Signals and Cues: Capturing information in an animal world
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Transcript of Signals and Cues: Capturing information in an animal world
Signals and Cues: Capturing information in an animal world
Lesson Goals
– 1) Understand the difference between signals and cues
– 2) What is communication?– 3) How does communication evolve?– 3) How does the environment influence signals?– 4) Understand how the marine environment
influences the propagation of different information modalities
Information needed!
• Animals perform a variety of different behaviors necessary for their survival– Foraging Locating food; handling– Mating Finding mates; advertising fitness– Defense Where and when is danger present
• And all those behaviors require animals to process information about themselves and their surroundings
Information Comes in Many Modalities
Visual
Olfaction
Tactile
Acoustic
IR
Seismic/ Vibrational
Electroreception
The Transfer of Information
Two Classes of Information• 1) Signal- a behavior, trait, or action intentionally
generated by one individual (the transmitter) which is selected for its effects in altering the behavior of a second individual (the receiver)
typically a +/+ interaction
Transmitter/Sender ReceiverEnvironment
Signal
Cue
An Example of a Signal
The Transfer of Information
Two Classes of Information• 2) Cue- an unintentional action or trait from which
a receiver can gather information but it has not been selected to alter the behavior of receivers
+/+ or -/+
Transmitter/Sender ReceiverEnvironment
Signal
Cue
An example of a cue
• Blue crabs track to chemical cues given off by clams
How Cues Become Signals
• Initially, all information begins as cues• Cues may be more likely to be selected for if
the species is already sensitive to cue/modality: sensory exploitation (a pre-adaptation)
How Cues Become Signals
• Some species of sword tail fish don’t possess sword tails
• But if you attach a false tail to a male the females suddenly prefer him!
Sensory preferences can exist in current species that have never encountered a particular signal before.
Example: Female X. maculatus fish
How Cues Become Signals
How Cues Become Signals
• If a cue provokes a response from a receiver that it beneficial to the transmitter, the cue will be modified into a true signal through the process of Ritualization• The refinement of an inadvertent cue into a true signal
How Cues Become Signals• Through ritualization the cue will either be simplified
(reduced # of components)• exaggerated, • repeated • Or stereotyped (reduction in variance) through the
process of selection• Selection will favor signals that elicit a response the
benefits the sender (on average)• Selection will favor responses that benefit receivers (on
average; but see deceit)
True Communication
• Communication: an exchange of a signal between a sender and a receiver that benefits both parties
True Communication
• Senders and receivers are selected to perform in their own self interest
• Signals must carry honest, interesting information
But what happens when the one party doesn’t benefit?
• Eavesdropping- receiver intercepts a signal or cue from sender – - (S) /+ (R) interactions (but can vary)
Example of eavesdropping
• Galapagos marine iguanas and mockingbirds
• Forktailed drongos and meerkats– Drongos occasionally make false alarm calls
Example of eavesdropping
But what happens when the one party doesn’t benefit?
• Eavesdropping- receiver intercepts a signal or cue from sender – - (S) /+ (R) interactions
• Deceit- sender exploits a sensory bias of or a pre-existing signal to receivers to benefit themselves– + (S)/- (R) interaction
Example of Deceit
• Photuris fireflies– Female Photuris fireflies flash at male fireflies (in a
different genus) to suggest they are a receptive mate
– And instead eat the incoming firefly!
Example of Deceit
• Cuttlefish have highly sophisticated chromatophores that allow them to change the color of their skin– Males and female exhibit differing patterns
Deceit
• Why isn't their more selection against dishonesty?
Deceit
• Why isn't their more selection against dishonesty?
Deceptive signals are infrequent in comparison with honest signals
Evolution will favor cues that clue animals about dishonest situations
Maintaining Honest Signals
• Why might it be hard to fake signals?
Maintaining Honest Signals
• Indexes- signals that cannot be faked as it is causally related to the quality being signaled
Maintaining Honest Signals
• Costs of producing a fake signal are high– Handicap- a signal whose reliability is ensured
because it is costly to produce
Maintaining Honest Signals
• Both the sender and receiver have a common interest
-genetic relatedness
• Deception is often punished
Review
True Communication
Manipulation/ Deceit
Cues, Eavesdropping Ignoring/Spite
Receiver Benefit
Sender Benefit
+
-/0
+ -/0
The Transfer of Information
Transmitter ReceiverEnvironment
Signal
Cue
Living in a Marine World
• Represented by many different habitats that will select for different cue/signal modalities
Living in a Marine World
• Animal behavior is often influenced by the modality of perception and its interaction with the environment
Chemical Cues/Signals
• Most common; most studied– Invertebrates are 95% of marine animals
• Cues are released as– Pheromones (signal!)
