BIO375 FINAL

Direct Benefits

Benefits directly to female in mate choice

Resources, etc.

Food given from males (seabirds, scorpion flies)

Ejaculation transfers nutrients (spermatophores)

Male himself is nutritious

Indirect benefits

Benefits to the offspring later

Parental care, good genes, etc.

’Good Genes condundrum”

Indirect benefit? Direct benefit? How does it not go to fixation? How does on tell if another has good genes? Is it based on visible health? Etc.

Runaway sexual selection

Peacocks tail: unnecessary and detrimental to their ability to survive

By proffering males with certain traits females produce offspring that have genes for the trait and for the preference

Eventually females by choosing males with certain traits are also choosing ther preference for the trait

Any skew in females in population can cause preference and trait to runaway in positivitie feedback

mate choice copying

Study in Japanese Medaka show that other females can be influenced by female choice

If the receptive female did not spawn with a male the observer female preferred male with most intense courtship

If the receptive female did spawn the observer preferred that male regardless of courtship intensity

It’s giving they want what they cannot have

If other female desires male that female also desires that female because something must be good about him

intersexual selection

Female choice

intrasexual selection

male-male competition

paradox of the lek

If females choose males with a particular allele then selection will drive allele to fixation

parasite mediated sexual selection

Suppose females prefer male with snazzy display and display is energetically costly

Only males in good health can mobilize energy to display

If male health depends on resistance to parasites or pathogens, then by choosing displays, females acquire genes for health

Genetic variation is maintained because parasite evolves as well, and so which host genes best confer resistance to the parasite change over time

Red queen may be responsible for sexual selection!

number vs quality example

Great tits

Average brood size thats the optimum

Too many it affects survival

Too less not as much fitness advantage for mom

Black billed magpie

Tested different hosts of differing natural clutch size

They had optimum of that natural size

There is a trade off between number and quality

Clutch size produced by a female is close to the optimum for that female

Somehow females assess their ability and the conditions, and adjust clutch size appropriately (conditional mixed strat)

care vs mating examples

Male indigo buntings

Juncos

Male T implanted juncos sang more

Move around more, including leaving their territory more often

Gained more extra pair paternity elsewhere

What might happen if you reduced T in males?

Increase offspring survival through PC BUT

Cost to

Number of offspring increases current attempt

Number of mates

Probability of future attempts

care vs survival examples

assassin bug

Males guard eggs

Guarding has no effect in the lab

In the wild guarding leads to higher egg hatching success due to lower parasitism of eggs

Guarding males have lower survival than either females or non guarding males

care vs future examples

Collared flycatchers

Level of care adjusted in response to changes in potential costs

Evidence for costs both within same breeding attemp and across attempts

Are sexes the same or do they differ?

parental care game (Maynard smith’s)

Males: care or desert

Females: care or desert

Move care vs less care

Built in biases based on difference between sexes

Survival of offspring depend on number of care-givers

S2>S1>S0

Number of offspring in current brood = w

If male deserts he has probability (p) of acquiring new mate

He will continue to desert this mate as well

It only goes as far as mate number 2, so after it does not matter

If female deserts she ALWAYS finds new mate, has fecundity = W (sometimes 2w but not always)

She also continues to desert the second mate and ends at 2

Assumptions

Males and females equally good at care

Strats are fixed

If biparental care it would result in wS2 for both

If male deserted and female cared it would be wS1 for female and wS1(1+p) for male

If both male and female deserted it would be WS1 for female and wS1 for male

If the female deserted and male cared it would be WS0 for female and wS0(1+p) for male

When should both sexes provide care?

When switching by either sex is not better, so

Females care when wS2>WS1 and

Males care when wS2>wS1(1+p)

Value of care is important!!

