Animal Communication
ABGG core course Fall 2012
Assignments
1. Position paper for discussion next Friday (Oct. 12) • I will send the question out today.
2. Homework question on Bayesian updating • Submit over email after my lectures are done;
we will not cover the material that you need in time for you to answer this before discussion section.
Readings
Friday:Enquist, et al. Chapter 16: Signaling. In Evolutionary Behavioral Ecology, Eds. Westneat and Fox
Rowe C, Skelhorn J, 2004. Avian psychology and communication. Proceedings of the Royal Society of London, Ser B 271:1435-1442.
Monday:
E. A. Hebets and D. R. Papaj. 2005. Complex signal function: developing a framework of testable hypotheses. BES 57, 197-214. Rendall D, Owren MJ, Ryan MJ, 2009. What do animal signals mean? Anim
Behav 78:233-240.
Seyfarth, Cheney, et al. (2010). The central importance of information in studies of animal communication. Anim. Behav. 80(1): 3-8. Bradbury and Vehrencamp, Web Topic 1.2. Information and Communication
(don’t get bogged by the details!) Following Friday:
Maynard Smith and Harper. 1995. Animal Signals: Models and Terminology, J. Theoretical Biology, 177: 305-311.
Számadó, S. 2011. The cost of honesty and the fallacy of the handicap principle, Animal Behavior, 81: 3-10.
Next year use Hurd and Enquist 2005 instead of Maynard Smith?
Animal Communication
1. What is Communication
2. Why do signals take the diverse forms that they do? 3. What is the function of signals?
acoustic olfactory visual seismic
tactile electrical IR
I. The Basics
a. Definitions
b. What do animals say to one another? c. The Process of Communication
II. Signal Form
a. Overview of factors affecting signal form b. Sender mechanisms (constraints and opportunities) c. Environmental effects
i. Sensory Drive
d. Receiver mechanisms (constraints and opportunities) i. Sensory Exploitation
e. Summary
III. Signal Function
a. Conflicts of Interest b. Information & decision making c. Honesty in advertising d. Active areas of current research
Animal Communication Outline
I. Basics, a. Definitions
• Selection will favor signals that elicit a response that benefits the sender (on average)
• Selection will favor responses that benefit receivers (on average). However, not all communication must do so (e.g. manipulation/deceit)
• Sender ≈ Signaler ≈ Manager ≈ Manipulator • Receiver ≈ Perceiver ≈ Assessor ≈ Mind-reader
Communication: the provision of a signal (typically containing information) from one individual (the sender) to another individual (the receiver), which can be used to make a decision
Signal: a packet of energy or matter generated by one individual (the sender) which is selected for its effects in altering the behavior of a second individual (the receiver)
sound
Color/Pattern
Scent
movement
etc...
I. Basics, a. Definitions
I. Basics, a. Definitions
• In practice, we can only assess signal function via receiver response
• Note that signals are not selected to convey information, they’re selected to elicit a beneficial response (hence
“manipulators”) ...but receivers are selected to respond to signals that are informative, so over evolutionary time, informative signals will elicit more responses (hence “mind-readers”)
• Many argue that the concept of information causes more confusion than clarity, since it implies selection to inform (see Rendall et al. 2009 reading)
Signal: a packet of energy or matter generated by one individual (the sender) which is selected for its effects in altering the behavior of a second individual (the receiver)
Cue: an action or trait from which a receiver may acquire information and make a decision, but it has not been selected to alter the behavior of receivers.
• Exploitation of cues by receivers is called eavesdropping • This is not communication by the definition we will use; why?
I. Basics, a. Definitions
Ritualization: the process of signal evolution from a cue Begin with a cue...
