Communication&

The Evolution of Signals

NSF GK12 Workshop: May 9, 2009

Nancy Burley

Professor of Ecology & Evolutionary Biology

University of California, Irvine

Behavioral Ecology

• Animal behavior as “everyone’s” science.

• Behavioral ecology is study of animal behavior from perspective of evolved functions of behaviors; focus on social behavior

• Communication illustrates major points about evolutionary processes.

• Emphasis on “why” questions

Examples of “Why” Questions

• Warning calls in Belding’s ground squirrels

• Interspecific imitation of mating signals by female fireflies

• (def.) Signal – a trait that has evolved through natural selection because it has enabled its bearers to convey information to other organisms.

• Communication involves transmission of signals, either in intraspecific or interspecific context.

A simple (intraspecific) signaling system

Sender Receiver

Environment

• Belding’s ground squirrels as example of intraspecific communication

• Examples of Interspecific communication

• Trumpet creeper hummingbird

• Viceroybutterfly (example of Batesian mimicry, in which a palatable species possesses an evolved resemblance to a toxic species)

• Photuris Photinus communication

Interaction Sender benefit? Receiver benefit?

Squirrel - squirrel Yes Yes

Flower - hummer Yes Yes

Viceroy - bird Yes No

Female Photuris –

Male Photinus

Yes No!

Summary of Examples

Two kinds of messages

• Signals – messages that serve an evolved function (which benefits the sender and may or may not benefit receiver)

• Signs or cues – messages that do not an evolved function (including intercepted signals)

• (def.) Communication is a process of information exchange in which senders influence (the behavior of) receivers by the use of evolved signals.

How do signals originate?

• agnolotti • Bollywood• Crunk• Ginormous• Gray literature• IED • Polyamory • Nocebo• Perfect storm• Speed dating • Mouse potato

In humans,creation of new signals is fast and easy.

In other animals, signals must evolve through mutation and selection. Opportunity for new signals constrained by ability of receivers to “get the message.”

Routes to evolution of new signals:

1) Ritualization of cue provided by sender.

Ritualization = evolutionary refinement (reduction of ambiguity) and exaggeration

• (def.) Intention Movement: incidental movement that “gives away” what animal is about to do.

• Sky pointing: about to take flight.

• This bird displaying a highly stylized version of sky pointing that is exaggerated.

Sequence of signal evolution

1) sends cue

2) selection onreceiver to “get”message

3) selection onsender to refinemessage ritualization

Routes to evolution of new signals:

1) Ritualization of cue provided by sender.

2) Receiver predispositions or biases.

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Parent-offspring communication in herring gulls

Adult herring gulls have a red spot on beak.

When hatchlings peck it, parents stimulated to regurgitate food.

• Tinbergen: chicks respond to spots of many colors & locations.

• Thus, any spot on parent beak might have triggered offspring reaction.

Sequence of signal evolution

2)mutation causes sender to display stimulus

1)Receiver responds to certain stimulus

3)increased RS of sender;increase in frequency of signal; evol. refinement

Examples of signal evolution that capitalize on receiver biases

• Bittern on nest

• Frog with “eyes” on back

• Lattern bug

• Orchid

• False coral snake

• Cichlid “egg dummies”

Deceit vs honesty of signals

• Obviously-deceptive signals common in interspecific communication.

• In intraspecific communication, signal honesty may evolve, because receivers evaluate reliability of signals and favor those that are reliable (“honest advertisement”).

Honest Advertising

• Multiple stages of assessment– vigor of ritualized

displays– multiple stages

of testing, each one escalated

– e.g., red deer

• Difficulty of predicting receiver bias and meaning of novel signal.

• Example: estrildine finches

Degree of honesty of signal may change over time

• Example: begging call loudness in nestling birds

• open circles -- high intra-brood relatedness

• closed circles --low relatedness.

Summary• Clear thinking about animal communication enhances understanding

of evolution. • Unpredictability of evolution• Constraints on evolutionary response• Signals evolve to benefit their bearers, not a “species” or group of

species. • Communication is the use of evolved signals to manipulate or

influence others of same or different species.• Signals may be “honest” or “deceitful”.• Dynamics differ between interspecific and intraspecific systems.• Response to “receiver bias” is an important route for evolution of

novel signals.