If S2 is not much more than S1 then no incentive to stay

Opporotunity for additional matings is important

Value of p affects desertion by males

parental care, parental effort, parental investment

Any trait in parents that increases offspring fitness

The cost of parental care to the parents fitness

Often measured by its effect on other activities

lacks’ hypothesis

As number of offspring increases there is an increase constraint on fitness

As the number increases the survival of offspring decreases

There is a predict intermediate optimum

Conditions for monogamy

Few mating opps

Females dispersed

Female Voles clump when food clumps

Female voles disperse when food disperses

When clumped males follow females and are not monogamous as greater opp to mate

When disperses males follow females and are monogamous as less opp to mate

Females respond to resources, males respond to females

Biparental care esp. valuable S2>>>S1

Ex. Seabirds

Female female aggression

Ex WOLVES

Alpha female receives male care and attention

Limits p for male

conditions for polygamy

Shirking cichlids

Maternal care very valuable

S1>>>S0

Paternal care of modest value

S2=S1

Many mammals

Resources held by males offset any difference between S2 and S1

Mating opportunities high (high p)

– Mammals: Harem defense due to female clumping

because of predation

conditions for polyandry

maternal care adds little to parental care

W is really big compared to w

Example spotted sandpipers

Rich habitat, females can relay eggs quickly

Paternal care highly valuable

Either S2=S1 >> S0 or S3>S2

Example sea horses

Male brood pouch

Fish

Males defend spawning sites and stay there

Low p for male

Skewed sex ratio (spotted sandpipers as well)

Female choice

Strongly avoid already paired males

conditions for promiscuity

Parental care has no value to offspring fitness, and or remateability is very high

Desert is the evolutionary stable strat for both parents

S1 =~ S0

p for males and W for females perhaps both large

Sexual conflict

Traits favoring particular mating pattern in one sex (e.g., polygyny in males) are costly to other sex (females) and vice-versa (polyandry for females)

Dunnocks example

Complex mating systems

Monogamy for some, polyandry for some, polygyny for some, polygynandry for some

The larger the female territory the more males within it

Small territories with two females more likely to be polygynous

REMEMBER OPTIMAL TERRITORY SIZE MODEL

Benefit/resource gained vs cost of defense

Polyandry is good for females

Polygyny is good for males

Conditional polygny example

FERAL HORSES!!!!

My favorite example tbh

Dominant male and group of females

Key resource: water

Permanent ponds

Ephemeral: dependent on weather

When more females more clustered males will take on larger harems

When females are dispersed males are more likely to follow monogamy

Polygyny is increased with distance from permanent water source and decreased with more precipitation

Im ABSOLUTELY using this example on the test if given the opp

Horses are my fav

promiscuity example

Lotta insects

phylogenetic analysis of mating systems

Cichlid fishes and their species

Polygyny threshold model

why live in groups?

protection from predators (vigilance, dilution, protection/group defense, selfish herd, confusion), increased foraging success (synergy, cooperation, information), information center

Costs

Competition for resources

(Exploitative, interference)

Cost of aggression

Increased exposure to disease/parasites

Limited choices of mates

why live in groups? Examples

Starlings

Able to respond to predators more quickly with more pairs of eyes

Red wing blackbirds

Breeding synchrony that has many birds together, less chance of being killed with so many other birds around

musk ox

Multiple individuals respond to threats and drive off predators

Get into defense formations

Fish schools and bird flocks work on confusion

Black headed gulls

Captive birds in flocks consumed more fish than solitary birds

Fish fleeing one headed to another. Easier to catch

Wild dogs

Live in permanent social groups

Hunt together in a pack to help increase chances of success

Larger packs foraged more often

Had to chase prey over a shorter time

Less energy expended and more energy gained

Fruit bats

Dilution and also gain social information

development of locust swarms

arise from combination of two individual traits (Buhl et al. 2006):

1. Developmental plasticity in the face of density

2. Responses to other locusts

Plasticity: The ability of a genotype to produce multiple phenotypes in response to variation in environment.

Developmental plasticity is an effect of environment early in lifetime that has life-long impacts. [Tinbergen’s 2nd Question!]

