Lecture 21-28 (Psych 3T03)

Sibling rivalry - what do they fight over/

food, resources, parental attention

When is sibling rivalry most intense?

siblings are close in age, of the same gender, or one child is intelectually/physically gift

Why does sibling rivalry occur?

individuals share only 50% of their genes with a sibling but 100% with themselves; so the benefit of giving scarce resources to a sibling, must be twice as great as the benefit of keeping the resource to oneself

Facultative siblicide

may or may not occur; there will be aggression but depending on environmental conditions death may or may not occur

Obligate siblicide

almost always at least one sibling will be siblicided

e.g. bluefooted booby - siblicide

siblicide is common but not always; facultative

How can siblicide possibly advance a parent’s fitness?

It leads to offspring reduction, allowing the remaining (usually stronger) offspring to gets all the resources (not wasting on poor quality offspring)

similar causes for infanticide or parental favouritism

Why does siblicide exist? 2

1) a way to deal with overproduction

2) a consequence of asynchronous birth

not mutually exclusive

why does siblicide exist - a way to deal with overproduction

parents sometimes produce more offspring than they can raise - one mechanism to solve this is brood reduction

Why does siblicide exist - asynchronous birth

young can be born at different time (e.g. by asynchronous hatching cause by immediate incubation and time between egg laying events)

firstborn gets a head-start on monopolizing resources

Unequal feeding rates, aggression exaggerate the size different and end in starvation or the killing go the youngest/weakest offspring

e.g. spotted hyena (siblicide)

• Usually have twins; these are born in a burrow far away from the rest of the clan’s den

• Spotted hyena newborn cubs are born well developed, with open eyes and full sets of strong teeth – odd because they wont hunt or eat meat for months

• We think these teeth are for competition reasons – they slash each other and shake each other by the necks

e.g. blue herons vs great egret siblicide

great egrets show high siblicide (85% in 4 egg, 35% in 3 egg), and parents do not interfere

blue herons very rarely show siblicide

why difference in siblicide between great egret and blue heron?

blue herons, the big fish can’t be monopolized but great egrets, bolus (fish ball, small fish) can be monopolized by one chick

results of great egret and blue heron cross-fostering

blue heron chicks showed increased aggression and siblicide was common (almost always the youngest) - easy to monopolize food - facultative species

great egret chicks slightly decreased siblicide and aggression but not significantly, even though food was not monopolizable = obligate effect

sibling rivalry in pigs - why do they compete

more piglets born than can be sustained (fewer teats, not enough milk for large litters)

results of farrowing on piglet sibling rivalry

unclipped gain more weight than clipped littermates

also, in bigger litters, tehre was more of a mass difference between unclipped and clipped littermates

Parental responses to too many kids? 7

neglect / feeding rules (neglect the small/weak)

feed food that can be monopolized by strongest offspring

direct brood reduction (infanticide)

ansynchronous vs synchronous incubation

making first eggs bigger than the last eggs

putting more androgens into earlier eggs

promote or ignore sibling rivalry

Why not make fewer kids?

• Parents might produce more young than they need as an insurance policy

• Unpredictable ecological conditions (good years lots of RS, poor years brood reduction)

• Overproduction of young and subsequent needed brood reduction (egrets, pelicans, cootes)

Why are predators with small prey typically small and asocial?

Often predators live alone, especially those that take mainly small prey. They may do best hunting alone and resources may not be abundant enough to support a group (e.g. small carnivores like mustelids, small cast). Resource distribution can prohibit group formation

Benefits of group living - predation

increased vigilance

dilution effect

group defense

confusion effect

e.g. ostriches - increased vigilance

in ostriches, similar time with someone having their head up regardless of group size - but this allows big group in time each individual has to look instead of feeding

no predictable pattern - so cannot be exploited by predator

e.g. goshawks hunt wood pigeons

less successful when attacking large flocks because of increased vigilance - greater reaction distances, lower attack success

group living - predation - dilution effect

chances that you will be eaten go down in a larger group e.g wild horses and tabanid flies

dilution effect - domain of danger

safety can depend on position within group = individuals approach others to reduce their domain of danger

trade off domain of danger

exterior positions may be better for foraging and inside position might be safest. Trade-off between predation risk and foraging

arabian babblers group defense

Live in stable order with well-known dominance order

Work together to drive off predators (snakes)

