Chapter 12: Evolutionary Biology

Altruism

Fitness gain for recipient and cost for the actor, behaviors that help others survive and have young at a cost to the helpers own chance in doing so

Cooperation (mutual benefit)

Fitness gains for both participants

Selfishness

Actor gains, Recipient loses (fitness)

Spite

Fitness loss for both participants

What is the Greater Ani?

A bird that nests communally in tropical America.

What do female Greater Anis do before laying their eggs?

They toss out any eggs already laid by coalition partners.

What happens to the first females that lay eggs in Greater Ani groups?

They lose their eggs to other females.

What is the reproductive success trend among female Greater Anis in large groups?

All females have higher reproductive success overall.

What does the behavior of Greater Anis exemplify?

Cooperation.

What do cane toad tadpoles eat?

Cane toad eggs

What is the effect of reduction in population density on cane toad tadpoles?

It results in faster growth.

What does the behavior of cane toad tadpoles eating their own eggs exemplify?

Selfishness because the tadpoles are eating the eggs to benefit themselves while causing the other toads a fitness cost by eating their eggs

What is a theoretical possibility according to W. Hamilton?

Spite is a theoretical possibility if the recipient is negatively related to the actor.

What happens if a spiteful actor removes a negatively related recipient?

All the remaining individuals benefit, not just the actor's kin.

Why is selection for spite considered weak according to W. Hamilton?

Because the removal of a negatively related recipient benefits all remaining individuals.

Why might spite be favored according to E.O wilson?

Spite could be favored without negative relatedness if the act also specifically benefits positively related individuals

What are Bacteriocins? (spite example)

Lethal chemicals produced by some bacteria, they are immune to makers but costly to produce

What happened in the soil bacteria study (spite)?

No strain inhibited growth of bacteria from the same sample locale, all strains were deadly to bacteria from other locales

What do Beldings Ground Squirrels do when predators approach?

They give alarm calls.

What type of call do Beldings Ground Squirrels use in response to mammals?

A trill.

What type of call do Beldings Ground Squirrels use in response to hawks?

A whistle.

How does raising the alarm affect a Beldings Ground Squirrel's chances of capture?

It reduces its own chances of capture.

What is safer for the caller squirrel, a trill or a whistle?

A whistle which signals for birds which may pose more of a threat to the squirrels than mammals

What concept is illustrated by the behavior of Beldings Ground Squirrels when they trill?

Altruism

What gender of ground squirrels are most likely to give alarm calls?

Females, mothers, daughters, and sisters were more likely to assist each other chasing off trespasser compare to unrelated individuals

How common is Altruism in nature?

Appears to be common in nature, Darwin mentioned that altruism was a "special difficulty for his theory"

What are some basic examples of altruism?

Macaws raise siblings instead of reproducing

Humans run into burning house to save a child

What are the evolutionary explanations for why altruism survives selection?

- Kin selection

- Reciprocity

- Mutualism

- Manipulation

What is William Hamiltons genetic model?

Shows how an allele for altruistic behavior could persist

What is the coefficient of relationship (r) ?

Probability that a particular allele in two individuals is identical by descent

Hamilton's Rule

Altruistic behavior will spread if..

Br - C > 0

B = benefit to recipient

C = cost to actor

What is the bottom line of altruism evolution?

Altruism will spread when benefits to recipient are great, cost to actor is small, and participants are closely related

What is direct fitness?

Fitness resulting from personal reproduction

What is indirect fitness?

Fitness resulting from reproductive increase due to help given by relatives

What is the equation for total fitness?

Total fitness = Direct + Indirect

When does indirect fitness accrue?

When genetic relatives reproduce more than they would have without aid by the actor

When does Kin selection occur?

when natural selection favors the spread of alleles that increase indirect fitness

What is kin selection?

The process by which evolution selects for individuals who cooperate with their relatives

What does kin selection explain?

Many cases of apparent altruism, true altruism doesn't exist in nature

How can you assess relatedness?

Perform a path analysis where...

parent offspring related to offspring (1/2)

Full siblings related 1/2

Half siblings related (1/4)

Cousins related 1/8

What do female red squirrels defend?

A feeding territory

What is the social structure of female red squirrels during lactation?

Solitary except for kittens (young)

What happens to many litters of red squirrels during lactation?

They are orphaned and adopted by genetic relatives

How does the size of litters affect kitten survival in red squirrels?

The size of litters affects kitten survival

What is the effect of adding a kitten to a litter of red squirrels?

It reduces the chance of existing offspring surviving

What is the probability of red squirrel kittens survival dependent on?

