Signal Costs and Constraints

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Buddy Goodman
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1 Signal Costs and Constraints Costs to senders of signaling Costs to receivers Constraints on senders and receivers Transmission constraints Reading: Ch. 17

2 Peer evaluation of group projects Please evaluate each member of your group with respect to the following criteria. A. Rate each person s performance including your own on a scale of 0-3 with 0 being few if any contributions, 1, a marginal level of contributions; 2, a reasonable contribution level; and 3, above expectations level of contribution. B. In the space marked points distribution assign a maximum of 10 points to each member, including yourself. The points each member receives should reflect his/her overall contribution to the project. Member s name Helped write proposal Helped collect data Helped analyze data Helped prepare presentation Point distribution Please make any additional comments you would like me to consider when grading the group presentation.

3 Signal detection and mate choice

4 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

5 Sender Costs Conspicuousness to predators and parasites High for visual, auditory, or olfactory signals Low for deposited olfactory marks Energetic costs of signaling High for visual or auditory displays with high duty cycle Lost time Conflict with original function

6 Guppy coloration and predation Guppy coloration differs depending on which predator is present, This result led Endler to propose sensory drive model

7 Female choice in Túngara frogs Calls consist of whines and chucks Females prefer males with deeper chucks Chuck frequency constrained by male body size

8 Sensory exploitation in tungara frogs

9 Sensory bias predicts preference precedes trait evolution

10 Frog mating calls attract bats Chucks make calling frogs more vulnerable to eavesdropping by predatory bats

11 Male crickets attract females and parasitic Ormia ochracea flies

12 Female fly ears are tuned to hear male cricket calls

13 Female red-winged blackbird calls attract predators and defense Nests w/playbacks are discovered by predators Males defend nests w/chits

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 Gray - generate lift White - produces drag

17 Receiver costs Vulnerability to predation while inspecting or comparing signals Choosiness may decline in presence of predators Time lost in assessment Susceptibility to exploitation, i.e. codebreakers

18 Predator presence influences mate choice in guppies

19 Code-breaking Rove beetle mimics ant pheromone Photuris fireflies imitate Photinus female flashes to catch Photinus males

20 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

21 Transmission constraints

22 Sender constraints

23 Body size constrains frequency Leptodactyline frogs Birds

24 Receiver constraints Phylogeny, memory

25 Visual resolution and body size

26 Is learning a cost or constraint? Neural tissue required for learning and memory is energetically costly to maintain Learning is often time-consuming and mistake-prone And often restricted to a limited sensitive period Evidence for enlargement of specific regions devoted to specific processing or memory tasks

27 Constraints on sender learning? HVC and repertoire size

28 Hippocampus size and caching

29 But, hippocampus also shows experiential changes

Total brain mass (log 10 mg) 4 3.5 3 2.5 2 y = 0.700x + 1.917 y = 0.769x + 1.655 Neocortex volume (log 10 cm 3 ) 4 3.5 3 2.5 2 1.5 y = 0.782x + 1.248 y = 0.918x + 0.804 1.5 0 0.

30 Total brain mass (log 10 mg) y = 0.700x y = 0.769x Neocortex volume (log 10 cm 3 ) y = 0.782x y = 0.918x Body mass (log 10 g) Body mass (log 10 g) Microchiroptera Megachiroptera Calculate encaphalization quotients as observed/fitted values

31 Combined testis mass varies across species from 0.1% to 8.4% of body mass Combined testis mass (log 10 mg) y = 0.758x y = 0.456x Body mass (log 10 g) N = 87, F = 16.22, R 2 = 0.16, P < N = 20, F = 38.93, R 2 = 0.68, P < Microchiroptera Megachiroptera Calculate testis quotient as observed/fitted values

32 Breeding system correlates with testis size Testis quotient SM-SF SM-MF MM-MF Roosting association 0.6 monogamy polygyny polygynandry Mating system 0.6 no yes Female promiscuity

33 N = 63, F = 5.38, R 2 = 0.08, P = N = 36, F = 10.06, R 2 = 0.22, P < Neocortex encephalization quotient Constrast in neocortex encephalization quotient Testis quotient Contrasts in testis quotient Significant trade-off exists only for echolocating bats

April 12: Reproduction III: Female choice. Female choice

April 12: Reproduction III: Female choice Female choice In general, females are expected to be choosier than males because they have more to lose by making bad mating decisions Costs and Benefits: Possible