Adult does really badly against a snake on its own but as a group they can mob it and shoo it off

costs of group living - predation

makes prey more conspicuous

Group living makes prey more conspicuous - e.g. fieldfare

colonial fieldfare nests suffered higher predation rates than solitary nests

But, solitary nests never actually fledged any young, due to parental co-defense (mobbing predators)

group living - food benefits

facilitates information spread about food locality and safety

more time to feed because others take turns watching for predators

improved changes of catching difficult prey

information center hypothesis

parasitize (not cooperate) information about food location, patch quality; reduce cost of search, travel and sampling

When is information center hypothesis most effective?

when food sources are temporary/ephemeral

e.g. quelea quelea - group living and finding feeding sites -

mutual parasitism

group A learns where god food is, group B learns where poor food is (different place)

All of group B follows group A, none of group A ever followed group B

costs of group living - feeding

competition for food

interference influencing prey capture rates

e.g. group size and feeding in lions

single lionesses have much higher food intake per day compared to groups of 2-4 which really struggle, especially in prey scarcity

it takes 5+ lionesses to reap benefits of group hunting

but this doesn’t consider that time cost for smaller groups/ individual lionesses

feeding interference - e.g. redshanks

forage alone during the day using visual search, because feeding rates are negatively affected by density, as shrimp hide

but at night, they cluster in groups and feed by sweeping beaks across the sand - no effect of density so they flock to reduce predation

Costs of group living - reproduction

cuckoldry increases with larger and denser groups (e.g. egg dumping)

cannibalism and reproductive interference (egg destruction and cannibalism of chicks by neighbouring pairs)

increased disease

benefits of reproducing in a social group

extrapair copulation, cuckoldry

interference with competitors

e.g. colonial cliff swallows - disease

benefit from higher food delivery rates (leran about ephemeral food sources)

BUT ecoparasitism, with large groups of colonial cliff swallows had nestlings with more bugs, lower body weight and reduced survival. Fumigated nests had chicks that grew better

Hydrodynamic advantage

animals may save energy by taking adavantage of vortices creaed by other group members

not a ton of lab evidence but observed in nature

Thermoregulation advantage

roosting together allows warm-blooded animals to save energy by collectively keeping warm

e.g. brown fur seal

mothers leave for up to a week at a time while pups nurse but are able to find her own when she returns using calls

66% of pups-moms reunite after 7 mins, remaining with 11 minutes

calls are very distinctive/varied

pups respond faster and most strongly to their own mothers call

e.g. free-tailed bat - discriminating parental care

mothers can find pup among 4000/m² using smells and audtiory signals

this was confimed by enzyme data to be 80% accurate, and DNA to be 90%

e.g. free-tailed bat - What was Davis’ original conclusion and why is it wrong?

Originally demonstrated a pup would latch to any mother, decided that all females were “an anonymous dairy herd”

but mother bats incur costs (depletion and predation risk)

When should we expect that cognitive and/or physiological mechanisms will evolve for recognizing your own offspring and favouring them over alien young?

when there’s a natural risk of making an error. That is, if and only if parents are exposed to situations in which they might misdirect parental investment to benefits of rivals’ fitness

discriminative parental care - cliff swallows vs barn swallows

cliff swallows nest colonially so young move between nests more —> parents recognize chicks by voice and face

barn swallows nests are dispersed so no need for parental recognition - they will accept fostering

cliff swallows chicks’ voices are more distinctive (highly strucutred, more complex) than barn swallows

Adult cliff swallows are faster and more accurate at learning to discriminate the voices of chicks

e.g. sheep and kin recognition

immediately at birth, the ewe learns her lambs’s odour and rejects others

how does a ewe learn her lamb’s odour?

olfactory bulb is reprogrammed during birth by oxytocin, mitral cells wtich to respond only to lambs, 70% to any lamb, 30% only her own

What sorts of discriminations would we expect evolved parents to make wrt how to best allocate parental resource?

