BZ 300 Exam 3

Panda Signal

means that evolution builds new traits by reusing old parts, instead of creating new ones from scratch — just like a panda using its wrist bone as a thumb.

Evolution is a tinkerer, not an engineer — it works with what’s available, adapting old structures for new functions.

signal

something that specifically evolved to carry certain info

ex. bird singing a mating song to attract a mate

cue

A piece of information that was not evolved to communicate, but another animal can still use it

it can lead to a signal being created by becoming more specific and modified if its usefyl for both receiver and sender

ex. smell of mouses urine to tell an owl where it has been 

ex. bees dancing when finding food can cue other bees to know that there is food in a certain location, but bee does not mean to communicate that

sensory exploitation

when a signal evolves to take advantage of pre-existing sensory biases in the receiver.

Using another animal’s sensory bias to your advantage

sensory bias example

female fish are biased to being attracted to something orange because of food, so if a male happens to be orange, that male will attract more females so that orange male will leave behind offspring who are also orange and that’s how orange will evolve over time

• this shows how a pre-existing bias can evolve into a signal 

sensory bias as a neural constraint

how animals’ brains are already tuned to notice certain features, which can influence how signals evolve.

Example: Zebra Finches with Artificial Crests

• , zebra finches (which don’t naturally have head crests) were given fake colored crests.

• the female brain had a pre-existing bias for certain bright contrasts (like white on the head),

• so even though the “white crest” was unnatural, it triggered a stronger attraction.

what is this saying about the origin of the traits?

• the origin of the trait has no adaptive value

• it’s simply because of sensory bias 

• then it evolves finally as a signal

Can sensory bias come from evolutionary past?

Yes—meaning animals can still respond to signals that their ancestors used, even if those signals no longer exist in the species today

Example of sensory bias from evolutionary past?

• Swordtails have a long tail extension (“sword”) used in sexual signaling.

• Platyfish don’t — but when researchers added an artificial sword to platyfish males, females still preferred them!

• Even though platyfish lost the sword trait, their brains still carry the old sensory preference for it from their common ancestor.

Extra androgen hypothesis in hyena

higher levels of testosterone has evolved in females to have a bigger size

• higher levels of testosterone in females lead to females having bigger cubs 

• psudeo penis in females develops as a byproduct of this extra testosterone which can be used for communication which is now a secondary signal for female hyenas 

byproduct hypothesis

means a signal or trait can evolve as a side effect of another adaptive trait — not because the signal itself was directly favored by natural selection

honest signals

signals that reliably show the signaler’s actual condition or ability.

• Otherwise, everyone would “fake” them, and communication would break down.

• they need to have a cost!!

Handicap Principle

Any honest signal is a handicap due to their cost

• Signals usually have costs to produce or maintain — only strong or healthy individuals can afford them.

• cost is what prevents cheating 

4 kinds of questions we can ask about the hyena psuedopenis 

• what are the mechanisms driving this? the hormones are the mechanism that are driving the bigger size 

• G by E questions— how much of the pseudopenis is driven by genes and environment?

• comparative— are there other groups that have similar structure?

• cost and benefit question— what are the pros and cons of this structure?

multimodal signaling

when an animal uses more than one type of signal (for example, visual and auditory) to communicate.

• increases honesty 

how does multimodal signaling promote honesty and increase reliability?

• Increases reliability and efficiency (since if one signal fails, the other can still communicate the message).

• Enforces honesty in signaling, because maintaining multiple costly traits prevents “cheating.”

Deceitful Signaling

when an organism sends a signal that mimics another signal to manipulate the receiver for its own benefit.

benefit sender, cost to receiver

Negative Frequency-Dependent Selection

The rarer a trait is, the more advantage it has.—— Maintains diversity

Positive frequency-dependent

makes the common signal stronger and more widespread because being typical is safer or more effective.

• Promotes uniformity

  

Eavesdropping

when a signal meant for one receiver is overheard and exploited by another species (a non-intended receiver).

ex. Bats listening to frog mating calls

What kind of conflict does eavesdropping create?

a conflict between communication benefits and predation costs, driving the continuous adaptation of both sender and eavesdropper species.

