View
223
Download
1
Category
Preview:
Citation preview
Today’s class: Synchrony in flashing fireflies
“The Glowworms ... represent another shew, which settle on some Trees, like a fiery cloud, with this surprising circumstance, that a whole swarm of these Insects, having taken possession
of one Tree, and spread themselves over its branches, sometimes hide their Light all at once, and a moment after
make it appear again with the utmost regularity and exactness”
- Engelbert Kaempfer’s (1727) account of traveling in Thailand
Today’s class: Synchrony in flashing fireflies
The firefly lifecycle
larva pupa beetleegg
The firefly lifecycle
larva pupa beetleegg
all stages produce light
Functions of glowing
to teach predatorsthey're disgusting
to locate potential mates
Firefly courtship
male flies around, flashing
lets him find her
female responds
Species-specific flash codes
(but watch out)
Photuris females flash like Photinus females....
then eat the Photinus males that respond
aggressive mimicry
So, what causes the synchronized flashing?
early theories:
‘it’s just an illusion’
‘there’s a leader beetle’
‘there’s some outside trigger’
So, what causes the synchronized flashing?
modern theory:
self-organisation!
to understand how it works, we first need to understand the mechanism behind rhythmic firefly flashing
the beetles cause each other to flash in unison, without any leader or external trigger
Mechanism: The ‘sawtooth model’
neural oscillator, affected by light
time
flash
motor delay
oscillator
threshold
basal level
Why we know light affects the oscillator
fireflies will respond to any
kind of light
makes their oscillator easy
to study
Entrainment
by studying the light’s effect on the firefly’s flashing, it’s possible to deduce the workings of its oscillator
light, flashing in a rhythm
firefly, who flashes back
The problem
light actually affects different species in different ways
one dimension that matters here is mating system
Synchrony and mating systems
‘rovers’
individuals are solitary, and distributed
‘leks’
males and females congregate in trees
occassional, brief synchrony
habitual, mass synchrony
Synchrony in rovers
the mechanism in rovers tends to be simpler
so we’ll start with one of those
Photinus pyralis,a North American firefly
Reminder: The ‘sawtooth model’
neural oscillator, affected by light
now the question is: how does light affect a Photinus pyralis oscillator, and how does this allow them to synchronize?
time
flash
motor delay
oscillator
threshold
basal level
Entrainment in Photinus pyralis
time
flash
regular flashing is a single flash every six seconds
Entrainment in Photinus pyralis
time
flash light continuation of the regular flash pattern
no effect of the light
flash a light early in the firefly’s regular cycle,then the firefly’s flashing is unaffected
threshold 8, latency 2, window 2, start-firefly-0 1, light-cycle 10
Entrainment in Photinus pyralis
time
flash light continuation of the regular flash pattern
effect of the light
flash a light late in the firefly’s regular cycle,then the next flash is advanced
threshold 8, latency 2, window 2, start-firefly-0 3, light-cycle 10
Entrainment in Photinus pyralis
time
flash
flash lights at a frequency at the firefly’s natural rhythm, then the firefly usually matches it perfectly after a few flashes
light
threshold 8, latency 2, window 2, start-firefly-0 3, light-cycle 10
Entrainment in Photinus pyralis
time
flash light
flash lights at a frequency faster than the firefly’s natural rhythm, then the firefly matches it, but is always late
threshold 8, latency 2, window 2, start-firefly-0 3, light-cycle 8
time
flash light
flash lights at a frequency slower than the firefly’s natural rhythm, then the firefly flashes after every light, but also in between
Entrainment in Photinus pyralis
threshold 6, latency 2, window 2, start-firefly-0 3, light-cycle 10
Mechanism: Any ideas?
