Lecture 9

Front 1

Sexual Dimorphism (vs other groups) . . .

Back 1

More noticeable in birds than any other group

Front 2

Natural Selection

Back 2

1. Individuals within a population vary

2. Some of this variation is inherited

3. Some individuals are more successful at surviving and reproducing

4. Survival and reproduction is tied to the inherited characteristics of individuals. Those with most favorable variations are naturally selected – they are disproportionately represented in future generations

Front 3

Directional Selection

Back 3

mode of natural selection

extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.

Daphne birds - drought - seed size change - increase of beak depth

Front 4

Why can't natural selection explain the sexual dimorphism (the long tail of males) of Long-tailed Widow Birds

Back 4

If long tail was adaptive both male and females would have it

long tail
easier to be caught
more energy for growht

Front 5

Fitness (according to natural selection) really equals . . .

Back 5

Reproduction

(Failing to mate = Die young)

Front 6

What is needed for success in fitness (aka reproduction)? What part involves "sexual selection"?

Back 6

1. Survival to reproductive age

2. Finding a Mate (Involves sexual selection)

3. Reproducing successfully

Different Bird Species Vary in ALL 3 parts

Front 7

What is sexual selection?

Back 7

heritable variation in a trait that affects mate acquisition

This successful trait will increase in frequency over time

Leads to sexual dimorphism

Front 8

Why does sexual selection lead to sexual dimorphism?

Back 8

Eggs are more expensive than sperm

Reproduction is more expensive for females

Females then mate with few(one) male (vs males who can mate with many)

Females must choose only ones of high fitness

(higher cost with failed reproduction)

Are very picky

Males must then compete (against other males)

Male trait (normally) become more elaborate

Front 9

Traits selected for via sexual selection (that lead to sexual dimorphism) are called . . .

Back 9

Secondary sexual characteristics

Front 10

Two possible ways sexual selection occurs?

Back 10

1. Intersexual Selection (Female choice)

2. Intrasexaul Selection (Male choice)

Either can lead to sexual dimorphism

Front 11

Intersexual Selection: Pheasants

Back 11

VIDEO

Front 12

How does Intersexual Selection lead to Sexual Dimorphism?

Back 12

1. Models of arbitrary mate choice (aesthetic)

(Doesn't mean quality)

2) Honest advertisement models (“good genes”) i.e. must be a cost associated with development and/or maintenance of trait

Front 13

Runaway Sexual Selection (Fisherian)

Back 13

Extreme male traits can evolve through a process in which the male trait and the female preference for that trait become genetically linked.

(Even if a disadvantageous trait according to natural selection)

Front 14

Sensory Bias Model of Sexual Selection

Back 14

Females are attracted to traits in males that stimulate their sensory systems

(Preferences are due to biases in their sensory system)

The 'preference' exists before the male trait does

When male trait does exist it spreads quickly due to preference

Front 15

Sensory Bias Model of Sexual Selection
Example: Least Auklet

Back 15

some ornaments are likely to be favored by sexual selection because mutual male and female mating preferences benefit individuals with the most elaborate expression of these traits.

Naturally crestless least auklets have a mating preference for foreheaded crests like those of other auklet species even though not naturally expressed

This means the crests are not just for species recognition

Front 16

"Good Genes" Model of Sexual Selection

Back 16

mates are chosen based on characteristics that reflect "good genes" of the mate and the viability of that mates potential offsprings' genes

Females choose males that are older/experienced, with better territories, good providers, healthy, sexy, more successful

Front 17

"Sexy Sons" Hypothesis

Back 17

Females choose the attractive males so they can have attractive sons and therefore more grandchildren

(Other benefits such as caregiving, territory, gifts given are irrelevant)

Not well supported (yet)

Front 18

Hamilton-Zuk Hypothesis

Back 18

Certain secondary sexual characteristics expressed in males (like certain bright colours) = higher resistance to parasistes

Bright coloured males = chosen by females

Front 19

What hypothesis do Wild Turkeys' Snood/beard/spurs/tail fan traits support?

(Females are attracted to these traits)

Back 19

Good Genes Hypothesis

Large/extensive versions of these traits means the male has high energy reserves (can afford it)

OR

Hamilton-Zuk Hypothesis

Increase snood length, and the width of skull caps = decrease the coccidian oocyst loads in feces

Front 20

Handicap Principle

(eg Long tailed widow bird)

Back 20

Secondary Sexual Characteristics that are costly and wasteful or energy

But it shows to the female that the male is of high quality because (unlike low quality males) they can afford the disadvantage it creates

Front 21

Preference for Symmetry

(eg Barn Swallows)

Back 21

Assymetry

Environmental stress (habitat disturbance)

Or both environmental and genetic factors

Front 22

Intersexual Selection: Sexual Dimorphism of Coloration in House Finches

Back 22

Males' colour type/amount/brightness = amount of carotenoids ingested = better quality

Better quality = Better parental care and genotypic quality

Naturally bright males = High nest attentiveness, parental care and overwinter survival (not age related)

(These traits are passed on to sons)

Artificially brightened males = Paired more quickly

Females chose

Better providers

Healthiest males

Sexiest males

UNKNOWN WHY

Front 23

Intersexual Selection: Sexual Dimorphism of Coloration in Barn Swallows

Back 23

Males are more colorful and have longer, more deeply forked tails

Longer tails lengths = get mates more quickly

Symmetrical tail = Get mates more quickly than any other asymmetrical tails

Front 24

Red-backed Fairy Wrens: Two possible male strategies

Back 24

Bright Males:actively pursue extra-pair copulations, resulting in increased reproductive success

Dull Males: invest in mate guarding, parental care, nest helpers and experience reduced aggression, which may increase within-brood paternity and survival

Front 25

What would a smart red-back fairy wren do?

Back 25

pair w/dull male but solicit copulations from bright male

Front 26

Male-Male Interactions

Back 26

compete for access and prevent other males from mating

Combat (lekking)

Sperm Competition

Infanticide

Front 27

Lekking

Back 27

eg Greater Prairie Chickens

Front 28

Capercailie Lekking

Back 28

VIDEO

Front 29

Why is it hard to separate the two types of sexual selection (Intersexual and Intrasexual selection)?

Back 29

Secondary Sexual Trait = Trait x

Trait x could be helpful for male-male interactions and make them more attractive for females (those with the trait give female's better repoductive success)

Front 30

What types of females chose males by secondary sexual characteristics and why?

Back 30

Females that don't require males to have parental care choose by SS characteristics because they show genotypic quality (that can be passed to children)

Front 31

Common Yellowthroat Coloration correlated to mating success?

Back 31

Mask size not yellowness mattered to females

Front 32

Jack-Pine Warbler Coloration correlated to mating success?

Back 32

Increased mask size = increased male mating success

because it helped with male-male competition not female choice