction to their previous position and to other objects and locations in the environment

This allows the animal to return straight to the nest rather than returning to each previous point

Question 22

What is another name for path integration?

Answer 22

Velocity integration

Question 23

What is a vector memory?

Answer 23

At every point they travel, ants make calculations of vectors

The vectors from the final point (the feeder or food source) is the sum of all other vectors (the path of the animal) - the ant performs a summation of path integration

If the home vector at the feeding location is memorised then next time it is possible to travel straight to it

Question 24

Describe the experiments by Wittlinger (2006)

Answer 24

Ants were trained to walk from their nest to a feeder kept 10m away
The walking was performed inside a channel 7cm wide with walls 7cm high - open top allowed the ants a view of the sky to facilitate their use of the celestial compass
Great care was taken to minimise optical flow cues
Ants reaching the feeder were transferred to a different channel placed a little away from the original channel - they promptly began walking in the new channel in the homeward direction
After walking a certain distance, presumably their estimate of where the nest ought to be, and not finding it, they abandoned their straight and steady homeward run and began to search for the missing nest
The point of the experiment was to see how far the ants will walk in the homeward direction before beginning to search for the missing nest - this will tell us what the ants had estimated as the distance they had walked from the nest to the feeder and hence the distance they needed to walk back to reach the nest

Question 25

What did Wittlinger et al. (2006) find?

Answer 25

Normal ants walked up to 10.2m before abandoning the straight path and beginning to search as might be expected because they had walked a distance of 10m to reach the nest in the first place
In the test experiment, operated ants were ants which had they legs either elongated or shortened
Ants walking on stilts overshoot the distance and walked up to 15.3m before beginning to search for the missing nest
Ants walking on stumps undershot and began to search after walking 5.75m

Question 26

Describe Wittlinger et al.’s (2006) quantitative predictions?

Answer 26

In the lab they performed the same manipulation and measured how much the ant step became longer or shorter with the modifications

This change in step size gave the researchers a quantitative prediction for how the estimation of distance would become longer or shorter based on the modifications - matched their hypotheses both quantitively and qualitatively

Question 27

What else does step size in ants affect that should be considered?

Answer 27

From their predictions and corrected predictions
found that: size of the step also affects the SPEED the ant travels - should be accounted for in future research

Question 28

How is path integration in ants implemented?

Answer 28

Measuring direction
- Sun as a compass
- Wind as a compass
Measuring speed/travelled direction
- By step counting

Question 29

What is the bee waggle dance?

Answer 29

The waggle dance tells the watching bees two things about a food source location - the distance and direction away from the hive

Question 30

How does the waggle dance reflect the distance?

Answer 30

The bee waggles in a forward straight direction then circles around to repeat the dance
The length of the middle line called the waggle run, shows roughly how far it is to the food source
1 sec = approx 1km

Question 31

How does the waggle dance reflect the direction?

Answer 31

Bees know which way is up and which way is down inside their hive and use this to show direction
Bees dance with the waggle run at a specific angle away from straight up i.e., 90 degrees
Outside the hive, bees look at the position of the sun, and fly at the same angle away from the sun
If the sun were in a different position, the angle would stay the same, but the direction to the correct flower patch would be different

Question 32

What does the round dance tell us?

Answer 32

Tells the watching bees only one thing about the food source location - that it is somewhere close to the hive

Used for food sources 25-100 meters away from the hive or closer

Question 33

How can we track bees as they fly to see if they follow the dance instructions of other bees?

Answer 33

Transponders = tiny electronic device which reflects electromagnetic waves and allows the researchers to follow the bees

Question 34

What did Riley et al. (2005) do?

Answer 34

Allowed some bees to visit a feeder
But kept a group of bees that did not visit the feeder BUT observed the waggle dance of the bees that had visited the feeder and returned to the hive

Then they monitored where the bees who had observed the waggle dance flew

In most cases the bees flew in the right direction and for the right distance

Question 35

What happened when Riley et al. (2005) changed the release points?