time
flash light continuation of the regular flash pattern
effect of the light
Mechanism: Phase advance resetting
when the firefly sees a light in its late window, its pacemaker is raised to the threshold level, triggering a flash
time
flash
motor delay threshold
basal level
oscillator
Mechanism: Phase advance resetting
when the firefly sees a light in its late window, its pacemaker is raised to the threshold level, triggering a flash
time
lightlate window
Phase advance resetting: NetLogothreshold 8, latency 2, window 2, start-firefly-0 3, light-cycle 10
Phase advance resetting: Summary
• a flash resets the pacemaker to the threshold level
• there is a critical window where resetting can occur
properties
• allows the firefly to synchronize with a light flashing at its natural rhythm
• ...unless the light's flashes always occur outside of window
effects
Synchrony in phase advance resetters: NetLogo
number 1500, threshold 8, latency 2, window 2 (waves) or 4 (sychrony)
Synchrony in phase advance resetters: Summary
• almost perfect (with some never synchronizing due to window)
• very brief, quickly settling back into seemingly random flashing
• 'wave like', with groups of fireflies flashing in sequence
depending on the pacemaker's properties and the spatial situation, synchrony can be:
(threshold 8, latency 2, window 4)
(threshold 8, latency 2, window 4, movement on)
(threshold 8, latency 2, window 4, movement off)
Synchrony in habitual synchronizers
Pteroptyx cribellata,a South Asian firefly
Entrainment in Pteroptyx cribellata
time
flash
regular flashing is a single flash every second
time
flash
flash a light almost anywhere in the firefly’s regular cycle,then next flash is delayed
continuation of the regular flash patternlight
effect of the light
Entrainment in Pteroptyx cribellata
threshold 8, latency 2, window 0, start-firefly-0 4, light-cycle 10
time
flash
exception: flash a light just before a regular flash, and then the next flash is regular - but the one after that is advanced
light
effect of the light
Entrainment in Pteroptyx cribellata
threshold 8, latency 2, window 0, start-firefly-0 0, light-cycle 9
time
flash
flash lights at a frequency at the firefly’s natural rhythm, then the firefly always matches it perfectly from the next flash
light
Entrainment in Pteroptyx cribellata
threshold 8, latency 2, window 0, start-firefly-0 4, light-cycle 10
time
flash light
flash lights at a frequency a little faster than the firefly’s natural rhythm, then the firefly matches it, but is always late
Entrainment in Pteroptyx cribellata
threshold 8, latency 2, window 0, start-firefly-0 4, light-cycle 9
time
flash light
flash lights at a frequency a lot faster than the firefly’s natural rhythm, then the firefly never flashes at all
Entrainment in Pteroptyx cribellata
threshold 8, latency 2, window 0, start-firefly-0 4, light-cycle 6
time
flash light
flash lights at a frequency slower than the firefly’s natural rhythm, then the firefly flashes before the next light
Entrainment in Pteroptyx cribellata
threshold 8, latency 2, window 0, start-firefly-0 4, light-cycle 12
Mechanism: Any ideas?
time
flash continuation of the regular flash patternlight
effect of the light
Mechanism: Phase delay resetting
time
flash
motor delay
oscillator
threshold
basal level
when the firefly sees a light, its pacemaker is immediatelyset back to the basal level
Mechanism: Phase delay resetting
time
light
in almost all parts of a firefly’s flashing rhythm,this causes a delay in the next flash
Mechanism: Phase delay resetting
time
light
however, if the light occurs when a flash has already been triggered, then the next flash is advanced
Phase delay resetting: NetLogothreshold 8, latency 2, window 0, start-firefly-0 4, light-cycle 10 (for synchrony) or start-firefly-0 1, light-cycle 9 (for advancement)
Phase delay resetting: Summary
• a flash resets the pacemaker to the basal level, anywhere in its cycleproperties
• generally, this causes a delay in the timing of the next flash
• but, if a flash has already been triggered, the next flash may seem to be advanced
• allows the firefly to synchronize with a light flashing at its natural rhythm
effects
Synchrony in phase delay resetters: NetLogo
• always perfect synchrony within a few cycles
number 1500, threshold 8, latency 2, window 0
Synchrony in habitual synchronizers
Pteroptyx malaccae,a South Asian firefly
Entrainment in Pteroptyx malaccae
flash light
unlike the other two species, Pteroptyx malaccae can match a rhythm that is slightly slower or faster than its natural rhythm