1) phenotypic quality: how able is this offspring to cnovert parental investment into increaments in paretnal fitness?

2) quantity and need: how much difference will this investment make?

3) identity: is this infant really mine? - most important

humans - parentage matters

human parents spend more money on genetic children and least on their step-children. Having a step-parent is the most powerful epidemiological risk factor for child abuse.

humans - offspring quality matters

parents will sometimes abandon or even kill their own offspring. The frequency of infanticide increases if the offspring is seriously ill, has major birth defects, severe physical deformities and hence poor probable future fitness

Direct descendents

offspring and grandoffspring; contribute to direct fitness

non-descendant kin

brothers, sisters, aunts, uncles, nephews, nieces - contribute to indirect fitness

Inclusive fitness (eq)

direct fitness + indirect fitness

Coefficient of relatedness (“r”)

% of genes that two individuals share by common descent

Coefficient of relatedness (equation)

sum (0.5)^L

L = number of generation links and

sum = all possible pathways

Hamilton’s Rule

Makes sense to help any kind of kin as long as… (r x b) – c > 0 (aka altruistic acts will spread)

Benefits of an alarm call?

Gives relatives time to escape, diverts attention away from a nest, tells predators they’ve been spotted, group might mob/be chaotic in a way that makes it harder for the predator to attack

Costs of alarm call

Callers are most likely to be attacked by the predator perhaps because the call makes them more conspicuous, wastes time you could be using to escape

E.g. beldings ground squirrel

females stay at natal burrows, males disperes

adult females called more often than expected by chance and males way less

individuals help relatives more than non relatives

Kin recognition

the ability to identify/discriminate relatives and determine genetic relatedness

Kin selection

evolutionary strategy that favours the reproductive success of a relative at a cost to one’s own life, energy, fitness, reproduction

Kin recognition systems

production of kin phenotypic cues —> perception of cue and comparison to individual/template —> action

e.g. beldings ground squirrels sensory and perceptual mechanisms

odours from the oral and dorsal glands

ground squirrels explored odours of non-kin longer and could even make accurate discriminations among never before encountered (‘unfamiliar’) kin

Sweaty t-shrit study

Women most attracted to the smell of shirts worn by men with most dissimilar MHC genes from their own

Mechanisms of kin recognition

indirect: location and association/familiarity

direct: phenotype matching, self-referent phenotype matching

kin recognition - location

treat any individual in my nest or burrow as kin. Makes sense if location predictably contains kin (i.e. your house only contains relatives, not a lot of movement between nests)

kin recognition - association/familiarity

treat any individual with which you are associate or familiar with as kin. Most animals raised in family groups, so the phenotypes of nestmates and parents are reliable cues of kin recognition

kin recognition - phenotype matching

individuals inspect and learn certain characteristic (phenotypes) of their relatives and use these characteristic as a recognition guide when encountering unknown individuals

kin recognition - self-referent phenotype matching

armpit effect

learn your own phenotype and later compare or match unknown phenotypes with this learned template (When you don’t have the ability to learn from your relatives; your parents/siblings aren’t around to give you an idea )

Traits that cuckoos look for…

species with insect eating young, open nests, slower development that their own

Brood parasite adaptations

choose nest carefully (right species, right diet, right time)

remove egg when they lay theirs

mimetic eggs

short incubation time and fast chick growth rates

counter adaptations of hosts

choose nest sites that are hard to parasititze, group defense

morning inbuation

mottled eggs (recognizable)

ejection (puncture or push imposter)

brood desertion

Cuckoo egg discrimination in common hosts, suitable hosts and unsuitable hosts

common hosts: all discriminates against a model egg that did not match their own

suitable hosts: as much rejection or mroe

unsuitable species did not discriminate unlike eggs

Bill size and rejection costs

Species with smaller bills suffer greater rejection costs (damage to their own eggs) and were more likely to reject model egg by desertion than species with larger bills which tended to reject by ejection (They kept accidentally damaging their own egg)

mechanisms of host rejection of parasite egg

Desertion: required time and energy to start a new clutch - find new nest site, build new nest, lay new clutch

Egg ejection: may not be physically possible, may lead to damage of own eggs or mistakenly removing/rejection ones own eggs

If hosts can discriminate eggs why don’t they reject cuckoo chicks?

