Signal Costs and Constraints

1. 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

2. Decision threshold Four possibilities: hit or correct detection, false alarm, miss, and correct rejection

3. Signal detection theory ROC = receiver operating characteristic: plots correct detection against false alarms. As the threshold criterion moves left to right, the PCD vs PFA moves down to the left. Greater separation between signal and noise increases d.

4. ROC curves

5. Signal detection and mate choice

6. 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

7. 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 between theoretical considerations and empirical evidence. Biol. Rev. 76: 365-376.

8. Guppy coloration and predation

9. Frog mating calls attract bats

10. Male crickets attract females and parasitic Ormia ochracea flies

11. Female fly ears are tuned to hear male cricket calls

12. Female red-winged blackbird calls attract predators and defense

13. Sage grouse displays are costly

14. Singing consumes energy Gray treefrogs Carolina wrens

15. Time lost: lekking antelope males don’t feed

16. Conflict with original function Elongated tails create drag during turns

17. 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

18. Sender constraints

19. Body size constrains frequency Leptodactyline frogs Birds

20. Constraints on sender learning: HVC and repertoire size

21. Receiver costs • Vulnerability to predation while inspecting or comparing signals • Time lost • Susceptibility to exploitation, i.e. code-breakers

22. Code-breaking rove beetle

23. Receiver constraints Phylogeny, memory

24. Visual resolution and body size

25. Hippocampus size and caching

26. Memory differs in food storing corvids

27. Memory differences are task dependent

28. Hippocampus shows experential changes

29. Transmission constraints

30. Tactile communication