lecture 15: defensive behaviours Flashcards
types of defensive behaviours
- avoidance behaviours
- escape and retaliation behaviours
phases of predatory act and selected defenses example of each
1) search and detection
*selected defenses:
- hiding
- crypsis
- diel activity patterns
2) pursuit
*selected defenses:
- running/fast swimming
- some escape behaviours (like tail flip)
3) subjugation (subdue)
*selected defenses:
- armour
- retaliation
- toxicity
- autonomy
- structural add ons
2 examples of selected defense of search and detection phase of predation
👉🏻HIDING (avoidance)
• DIEL ACTIVITY PATTERN
- example = snails (olivella biplicata)
- when sun is down, comes up to surface and feeds in top sediment layer
during day they burrow down into sand to hide from visual predators
***study
- chemical effluent from sea star (predator) triggered them to burrow (hide)
- around 8pm snails burrowed either way — so can say its hardwired
** based on chemical effluent of predator AND hardwired with time of day
EXAMPLE OF A KAIROMONE
- benefits receiver of chemical cue
• SHADOW REFLEX
- example = zoea larvae
— just an arrest in behaviour (will just stop swimming and will sink to avoid
***study
- looked if chemical cue (kairomone) would impact this reflex in zoea
— found that the chemical cue from ctenophore (predator) just made zoea more “on edge” — way more sensitive to light changes = different threshold
• CRYPSIS
- example = decorator crab
— hardwired behaviour to take things from around them and hide themselves
***study
- wet weight of decorations increased in presence of predator (kairomone)
what is a kairomone ?
chemical cue produced by one species that triggers a behavioural change of a different species
benefits the receiver of the chemical cue
examples of selected defense of PURSUIT phase of predation
👉🏻 ESCAPE BEHAVIOUR
simple startle responses
example = feather duster worm
- no other protection so vulnerable to predators — will rapidly contract
escape behaviour: startle reflexes criteria- giant axons
**giant axons !!
1) all or none response (no gradient)
2) high threshold
- water around always moving but if different than normal = threshold
3) short latency
- v important
- rely on speed
giant axons
- what is it
- importance
- typical way that invertebrates speed up conduction velocity of membranes depolarizations
- sends messages down an axon
– an interneuron –> transmits messages between different types of neutrons
*** like the message of danger being transmitted from sensory neurone to motor neurons
- the speed of communication changes based on size
(velocity dependent on diameter) - giant axon massive compared to other axons
V = kD^e
velocity = k x axon diameter ^exponent
what invertebrates are giant axons particularly important in
annelids
decapods (like lobsters) - for tail flips
escape behaviour: complex escape behaviours
- nudibranch escape swim
— large flopping motions lift them off the substrate and into the water current
— can do this due to huge ganglia (like brains) of the central nervous system
central pattern generator = goes thru cyclical motion that goes thru back and forth
— animal not consciously telling what to do but reflex and cyclical pattern
— alternating output to motor neurons innervating dorsal and ventral longitudinal muscles
**on ganglia have neural cell bodies - these are large enough that a microprobe in here and expose them to stimuli and see how they react
** all of them have the same placement = good model organisms
escape behaviour: decapods: retaliation vs armous
clawed lobster vs spiny lobster vs slipper lobster
all can tailflip
1) clawed lobster
– chelipeds as weapons
2) spiny lobster
- no chelipeds
- 2nd pr. antennae as weapons
- “whipping” spines
3) slipper lobster
– no chelipeds
- very thick carapace
- like a tank
- tenaciously cling to substrate
***STUDY 1
- wanted to see whether the armour or retaliation is more effective
– punctured lobsters to see how much more protected the slipper lobster is w thick carapace
– slipper lobster had thicker carapace AND took more force to puncture
***STUDY 2
- 20 individuals normal and protected
- 20 individuals w protection taken away
– RESULTS: slipper lobster continued to be protected - less died –> clawed lobsters mostly died
‼️- amt of predation was best explained by thickness of carapace, not weaponry
what is an interneuron?
a neuron transmitting a message from one type of neuron to another
– like sensory neurons to motor neurons
an example is a giant interneuron