Signal Tuning and Adaptation

how natural selection shapes animal signals (like bird songs) so they’re best suited to their environment and minimize risk while maximizing communication success.

signal tuning

the idea that communication signals adapt to the conditions where they’re used.

ex. mob and seet calls in birds— one is used to warn conspecifics about predator, the other is to get other conspecific to help you defend

A— key: aroused state leads to a involuntary response which evolves into a signal so that when a dog sees another dog with raised hair, it interprets that as aggressive

A— review honest signals; they can only be carried by individuals of high quality which is costly, but its purpose is to avoid costly interactions

What is the relationship between the cost and benefit of honesty and the quality of the individual

Sexual Selection

• how natural selection acts on males vs females

common pattern

males— more eager to find mates and compete for mates

females— more picky on who they mate with 

• but it can be exactly the opposite in some species

Sexual Dimorphism

males and females look different because of sexual selection — one sex competes, the other chooses.

• can be driven by social competition or Bateman’s gradient

• Males often compete for mates → evolve traits like strength, size, color, or songs.

• Females usually choose mates → evolve to be choosier or more camouflaged.

Female Choice (Intersexual selection)

One sex (usually females) chooses which individuals of the other sex to mate with.

• Females select males with the most attractive or high-quality traits (e.g., bright feathers, complex songs, courtship displays).

Male–Male Competition (Intrasexual selection)

• Members of the same sex compete with each other for access to mates.

Usually: Males compete with each other (physically or through displays) for access to females.

Results:

• Traits like weapons, strength, large size, or aggression evolve.

• Leads to dominance hierarchies and male–male competition.

how does reproductive behavior relate to signals?

reproductive behavior and signaling are deeply connected because signals are the tools animals use to coordinate, attract, and assess mates during reproduction.

Anisogamy

The difference in size and cost between male and female gametes.

• Males produce many small, cheap sperm.

• Females produce fewer large, energy-expensive eggs.

Bateman’s Principle/Gradient 

this principle describes how reproductive success differs between the sexes. it describes how reproductive success changes with the number of mates an individual has.

• Males: Reproductive success increases rapidly with more mates.

• Females: Reproductive success levels off after one or a few mates (because they’re limited by egg production, not mating opportunities).

How does Bateman’s Principle/Gradient effect variance in males and females?

• males have higher variance in reproductive success — a few males father many offspring, while others get none.

• Females have lower variance — most reproduce, but with fewer partners.

• These two forces create the fundamental asymmetry between sexes — the root cause of most sex differences in reproductive behavior and signaling.

male-biased operational sex ratio (OSR)

more males competing for fewer receptive females because females are caring for young

What leads to sex role reversal and

If males invest more (for example, by guarding eggs or providing food gifts), then:

• Males become the choosy sex.

• Females compete for access to those investing males.
  ➡ This leads to sex role reversal and a female-biased operational sex ratio.

Operational Sex Ratio (OSR) =

The ratio of sexually active males to sexually receptive females at a given time.

• It’s not just how many males and females exist —
  it’s how many are ready and available to mate right now.

• this is the primary driver of differences in mating

• dispersion of resources is an ecological factor— if males can monopolize resources, then they can mate

female-biased OSR

when there are more available females than males at any moment.

What determines OSR

investment of males vs females in mating and young

• could be driven by G x E inetraction

conditional mating tactics

different behaviors that males switch between based on their size, strength, or environment.

• the small beetle is just making the best of a bad situation

behavioral polyphenisms

when one species shows multiple behaviors depending on conditions.

ESS

evolutionary stable strategy

• it’s a behavioral strategy that, once most of the population uses it, can’t be beaten by any alternative strategy.

alternative strategy vs conditional tactics

• alt strategy: Behavior differences are genetically based — fixed for life

  • Inflexible — controlled by genetic polymorphism

  • Individuals are “born” into one strategy type and can’t switch.

• conditional tactics: Behavior changes depending on the individual’s condition or environment.

  • Flexible — not genetically fixed.

  • A single individual could switch tactics if its situation changes.

“Conditional = can change; Alternative = always.”

Sperm competition

AFTER MATING

happens when the sperm from two or more males compete to fertilize the same female’s eggs.

• It’s a form of sexual selection that happens after mating — not during courtship or fighting, but inside the female’s reproductive tract.

How do males compete in sperm competition

• certain males produce more sperm

• faster/better sperm

• removal or sperm block 

mate-guarding behaviors

After mating, males want to ensure paternity — that the offspring the female produces are theirs so they develop methods to ensure their own sperm binds with the females egg

mate guarding example

• Mating plugs: males leave a physical plug in the female’s genital opening (common in insects and reptiles).

