Navigation (In Insects) Flashcards
What is the brain?
A movement controller - movement is a core distinction between plants and animals
Is movement evolutionary?
Yes - it is the most evolutionary old function of the nervous system
What are the two types of movement the brain controls?
Motor control
Navigation
What is motor control?
Moving body parts with respect to each other
What is navigation?
Moving around the environment across distances greater than one’s body size
How do we decide where to go?
- Moving around randomy which eventually brings you to nutrients
- Chemotaxis
What is chemotaxis?
Idea an organism can sense chemical gradients, its moving up or down the gradient i.e. where the concentration is higher or lower
Even some bacteria are capable or chemotaxis
What are some examples of chemotaxis?
- Dogs- following a trail of pheasants through smell and the change in the chemical gradient across the grass
- Ants using pheremones
- Even humans are capable of it even if its not obvious in modern life
What behaviours are similar to chemotaxis?
Phototaxis
Thermotaxis
What is phototaxis?
Moving along a gradient of light (illumination)
What is thermotaxis?
Moving along a temperature gradient
What is beaconing?
Moving towards a directly perceptible sensory cue
–Chemotaxis, phototaxis and thermotaxis are grouped together to be called beaconing
What are other examples of beaconing?
Phonotaxis (e.g. mating calls)
Visual beaconing
How small are insect brains?
Insect brains are small
A fly brain is similar in size to one neuron in a mammalian brain, but their tiny brain does contain 100,000 neurons
But it is still a simple brain
What are the three navigation mechanisms in insects?
Visual beaconing (and view memory)
Path integration
Vector memory
What is visual beaconing?
Moving towards a visually perceived target
What is the main finding of Graham and Cheng (2009)?
Ants use the panoramic skyline as a visual cue during navigation
What did Graham and Cheng (2009) do?
Placed a feeder near the ants - ants find feeder after a few days and begin to travel to it
Ants can see a panoramic view which they use to know how to get from the feeder back to the nest
Graham & Cheng recereated a scene similar to the panoramic view the ants can see out of cardboard and built an arena with this artificial panoramic view
Ants were then placed in centre of the arena to see which direction the ants would run in
What did Graham & Cheng (2009) find?
Majority of ants ran in the direction of the nest in the panoramic view relative to the feeder
What did Graham & Cheng (2009) find when the arena was turned relative to the compost area?
When there was no correspondence to the visual compost area (arena moved away from compost area), the ants relied on their memory of the visual panoramic view to be able to return to the nest
How do ants use visual beaconing?
By going from one visually recognised location to the next, complex routes can be traversed, which makes returning straight to the nest 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
What is required for insects to be able to wander around and then travel straight back to the nest?
Path integration
What is path integration?
By integrating all changes of direction with the distance covered, insects can generate an estimate of their current position relative to a starting point, enabling a straight-line return
What is path integration also known as?
Velocity integration
What is vector memory?
At every point they travel, ants make calculations of vectors
The vector 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
What two things does the bee dance convey to other bees?
The DISTANCE and DIRECTION away from the hive of food sources e.g. flower patch
How do bees show direction?
The waggle dance
Bees pick where they perform the waggle dance in relation to a vertical line
Bees waggle dance at a specific angle away from straight up, other bees in the hive observe this dance
Outside the hive, bees look at the position of the sun, and fly at the same angle away from the sun.
What does the duration of the waggle dance represent?
The distance of how far away the food is
1second is roughly 1/2km
What does the waggle dance demonstrate about bees?
The they can memorise vectors and have a language to communicate this vector memory to each other
What is the round bee dance?
The bee walks in a circle, turns around, then walks the same circle in the opposite direction
It shows that the food source is close to the hive, it doesn’t convey information about direction
How can we track bees as they fly to see if they follow the dance instructions of other bees?
Glue transponders (tiny electronic device) to a bee, it’s a passive device but it reflects electromagnetic waves and allows the researchers to follow the bees
What did Riley et al. (2005) do?
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
What happened when Riley et al. (2005) changed the release points?
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
What overall did Riley et al. (2005) demonstrate?
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
What two components are required for path integration (in the ant) to be implemented?
Path integration requires two components:
1. which direction its going e.g. a compass
2. the speed/distance it travels or has travelled
How do ants know how far they have travelled?
Step counting
What were the three modifications Wittlinger et al. (2006) made to ants to see how ants know how far they travelled?
- Group had stilts on
- Normal (control) group
- Group with stumps
What did Wittlinger et al. (2006) do?
Researchers put a feeder a certain distance from the nest of desert ants
Ants would discover the nest and collect food from it
Then researchers picked some ants from the feeder, made the leg modifications and then released them but not on the path that leads to the nest, but a path that runs parallel to it
They measured how far the ant would run before starting to go in circles trying to find the nest
What did Wittlinger et al. (2006) find?
Normal ants- on average travelled 10m (they perform path integrtation so they knew they were 10m from the nest, ran until the path integrator was 0 again)
Ants on stilts- ran for longer, 15/16 metres (not surprising if using step counting as their steps would be bigger so travel further in the same number of steps)
Ants on stumps- start looking for the nest after a shorter distance of 5/6 metres
So we have evidence ants use step counting
Describe Wittlinger et al.’s (2006) quantiative predictions?
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
What else does step size in ants affect that should be considered?
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
How do bees know how far they have travelled?
Optic flow
What did Srinivasan et al. (2000) do to measure how bees use optic flow to measure distance?
3 conditions
- Feeder directly outside hive
- Feeder 6m from hive down tunnel with vertical stripes
- Feeder 6m from hive down a tunnel with horizontal stripes
What did Srinivasan et al. (2000) find?
When feeder was directly outside the hive, bees performed round dance (showing food close to hive)
When feeder was 6m away down vertical striped slinger truck tunnel, bees performed a waggle dance to signify that the feeder was very far away
When feeder was 6m away down horizontal striped slinger truck tunnel, bees performed a round dance again
Why were the vertical stripes significant in confirming that bees use optic flow to measure distance?
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
What animal do we perform neuronal expeirments on to assess orientation and path integration?
Drosophila (species of fly)
What central part of the drosophila brain do we examine?
Ellipsoid body - importantly this area expresses a fluorescent protein called GCaMP that changes the way it fluoresces depending on the level of neural activity
What did Seelig & Jayaraman (2015) do?
Removed cuticle that covers the brain to look inside it, then head-fixed the fly
Fly positioned on a small styrophone ball that is suspended by compressed air blowing underneath
Virtual reality setup, position an array of LEDs in front of the fly
If the fly moves on the ball the researchers can measure precisely how much the fly turns
Researchers then measure neural acitivty of the fly as it turns on the ball in this virual reality
What did Seelig & Jayaraman (2015) find?
Neurons in the ellipsoid body encode the neural acitivity about the direction in which the fly is facing
The neurons that are active inside the EB turn correspondingly to the flys movement - If the fly turns, the neurons turn by the same amount
So it is possible to tell purely from neuronal activity in the EB which direction the fly is facing.
What is Seelig & Jayaraman’s (2015) study a demonstration of?
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
