S. Alem, C. Clanet, V. Party, A. Dixsault, & M. D. Greenfield. 2015 What determines lek size? Cognitive constraints and per capita attraction of females limit male aggregation in an acoustic moth. S. Alem, C. Clanet, V. Party, A. Dixsault, & M. D. Greenfield. 2015 Animal Behaviour 100: 106-115

Leks Classically – form because of strong ♀ choice ♀ gains - improved choice comparisons - reduce time and energy in mate seeking Why do ♂s aggregate? - ♂s at leks have a higher /♂ mating success than alone - ♀s prefer aggregations - location of lek ⟶ better signal transmission - lower /♂ predation risk

Leks If leks offer ♂ increased /♂ matings - what determines lek size? - Never get huge leks Why is there a limit? Aggression Disease Stress -increase faster than attractiveness of lek to female Costs to male Costs Attractiveness

Leks If leks offer ♂ increased /♂ matings - what determines lek size? - Never get huge leks Why is there a limit? Constraints on Female -rate of arrival of ♀s could decelerate benefit - /♂ mating success drops -too expensive for ♀s to travel far -in larger leks - difficult for ♀s to find ‘best’ male

Perceptual Constraints -saturation of female receptors -if saturated, n+1 or n+2 lek = n lek & no benefit to a male from changing groups ∴ there will be a limit on lek size

Which influences are responsible for lek size? Do influences coincide? Does the number of ♂s on a lek = maximum benefit ♂ : ♀ ratio? OR Is there a sexual conflict? - ♂ avoiding predation in large groups - ♀ wanting access to more ♂s

This study 1. Measure per capita male attractiveness as a function of lek size 2. Measure tendency of males to aggregate in leks 3. Mechanisms by which females distinguish leks and assess lek size

Methods Species Achroia grisella Lesser wax moth Symbiont of bee hives

Methods Eclose in hive Species Remain in vicinity of hive Males in groups of 2 - 10 Achroia grisella Lesser wax moth Sing for 6 -10 hrs each night Die in ≤ 10 days

Methods Upstroke = 2 pulses (one on each side) Downstroke = 2 pulses (one on each side)

Methods Time Upstroke = 2 pulses (one on each side) Downstroke = 2 pulses (one on each side) Time

Methods 95 dB 95 dB 95 dB 95 dB Ultrasonic - 70 – 130 kHz

Methods Protocol Raised in lab Isolated by sex (to ensure virginity) Used in mating experiments (♀s mate once only)

Experiment 1 – Female preference for leks of singing males Release point Cage with male Empty cage 20 females tested Groups of 2, 3, or 4 males vs 1 male

Experiment 1 – Female preference for leks of singing males Calculations (for each lek size) Number of ♀ choosing a lek = per capita attractiveness Number of ♂ in a lek Per capita attractiveness Per capita attractiveness = relative per capita attractiveness Number of ♀ choosing single male

= proportion of females choosing a lek = attractiveness of a lek relative to single male Random choice Per capita attraction = 1 Relative per capita attraction Female choice Lek size

Experiment 2 – Marginal female preference for larger leks Release point Cage with male Empty cage Groups of males, one with n males, other with n+2 (1 vs 3, 2 vs 4, 3 vs 5, 4 vs 6, 5 vs 7, 6 vs 8, 7 vs 9) Prediction: Female preference for larger leks decreases with larger leks

Experiment 2 – Marginal female preference for larger leks = proportion of females choosing a lek = attractiveness of a lek relative to single male Random choice Per capita attraction = 1 Female choice Relative per capita attraction Lek size

Experiment 3 – Distinguishing acoustic features of leks How do females detect and distinguish leks from solitary males? Recorded males in groups and alone

Experiment 3 – Distinguishing acoustic features of leks How do females detect and distinguish leks from solitary males? Recorded males in groups and alone Solitary How often these pulses are repeated is “pulse pair rhythm”. Grouped Difficult to detect rhythm

Experiment 3 – Distinguishing acoustic features of leks How do females detect and distinguish leks from solitary males? Recorded males in groups and alone Grouped Difficult to detect rhythm Considered only pulse pairs that were ≥ 2 msec after previous pair Also considered pulse pairs that were 5 msec after previous pair (refactory period of axons in moth)

Experiment 3 – Distinguishing acoustic features of leks How do females detect and distinguish leks from solitary males? Results 1. Males increased pulse pair rate about 10% when in groups 2. No change in mean peak amplitude 3. Pulse pair rhythm of a lek >> that of solitary male 4. Not a linear increase with 3 males - overlap

Experiment 4 – How do females discriminate leks from solitary males? Playback experiments: 1. Can ♀s distinguish leks by acoustic features alone? 2. Do ♀s use the rhythm broadcast by leks to distinguish them? 3. Do ♀s attend to additional features in overall song broadcast by leks?

Experiment 4 – How do females discriminate leks from solitary males? 1. Can ♀s distinguish leks by acoustic features alone? ♂ ♀ ♂ ♂ ♂ Results: 1. Females can distinguish leks on acoustic cues alone 2. Females use pulse pair rate to distinguish leks 3. Females do not use acceleration of rhythm to distinguish leks

Experiment 5 – Do singing males join other male singers? Release point Cages with males (1 → 5) Empty cage

Experiment 5 – Do singing males join other male singers?

Discussion 1. Females prefer leks over solitary males – based on per capita attractiveness 2. Females judged leks based on pulse pair rhythm. Role of neuroethology? Results suggest that neural constraints (ability to distinguish pulse pair rate) dictate maximum lek size Sound intensity not a factor

Discussion Why do females ignore rhythm accelerations? -duty cycle and chances of simultaneous sounds Matching lek size and female preference -compare ♂ and ♀ responses -roughly matched on lek size – about 3 Inter-male aggression may play a role May be a product of similar neural constraints

Questions??