• Chemical repellents: males release substances that make females unattractive to others.

• Postcopulatory clasping: males physically hold females after mating (like damselflies in the picture)

“Guard now, gain paternity later.”

females choosing direct vs indirect benefits

direct— female chooses male for personal gain

indirect— The female doesn’t get a direct reward but her offspring inherit good genes or desirable traits.

“Good Genes” Hypothesis

Females choose males with traits that signal genetic quality, so their offspring will inherit those good genes (and be healthier, stronger, or more attractive)

Hamilton–Zuk Hypothesis (Parasite Resistance)

females can choose males based on immune competence

• if a male can indicate its higher immune competence by some signal, than females should choose to mate with them

• immune systems are very costly, so if you’re able to express a bright feather while also expressing high immune competence, you must be a good mate

Cryptic female choice

when a female influences which male’s sperm actually fertilizes her eggs after mating.

• So even after mating with multiple males, the female still has some control over paternity — often without males knowing.

how does Cryptic female choice work?

Females can manipulate sperm use in different ways — examples include:

• Sperm storage: keeping sperm from one male longer than others.

• Sperm ejection: physically ejecting or dumping sperm from a less preferred male.

• Chemical selection: her reproductive tract may favor sperm from genetically compatible or attractive males.

• First or last male precedence: deciding whether the first or last male’s sperm gets used.

• Biased resource investment: putting more resources into offspring from a preferred male.

Runaway selection

happens when females develop a preference for a male trait — and over generations, both the trait and the preference become genetically linked and reinforce each other.

Genetic Polymorphism

different genes→ different inherited traits that are fixed

Behavioral Polymorphism

• subset of genetic polymorphism

Different genes→ different inherited behavioral differences

Behavioral Polyphenism

Same genes→ different behavior based off of conditional tactics that can shape them in utero, larval or juvenile stages

• flexible

Chase-away selection

type of intersexual selection (mate choice) —
but unlike runaway selection, it’s conflict-based, not cooperative

• Males evolve traits that trick or exploit females’ preferences, even if it hurts the females — and then females evolve resistance to those tricks

what are some ways that females influence male reproduction?

what are some ways that males influence female reproduction?

Why did monogamy evolve?

one male to one female for life (rare)

1. mate limitation

2. mate guarding (f is guarding her m from mating with others)

3. mate cooperation (both parents are needed to raise young)

social monogamy

• BIRDS

Social monogamy means a male and female form a long-term social pair bond —
they live together, share a territory, and often cooperate in raising offspring.

BUT — it doesn’t necessarily mean they only mate with each other!

why are birds classic example of (social) monogamy?

• chicks are very demanding so  biparental care is very important for survival of chicks 

• important for male to assist the female

• all about costs and benefits 

Mate limitation hypothesis

Is paternal care a cause or consequence of monogamy?

• we’ve been focusing on the importance of paternal care is a cause of monogamy

• but is it a consequence????

• Monogamy evolves when potential mates are hard to find or far apart,
  so it’s better to stay with one partner than waste time searching for others.

• so this hypothesis states that mate limitation is the primary cause of monogamy

Why did polyandry evolve?

*One f mates with multiple males*

• territory scarcity and male cooperation

  • if there’s limited territory, males may have to defend same areas and share one female and help raise the one female’s young together

• sex role reversal

  • females defend territory while males take care of young so females may need to mate with multiple males to ensure all of their young is taken care of 

Polygny

When a single m has multiple f partners

Good genes hyoothesis

• sons of successful mate more, so the good genes get passed on more than the unsuccessful (bad genes)

Genetic compatibility hypothesis

proposes that individuals choose mates whose genes are different yet complementary to their own — meaning that the combination of both parents’ genes will produce the most viable, healthy offspring.