however, this process is very slow, taking many cycles
Mechanism: 'Perfect' resetting
a variant of phase delay resetting
• a flash early in the cycle raises its threshold slightly, a flash late in the cycle lowers its threshold slightly, within limits of a minimum and maximum threshold
• in this way, Pteroptyx malaccae can adjust to rhythms 15% faster or slower than its own
what explains the slow entrainment:
• a flash lowers the level of the pacemaker by a small amount, rather than to zero
what explains its ability to adjust to different rhythms:
Mechanism: Perfect resetting
• allows the firefly to synchronize with a light at or close to its natural rhythm
• entrainment is always very slow; it takes many cycles to reach synchrony
effects
• a flash lowers the level of the pacemaker by a small amount, rather than to zero
• in addition, the pacemaker can adjust its period as well as its phase
properties
Other similarly synchronizing species
frogskatydids fiddler crabs
Just for fun: Fiddler crabs
Functions of synchrony
the 'beacon' hypothesis
synchronous flashing helps females find the mating trees
Functions of synchrony
the 'female recognition' hypothesis
if males don't flash in synchrony, they can't detect female response flashes
the 'male recognition' hypothesis
if males don't flash in synchrony, the female can't detect the species specific flash
or, conversely:
Functions of synchrony
the 'interloping' hypothesis
if males synchronize with each other, they can hope to steal each other's mates
Functions of synchrony
the 'predator avoidance' hypothesis
if males synchronize with each other, it makes it more difficult for predators to locate them
And now for something completely different (or not?)
phase alternation
many species of katydid, grasshopper, and frog
true katydid
Entrainment in alternating species
time
regular chirping is a series of phrases, each consisting of several pulses
chirp
Entrainment in alternating species
time
to simplify a bit, assume that every phrase consists of just one pulse
chirp
Entrainment in alternating species
time
chirp continuation of the regular chirp patternbeep
produce a beep early in the katydid’s regular cycle,then the next chirp is advanced
effect of the beep
threshold 8, latency 2, window 2, start-firefly-0 3, light-cycle 10
Entrainment in alternating species
time
chirp
produce a beep late in the katydid’s regular cycle,then the next chirp is delayed
threshold 8, latency 2, window 2, start-firefly-0 5, light-cycle 10
beep
effect of the beep
Entrainment in alternating species
time
chirp
produce regular beeps in the katydid’s natural rhythm, and alternation ensues
threshold 8, latency 2, window 2, start-firefly-0 5, light-cycle 10
beep
Mechanism: Any ideas?
time
chirp continuation of the regular chirp patternbeep
effect of the beep
Mechanism: Accelerated resetting
time
beep
motor delay
oscillator
threshold
basal level
a variation of phase delay resetting, where the oscillator rebounds quickly after inhibition by a beep
Mechanism: Accelerated resetting
time
beep
produce a beep early in the katydid’s cycle, and rapid resetting causes the next flash to advance
Mechanism: Accelerated resetting
time
beep
threshold
produce a beep late in the katydid’s cycle, and rapid resetting isn’t enough to prevent a delay
Accelerated resetting: NetLogothreshold 8, latency 2, window 2, start-firefly-0 3, light-cycle 10
Accelerated resetting: Summary
• a beep resets the pacemaker to the basal level
• after resetting, the pacemaker rebounds rapidly
properties
• can produce advancement or delay of the katydid’s next chirp
• allows the katydid to alternate with a chirp flashing at its natural rhythm
effects
Function of alternation
females of many species prefer the leading of two chirps
phase delay resetting helps a male avoid chirping right after another male
rapid resetting helps a male avoid being silenced completely if the other male chirps faster
Synchrony in flashing fireflies: Conclusions
• what seems like a massive act of coordination can in fact be explained by self-organisation➡ e.g., the habitual synchrony of South Asian fireflies
• what seems like similar behavior can in fact be caused by subtly different mechanisms➡ e.g., the phase-delay resetting of Pt. cribellata vs. the
perfect resetting of Pt. malaccae
• what seems like very different behavior can in fact be caused by very similar mechanisms➡ e.g., the firefly synchrony vs. katydid alternation
Recommended