Youngsters have two morphs:

1. Solitaria: Avoids other locusts

2. Gregaria: Attracted to other locusts

Developmental switchpoint

- depends on density

-solitaria occurs at low densities

(Think of solitary)

-gregaria at high densities

(Think of real social George)

Gregarious locusts try to eat other locusts

Cannibalisitic

(Spiders georg, hes real lonely and social and eats a bunch of spiders which isnt really cannibalism but hes a little freak nonetheless)

higher density causes high exploitative competition for normal food, leading to search for protein and salt

found a locust’s response to attempted cannibalism, cued by another locust approaching and touching from behind, is to…run away!

Combination of attraction to others and avoidance of cannibalism is that all locusts end up running away in the same direction. Produces a “marching” swarm.

Individuals revert to random movements when solitary, but ‘coordinated’ movements when together.

Once the youngsters mature the swarms become plagues

kin selection (Hamilton’s rule)

Individuals most likely to carry unexpressed genes are close relatives. “Kin selection” might favor altruism if it is directed toward relatives.

Altruism among relatives may be favored

Example 1: Parental Care

Parent provides benefit to another at cost of itself

Why does this evolve?

Copy of gene for parental care likely to be in offspring, so if benefit is high and cost is low, then the parental care allele helps copies of itself!

The most likely other individuals with copies of a new allele are offspring.

THREE variables are important

Cost to actor (C)

Benefit to recipient (B)

Probability that recipient shares a given allele with actor, called relatedness (R)

A form of conflicting demands, with fitness components in separate individuals

RB>C is conditions needed for altruism to spread

reciprocal altruism (prisoners dilemma game, tit-for-tat solution)

Be altruistic to someone who will later be altruistic back to you

Current cost

Delayed benefit

Delays make this susceptible to cheating

vigilance

More eyes looking and warning about predators

dilution

If predators forage at constant rate, then joining a larger group dilutes the risk

selfish herd

predator attacks from outside

– safest place is toward middle, with others in the way

additional clustering during attack

Bird flocks, fish schools, and ungulate herds spread out when foraging, cluster tightly when attacked

Example liostenogaster wasps

Ants attack outside

Wasps attack anywhere

Nests more clustered where ants but not wasps

information center

Improved foraging via information

Successful foragers return to center and tell others how they were successful

Cliff swallows

Most successful in larger group

More likely to follow a good forager when leaving a colony

Rats

Three arm maze with random food

Sniff demonstrator rat who had smell of the day

Test subjects went to arm with food

Altruism

Any action that benefits another at some cost to the actor

relatedness

The probability of sharing a particular allele that is identical by descent.

Relatedness is not the proportion of alleles shared, but the probability a particular allele (a new mutation impacting altruistic behavior) is shared.

reciprocity

Mechanism

Organism acts altruistically towards another on the basis that it will receive the same in the future

eusociality hypotheses

haplodiploidy hypothesis, queen control, monogamy hypothesis

haplodiploidy hypothesis

Sex determination is haploidiploid

Females are diploid and arise from sex, males are haploid and arise through parthenogenesis

Affects the pattern of relatedness

Sisters relatedness to brothers = 0.5 avg

Brothers relatedness to sisters = 0.25 avg

Females have a higher relatedness with sisters (0.75) Than daughters or sons (0.5) or with their brothers (0.25)

Male offspring are equally real tend to brothers, offspring, and sisters (0.5)

Bias for altruism by females to their sisters

Sex of recipient of help matters

queen control

Queens related to offspring equally (0.5) so she prefers a 1:1 sex ratio

The monogamy hypothesis

Females mate with just a single male

0.5 relatedness between all siblings

hyymenoptera (bee, ants, wasps) example (eusociality)

Arose from subsocial route

All haploidiploid but not all eusocial

Ancestry monogamous

termites example (eusociality)

One breeding pair, lots of sterile workers

Male and females diploid

King remains with colony and assists

Workers are both male and female

No obvious genetic bias

Direct benefits: sharing symbionts

Wood low in nutrients so they share these to help digest

High cost of dispersal

If young adults unlikely to breed on their own kin selection would favor caring for kin instead

