UNIT 2 CONCEPTS

Intrasexual selection

Competition between same sex

Intersexual

competition between two sexes

What shapes secondary sexual traits

intersexual and intrasexual selection

What are primary sexual traits

gonads, gametes, horomones

Why do scientists often study male mating more?

often have showier phenotypes and as a result male-male competition and males attracting females are more studied.

What is different about Darwins study of mating patterns and todays mating patterns?

the fundamentals of competion differ between males and females.

What happens as a result of males showier phenotypes?

they often have fitness costs, though secondary sexual trait may increase mating and reproductive success in makes it costlier to survive.

What are the increased costs of survival that come with showier phenotypes?

predation, and growth and maintance

Predation

the traits are easier to detect by females and rivals, but also
predators

Growth and maintenance

he traits are physiologically costly to grow and upkeep

male-male competition consists of

fights for territory, resources, direct access to mates, scramble competition, sperm competition, alternative mating strategies, mate guarding

Female choice

direct female choice (more often studied), cryptic female choice (just as important and sometimes more important than direct choice)

male-male competiiton favors

larger size and bigger weapons

selection has favored what in male-male competion and what phases

ritualization of fights and 3 phases in total

First Phase of male-male competion

where males size each other up, often leads to one deciding they
don’t have a chance and bowing out

second phase in male-male competition

start to get more physical and test the strength of the opponent

third phase in male-male competition

fighting with injury and sometimes death, fight progresses here if there are really high stakes and this leads to favoring faster and more robust sperm.

Female choice reasons

Direct, Indirect, Non-adaptive hypothesis,

Direct Benefits

lots of sperm, nutritional gifts, and good parenting. males provide a benefit that directly affects the female’s ability to function in her environment. This might be food, secretions, or water that she puts directly into survival

Indirect benefits

good genes, What the male gives her does not directly benefit HER per se, but rather benefits her through the increased quality of her offspring. The male passes on his good genes to the offspring. Males can signal how good their genes are by showing off extravagant tails, bright colors that indicate he is a good forager, etc. Any trait that is hard to both maintain and survive is a good indication that
he has good genes

Non-adaptive hypothesis

fisherian, sensory bias. Correlated selection: could be a by-product of a genetic correlation with males (sexes share most of genome, so behavior favored in one sex could exist in the other due to correlational selection)

Examples of female choice:

widowbird, peacock

sexual behavior

any behavior that may contribute to reproductive success, such as behaviors that are employed in mating, courtship, or pair bonding, no matter the context in which they are observed

Different Sexual Behavior(DSB)

Sexual behavior targeted toward/ recieved by same-sex individuals

same sex behavior

sexual behaviors targeted/towards same sex individuals

Sexual behavior is defined by what kind of interactions

discrete behavioral

Adaptive mechanisms for evolution of SSB

Social Glue, learning/practice, indirect inseminaiton

non-adaptive hypothesis for SSB

mistaken identity

Social Glue hypothesis

Same-sex sexual interactions promote social alliances and reduce conflict same Examples: male dolphins, female woodpeckers, female Japanese macaques

Learning/Practice

Immature individuals learn more successful courtship or mating skills through same-sex activity with conspecifics Example: juvenile fruit flies practice courtship

Indirect Insemination

Males can inseminate females by depositing sperm on other males
Example: flour beetles leave sperm packets on other males during same-sex copulations

“Mistaken Identity” hypothesis

Same-sex sexual interactions occur because of weak sex discrimination Examples: fruit fly male-male courtship is more common when populations are male biased Humbolt squid males deposit sperm packets on any individual they come across regardless of sex (may be adaptive because they rarely encounter individuals of the same species and identifying sexes incorrectly may cause them to miss out on reproduction entirely)

Sex-discrimination

Identification of another individual’s sex based on sex-related signals
Requires sensory mechanism for identification and sex-related signals, both can be costly Indiscriminate mating can therefore be adaptive by avoiding the costs of discrimination and sex signals. Especially true when costs are high and signals are weak

Hypothesis for the evolutionary origins of DSB and SSB

Ancestral DSB, Ancestral indiscrimate mating

Hypothesis Ancestral DSB

historically an implicit assumption, indiscriminate and SSB are derived-independent origins for most “tips” of the trees, focus on why SSB is adaptive and/or not highly costly for individual species, focus on persistence rather than origin of SSB.

