Mating Games and Signalling

• Searching vs signalling for mates

• Hybrid mating avoidance

• Courtship control and persistance

• Mechanisms of mate choice

• Postcopulation signals

Consequences of anisogamy

• Males produce large numbers of sperm, and can fertilize many females

• Males compete for access to females

• Sedentary males compete by sperm competition

• Mobile males can either search for females, defend resources, or wait for females to encounter them

Male mating strategies

Sexual selection and signalling

• Mate attraction and courtship signalling is influenced by– The operational sex ratio– The male mating strategy– The relative importance of intrasexual (male-

male competition) vs intersexual (female mate choice) selection

Mobility gameContinuous asymmetric scramble among adults with equal sex ratio.Each adult rotates between mate searching, gamete production, courtship, copulation, parental care, and recovery.Each sex seeks strategy that minimizes its cycle time given partner behavior.Which sex should search and which should signal?Operational sex ratio favors sex with shortest gamete + recovery time.

Mate searching patterns

Males tend to search

Females tend to searchwhen there is resourcedefense since males aretied to resources

Nonsearching sex emitsattraction signals

Exaggerated signals aregiven by males due to sexual selection

Discrete asymmetric scramble

Mates encounter and must decidewhether or not to mate

Offspring viability decreaseswith level of hybrid incompatibility

ESS decision thresholds vary withthe ratio of investment in male tofemale gametes, gm/gf

Females become more choosy as their investment relative to a male increases and the sex ratio is male-biased

Whether mating and fertilization occurs in the conflict area depends on a male’s ability to forcematings and female’s ability to control fertilization after mating.

Hybrid mating game

Character displacement in damselfliesExpect species specificity of mate attraction signal when femalesemit the signal since they have more to lose from a hybrid mating

Courtship persistence games• Discrete courtship persistence game

– ESS1: male persists, female passive, when cost of rejecting is high for female

– ESS2: female rejects and male nonpersistent, when cost of persisting is high for male

– ESS3: male persists and female rejects: when costs of rejecting and persisting are both low

• Sexual arms race– Stable ESS requires variation in arms level– Males typically win given their ability to invest in armaments

• Sexual war-of-attrition– Females decide contest duration based on perceived value of male

Courtship duration patterns• Females control courtship in male resource defense and self-

advertisement systems– courtship is typically prolonged and involves many male display

behaviors

– e.g. most birds, lekking and paternal care species

– Females also control courtship in predatory species, e.g. spiders, preying mantis, lions

• Males control courtship in female defense systems– courtship is often short or absent, females may even solicit matings to

insure fertility

– some insect males mate with females before eclosion

– some sea slugs use “love darts”

Mechanisms of mate choice

• Direct benefits (choice influences mate fecundity or survival)

• Indirect benefits (genes passed to offspring)– Fisher’s process - predicts arbitrary traits– Good genes - predicts traits indicate genetic quality

• Condition dependent indicator traits

• Revealing indicator traits

Direct benefits of female preferences for male frequency in Australian frogs

Fisher’s Runaway process

• If females exhibit preference for a male trait

• And selection does not act on females

• Then sons and daughters will carry genes for both the preference and the trait

• This creates a genetic correlation between preference and trait

• And leads to geometric increase until further increase in the male trait is opposed by natural selection

The Fisher Runaway process

Arbitrary traits

Arbitrary traits in zebra finch?

Good genes models

Require a mechanism for maintaining heritable variation in offspring viabilityRecurrent deleterious mutationsParasite-host coevolution maintains parasite resistance

Peahens prefer males with eyespots which have better offspring survival

Female preference for repertoire size in Acrocephalus warblers

Condition dependent traits

Only males in good condition can make a large investment in a traitwhich then has less affect on their survival

Sage grouse condition and display

Revealing trait

All males attempt to display the trait and pay the same cost, butthe effect of the trait is less in low quality males

Barn swallow tail effects

Cyrtodiopsis population eyespan allometry

2

4

6

8

10

12

14

16

18

4 6 8 10

Body length

Soraya, male

Soraya, female

Malaysia, male

Malaysia, female

Langat, male

Langat, female

Brunei, male

Brunei, female

Brastagi, male

Brastagi, female

Swallow & Wilkinson, in prep

C. dalm

anniC

. whitei

C. q.

10 changes

100

96

99100

100

100

100

100

100

76

60

67

= average sex ratio

Maximum Parsimony Phylogram

Wilkinson et al, in press

0

2

4

6

8

10

12

14

0 0.1 0.2 0.3 0.4 0.5 0.6

Proportion of males in progeny

Predicted drive

Predicted nondrive

Sperm development predicts SR

Eyespan covaries with sperm development

Population variation in bowers

Bower evolution

Postcopulation signals• Synchronizes orgasm

– Humans, gibbons?

• Females advertise status to other members of social group– Hammer-headed bats, chimps

• Females incite competition among males– Elephant seals

• Advertise mate guarding by males– Little brown bats