Cyclical inbreeding can create biases in relatedness

Sibs r=1

Offspring r=0.5

Termites are generally monogamous

Some are inbred but many are not

naked mole rats example (eusociality)

One of only 2 eusocial vertebrates known

Blind and hairless

Subterranean

One queen

3-4 male breeders

Males stay with queen and help some

Male and female offspring of queen are workers

Division of labor: soldiers, foragers, care-takers

Reproduction suppressed by queen aggression

New colonies form by fission

Benefits: food hard to find, colony defense

Very difficult to disperse because of environment

High similarity in dna between moles in a colony

0.85-0.95

High similarity due to inbreeding (equivalent to 60 generations of sib-sib mating)

High r through inbreeding

Low fitness to solitary led to long lived associations leading high relatedness through inbreeding

Genetic relatedness then contributes to who helps who

Eusociality

complex social system with overlapping generations, sterile worker castes, and cooperative care of offspring

Workers give up personal reproduction

Little cost to help big benefit to help

Subsocial pathway to eusociality

helpers are offspring that stay in the nest and help care for siblings

Helpers sacrifice more reproduction than in parasocial groups

parasocial pathway to eusociality

multiple founders sets come together to reproduced in the same nest

Mendel’s law of segregation

mechanism

sex ratio

males 2x big as females, so females produced more

Fitness depends on expense of producing male or female and their reproductive value

Reproductive value is the expected lifetime RS of an individual

Sex ratio in ants example

sex ratio reciprocal of weight ratio 1:1, implies queen control

Sex ratio 3:1 with emphasis on females, implies worker control

Ants match 3:1

sweat bees

Have both parasocial and subsocial nests

Subsocial nests: workers should allocate more to females as they help and are more related as sisters under the queen

Parasocial: workers should allocate equally to female and male as workers will replace queen eventually and have similar relatedness to nieces and nephews

Sagebrush crickets example

nutritious males

Females chew on males wings

Hemolyph consumed from wings

Virgin males prefered

Strength of preference depends on food supply

Damselfish parental care

males court from nesting sites

Females lay eggs at site and move on

Males will cannibalize some eggs

Males who court more intensely are less likely to cannibalize and more likely to defend eggs

Females prefer to spawn with more intense courter

Parent care indirect or direct?

Both!

If male takes over care its direct

If male helps with care it’s indirect

Can be both simultaneously

Sticklebacks example in parasite mediated sexual selection

female prefer males that have brighter red

Bright red is carried by males in good condition

Parasites cause reduction in male red color

Females can identify parasitized males by red color

Not clear if direct benefits or good genes tho

Red necked pheasants example for parasite mediated sexual selection

females prefer to mate with males having longer spurs

Males with long spurs are older, larger, and have higher survival

major histocompatability locus MHC

Males with long spurs tend to have similar MHC genotype within a year, but different accross years

For example all long spurred males in 2024 would have simialr genotypes but different to the long neck spurs of 2018

Offspring of females mating with long spur males have higher survival

We do not know what parasites are involved and how they maintain variation

It’s giving coevolutionary arms race of evolving genotypes

Waxmoths sexual selection

Females prefer males with higher Pulse-

Pair-Rate (PPR) calls

• Playbacks of bat calls caused males to pause

in “singing”.

• Playbacks of bat calls near preferred males

erased female preference.

Males more likely to silence when alone

Good males in a crowd of wimps are less likely to silence

Good males in a crowd of studs are EVEN less likely to silence

Male-male competition

Implications of anisogamy

Males: strat. Of finding mates

Females: strat. Of improving offspring survival

Conflicting Demands

When a change in a trait (tendency to

provide care) increases one component of

fitness (offspring survival) and decreases

another.