Timeline for evolution of sex discrim under ancest. DSB

asexual reproduction→ simultaneous evolution of sex and sex discrimination

Hypothesis Ancestral Indiscriminate Mating

Exclusive DSB and prevalent SSB are derived, Assumes that sex discrimination evolves only after the evolution of sexual
reproduction, Focus on evolutionary contingency and constraint, along with adaptive value of SSB, Predicts more variation in DSB and SSB

Timeline for evolution of sex discrimination under ancestral indiscriminate

Asexual repro. -> evol. of sex -> evol. of sex discrimination -> evolution of exclusive DSB

Proximate Explanations

What physical mechanisms affect trait expression?, Genetic-developmental pathway, Neuronal-hormonal mechanisms, External/environmental triggers

Ultimate Explanation

How and why does a trait evolve?,Evolutionary history of the trait (contingency and constraint from other traits), Adaptive value (costs vs. benefits for fitness), Non-adaptive evolution

Ways that males compete

Fights for territory, resources, and access to mates. Scramble competition. Sperm competition. Alternative mating strategies. Mate guarding. Attraction of femaless

Competition may not always be from sexual selection because

Sexual selection favors traits that increase competitiveness for mates....or for resources that influence the quantity/quality of mates obtained, Natural selection favors traits that increase fecundity or offspring survival are naturally selected

nonadaptive hypothesis for wht females compete

Correlated selection: could be a by-product of a genetic correlation with males (sexes share most of genome, so behavior favored in one sex could exist in the other due to correlational selection)

Natural selection hypothesis for female competion

Female competition for non-mating resources (i.e. resources for maternal investment): access to food especially when females invest heavily in parental care.Offspring protection: defending eggs or offspring from infanticidal females

Competition for access to mates:

as OSR becomes more female biased, females should compete for access to mates. In sand gobies, females compete more when OSR is more female biased, but all females mate...so might not be for competition for number of mates, rather the quality of the mates...)

Competition for high quality mates:

females should compete for access to males that provide direct benefits (nutrients, space, parental care, etc.)

Competition for male parental care:

can deter other females from settling. Or could have access to best mate (sharknose goby females that are most aggressive get largest males, who are also best at providing parental care).

Competition for males that provide indirect (Genetic) benefits.

When sperm is limited, and males try to preserve sperm for new or preferred females..

Competition over mating opportunities

Can compete for mating opportunities or mating resources (resources that qualify female as a mate). Female-female competition increases when mating opportunities or resources are limited. (nesting sites...which can be limited independent of OSR)

Whenever there is female-female competition for access to mates, then

males should be choosy!

Sensory Exploitation

Females have a pre-existing bias for a particular sensory stimulus (often from a foraging context), and males exploit this sensory bias. The bias will exist in the phylogeny prior to the preference evolving, and there are multiple ways the bias can be exploited. Preference evolves before the trait (will need to use phylogeny)before

Fisherian Selection

The selection on female preference leads to the evolution of male display Because the display is genetically correlated to the preference. No benefits are involved. Both preference and display are heritable. Fisher’s process goes through a cycle of genetic correlations that are eroded after directional selection and trait elaboration reduces heritability in the traits (without heritability of both signal and preference, there cannot be a genetic correlation). This means that genetic correlations may be fleeting and difficult to detect. A lack of understanding of this full process is why many folks have a hard time understanding that Fisherian selection is important. However, it likely occurs for most sexual traits.