If the sender benefits from the receiver’s response to a cue, the cue will be modified into a true signal via the process of
ritualization, which includes at least one of the following:
• Simplification • Exaggeration • Repetition
• Stereotypy (not necessarily w/o plasticity) • Emancipation from original context
I. Basics, a. Definitions
True Communication: an exchange of a signal between a sender and receiver to the benefit of both parties (Bradbury and Vehrencamp, 1998)
• Senders produce signals to increase the chances that the receiver will choose an action beneficial to the sender • The receiver responds to the signal to increase its chance of
choosing an action that benefits the receiver
• Both parties may benefit, but they are not being altruistic; either both parties have common interests, or they have different interests and have reached a stalemate (e.g. an equilibrium)
I. Basics, a. Definitions
Manipulation / Deceit: Dishonest or deceptive signals that benefit the sender but the lead the receiver to respond suboptimally
• Receivers are expected to evolve resistance or ability to detect cheats (if possible)
• Is communication, but not “True Communication”
I. Basics, a. Definitions
Receiver benefit True communication Cues, eavesdropping Manipulation, deceit Ignoring, spite 0 or – + + 0 or – Sender benefit Broad definition of Communication Not Communication
I. Basics, a. Definitions
Summary of Terms: Identity can be identified at multiple levels:
Species Identification: Signals are often used to identify
conspecifics for mating, flocking or other social interactions
PIED FLYCATCHER COLLARED FLYCATCHER allopatric
sympatric
Saetre, et al. 1997
I. Basics, b. What do Animals Say?
i. Sender Identity
Character displacement /
reinforcement Called?
Group Identification: Members of the same sex, age group,
mated pair, family group, foraging group, night roosting group, or other social unit share one or more variants of a given signal type
I. Basics, b. What do Animals Say?
i. Sender Identity
Example: Killer Whale Groups (Pods)
I. Basics, b. What do Animals Say?
i. Sender Identity
Individual Identity: Each individual has a somewhat unique
variant of some signal type that is widely used throughout the population
Can be used to recognize offspring/parents, mates, and/ or group members in gregarious species
P1 P2 P3 P1 P2 P3 P1 P2 P3 5 10 kHz msec 200 0
Example: Orange-fronted Parakeet contact call
Often involves complex calls, color patterns or scents, learned by receivers
Individual Identity: Parent-offspring recognition
Many species rely on locational cues (nest site), which leaves parents vulnerable to brood parasitism
In birds, this can lead to arms races between parent discrimination and parasite mimicry of eggs, gapes and nestling begging vocalizations
I. Basics, b. What do Animals Say?
i. Sender Identity
Single warbler chick
Single Cuckoo Warbler brood Parasitic whydah Host waxbill Red-chested Cuckoo eggs; 3 races Schuetz, 2005
Kuiper & Cherry 2002
I. Basics, b. What do Animals Say?
i. Sender Identity
Can eventually lead to the evolution of host-specific parasite
Location of the sender:
Few animals can indicate their location semantically (like humans do). Instead, they adjust signal properties to make location of the signal source obvious or difficult to determine
For example, Staccato broadband sounds are easier to locate; single low or high frequency sounds with gentle onsets/offsets are harder (Marler 1955)
Visual displays often call attention to location
I. Basics, b. What do Animals Say?
ii. Location
Content based on Context:
The kinds of information that are useful to a receiver will also depend on the nature of the decision that it is currently facing, and that depends on the circumstances; the kinds of decisions useful to senders are also context-dependent There are 7 basic contexts in which signals are used by
receivers to make decisions:
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
1. Conflict: Animals rarely fight to the death but more often
exchange signals until they can determine without fighting who would win if they escalated
Stalk-eyed flies Ground squirrel
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
2. Territoriality: Animals may engage in conflict to establish a
territory, but once settled, they largely maintain it by announcing their continued presence with signals
Capybara marking territory Panda
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
3. Sexual Interactions: Usually, males have to persuade
females to mate, and females want to assess and choose the best male; this invariably involves signals
Jumping spider
King Bird of Paradise
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
4. Parent-Offspring Exchanges: Parents adjust care and food
depending on number of offspring and relative need, whereas offspring usually want more for themselves; signals mediate this conflict
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
5. Social Integration: Coordination of the activities within a social group of animals is invariably mediated by signals
Contact calls Separation calls Movement initiation calls
Golden lion tamarin
Pinyon jay
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
6. Environmental Information: Some animals announce
food finds to others, and most social animals produce alarm signals to alert others to predator risks
