One last time: haplodiploidy

reproduction

0.5 of genome from dad X 1.0 = 0.5

0.5 of genome from mom X 0.5 = 0.25+

r = 0.75

Leafcutter ant queen + workers

Male leafcutter

ant

SEXUAL SELECTIONA type of natural selection that acts differently

on males and females of the same species

Traits that increase mating success are selected for

Pheasants

SEXUAL SELECTIONDamselflies

SEXUAL SELECTION

Elephant seals

Sexual dimorphism: male and female have different forms

SEXUAL SELECTIONWhy aren’t all species dimorphic?

SEXUAL SELECTIONDimorphism arises from competition for mates

Males produce sperm: cheap

Females produce eggs: expensive

# mates

#kids

BATEMAN PRINCIPLE

BATEMAN PRINCIPLE

The sex that invests most in reproduction is a limiting resource

that opposite sex competes for

Female is usually limiting sex (expecially in mammals), but not always

SEXUAL SELECTIONRole reversal

Greater Painted Snipe

SEXUAL SELECTIONWhich is the limiting sex?

PipefishSeahorse

Sea dragon

SEXUAL SELECTIONParental care

Male may be needed to care for young

SEXUAL SELECTION

Sage grouse Peacock

SEXUAL SELECTION1. Runaway selection: trait initially useful

for survival is exaggerated by sexual selection

Long-tailed Widowbird

SEXUAL SELECTION1. Runaway selection: trait initially useful

for survival is exaggerated by sexual selection

SEXUAL SELECTION2. Handicap principle: ornaments show

that males are high-quality

Ornaments expensive to produce, only males in good condition can have them

Ornamental males less likely to have disease

SEXUAL SELECTION

Satin bowerbird

OPTIMIZING FITNESS

Natural selection should favor strategies that lead to higher fitness

Every trait has costs and benefits

OPTIMIZING FITNESSGulls “mob” predators that approach nest sites

OPTIMIZING FITNESSHow daring should the gull be?

Distance from predator (m)

1 2 31.5 2.5 3.50.5

Units ofFitness

Cost of action

Benefits of action

Daring mobber

Cautious mobber

OPTIMIZING FITNESS

Optimal strategy:

Benefits - Costs = Maximum

Natural selection should favor optimal strategy

GENE FLOWthe movement of genes from one population to another

“Hide” allele

“Run” allele

TYPES OF SELECTION

1. Directional

Trait

Frequency

Evolutionary change

2. StabilizingMost common: maintains status quo

3. DisruptiveSpeciation

DIRECTIONAL SELECTION

Darwin’s finches

Severe drought 1976-1977

Killed plants with small seeds: birds with larger beaks survived better

Geospiza fortis

10.5 mm 11 mm

Boag and Grant 1981

STABILIZING SELECTION

Human birth weightExtreme light weight and extreme heavy weight both selected against

8 lbs

DISRUPTIVE SELECTIONThree-spined sticklebacks

Dolph Schluter

benthic

limnetic

Descended from common ancestor

Selection favored large fish near shore and small fish in open water

Assortative mating led to speciation

Assortative mating:Like mates with like; non-random mating