Lec 12

Question 1

Sex vs. gender

Answer 1

Sex: What type of gametes does na individual have - large or small? Large gametes = females, small gametes = males

Gender: non-binary concept related to how individuals view themselves within societal constructs, often related to, but not always the same as, an individual’s biological sex

When we use the terms “male” and “female” in this course, we are referring to the TYPE OF GAMETE that individual organism produces

Question 2

Is selection the same on males and females?

Answer 2

We look at how many gametes can be produced for a given amount of resources

For the same amount of resources, the female can produce 2 gametes and the male can produce 2000

If the goal is to have as many offspring as possible, what mating strategy should MALES pursue? What mating strategy should FEMALES pursue?

Question 3

If the goal is to have as many offspring as possible, what mating strategy should MALES pursue? What mating strategy should FEMALES pursue?

Answer 3

Males mate with as many individuals as possible, females choose mates carefully

Question 4

Fitness

Answer 4

Relative genetic contribution of individuals to future generations

Question 5

2 components of fitness

Answer 5

Survival

Reproduction

For your genes to make it to the next generation, you need to SURVIVE and PRODUCE OFFSPRING

Question 6

Selection operates ______________ on males and females

Answer 6

DIFFERENTLY due to differences in investment in reproduction

Question 7

What are the consequences of anisogamy for selection and evolution in males vs. females?

Answer 7

Darwin’g theory of sexual selection
-Sexual selection “depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring”

Question 8

Traits invovled in reproductive fitness

Answer 8

Sexually selected traits

Question 9

Anisogamy leads to sexual selection

Answer 9

By definition, males produce many tiny gametes (sperm), females produce fewer, large gametes (eggs)

Sexual selection in males and females is then driven by differences in investment (time, effort, resources) parents devote to each offspring

Question 10

Which is a consequence of anisogamy?

Answer 10

Females are very choosy about their mates, and males evolve to be attractive to females

Question 11

Consequences of anisogamy and differential investment

Answer 11

Differences in the way males and females maximize fitness lead to differences in behavior, morphology, and physiology

Females have more to lose from mating “wrong”, so they are MORE SELECTIVE about choosing mates

Since females are choosy, and males mate multiply, males compete for access to females

Question 12

Mechanisms of Sexual Selection

Answer 12

Selection that acts on an organism’s ability to obtain a mate

Intrasexual selection (male competition);

• WITHIN the sexes
• Flashy, competitive males
• “Male-male competition”
• Selects for traits that aid in combat, territory defense

Intersexual selection (female choice)

• Between sexes
• Drab, choosy females
• “Female choice”
• Selects for traits that increase attractiveness

Question 13

What are males competing for and why?

Answer 13

Males compete for access to females, or monopolization of resources that attract females

Question 14

Anisogamy = Skew in OSR

Answer 14

OSR = Operational sex ratio = ratio of AVAILABLE males to females

Smaller gametes and less parental care means males are more available in the mating pool

Reproductive Skew:
When more males than females are available to mate, competition for mates INCREASES
-A lot of males must compete for few females

there is not a perfect correlation between reproductive skew and competition because male mating success depends on:

1) Pool of available females
2) Ability of a male to monopolize access to females

For males to reproduce, he needs to mate with a lot of females

Question 15

When there are more males than females available to mate what happens to competition for mates?

Answer 15

Increases

Question 16

Intrasexual selection in elephant seals

Answer 16

Elephant seals breed on small beaches at particular times of year (you can go see them on the Central Coast)

Females are clumped on small beaches
-Females come give birth on land and mate immediately after

This allows males to monopolize access to females
-Males spen ALL of their time during short breeding season to monopolize females, do NOT assist in raising young

Males provide NO parental care or investment in offspring

Only about 1% of males EVER mate
-ONLY the biggest, strongest, most territorial

Question 17

Territory defense in kittiwakes

Answer 17

Males find a nest site

Males and females jointly build a nest on a cliff face

Males and females both incubate the eggs and feed chicks

Both males and females participate in nest defense

Kittiwakes are monogamous and the same pairs will often stay together for many years

Question 18

In which group is INTRASEXUAL selection stronger?

Answer 18

Elephant seals, because only a few males are able to mate so there is intense competition and the evolution of competitive traits

Question 19

Male competition (intrasexual selection) summary

Answer 19

Males invest less per gamete

They maximize thier fitness by mating wtih as many females as possible

Males compete with each other for access to mates or matings

Strength of competitions depends on OSR

A skew in OSR (ratio of available males : females) typically means stronger male competition

Competition is also influenced by how effectively males can monopolize access to females

Question 20

Female choice has been harder to understand than male competition

Answer 20

The female could in most cases escape, if wooed by a male that did not please or excite her; and when pursued, as so incessantly occurs, by several males, she would often have the opportunity, whilst they were fighting together, of escaping with, or at least temporarily pairing with, some one male

Nevertheless, when we see many males pursuing the same female, we can hardly believe that the pairing is left to blind chance - that the female exerts no chocie, and is not influenced by the gorgeous colors or other ornaments with which the male alone is decorated

Question 21

Which male obtained the most nests in his territory?

