Evo Animal Behavior L5-L7

What does “playing possum” mean?

It’s an innate defense behavior where a possum plays dead to avoid predators.

What happens physiologically when a possum plays dead?

Body temperature, breathing, and heart rate drop; foul odor released; body limp; mouth open, tongue blue.

Why does playing dead help the possum?

Predators prefer fresh prey and avoid what appears dead.

What unusual items do bearded vultures use to build nests?

Human artifacts like shoes, tools, and slingshots.

What does this nesting behavior show?

Object use and intelligence similar to tool use in birds.

What causes color differences between male and female tanagers?

The achromatic layer—white in males (bright colors), black in females (camouflage).

Why do females have more black layers?

Provides warmth and better camouflage.

What defines a mating system?

How individuals are socially organized by number of partners per breeding season.

What are the three main mating systems?

Monogamy, Polygyny, Polyandry.

Can species switch mating systems?

Yes, depending on ecology—like food, habitat, or sex ratios.

Who linked ecology and mating systems?

Stephen Emlen and Lewis Oring.

What two main constraints determine mating systems?

Evolutionary (sexual conflict) and ecological (resource limitation/distribution).

When is monogamy most likely to evolve?

When resources are scarce or scattered and females are widely distributed.

Why is monogamy rare in large, visible animals?

Easier to find and “cheat” with other partners

What is extra-pair copulation (EPC)?

When an individual in a monogamous pair mates outside the pair bond.

List male costs and benefits of monogamy.

Cost: fewer mates and offspring. Benefit: paternity assurance and biparental care.

List female costs and benefits of monogamy.

Cost: possible bad sperm. Benefit: help from male increases offspring survival.

What factors drive monogamy?

Scattered females, parental care, infanticide risk, predation/STDs, mate guarding, and paternity assurance.

What did Dr. Foltz’s oldfield mouse study show?

90% of offspring matched the father in the burrow—evidence for genetic monogamy.

How did the California mouse experiment show biparental care?

When one parent left to get food, offspring survival decreased—both parents needed for warmth.

What does Kirk’s dik-dik do to guard mates?

Males follow females and cover feces with dirt to hide estrus scent.

How do parasitic wasps prevent other males from mating?

Males guard females and even mimic mating position to block rivals.

What are serial and social monogamy?

Serial: one mate per season. Social: pair-living without guaranteed sexual exclusivity.

When does polygyny occur?

When resources are clumped and females are receptive at different times.

Why might females accept polygyny?

Benefits (resources, protection, high-quality male) outweigh cost of sharing.

What is the Polygyny Threshold Hypothesis?

Females choose polygyny if access to a high-quality male or territory outweighs the cost of sharing him.

What are the three kinds of polygyny?

Female-defense, Resource-defense, and Lek.

When does female-defense polygyny occur?

When females group for safety and males guard the group.

Examples of female-defense polygyny?

Bighorn sheep, elephant seals, lions, and silverback gorillas.

When does resource-defense polygyny occur?

When males control valuable territory that attracts multiple females.

Example species for resource-defense polygyny?

Red-winged blackbirds—females choose high-quality nesting sites even if they share males.

What defines a lek mating system?

Males display in a communal area with no food or nesting resources; females choose mates.

What is the lek paradox?

Most females pick the same male, yet leks persist—possibly due to kin selection or changing conditions.

Example species with leks?

Sage grouse and manakins.

What did studies of manakin leks show?

One central male got ~75% of matings; others had few to none.

Why do subordinate males stay in leks?

Kin selection, waiting for alpha’s death, and female lek fidelity.

How common is polyandry?

Very rare (<1% birds, <5% mammals).

What are typical traits in polyandrous species?

Females are larger, hold big territories, and males provide most parental care.

When does polyandry evolve?

When predation and clutch loss are high, favoring multiple broods.

Example of polyandry in birds?

Wattled Jacana—females mate with several males; each male incubates and raises eggs.

Example of polyandry in fish?

Pipefish—females bright and large; males brood young in pouches.

Example of polyandry in reptiles?

Snakes like anacondas—many males compete for one female.

What is the Unguis (D1)?

The thumb (first digit) — the last finger to develop.

What are the main variations of thumbs among species?

• No thumb → guinea pigs

• D1 only → porcupines

• D1 + nail (ancestral state) → squirrels

• D1 + claw → prairie dogs, blind mole rats

What does thumb development depend on?

It depends on habitat and food-handling behavior.

How does habitat affect thumb development?

• Arboreal → trees

• Scansorial → climbing

• Subterranean → digging underground

How does food handling affect thumb development?

• Oral feeding → only the mouth is used

• Oromanual food manipulation → hands + mouth used to eat (e.g., squirrels)

What behavioral impact does having a thumb create?

Having a thumb allows more complex food handling and climbing behaviors.

What is the ancestral trait for parental care?

