Download 06_prughNS2

One last time: haplodiploidy
Leafcutter ant queen + workers
Male
leafcutter
ant
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
SEXUAL SELECTION
A 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 SELECTION
Damselflies
SEXUAL SELECTION
Sexual dimorphism: male and female have
different forms
Elephant seals
SEXUAL SELECTION
Why aren’t all species dimorphic?
SEXUAL SELECTION
Dimorphism arises from competition for mates
Males produce sperm: cheap
Females produce eggs: expensive
BATEMAN PRINCIPLE
#
kids
# mates
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 SELECTION
Role reversal
Greater Painted Snipe
SEXUAL SELECTION
Which is the limiting sex?
Seahorse
Sea dragon
Pipefish
SEXUAL SELECTION
Parental care
Male may be needed to care for young
SEXUAL SELECTION
Sage grouse
Peacock
SEXUAL SELECTION
1. Runaway selection: trait initially useful
for survival is exaggerated by sexual
selection
Long-tailed Widowbird
SEXUAL SELECTION
1. Runaway selection: trait initially useful
for survival is exaggerated by sexual
selection
SEXUAL SELECTION
2. 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
Every trait has costs and benefits
Natural selection should favor strategies that
lead to higher fitness
OPTIMIZING FITNESS
Gulls “mob” predators that approach nest sites
OPTIMIZING FITNESS
How daring should the gull be?
Daring mobber
Benefits of action
Units of
Fitness
Cautious mobber
Cost of action
0.5
1
1.5
2
2.5
3
3.5
Distance from predator (m)
OPTIMIZING FITNESS
Optimal strategy:
Benefits - Costs = Maximum
Natural selection should favor optimal strategy
GENE FLOW
the movement of genes from one population to
another
“Hide” allele
“Run” allele
TYPES OF SELECTION
1. Directional
Frequency
Evolutionary change
Trait
2. Stabilizing
Most common: maintains
status quo
3. Disruptive
Speciation
DIRECTIONAL SELECTION
Darwin’s finches
Geospiza fortis
Severe drought
1976-1977
Killed plants with small seeds:
birds with larger beaks survived
better
Boag and Grant 1981
10.5 mm 11 mm
STABILIZING SELECTION
Human birth weight
Extreme light weight
and extreme heavy
weight both selected
against
8 lbs
DISRUPTIVE SELECTION
Three-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; nonrandom mating