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 game Continuous 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 search when there is resource defense since males are tied to resources Nonsearching sex emits attraction signals Exaggerated signals are given by males due to sexual selection

Hybrid mating game Discrete asymmetric scramble Mates encounter and must decide whether or not to mate Offspring viability decreases with level of hybrid incompatibility ESS decision thresholds vary with the ratio of investment in male to female 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 force matings and female’s ability to control fertilization after mating.

Character displacement in damselflies Expect species specificity of mate attraction signal when females emit 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 viability Recurrent deleterious mutations Parasite-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 trait which 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, but the effect of the trait is less in low quality males

Barn swallow tail effects

To address these questions we have used stalk-eyed flies in the genus Cyrtodiopsis. In some species, such as this Cyrtodiopsis whitei, a male’s eye span can exceed his body length. Males use eye span to assess body size during head-to-head contests. When two males of similar size encounter one another, ritualized fights result in which forelegs are extended and one male attempts to dislodge the other by grabbing him. Winners of a contest control access to nocturnal aggregation sites on rootlets which attract from 1 to 25 females at dusk. Females prefer to roost with long eye span males. In the morning, one male mates with as many of these females as possible. We have observed up to 24 copulations in 30 minutes in the field.

Cyrtodiopsis population eyespan allometry Swallow & Wilkinson, in prep

C. dalmanni C. whitei C. q. Maximum Parsimony Phylogram 10 changes 100 96 99 76 60 67 Maximum Parsimony Phylogram = average sex ratio C. dalmanni C. whitei The red lines summarize the results of Kruskal Wallis one-way ANOVAs and indicate that the sex ratio distributions differ between species, but not between populations of each species. Comparison the progeny sex ratio which would be expected if a female mated at random shows drive is absent in CQ, present but relatively weak in each of the four CD populations, and similarly strong in the two populations of CW. We developed a phylogenetic hypothesis for these populations using about 1 kb of mtDNA sequence which we obtained from 5 individuals in each population. The high bootstrap values indicate that these populations have been genetically isolated for some time. Thus, X chromosome drive appears to be conserved over short evolutionary time scales as expected if it is maintained in a stable polymorphism. C. q. Wilkinson et al, in press

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