Costs of recognition errors (mis-imprinting costs or accidentally learning that the parasite nestling is the parents own young can exceed the benefits of correct learning)

Safer to raise any chick in their nest

Costs of mistakenly rejecting are worse than costs of raising a cuckoo

e.g. American cootes - conspecific brood parasitism

Parasitic chicks suffer higher mortality than host chicks

mothers learn based off which 3 were first hatched / received on first day

because first 3 chicks are almost always their own (need to lay before getting parasitized)

Obligate brood parasite

like cuckoos, cannot raise their own young, always raised by birds of another species

e.g. cowbird brood parasitism

cowbird hicks have redder mouths than their hosts - signal need to parents and manipulate being fed more

cuckoo acoustic mimicry

cuckoo’s chick begging call matches four reed warbler

Cuckoo and reedwarbler brood sounds had very similar feedign rates, much more than control

e.g.catfish - brood parasitism

catfish lays eggs with host cichlids, so she mouth broods them and then the catfish emerges first and eats the other eggs

Why does natural selection favour defector/

Defectors have a higher fitness because it saves its resources for itself, so abundance of cooperators reduced to extinction over time

Examples of cooperation

defence, hunting, courtship, harvesting, care of young

4 types of social interactions

mutualism, selfishness, altruism and spite

How does cooperation evolve? 3

mutualism, kin selection, direct benefits

cooperation - mutualism

immediate direct fitness returns for all parties; net gain despite costs

e.g. indigo buntings

dominant (bluer) males don’t tolerate other dominants or intermediates but they do allow subordinate males on their territory

Subordinates gain mating access

dominants benefit by mating with same females the subordinates do, so the subordinates raise some of his chicks

subordinate and dominant get more mate pairs than intermediates

cooperation - via kin selection

if cooperators are related (rb>c or r>c/b) aka natural selection can favor cooperation if donor and recipient are relatives

r must exceed c/b ratio

e.g. black-tailed prairie dog

% of alarm calls with offspring is very close that that of non-descendant relatives, in both males and females

when no close genetic relatives, females call more than males, but both less than other conditions

complex social relationships, maybe dissuading predators

difference between beldings ground squirrel study and prairie dog study

Squirrel work focuses on direct descendants and self-preservation, whereas Praririe dog research highlights a broader kin network and non-direct descendants

meerkats -direct benefits of cooperation

one stands guard as others forage

Although sentinel is more conspicuous, not one was ever eaten or taken - guarders were closer to shelter compared to foragers, first into bolt hold after makting a call

Direct benefits of cooperation

reciprocity

increased survival (pat to stay, group augmentation)

increased reproduction (extraparental experience, social prestige, territory/mate inheritance)

Reciprocity / reciprocal altruism

if there’s not time delay, its mutualism, but if there is a delay, its much easier to cheat

defecting can spread easily, so conditions to prevent it

Conditions for direct reciprocity

1. Repeated encounters between the same two individuals

2. Both individuals must be able to help

3. Help must be less costly for donor than it is beneficial

e.g. vampire bats - direct reciprocity

food sharing is based on past social experience, not as much on kinship

all 3 conditions met - repeated interactions, role exchange, recognize cheaters, benefit greater than cost

Increased survival - cooperation pay-to-stay

help in order to be tolerated; punished or kicked out if cheating

e.g. superb fairy wren - pay to stay

helpers artificially removed, aggression upon return increased with nesting stage

non—breeding passively accepted, fertilization and incubation fairly aggressive

nestling dependent and needs feeding - high aggression as punishment for not helping

e.g. seychelles warbler - Increased reproduction - extraparental experience

Birds with either helping experience of past breeding experience had similarly low time to fledge

Inexperienced birds kept making bad nests, remaking them, nests fell out of trees = took them so long to get young to fledge

e.g. pied kingfish - increased reproduction - opportunities to inherit and mate

primary male helps much more, benefits from his siblings success but incur higher survival costs

secondary males don’t do much so lower costs; and then often inherit females that they had helped