Answer 21

Elongated tail

Question 22

Why do female preferences for costly male traits evolve?

Answer 22

Darwin originally argued that females have an “aesthetic sense” - these are now termed “arbitrary preferences”

Later work suggested that some female preferences are tied to benefits that females gain from mate choice

Male signals evolve to advertise benefits to females

Question 23

What are some benefits females could look for in a mate? 2 main models of female mate choice

Answer 23

Models based on benefits to female AND underlying genetic mechanisms of mate choice

Direct benefits

Indirect benefits

Question 24

Direct benefits

Answer 24

Good resources

Females get direct fitness benefits from mating with a particular mate

Males advertise territory quality, access to resources, or parental care

Choice of mate increases female fitness

Females prefer more dominant males

Dominant males provide more food to females

Dominance status may therefore advertise direct benefits of mating to prospective females

Dominance status and competitive traits can be PROXIES for certain types of direct benefits

Yellow tail may signal to female that male has traits she wants and to other males that he is stronger

Question 25

Indirect benefits

Answer 25

Good genes Females get genetic benefits from male - affect the fitness of her offspring Attractive sons High-quality offspring (good immune system) Models of indirect benetifs: 1) Fisherian Runaway 2) Handicap/good genes hypothesis

Question 26

Evolution of direct benefits mate choice is ____________

Answer 26

Easy Female just needs to optimize her own fitness

Question 27

Fisherian runaway: Females prefer high-quality males

Answer 27

Starting point: Male has some trait that confers survival advantage (Fisher) Males with preferred trait have higher mating success. If trait is beneficial, now males benefit because they are better AND attractive to females Females will benefit because their offspring will be better at surviving AND their sons will be attractive Trait will continue to get bigger, and preference will get stronger

Question 28

What happens to size/frequency of a preferred male trait over time? What happens to female preference for that trait?

Answer 28

Trait becomes larger/more common, preference becomes stronger

Question 29

Fisherian runaway: Females have arbitrary preferences

Answer 29

Starting point: Male has a trait the females arbitratily like -Doesn't confer survival advantage, just like a trait Males with preferred trait still have higher mating success Female preference spreads Males benefit because they are attractive to females Females will benefit because their sons will be attractive Trait will continue to get bigger or more elaborate

Question 30

When does Fisherian runaway stop?

Answer 30

Eventually the cost of the elaborate trait in terms of survival is greater than the benefit to reproduction and the trait stops getting bigger

Question 31

Fisherian runaway: Females gain attractive sons

Answer 31

Starting point: male has a trait the females like (either arbitrarily or because it confers a survival advantage) Males with preferred trait have higher mating success Female preference spreads Males benefit because they are attractive to females Females benefit because their sons will be attractive Trait will continue to get bigger or more elaborate, preference will continue to spread Negative genetic correlation between male sexual attractiveness and survival

Question 32

When does Fisherian Runaway stop?

Answer 32

When the cost of the trait to survival is greater than the benefit from mate choice

Question 33

Fisherian runaway generates (and requires) linkage disequilibrium

Answer 33

There must be a genetic basis to the female preference and the male trait Over time, alleles for stronger preferences become associated with alleles for more elaborate trait As long as the males with the more elaborate trait have higher fitness, the loci will stay in association In heliconius butterflies, the gene for mate preference is located next to the gene for color patterning on the same chromosome Assortative mating occurs because the preference for wing color is located right next to wing pattern gene\ Linkage disequilibrium is difficult to maintain over time Handicap hypothesis proposed due to criticism that Fisherian Runaway would break down over time

Question 34

The Handicap hypothesis/condition-dependent indicators

Answer 34

Females prefer male traits because they are costly Only the highest-condition males can produce the biggest traits If there is a genetic basis to condition, offspring benefit from having hihg-quality fathers -Males must be healthy and strong in order to produce long tails/bright colors Traits must be condition-dependent rather than fixed Only the highest-condition males can produce the biggest traits It is energetically costly to carry a big tail around Better quality males have more energy to invest in their displays, so their displays are larger -Good at finding resources, no parasites or diseases, etc. = can have larger displays If low-quality males invest beyond their abilities, they die (which is bad for fitness)

Question 35

Handicap hypothesis: Costly traits advertise good genes

Answer 35

In peacocks, males with larger tail spots had more surviving chicks, suggesting they have better genes than males with small eyespots

Question 36

Why would a female preference for a trait that has no fitness value or benefit lead to that trait increasing in frequency in the population?

Answer 36

Because the sons of males with the trait are attractive to females and have higher reproductive success

Question 37

Indirect benefits: THe Hamilton-Zuk hypothesis

Answer 37

The expression of traits is associated with resistance to parasites or pathogens Hamilton and Zuk (1982) proposed that females choose mates that are resistant to disease General good health and freedom from parasites are often strikingly indicated in plumage and fur, particularly when these are bright rather than dull or cryptic Thus only resistant to parasites will be able to display conspicuous traits

Question 38

Threespine sticklebakcs

Answer 38

Males develop bright red coloration and build nests where females come to spawn Males also care for eggs and fry

Question 39

What is the main difference between the handicap and runaway models?

