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