Marmot alarm call Honeybee dance
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
7. Auto-communication: Contrasts between outgoing and
returning signals can be used to provide information about the environment
Examples: sonar in bats and toothed whales; electrical signals in electric fish
I. Basics, b. What do Animals Say?
iii. Context-dependent exchanges
Signaler Payoff to Receiver Cues Signals Prior Information Payoff to Sender environment
Signals & Cues
Receiver
Act 1
Act 2
I. Basics, c. The Process of Communication
Next year moveafter the definitions
I. Basics, c. The Process of Communication
Signaler Payoff to Receiver Cues Signals Prior Information Payoff to Sender environment
Signals & Cues
Receiver
Act 1
Act 2
mate reject
Depends on female’s decision Song
parasites Prob males are healthy
male female
Crouching, fluttering
Depends on decision & male’s health
Tactical Design What are the constraints on
signal production? How does transmission
through the environment affect the signal?
What is the receiver’s sensory system capable of detecting? Etc…
Efficacy-based approach proximate causes
Strategic Design What is the purpose of the
signal?
What info is being conveyed? What outcome does the
sender prefer? What outcome does the
receiver prefer? Etc…
Function-based approach ultimate causes Tactical vs. Strategic “design”
I. Basics, c. The Process of Communication
I. The Basics
a. Definitions
b. What do animals say to one another?
c. The Process of Communication
II. Signal Form
a. Overview of factors affecting signal form b. Sender mechanisms (constraints and opportunities) c. Environmental effects
i. Sensory Drive
d. Receiver mechanisms (constraints and opportunities) i. Sensory Exploitation
e. Summary
III. Signal Function
a. Conflicts of Interest
b. Information & decision making
c. Honesty in advertising
d. Active areas of current research
Animal Communication Outline
II. The Form of Signals
II. The Form of Signals, a. Overview
Factors that affect the form of signals: 1. Tactical (Efficacy) Issues:
• Constraints and opportunities in the production mechanisms of the sender
• Constraints and opportunities in the environment through which the signal propagates
• The sensory and perceptual system of the receiver 2. Strategic (Functional) Issues:
• What is the function of the signal? (e.g. mate attraction, alarm, etc.) • Do the interests of the sender and receiver coincide or differ?
Factors that affect the form of signals: 1. Tactical (Efficacy) Issues:
• Constraints and opportunities in the production mechanisms of the sender
• Constraints and opportunities in the environment through which the signal propagates
• The sensory and perceptual system of the receiver 2. Strategic (Functional) Issues:
• What is the function of the signal? (e.g. mate attraction, alarm, etc.) • Do the interests of the sender and receiver coincide or differ?