Answer 39

IN the handicap model, the preferred trait indicates some other preferred aspect of quality, whereas in the runaway model the preferred trait is the only target of the preference

Question 40

Comparing models of indirect benefits

Answer 40

In BOTH females are NOT getting any direct resources, only get benefits that accrue in offspring Fisherian: Trait evolves ONLY because it confers a mating advantage -Looking for benefits for the SONS Handicap hypothesis: traits chosen because they confer some OTHER advantage - they advertise general health/condition/quality -Advertise general health/quality (i.e. ability to find food, fight off parasites, etc.)

Question 41

Fisherian traits become indicators over time

Answer 41

Once a trait is very costly, it can act as an indicator of condition We therefore have to know how the evolution of the trait STARTED, which is hard to do

Question 42

Which is a stronger source of selection - direct or indirect benefits

Answer 42

DIRECT benefits are typically STRONGER because they directly impact fitness (as opposed to indirectly) Indirect benefits are harder to evolve because they require strong linkage disequilibrium between traits and preferences Models are NOT mutually exclusive! Environmental variability means females often evalueate multiple pieces of information about male quality

Question 43

Female choice summary

Answer 43

Females often choose mates based on benefits gained from mating with a particular male These can be direct benefits (increase female fitness) or indirect benefits (increase fitness of offspring) Males advertise beendfits to females via costly dipaly traits Costly display traits in systems with no direct benefits can evolve via Fisherian runaway (genetic correlation between trait and preference ) or Handicap principle (condition dependent signal of quality)

Question 44

How many males should females mate with?

Answer 44

According to our predictions under anisogamy, females should mate with the single best male However, multiple mating by females is widespread Why would females mate multiply?

Question 45

Benefits of multiple mating for females

Answer 45

Sperm replenishment (sperm stores depleted) Direct, material benefits (resources) Genetic benefits (trading up, genetic compatibility) Convenience (minimize harassment) Correlated evolution (with selection on males)

Question 46

Genetic benefits: Acquiring genes from superior mate

Answer 46

Most songbirds form social pairs where both parents raise chicks Female songbirds solicit extra pair copulations (EPCs) from males who are not their social partner More extra pair paternity in ornamented systems Females prefer more elaborate males as extra-pair fathers Females socially paired to least attractive males seek out more EPCs

Question 47

What are the evolutionary consequences of females mating multiply?

Answer 47

Continued competition among male sperm for access to female eggs Continued "choice" by females for the best male after mating

Question 48

Sperm competition

Answer 48

Competition between sperm of 2 or more males for the fertilization of ova One of the many forces that have led to incredible variability in sperm morphology

Question 49

Multiple mating and differences in investment set up sexual conflict

Answer 49

Optimal outcome of mating is different for males and females

Question 50

Can traits that increase male reproductive success but harm females (and vice versa) be selected?

Answer 50

Yes, because all individuals are just increasing their own genetic fitness and the individuals they mate with don't share their genes

Question 51

Multiple mating and differences in investment set up sexual conflict

Answer 51

Males will evolve strategies to maximize paternity, often at a cost to females, while females evolve defenses to maintain choice, often at a cost to male gametes

Question 52

Intromittent organs

Answer 52

Male genitalia evolves to remove rival sperm These can harm females, reducing their survival

Question 53

Accessory gland proteins

Answer 53

Many insects inject proteins along with sperm These influence female behavior and physiology: - Incapacitate rival sperm - Shield sperm from female reproductive tract - Increase rate of egg laying - Decrease propensity to remate These adaptations increase male fitness but decrease female fitness Very fast evolution of ASPs as females evolve defenses to male tactics

Question 54

Cryptic female choice for nesting males

Answer 54

2 male strategies: nesting (preferred by females) and sneaking (try to steal copulations) in ocellated wrasse Nesting males have faster sperm, sneaking males have more sperm Female ovarian fluid favors the faster sperm, increasing success of nesting males

Question 55

Waterfowl are a particularly dramatic example of coevolutionary sexual conflict

Answer 55

Male ducks often attempt forcible copulation Female ducks have evolved a corkscrew-shaped vagina to make it hard for males to inseminate them In turn, males have evolved a corkscrew-shaped phallus there is a strong correlation between the length of the male phallus and the umber of pouches (dead ends) and spirals in the female vagina These elaborate structures only occur in species with forced copulations

Question 56

Why does sexual conflict occur?

Answer 56

Males and females have fundamentally different reproductive strategies, with males trying to mate with as many females as possible and females trying to mate with only the best one or few males

Question 57

Sexual selection summary

Answer 57

Anisogamy causes males and females to pursue fundamentally different reprodcutive strategies Because female gametes are typically rare, males compete for access and females choose the best quality mates Males and females can be in conflict, expecialy when females mate multiply, with males evolving to maximize paternity and females evolving to exert choice