– Waste products
– Leaking chemicals
Kairomones
Chemical Cues/Signals
• Properties of these chemicals that can affect behavioral responses– Specific chemical compounds– Concentration– Spatial and temporal patterns
Chemical Cues/Signals
• Chemical cues are utilized in many facets of marine life– Finding Mates
Chemical Cues/Signals
• Chemical cues are utilized in many facets of marine life– Finding Mates– Detecting predators
Chemical Cues/Signals
• Chemical cues are utilized in many facets of marine life– Finding Mates– Detecting predators– Finding food
Chemical Cues/Signals
• Can be transported by– Diffusion
Chemical Cues/Signals
• Can be transported by– Diffusion– Laminar advection
Chemical Cues/Signals
• Can be transported by– Diffusion– Laminar advection– Turbulence
Reynolds Number
• Mode of transport is dictated by the Reynolds number
• U – velocity• L- length of
object/organism• ρ– fluid density• μ- fluid viscosity
* You do not have to memorize this equation, but know that Re is a function of velocity, density, viscosity, and animal size
Reynolds Numbers
Reynolds Number and Chemical Cues
• Moving at low reynolds numbers• Copepods
Navigating chemical cues
Chemical Cues/Signals
• Chemical perception at higher Re is also influence by odor plume structure that is affected by multiple factors such as– Speed of release
Chemical Cues/Signals
• And the depth of release
Chemical Cues/Signals
• Water moves at different speeds at different heights due to boundary layers
Chemical Cues/Signals
• Different animals have developed different strategies to detect chemical sources
• Blue crabs vs. whelks
Visual Signals/Cues
• Visual signal are likely the second most studied/common signal– Most important in vertebrate species
Visual Signal/Cues
• Also the most easily impaired modality– Many marine environments are very turbid
Visual Signals/Cues
• Light perception– Important in diel vertical migration
Visual Signals/Cues
• Light travels in waves and is characterized by frequency, wavelength, and intensity– Different frequencies = different colors
Visual Signals/Cues
• Wavelengths of light attenuate at different depths– Longer wavelengths
attenuate in deeper water
Visual Signals/Cues
• Refraction and Reflection– Light is bent away from the normal when traveling
from water to air
Visual Signals/Cues
Visual Signals/Cues
• Other types of light – Polarized light
Visual Signals/Cues
• Polarized light
Visual Signals/Cues
• Polarized light
Visual Signal/Cues
Visual Signals/Cues
• Other types of light – Polarized light– UV light
Visual Signals/Cues
• UV light
Auditory Cues/Signals
• Least studied in marine environments– With one notable exception for one group of
animals– Noises of the ocean
Sound Waves
• Sound travels at different wavelengths and frequencies
Sound Waves• Most underwater sounds are between 10Hz and 1MHz• Noise created by ocean turbulence contributes to low frequency
noise 0.1- 10 Hz
• Different frequency audio
Sound Waves Under Water
• Ocean sound propagation at frequencies lower than 10 Hz is usually not possible whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly.– At 1kHz, the wavelength is equal to 1.5 m– At 10Hz, the wavelength is equal to 150m!
Sound Waves Under Water• Sound travels 4.4x faster in water than in air• And speeds up with increasing depth (on
average) due to the pressure of the deep sea– Sound speed also increases with increasing
temperature and salinity
Sound Waves Under Water
• Therefore, Thermoclines and haloclines also influence sound speed
Sound Waves Under Water
Sound Waves Under Water
• Sound waves refract (bend) when they change speed due to temp, salinity, depth– Currents, thermoclines, and haloclines in the
ocean mean sound is always bending and refracting
Sound Waves Under Water
• Sound can be attenuated– At some distance the intensity if the sound will fall
below ambient noise– The main cause of attenuation in water is viscosity
• And absorbed – Frequencies can be filtered out by different media – Absorption of low frequency sounds is weak– Soft bottoms also absorb sound
Sound Waves Under Water• Vegetation, air pockets, and bubbles can cause
sound waves to scatter– Low frequency sounds travel further due to longer
wavelengths• Sound reflects at the water surface and off the
bottom– high impedance between air and water causes the
water surface to act as a reflector– Reflection or absorption off the bottom is related
to its makeup (soft sediments-more absorption)
Sound Waves Under Water
• So let just say sound propagation underwater is very complicated!
• For more info see DOSITS.org
Sound
• So if low frequency sounds transmit better why don’t all marine animals communicate with low frequency/ large wavelength sounds?
The sound wavelengths an animal can produce are limited by its body size
Producing Sound• Small animals cannot radiate high amplitude
sounds with wavelengths much larger than they are
• The smaller the animal, the smaller any sound producing organs will be, and this limits small animals communicating over significant distances to using high frequencies.
Auditory Cues/Signals
Sounds of Predators on Oyster Reefs
• Can mud crabs hear?
Sounds of Predators on Oyster Reefs
• Mud crabs respond to sound cues of catfish slightly more than chemical cues
Sounds of Predators on Oyster Reefs
• Response to sound is species specific
Auditory Signals/Cues
Marine mammals use sound to communicate long distances
• And we will end with this, just because I think its cool
• World loneliest whale