Trait elaboration is often curbed by costs

from natural selection (though sexual selection and natural selection do not always act in opposition to one another)

costs from natural selection

production, maintance, energetics, punishment, predation

production

energy required to grow the trait that is used to display

maintaince

keeping the trait in good connection

punishment

carrying a sexy trait might make you more of a target of competitor males, for example the black patch on black capped chickadee

predation

what makes a male sexy to females often makes them easy to spot predators

tundra frog

calling makes them more conspicuous to bats. Calls are comprised of a whine and then chuck(s). They reduce calling and number of chucks when bats are present. Bats can also zero in on the ripples produced in the water

example 1 of good genes

1. Offspring of individuals with good genes indicator traits have increased survival or reproductive success. These are indirect, genetic benefits to female fertility.
2. Female gray tree frogs prefer males that give long calls.
3. Welch et al., 1998 took the eggs laid by a particular female and fertilized half with sperm from a long calling male, and half with sperm from a short calling male. a. Thus, could control for genes of the female by comparing sibs.
4. Long calling males produced larvae that can survive and grow better than short calling males.

good genes example 2

Petrie et al. (1991) tested whether the number of eyespots in a male peacock’s tail signaled his genetic quality.
2. First showed that number of eyespots predicted a male’s mating success. Also, cutting off eyespots led to lower reproductive success in males.
3. Experiment: Females paired with random males, eggs collected, and chicks raised in common environment.
4. Offspring of males with more ornamented tails grew better and had higher survival to age two when released into wild

Hamilton-Zuk hypothesis (honest indicator)

predicts that only males are diease free and will be able to fully develop elaborate trait

There are many reasons why females may prefer particular males. What do you need to test?

alternative hypothesis determines one applies

Multiple hypothesis may apply for a particular trait

Red color in sticklebacks = good parental care (direct benefit) + good genes (indirect benefit).

There are often tradeoff of producing elaborate male traits

Increased predation (e.g. tungara frogs). b. Energetically expensive (handicap hypothesis).

Alternative mating strategies

arise because of the condition-dependence of a strategy (one strategy will be on average more successful than the other), or a genetic polymorphism (all strategies on average are equally successful)

two examples of genetic polymorphyism

Side-blotched lizards: [draw diagram of what each male does] Selection favoring each male type is frequency-dependent. One strategy only does well if uncommon. Isopods. its a parabolic curve

Examples of conditional mating strategies

Frogs: callers and satellites, Dung beetles: dimorphism in horn size. Depending on the environment, the switch point can change depending on food availability sigmoidal

Mating system is associated with

competition for mating/fertilization of limiting sex. This competition determines the evolution of sexual dimorphism two flavors

Primary sexual characteristics

Body structures directly involved in reproduction ( necessary for
reproduction, involved in gamete production): Genitalia, Testes / Ovaries, Gamete

secondary sexual characteristics

(improves chances of reproduction, involved in gamete delivery) These traits evolve as a result of competition for fertilization access (not really just access to mates).

Fecundity Selection

is a type of natural selection that influences the number/quality of offspring a female can produce because of self-limitations. These limitations have to do with how much of a resource she has left over after surviving to produce additional eggs.[gamete quantity/quality]

any aspect of how the quality of offspring is dictate by

fertilization event has to do with sexual selection

Different forms of sexual selection in males (which is favored by different mating systems)

male-male competition, sperm competition

The type of mating system dictates the nature of competition among
males/females, which will determine

he types of traits favored by sexual
selection (note: need to look at genetic mating system)

cryptic female choice

can choose which male sperm to use inside her
reproductive tract based on how well he displayed during copulation, or who she mated with later. If she mates with a second male that is really awesome, she might not use much of the first male’s sperm.

arbitrary traits

males might exhibit a trait that catches the female’s eye
because it is important for her to recognize in different contexts. For
example, if the female eats a lot of red berries, she may be predisposed to responding favorably to males with red traits.

