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
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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
• 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