The Evolution of Communication Chapter 9 Or You did NOT just say that?

Definitions of Communication Tinbergen, 1964: One party - the actor - emits a signal, to which the other party - the reactor - responds in such a way that the welfare of the species is promoted (adaptationist view) Smith 1977: Displays are acts specialized to make information available. Wilson, 1975: An action on the part of one organism that alters the probability of a pattern of behavior in another organism in a fashion adaptive to either one or both of the recipients. Slater, 1983: The transmission of a signal from one animal to another such that the sender benefits, on average from the response of the recipient.

An Origin of Signals Basic Idea: Preexisting perceptual (sensory) mechanisms bias the evolution of signals. Signalers “exploit” sensory bias in receivers of signals. Now some examples of Sensory Exploitation

Water mites Males uses leg to mimic food to trigger food detection in female. When female determines that she has grasped a male and not food, she mates with him.

Tungara Frog Capable of producing a whistle, whine, and chuck call. Chuck is the call females most prefer. Females will approach chuck calls However, chucking also attracts bat predators They key in on the multi-frequency chuck call.

Prediction on Use of Chucking Chuck if you can’t find a mate Not tested If you see a bat, stop chucking Yes If in a small group, chuck less often (Why?) If in a large group, chuck away Note – frog alarm calls signal for stop calling (the watchman’s song)

Chucking This is the only species that “chucks” However, all females in clade prefer chucking. Preference for chucking appeared before actual chucking. Why did this preference occur? Probably had some function other than mate choice. F F Tungara F chucking Chucking preference in females

Swordtail Females choose males by length of ray All females prefer swords, although swords only appear in 2 nd half of group.

Why do ravens scream their heads off when they find a carcass? Costs to yelling Attract predators Attract competitors

Possible Hypotheses Attract a larger animal to open the carcass for them. Attract other ravens to defend against predators Gang-up on territory owner

Testing Predict: Open a carcass yourself, and they get quiet. Observe: they still yell Predict: stop yelling once a certain number of ravens reach site. Observe: keep screaming, even in large groups.

Gang warfare A large number of intruder ravens can overcome a territory owner of a carcass. This allows intruders to feed Predict: owners don’t yell Observe: owners never yell Yelling attracts other intruders Benefit = getting to eat Cost = having to compete with others.

Singing as a Signal in Songbirds Two Hypotheses (for male singing) Attract mates Repel other males

Attracting Females Predictions Sing around females Yes Sing in the breeding season Yes Sing complex songs to attract more females Capable only by older, more experiences males in breeding Stop singing once mated Yes and No

Repel Other Males Predictions Sing in presence of males, with more singing for greater intruder presence Yes If you silence a male, intruders should increase Yes Fewer males intrude a tape than when silence.

Mate guarding Singing can also serve as a way to protect paternity Background Extra-pair fertilization of eggs is common. Females of numerous species may seek other males If males can run other males off, then hopefully, the eggs in the nest are his.

Whose bed have your boots been under? Assumption Singing conveys information about male quality or ability to guard female. Predict: Males sing when mate is most fertile (a day before laying). YES Males in better condition sing more. YES Intruder frequency will decrease when song quality increases Untested to date

Signalers and Receivers Signalers Individual that sends the signal (visual, sound, etc.) Receiver Any animal that can detect the signal Does NOT have to be the intended receiver How can spiteful signaling be naturally selected? Hurt another to put them worse off than yourself. (end of semester)

Incidental Receivers Biggest problem incidental receivers are predators Tungara Frog and Fringe-lipped Bat When frog chucks, it is using a location call (multi-frequency) Bats can home in on this and strike

Bird alarm calls Typically use calls that are hard for predators to detect. (seet call) Minimize the risk of warning by not drawing attention to yourself.

Deceitful signals Fireflies and lighting bugs 2 species: Photuris A and B Form cooperative signaling by males to females “mutually beneficial” Don’t mate with the wrong species So what’s deceitful?

The Deceit Male B’s respond to specific flashing patterns of female B’s. Female A’s mimic female B’s response to male B’s. Female A’s are predators on male B’s. This is selected caution in male B’s. Female A’s are only successful about 10% of the time. This selects for better mimicry in A’s.

Deception by Chickadees If a lot of birds are at a feeder, and the Chickadee can’t get any food, they sometimes give false alarm calls to everyone to hide. While the dominate larger birds are hiding, the Chickadees gets a quick meal. Tanager-shrikes do the same thing to get competitors to stop chasing insects they want.

Displays, deception and “honesty” Fact – Many animals settle disputes by ritualized displays. Animals actually rarely fight, too dangerous. A certain display is usually all that is needed to see who wins and who losses. So why not fake the winning display or signal?

Truth in sound Many of these signals are “honest” and can’t be faked. Only bigger toads can make deeper calls

Truth in sound II Remember roaring in elk? Must be in good shape to roar for a period of time. If that doesn’t settle it, then a side-by- side assessment will determine. Only under same roar and same size will a fight occur.