Genetic diversity hypothesis

• supports the genetic diversity hypothesis

• proposes that mammals will mate with others whose genetics differ largely from their own

• this is great because if its an unpredictable environment or a new pathogen arises, not all offspring will die and genes can still be passed on

Inbreeding avoidance hypothesis

proposes that mammals have developed mechanisms for avoiding incest because of natural and sexual selection (dispersal and kin recognition)

Resource defense polygyny

• When few males defend high quality territories and resources, females have to mate with them in order to survive and get those benefits

• strong males with territory and resources get the f

• weak males do not get the f

Female defense polygyny

When resources are evenly distributed, females will cluster together for protection, team work, etc and males will guard groups of females so they have access to mate with them

ex. lions— males will defend the pride which is where females cluster together for cooperative care of cubs

lek polygyny

when males cluster to one area that is invaluable in order to show off to attract females

this area does not have resources and males are not guarding anything, they are just showing themselves off

scramble competition polygyny

females and resources are far apart so males much search hard for a f to mate with

• the male’s success depends on his ability to find females quickly and efficiently

polygynandry

• m & f have multiple mating partners within the same group

• stable social groups

• can have cooperative and ecological benefits

Promiscuity

• m & f have multiple mating partners with NO social groups

• random mating

• often occurs when offspring require little care after their born so there’s no reason for parents to stay together

What kind of offspring do parents invest their time and resources into?

Offspring that have higher reproductive value because they’re more likely to pass on the parents genes

Signal of need

When food is abundant, parents respond to offspring who give signals that they are hungry and feed them

Signal of quality

When food is scarce, parents will be selective about who they feed because they want the strongest to survive

Fishers Sex Ratio

• In most species, parents should produce equal numbers of sons and daughters (1:1 ratio).

• This is because if one sex becomes more common, it actually becomes less valuable for reproduction.

local competition

• When relatives compete with each other, parents produce fewer of the competing sex.

• Example:

  • If males compete strongly for mates and often leave the group, parents may have more sons.

  • If daughters stay close and end up competing or mating with brothers, parents may have more daughters (to avoid too much male competition).

Local Enhancement

• When one sex helps the family more, parents produce more of that sex.

• Example:

  • If daughters help raise younger siblings or gather food, parents may have more daughters, especially when food is plentiful.

Interpretation of local competition and local enhancement

Parents usually aim for a 1:1 balance, but if one sex competes too much (competition) or helps more (enhancement), the balance shifts toward the more beneficial sex.

Trivers-Willard hypothesis

Maternal condition determines whether mothers produce a male or a female biased sex ratio.

• mothers in good condition should have offspring with higher variance (males)

• mothers in poor condition should have offspring with lower variance (females) bc a low-quality offspring can still gain fitness due to lack of intrasexual competition.

how has brood recognition evolved?

to help parents avoid wasting effort on the wrong offspring.

interspecific brood parasitism

one species (the parasite) lays its eggs in the nest of another species (the host), tricking the host into raising its young.

• Example: Cuckoos lay eggs in reed warbler nests.

• The host ends up feeding and caring for the cuckoo chick, which often pushes out the host’s own eggs or chicks.

tradeoff between cost & benefits for caring for offspring

• caring for current offspring leaves you less opportunities for future mating and less time to invest in self care for the parent 

• but if you invest less in current offspring, you can have more future mating opportunities 

why is there sexual conflict?

arises because caring for offspring benefits the current brood, but decreases future mating opportunities — each sex weighs this cost differently 

siblicide 

an adaptive behavior—> ensures strongest offspring survive when food is limited 

• parents may allow for this to happen if its more efficient for survival and reproductive success (less offspring ensures fewer, but stronger babies 

Model of Signal Detection

Animals use signal detection to decide between two categories —
for example:

• “Desirable” = my chick / my egg / a safe signal

• “Undesirable” = parasite chick / foreign egg / threat

But in real life, these signals overlap — they aren’t perfectly distinct — so animals must set a decision boundary.

This model explains how animals make imperfect but adaptive decisions when signals overlap.

They set a threshold that minimizes costly mistakes — and that threshold can shift depending on how risky or common deception is in their environment.

mafia hypothesis

• explains why hosts might tolerate parasite eggs — they’re avoiding revenge.

• Rejecting a parasite’s egg can lead to nest destruction and loss of all offspring, so accepting one extra egg may actually be safer for the host.

example of coevolutionary arms race

Gradualist Shift Hypothesis

Brood parasitism evolved gradually from normal parental care — through a series of small behavioral changes.

Direct Size Difference Hypothesis

This supports the idea that size difference alone could trigger parasitism — big chicks outcompete smaller ones, encouraging parasitic behavior.

brood parasitism

when one animal (usually a bird) lays its eggs in another species’ nest, leaving the other parents to raise its babies.