Is this naturally selected? Traits that influence competition for mates

yes

Those that directly inhibit fecundity or offspring survival are naturally selected

no it should be influence

Competition for resources has no relationship with the quantity or quality of mates obtained

false it influences the quantity or quality

sexual selection theory

clearly male-biased theory historically Often, we ask why male traits confer mating success to males, and then bring in the female aspects of it. This continues due to conspicuous traits, practical obstacles and gender bias.

evidence for female mate preference

No one actually tested this until the mid 1900s, with the first really solid test of female preferences in 1982 by Andersson. He
looked at birds with long tails and did a manipulative experiment to see whether long tails were preferred by females (and also controlled for male-male competition).There has been a continued focus on the evolution and benefits of male ornamentation, and not on the evolution and benefits of female preferences for several reasons:male ornaments are easy to see and measur

female preferences are complex

these are normally encoding the brain so its not easy to measure, usually assayed via behavior, exhibit preferences across multiple stages of mating, females can mate with the same kind of males but invest more of one, and can prefer males who can allocate more energy to the offspring

evidence that female preferences are adaptive includes

females that mate with preferred males have increased benefits and fitness-more or more fit offspring and females that are choosier gain the most benefits

WHy do females exhibit preference? How do they evolve?

adaptive reasons: direct, indirect, signals that indicate more benefits of females, and choosiers reap more benefits

genetic variation in preference in fisherian selection

genetic variation in trait and assoritve mating. ANy type of mechanism can favor a given female preferences. Then females with preferences

Fishers processes goes through a cycle of genetic correlation

that are eroded after directional selection and trait elaboration reduces heritability in the traits (without heritability of both signal and preference, there cannot be a genetic correlation).This means that genetic correlations may be fleeting and difficult to detect. A lack of
understanding of this full process is why many folks have a hard time understanding that Fisherian selection is important. However, it likely occurs for most sexual traits

runaway selection/sexy sons

preferences evolbes becasue of sexy son afbantage

for handicaps

the handicap itslef does not need to be heritable, just has to provide reliable index of fitness and fitness must be heritable

sensory exploitation

females has a pre-existing bias for particular sensory stimulus and males exploit this sensory bias(foraging) the bias will exist in the phylogeny prior to the preference evolving and there are multiple ways the bias can be exploited.

What is the lek paradox?

The lek paradox refers to the evolutionary question of how genetic variation in male traits is maintained despite strong and consistent female mate selection. If females consistently prefer certain extreme traits, those traits should become fixed in the population, yet genetic variation persists in male signal traits.

Why should female mate choice lead to a loss of genetic variation in male traits?

If females consistently select the most extreme or elaborate male traits, these traits should become common over generations, leading to a reduction in genetic variation as the less preferred traits disappear from the population.

What is one potential explanation for the persistence of genetic variation despite strong selection?

Mutations can introduce new genetic variation into a population, which may help maintain diversity in male traits. However, since most mutations are slightly deleterious or neutral, they do not fully explain the persistence of variation.

How does the handicap principle attempt to resolve the lek paradox?

The handicap principle suggests that only males of high genetic quality can afford to produce and maintain elaborate traits because these traits are costly. Males with poor genetic quality cannot "cheat" by displaying extreme traits, as they would suffer greater mortality. This ensures that only the fittest males are selected.

What is a limitation of the handicap principle in explaining the lek paradox?

While the handicap principle explains why only high-quality males can afford elaborate traits, it does not fully explain how genetic variation in these traits is maintained over generations.

What is condition-dependent trait expression?

This hypothesis suggests that only males in good physical condition—due to factors like early-life nutrition or maternal investment—can develop the most elaborate traits. Variation in resource acquisition leads to variation in trait expression, maintaining diversity.

How does condition dependence differ from the handicap principle?

Condition dependence focuses on a male's physical condition as the main factor in trait expression, while the handicap principle attributes variation in male traits to underlying genetic quality.

What is genic capture, and how does it relate to condition-dependent trait expression?

Genic capture suggests that many different genes contribute to an individual’s overall fitness and condition. Since condition affects the expression of male traits, genetic variation in fitness-related loci is indirectly captured in the variation of display traits.

How do genotype-by-environment interactions help resolve the lek paradox?

Different male genotypes may be favored under different environmental conditions. If the environment fluctuates, different genotypes (and their associated traits) are favored at different times, maintaining genetic variation in the population.

How can female mate preferences fluctuate with environmental changes?

Female preferences may shift depending on ecological conditions, such as resource availability or predator presence. If different traits are favored in different environments, selection pressures on male traits also fluctuate, preventing the loss of genetic variation.