Juncos example

Altered testosterone in males

Altered testosterone in females

Capture a subject

Slide a slim plastic tube of either T or empty under skin

Superglue, release

Females appear to have compensated for the loss of PC

Complete removal of males led to slower growth, slightly fewer offspring

Male PC also affected female juncos

Less care means female in not as good shape, more mass loss, renested later

T implanted females brooded less and were less aggressive to nest intruders

Lower brood survival

Biparental care example in house sparrows

both parents provide food for 15 days

Do they follow theory of optimal parent care?

Pair feeding rate increases offspring mass

Exp

Two nests with nestlings the same age

Observe 2h (PRE stage)

Swap 2 nestlings from one to the other

Observe 2h (MANIP stage: reduced vs. larger)

Repeated over 4 years

No effect at PRE

reduced declines

Larger increases

Parents adjust work level to number of mouths

But they do not fully compensate so all nestlings do worse

And apparently the level of food available affects how willing they are to extend themselves

And this may be adaptive behavior given their ability to renest

Conflict

When a trait in one individual increases their fitness but decreases the fitness of a social partner

Types of parental care strats

sealed bid = fixed strat of amount of care

Negotiated = conditional mixed Strat depending on something about partner

Example of pair coordination PC, long tailed tit

paretns alternate visits more than expected by chance

Alternating also resulted in synchrony

Pairs with higher metrics of these delivered more food and suffered lower nest predation

Burying beetles

Find a dead animal, typically a mouse

Roll into ball and bury it

Lay eggs in soil nearby

Join defense of carcass and eggs

When larvae hatch parents regurgitate partially digested carcass to larvae

Exp

Added weight to parent

Reduced care when weighted

Increased care from the partner of the weighted

Only partially compensated for partner tho (male more for female)

Shirking cichlids

how might conflicting demands keep both partners from shirking?

Value of care is important

Opp to remate is important

Polygyny via deception

Pied Flycatchers

– Territorial, defend cavity

– Female benefits from male care, avoids

already paired males

– Once paired, some males defend second

territory away from first

– Attract second female, then care for offspring

at first nest; second female either deceived or

delayed

3rd Q: evolutionary history

What were the sequences of changes leading to present day diversity in mating systems?

Were there certain kinds of transitions that are more common?

Integration of 3&4

What were the sequences of changes leading to present-day diversity in mating systems?

Were there certain kinds of transitions that are more common and what might have been the selective forces acting during those changes?

Can transition from

biparental to only male

Female only to no care

Biparental to only female

Male only to no care

And vice versa

CANNOT transition

Biparental to no care

Or

Male only to female only

And vice versa

Aggregation

Groups of individuals who act independently but arrive at same place and time

Ideal free distribution describes aggregation, unless social cues are used.

Many animal groups are more than this.

Emergent property

collection or complex system has this, but which the individual members do not have.

Quroum sensing (ants, bees, ungulates)

Individual process of assessing options, communicating to others.

– Others also assess options, and the weight of individuals for or against a particular option leads to a decision.

Dominance in coral dwelling gobies

based on size

Only dominant individuals breed

If subs get close in size to dom the dom becomes increasingly aggressive and evicts sub

Subs try not to grow too big so avoid food sometimes

Dwarf Mongoses altruism

breeding pair and their older offspring, with some immigrants

Multiple aspects of helping behavior

– Sentinels

– Foraging

– Grooming

– Lactating

Indirect benefits

Kin selection

Delayed direct benefits

Queuing for breeding spot

Relatedness decreases over time with sub age regardless of origin

helpers increase number of offspring

Breeding is hard to achieve when young as easier when older

Some may disperse as they get older to nearby group

Pied kingfishers in kin selection

Young fledglings increases with help

Primary helper is always a male offspring of breeding pair

RB>C

Secondary helper is usually an unrelated male

R=0

Only help when breeding is difficult on unrelated male (low C)

Can benefit: secondary helpers sometimes pair with female later (RB=0, but right side of equation may actually be negative because chances of breeding are higher if help)

