Signal Costs and Constraints

• Signal detection theory (pp. 429-438)

• Costs to senders of signaling

• Constraints on senders

• Costs to receivers

• Constraints on receivers

• Transmission constraints

Decision threshold

Four possibilities: hit or correct detection, false alarm, miss, and correct rejection

Signal detection theory

ROC = receiver operatingcharacteristic: plots correctdetection against false alarms.As the threshold criterion movesleft to right, the PCD vs PFA

moves down to the left.

Greater separation betweensignal and noise increases d.

ROC curves

Signal detection and mate choice

Implications• Communication is never perfect• Can improve communication

– if senders create more distinctive signals– if receivers acquire greater discrimination ability

• Which of these will happen depends on the relative costs to sender and receiver as well as constraints on signal production or reception

Sender Costs

• Conspicuousness to predators and parasites– Visual, auditory, or olfactory signals

• Energetic costs of signaling

• Lost time

• Conflict with original function

See Kotiaho, J.S. 2001 Costs of sexual traits: a mismatch betweentheoretical considerations and empirical evidence. Biol. Rev. 76:365-376.

Guppy coloration and predation

Frog mating calls attract bats

Male crickets attract females and parasitic Ormia ochracea flies

Female fly ears are tuned to hear male cricket calls

Female red-winged blackbird calls attract predators and defense

Sage grouse displays are costly

Singing consumes energy

Gray treefrogs Carolina wrens

Time lost: lekking antelope males don’t

feed

Conflict with original function

Elongated tails create drag during turns

Constraints

• Phylogenetic– Implies insufficient time or genetic variation

for evolution to modify trait

• Physical– Production of signal is impossible given the

organism’s morphology and physiology

Sender constraints

Body size constrains frequencyLeptodactyline frogs Birds

Constraints on sender learning: HVC and repertoire size

Receiver costs

• Vulnerability to predation while inspecting or comparing signals

• Time lost

• Susceptibility to exploitation, i.e. code-breakers

Code-breaking rove beetle

Receiver constraints

Phylogeny, memory

Visual resolution and body size

Hippocampus size and caching

Memory differs in food storing corvids

Memory differences are task dependent

Hippocampus shows experential changes

Transmission constraints

Tactile communication