II. The Form of Signals, a. Overview
Not all senders could (or should) make all signals; Why? Constraints and opportunities in the mechanism of signal production will affect the forms which signals take
i. Natural selection works with the raw material available, so signals often reflect evolutionary history / constraints
• Signals often evolve from existing structures and behaviors (cues), or other signals. Example 1: Intention movements:
II. The Form of Signals
b. Sender Mechanisms
Aggressive intentions Mating intentions
Example 2: New displays can evolve from other displays if a similar type of response is beneficial to senders
Courtship begging Baboon female mating solicitation Appeasement display by juvenile male
II. The Form of Signals
b. Sender Mechanisms
II. The Form of Signals
b. Sender Mechanisms
Snout-vent length (mm) F un da me nt al ca ll fre qu en cy (kH z)Call frequency in toads is an index for body size ii. Possible signals also limited by the laws of physics Example 1: Due to the properties
of sound waves, animals typically cannot make loud sounds with a wavelength longer than 1-2x their body size
Smaller animals = higher pitch
Thus there are limits to the frequency and amplitude of sounds that animals can make
Example 2: Body/vocal chord size also limits amplitude (i.e. loudness) Animals can use tricks like large resonators to make very loud sounds But this limits them to simple sounds Tradeoffs! large hollow hyoid cartilage ii. Possible signals also limited by the laws of physics
Male Howler Monkey
II. The Form of Signals
b. Sender Mechanisms
Signals must travel from the sender to the receiver through the environment, propagation varies by habitat
This favors signals that propagate well in the habitats in which they are used
Upon arrival, signals must be detected and recognized from background noise in their channel (visual, chemical, acoustic, etc...) to elicit a response
This favors signals that are conspicuous in their habitat
II. The Form of Signals
c. The Environment
This issue was first explored in the acoustic modality; the
“acoustic adaptation hypothesis” (e.g. Morton 1975; Wiley
and Richards 1978; Richards and Wiley 1980; Ryan and Brenowitz 1985)
Endler (1992) proposed “Sensory Drive”, a framework that describes how signals are shaped by the environment in 2 ways:
1) through environmental effects on propagation, and 2) through the receiver’s sensory system (Umwelt), since the
environment affects the evolution of sensory systems (i.e. sensory organs are tuned to detecting food and predators in their habitat)
II. The Form of Signals
c. The Environment
Example 1: Propagation in the acoustic modality
To avoid reverberation (echoes) when there are many reflecting objects in the medium (e.g. forests), Eugene Morton (1975) predicted that the sender should either:
a) avoid rapid modulations (either AM or FM) b) use sounds of such a low frequency that they are not
reflected by the majority of the objects
II. The Form of Signals
c. The Environment
• Grassland birds sing a diversity of complex
songs
• Forest birds avoid rapid modulations (either
AM or FM) or use lower frequencies
This is evidence that bird songs are shaped by the constraints of the environment to maximize propagation
Example 1: Propagation in the acoustic modality
II. The Form of Signals
c. The Environment
Brightness Contrast: Phylloscopus warblers in dark habitats have more white patches (Karen Marchetti 1993)
P. affinis P. pulcher
R. regulus P. proregulus
P. pulcher
II. The Form of Signals
c. The Environment
Example 2: Conspicuousness in the visual modality
Florican (from Life of Birds, BBC)
Movement contrast: Contrast movement with predominant
pattern of background
II. The Form of Signals
c. The Environment
Example 3: Conspicuousness in the visual modality
• In microhabitats where red has good contrast (limnetic zone): females with red-sensitive eyes and red-bellied males • In areas where red has poor contrast
(tea-colored water; deep benthos): females with less red-sensitive eyes and black-bellied males
• Male trait and female preference matches habitat type
Incipient speciation (parapatric) Threespine stickleback Gasterosteus aculeatus Boughman 2001 This is an active area of current research!
II. The Form of Signals
c. The Environment
Example 4: Conspicuousness and female sensory tuningSensory Drive may favor divergent signals among populations, leading to reproductive isolation and speciation
Jakob von Uexküll (1864-1944)
The Umwelt
What does the animal see, hear and smell? Jakob von Uexküll promoted the concept that each animal has a sensory world, or Umwelt The Umwelt is determined by the physiology of the sensory organs and the brain (which is affected by the environment)
The Umwelt of the receiver will influence which signals elicit a response once received
II. The Form of Signals
d. Receiver Mechanisms
Signals that are more effective at stimulating the sensory and perceptual system of the receiver will be favored by selection
II. The Form of Signals
d. Receiver Mechanisms
More recently...