Relatedness does affect likelihood of helping, but so does B and C too

Superb fairy wren

Breeding usually occur in group of three or more

Having at least 1 helper increases success

Helpers also increase female survival to next year

But over 80% of offspring are EPP

Helpers typically unrelated due to this

Genetic monogamy vs cooperative breeding

Monogamy hypothesis alternative 1

monogamy hypothesis alternative 2

Mechanism/Development and Kin Selection

1. Grow up with kin, so very familiar individuals

are likely to be kin

2. Unknown individual resembles a known relative

(phenotype-matching)

3. Kin are like yourself (self-referent phenotype-

matching or “armpit effect”)

Golden hamster example for phenotype matching

Swapped pups among broods at < 12 hrs; 1 foster and two normal pups per female

When mature (41-61 days later), tested response to flank-gland odor from different individuals

Non sibs reared together (foster sibs)

True sibs reared apart

Non sibs reared apart

They are wait the least to investigate non sibs, then foster sibs, and wait the longest to investigate true sibs

Hamsters distinguish social non-sibs from unfamiliar individuals (match to social relatives)

Hamsters distinguish unfamiliar sibs from both social non-sibs and from unfamiliar non-sibs (match to self)

Kin recognition in plants (Sagebrush)

Plants often avoid self-pollination

• Roots in some plants grow less if they bang into a relative vs non-relative.

Sagebrush emits a volatile chemical if chomped on by herbivore

Neighbors synthesize defense compounds more when such chemicals are released

Significantly more plants had more damage on side near damaged non relative

They then used air from a damaged plant in a similar design

Same thing!

Plant warned their relatives more effectively

Mutualism

a relationship between two species of organisms in which both benefits from the association

By product mutualism

cooperation as a collateral effect of selfishness, in which each derives a fitness benefit

Prisoners dilemma

You and companion captured, put in different cells.

• Police give you an offer: If you inform on your “friend”, he’ll be put away for long time and you get to go free. If you stay quiet, you both go to jail (short time).

• What do you do?

Tit-for-tat

Cooperate and then do what partner did last time

Required an additional condition that the game is played repeatedly and participants remember what their ‘friend’ did last time.

‘Forgiving’ Tit-for-tat even more stable

Vampire bats

Colony-dwelling, mix of related and unrelated females

• Bats regurgitate food to offspring and to others

• Individuals groom others as well

• Food-sharing has asymmetric C and B (C < B)

Cost less than benefits

Problem in bats = groups compose of kin

Kin selection might maintain this

Likelihood of food-sharing explained more by past food received and grooming than by relatedness.

No evidence that recipients harassed donors into sharing.

Guppy predator inspection

Live in groups

Predators cause groups to become tighter, except a few individuals who swim to danger

Predator inspection fits with the prisoner dilemma

Solitary individual (sucker) receives high cost

If several coop then cost is lowest

If everyone defects cost is intermediate

Do guppies play tit-for-tat?

Exp

Guppy at tank with pred at end and an observer to see how they react to an altruist or a defector

They do!

If the other fish is ‘nice’ they react nicely and if they defect they ‘retaliate’

Reciprocity and Tit-for-tat in Humans

• Strong bias toward familiar individuals

• Some effect of cost and benefit

• Aid-giving may depend on the nature of prior interactions with that specific person and the ‘trust’ you have in them

Meriam People: Signaling and Hunting

Men spear fish and hunt turtles; elaborate cultural practices linked to this activity

– Women collect shellfish; no special events

– Shellfish are much better energetically and nutritionally

– So why do men make poorer choice of spearing fish or hunting turtles, and why is this celebrated?

Hypothesis: Activity is a signal.

Turtle-hunters had higher reproductive success

• More social recognition

• Attracted better quality and younger mates

• Had more mates over lifetime

– Best spear-fishers are well-known, conspicuously

display catch

Evolutionary Psychology

Human behavior made up of Complex Conditional Strategies: Sophisticated mechanisms for collecting information and processing it.