No parental care — it evolved later as a derived behavior.

What is the benefit of parental care?

It increases offspring survival and the parent’s lifetime reproductive success.

What is the cost of parental care?

It reduces the parent’s own survival and future reproductive potential.

When will parental care evolve?

When the benefit to offspring survival outweighs the cost to the parent.

Give examples of animals with no parental care.

Sea turtles and flies.

Give an example of biparental care.

California mouse.

Give an example of male-only (paternal) care.

Gobi fish or giant water bugs.

Give an example of female-only (maternal) care.

Most birds and spiders.

What is “suicidal maternal matriphagy”?

When offspring eat their mother after she has cared for and fed them, as seen in spiders.

What does life-history theory describe?

How energy is divided between growth, maintenance, and reproduction.

What happens when parental effort increases?

Effort for future reproduction and personal survival decreases.

What two opposing strategies does natural selection favor?

Producing many small offspring with no care, or few large offspring that require care.

How do North American robins and Argentine thrushes differ in parental strategy?

Robins (short lifespan) return to the nest faster after danger; thrushes (long lifespan) wait longer because they can breed again.

In ray-finned fish, what factors are linked to parental care evolution?

Body size, fecundity, breeding season length, and number of reproductive events.

What is the ancestral state for fish parental care?

Biparental care — evolved without intermediate steps.

Why did many species evolve paternal care?

Males can guard eggs effectively, while females benefit more from continued growth and future reproduction.

What two factors promote paternal care?

Preventing rival males’ sperm from reaching eggs and indeterminate female growth.

Describe parental behavior of Gobi fish.

Males build nests, guard eggs, and fan them for oxygen for two weeks without eating.

What happens if a male Gobi is poor quality?

He eats his own eggs instead of caring for them.

Describe parental care in giant water bugs.

Females lay eggs on the male’s back, and the male carries and protects them until they hatch.

What is brood parasitism?

When a species lays its eggs in another species’ nest so the host raises its young.

Give examples of brood-parasitic species.

Cuckoos and cowbirds.

What are the costs of brood parasitism for each side?

Cuckoo—no cost; Host—loses its own offspring and wastes energy feeding another’s chick.

How does a cuckoo chick outcompete host chicks?

It hatches first and instinctively pushes host eggs out of the nest.

How do hosts like superb fairy-wrens counter brood parasitism?

Females sing specific songs to embryos so they can identify their own chicks.

What is menopause, and how common is it?

The end of female reproduction; it is rare and found in only six species (humans, some whales, gorillas, chimpanzees).

What is the Grandmother Hypothesis?

Post-reproductive females increase family survival by helping raise grandchildren.

What is the Prudent Mother Hypothesis?

Mothers stop reproducing when daughters reproduce to reduce food competition within the family.

What are the five steps in the mating process for fruit flies?

Orientation, tapping, song, licking, and copulation.

What is a nuptial gift?

A nutrient-rich secretion offered by a male to a female during courtship.

What does the FRUM gene do in fruit flies?

Regulates male courtship behavior and nuptial gift production.

What does Bateman’s principle state?

Males show higher variance in reproductive success, while females’ success depends on egg number and mate choice quality.

What are proxy traits?

Physical traits that indicate an individual’s genetic quality or health.

How do red junglefowl females choose mates?

By selecting males with bright red combs as a sign of good immunity.

What trait do mosquito fish females prefer?

Larger males, which may signal better fitness.

What does the Sexy Son Hypothesis state?

Females select attractive males so their sons will inherit the traits that make them desirable.

What does symmetry indicate in mate choice?

Genetic health and developmental stability.

What did the barn swallow experiment show?

Females prefer males with symmetrical tail feathers.

What is runaway selection?

A process where female preference for a trait causes it to become exaggerated over generations.

Example of runaway selection?

Male stalk-eyed flies evolving longer eye stalks due to female preference.

When does male mate choice occur?

When males invest heavily in offspring or females vary greatly in quality.

What trait do male spiny-footed lizards prefer in females?

Larger females and red tails (indicating unmated status).

Why do male bowerbirds build bowers?

To attract females and protect them during courtship.

What does the complexity of the bower indicate?

The male’s intelligence and skill.

What defines a mating system?

The number of mates and type of pair bonds an individual forms per breeding season.

What are the three main types?

Monogamy, polygyny, and polyandry.

When is monogamy most common?

When resources are scarce or scattered, and females are evenly distributed.

What is serial monogamy?

One mate per breeding season.

What is social monogamy?

A male and female live together but may not be sexually exclusive.

What did Dr. Foltz find in oldfield mice?

90% of offspring were sired by the male in the burrow.

Why is California mouse monogamy important?

Both parents are needed to keep pups warm in cold climates.

What factors drive monogamy?

Scattered females, high parental care needs, infanticide risk, and mate guarding.