Sexual Selection

I. Motivation

Sexual Dimorphism is Frequent

Figure 11-1

Figure 11-3

The sexual dimorphism in

long-tailed widowbirds

Scarlet Tanagers, male, femaleWesern Tanagers, male female

Human males and females differ in height

Why this sexual dimorphismSelection on survivorship and reproduction

Ability to obtain mates:

Sexual Selection:

Different reproductive success due to variation among individuals in success at getting mates

If there is heritable variation in a trait that affects to ability to obtain mates, then variants with higher success at obtaining mates will become more common over time

II. Limits to reproduction differ between the sexes

Guess What?

With few exceptions, females invest much more time and energy in the production of young

Figure 11-6

Asymmetries in sexual reproduction in rough-skinned newts

Asymmetries in sexual reproduction in rough-skinned newts

femalesmales

Exception to the Rule?”

Asymmetries in sexual reproduction in broad-nosed pipefish

Male withKids (in pouch)

Males

Females

Consequences of Asymmetric Limits on Fitness

• Members of the sex subject to strong sexual selection will be competitive (Male-male competition)

• Members of the sex subject to weak sexual selection will be choosy (Female Choice)

• Bateman’s rule, males limited by access to mates, females limited by resources

III. Natural Selection Limits Sexual Selection

e.g., marine iguanas

Larger iguanas expend more energy on metabolism

Male marine iguanas in combat

Large territorial males

Alternative mating strategies in coho salmon

IV. Male Access to Females

Sperm Competition

Sperm competition in damselflies

Sperm morphology in rodents All for one and one for All!

Sperm Swimming Speeds

Infanticide

V. Evidence for Sexual Selection on Traits

Long tail feathers are a ball-and-chain for male red-collared widowbirds

Female red-collared widowbirds prefer long-tailed males

VI.

Fisher’s Run Away Sexual Selection

An example from UMD

How runaway selection works in theory

VII. Good genes model of sexual selection

Are male gray tree frogs that give long calls genetically

superior to males that give short calls??

Courtship and mating in hangingflies

VIII. Origin of Trait Selection

Water mite waiting in ambush for a copepod, male has found her

A phylogeny of the water mite Neumania papillator and several related species.The boxes above the tips of the branches indicate which species have net-stance and which species have male courtship trembling. A colored box indicates the trait is present; an open box indicates the trait is absent. The two versions of the phylogeny show the two most likely scenarios for the evolution of these two traits. Redrawn from Proctor (1992).

Lilies from from SW Aust.

IX. Sexual Selection in Plants

X. SEXUALSELECTIONIN HUMANS

Kipsigis men and women

A. Preindustrial Finnish Population

B. Pimbwe, a horitcultural society in Tanzania

unokais (killers) versus non-unokais among Yanomamö men

Figure 11-50

Human Stature

Taller Polish Men Have More Children:

Importance of physical attractiveness in mate choice versus

parasite prevalence in 29 human cultures

GENETIC DIVERSITY REVEALED IN HUMAN FACESHanne C. Lie, Gillian Rhodes, and Leigh W. Simmons: Evolution 2008

XI. Conclusion

• Sexual Dimorphism• Sexual Selection• Males limited by access to mates• Females limited by resources• Exceptions• Universal, aspects found in plants and

animals• YOU too may be a target for sexual selection• Very Kewl