Michael Ryan, et al. (1990) focused attention on the receiver with the “sensory exploitation hypothesis” -- that signals can evolve to exploit biases in the sensory system
Guilford and Dawkins (1991) emphasized the importance of considering the sensory and perceptual systems of the receiver (“Receiver Psychology”), as did Don Owings, throughout his career; The Rowe and Skelhorn (2004) paper I assigned is a review of this topic
Example 1: Match between hearing and vocalizations in birds
So un d Pre ssu re L eve l d B Frequency (kHz) Field sparrow Red-winged blackbird
Canary Budgerigar
audiogram Power spectrum of songs
II. The Form of Signals
BLUE WHITE, BLUE, GREEN, YELLOW, ORANGE, RED 400 500 600 700 RED & ORANGE V B G Y O R
II. The Form of Signals
d. Receiver Mechanisms
Example 2: Match between signals and sensory systems of
eavesdropping predators
V B G Y O R
Endler
Sensory exploitation model (Mike Ryan 1990) (a.k.a. pre-existing preference or hidden preference): Pre-existing or latent preferences in receivers are exploited by
manipulative senders Receiver response may be costly
Exploitation is not stable: receivers are selected to stop responding (evolve resistance) unless there is a benefit (e.g. if the signals have useful information)
Not predicted to be stable over long term unless costs are low or females are somehow constrained, but this may be how many signals get started
this is “manipulation” on communication chart
II. The Form of Signals
d. Receiver Mechanisms
Sensory exploitation model:
Feeding: Females have Preference for
red objects
Mating: Males evolve red coloration to “exploit” preference
If females benefit from new signal, then it’s stable If it’s costly, then females selected to differentiate between mating and feeding (if possible)
II. The Form of Signals
d. Receiver Mechanisms
chuck T+ T+ T- T- T- P+ P+ T- P+ P+ T- Hypothesis 1: This genus started with no chuck (T-) = 2 changesTrait Preference Tungara
Frogs
+ +
II. The Form of Signals
d. Receiver Mechanisms
chuck Trait Preference T+ T+ T- T- T- P+ P+ T+ P+ P+ Tungara Frogs Males evolve signal to “exploit” response T- = 3 changes Hypothesis 2: This genus started with a chuck (T+) Ryan argues that the pref was present before signal -- +
II. The Form of Signals
d. Receiver Mechanisms
Preference for males with arbitrary (novel) traits in zebra finches
Zebra finches with novel crests
Artificial male ornaments Percent of social time females spent with each stimulus type 60 50 40 30 20 10 0 white crest green crest red crest none (N. Burley) Sensory Exploitation
II. The Form of Signals
d. Receiver Mechanisms
What’s the difference btwn sensory exploitation and sensory drive? Sensory drive model: Background noise, transmission properties, and adaptations
to predators and prey will shape signal propagation and receiver sensory design. Signals will thus reflect environmental constraints, and sensory systems that evolved in other context, e.g. predator detection.
Sensory drive is mainly signal form, not about signal origin or function
Sensory exploitation is a model of signal origin, form and function. It is a case of sensory drive where the receiver does not benefit or is harmed by the exchange (i.e. manipulation); does not include environmental effects on propagation. Also called “Sensory Traps”, when senders mimic another non-signal stimulus (West-Eberhard 1984, Christy 1995)
Unfortunately, both models sometimes called “sensory bias” (Basolo 1990)
II. The Form of Signals
d. Receiver Mechanisms
II. The Form of Signals
d. Receiver Mechanisms
Many signals are complex and multimodalThere are a number of efficacy-based and functional hypotheses Rather than lecture about this (no time!), I assigned a review:
E. A. Hebets and D. R. Papaj. 2005. Complex signal function: developing a framework of testable hypotheses. Behavioral Ecology and Sociobiology57, 197-214.
The Big Picture: How do animals deal with all this crap at
the same time? For example, with sound...
ü Body size limits minimum frequency that can be produced ü Lower frequencies suffer less attenuation due to heat losses
and scattering
ü Living close to the ground makes low-intermediate frequencies unsuitable
ü Background noise is least at intermediate frequencies ü Receiver is most sensitive in intermediate frequencies
II. The Form of Signals
e. Summary
am p litu d e frequency body size heat loss + scattering noise boundary reflections compound curve How do we put these together?Receiver’s audiogram
II. The Form of Signals
e. Summary
Etc.
There is thus an optimal frequency for that species given these constraints... am p litu d e frequency
f
optimalII. The Form of Signals
e. Summary
am p litu d e frequencyf
optimal...which will be different for another species with different body size, habitat, receiver, etc.