Answer 35

Took the bees after they saw the waggle dance and moved it a certain distance

Found that for the most part no matter where the bee is released from, it still goes in the right direction (signified by the sun) and for roughly the right distance

Question 36

What overall did Riley et al. (2005) demonstrate?

Answer 36

Bees don’t rely on the location of the hive, they seem to rely on the meaning of the vector that was communicated

Its not always precise and there is some variation in the trajectory of the bees but it still provides the bees with an evolutionary advantage

Question 37

How do bees measure have far they have travelled?

Answer 37

Using optic flow

Question 38

Describe the experiments by Srinivasan et al., (2000)

Answer 38

Experimental bees were housed in a two frame observation hive with transparent walls on both sides
In one series of experiments, bees were trained to forage at a feeder carrying sugar solution placed in a wooden tunnel 6.4m long - tunnel located outdoors near the hive
In experiment 1, the walls and floor of the tunnel were lined with a random visual texture, the feeder placed at the entrance of the tunnel
Bees returning from the feeder performed predominantly round dances - this is consistent with the fact that the bees perform mainly round dances when visiting food sources that are within 50m of the hive
However, when the feeder was placed 6m inside the tunnel, the bees performed primarily waggle dances - even though the distance flown had only increased by 6m to 41m from the hive so should be performing round dances still

Question 39

What is a possible explanation for the bees performing waggle dances when they should be performing round dances?

Answer 39

The flight in the narrow tunnel generated a large integrated optic flow on the eye, mimicking the effect of a long flight in natural outdoor conditions
The bees are experiencing a greater angular motion of the image when flying in the tunnel than when flying outdoors
The magnified image motion in the tunnel might cause the bees to infer a journey considerably longer than 6m

Question 40

How did Srinivasan et al., (2000) test this hypothesis?

Answer 40

In experiment 3, the tunnel and the feeder were positioned as in experiment 2 but the walls and floor were lined with axially oriented stripes
This tunnel provided negligible image motion cues, because the stripes were parallel to the direction of flight
Bees returning from this tunnel predominantly performed round dances even though the bees had flown the exact same distance in experiment 2
This is evidence that bees use optic flow to measure the distance they have travelled

Question 41

Why were the vertical stripes significant in confirming that bees use optic flow to measure distance?

Answer 41

When the bee flies through this tunnel to the feeder, the optic flow (movement of everything the bee sees, so as the bee flies forward everything moves backwards ) is strong and it essentially tricks the bees into estimating a much longer distance than it covers in reality

The stripes are close to the bee whereas in normal environments when the bee flies, the same kind of optic flow, e.g. when a tree moves past it, signifies a longer distance

Question 42

What animal do we perform neuronal experiments on to assess orientation and path integration?

Answer 42

Drosophila (species of fly)

Question 43

What central part of the drosophila brain do we examine?

Answer 43

Ellipsoid body - importantly this area expresses a fluorescent protein called GCaMP that changes the way it fluoresces depending on the level of neural activity

Question 44

How are the navigation primitives in insects implemented at the neuronal level?

Answer 44

Seelig & Jayaraman, (2015)
Used two-photon calcium imaging in head-fixed Drosophilia walking on a ball in a virtual reality arena to demonstrate that landmark-based orientation and angular path integration are combined in the population responses of neurons whose dendrites tile the ellipsoid body, a toroidal structure in the centre of the fly brain
Flies had GCaMP6 to monitor neural responses to LED light while walking on the fixed treadmill
When flies were exposed to a single vertical stripe stimulus, they observed a sector of activity in the EB that rotated concurrently with the stripe as the fly turned on the ball
EB is not a retinotopic map of visual scene, but represents the fly’s orientation relative to visual landmarks
EB neurons encode head direction

Question 45

What is the importance of Seelig & Jayaraman’s (2015) study?

Answer 45

Its a demonstration of how the compass, the direction in which the fly is facing, is implemented at the neuronal level

The EB is also found in the brains of ants and bees so based on this experiment it’s logical to conclude that they rely on the same representation