A function of litter size and genetic relatedness ( will genetic relative adopt kittens)

What is the trend with human wealth sharing?

People will leave a greater share of their wealth to kin

What is the greenbeard effect?

Genetic explanation for kin selection created by Richard Dawkins who said if there is an allele that simultaneously causes its carriers to grow green bears, to recognize green beards on others, and to behave altruistically towards them it will be favored by natural selection

What is the selfish gene model?

Selection occurs at the level of the gene mediated by the phenotype

What is the csA allele?

Protein that sits on the surface of amoebae and specifies the trait (protein) and ability to recognize the trait (adhesion)

Amoebae greenbeard alleles

Mixed wild type and knockout in agar ( wild type have csA and are altruistic) csA is a greenbeard allele

Why is parental care a special case of kin selection?

Even parents and offspring can have conflicts in costs and benefits

What is a weaning conflict in parental care?

Mothers begin to ignore or push young away near the end of weaning period, offspring will scream or attack mother, their fitness interests are not symmetrical

What is the coefficient of relatedness (r) for offspring to themselves?

r=1

What is the coefficient of relatedness (r) between parents and their offspring?

r=0.5

How are parents related to all their offspring?

Parents are equally related to all offspring.

What do offspring demand in terms of parental investment?

Offspring demand unequal amounts of parental investment.

Why do weaning conflicts occur?

At start of nursing benefit to offspring outweighs the cost to the parents, this ratio declines with time as young demand more milk which is costly for the parent, young can start finding their own food which decreases benefit, mothers should stop producing milk when benefit to cost ratio reaches 1

Weaning conflict stage and ratios

By continuing to nurse offspring devalue mothers cost of care, offspring should continue to try to nurse until benefit cost ratio is 1/2, period between 1/2 and 1 is weaning conflict where there will be aggressive if half siblings are involved then ratio should be extended to 1/4

Behavior in white fronted bee eater bird young adults

Young adults forgo breeding to help their parents raise their siblings, nest building, nest defense, food delivery and incubation

Why do young bee eater birds help parents?

Sons may either set up a territory or help at their parents nest, fathers coerce songs into helping by harassing songs as they attempt to set up territories and even prevent courtship feeding, harassment is preferentially directed at songs to prevent them from breeding and coerce them to help at the nest

How effective is father coercion in white bee eaters?

15 0f 47 harassment events resulted in successful recruitment to help

Why dont bee eater sons resist more effectively?

Sons are equally related to siblings and their own offspring, parents are more closely related to each of their offspring than to their grandchildren, helpers add 0.47 offspring to parental success which is nearly the same as own offspring so it isn't worth it to avoid fathers harassment

When is helping at the nest common?

Usually found in species where breeding opportunities are limited they are making the best of a bad situation

What is siblicide?

In birds and mammals it is common to kill siblings for the killing siblings benefit though this seems maladaptive because sibling r=12

Blue footed boobies siblicide

Birds that lay of two eggs and eggs are separated by 2-10 days, first chick often pushes the younger chick from the nest

What do older blue footed boobies do during food shortages?

during short food shortages siblings reduce food intake to share with siblings, during long food shortages they will kill their siblings

Study between Masked and Blue footed boobies

Chicks are more likely to die with masked booby nestmate parents do not intervene, blue footed boobies parents intervene, difference among species is not known

What did Robert Trivers propose?

That individuals will act altruistically if that favor is later returned

What two condition are needed for reciprocal altruism to evolve?

- Cost to actor must be smaller than or equal to benefit to recipient

- Individuals that fail to reciprocate must be punished

What factors make altruism more likely to evolve?

- Each individual repeatedly interacts with the same set of individuals

- Many opportunities for altruism occur in an individual's lifetime

- Individuals have good memories

- Potential altruists interact in symmetrical situations

- Roughly equal benefits and costs

When should altruism evolve?

Should evolve in long lived, intelligent social species with small group sizes, low dispersal rates, and mutual dependence activities

In what type of species is altruism less likely to evolve?

Species with dominance hierarchies

What is evolutionary game theory?

Used to analyze cooperation and conflict using a payoff system ( similar to economics) uses the concept of the evolutionarily stable strategy

What is the evolutionarily stable strategy?

A strategy which is most members of a population adopt it cannot be bettered by an alternate strategy

How does memory change the equation of evolutionary game theory?

Reciprocal Altruism

What is reciprocal altruism?

behavior that benefits another with the expectation that those benefits will be returned in the future

What is the typical social group size of female vampire bats?

8-12 females and their offspring

How often do vampire bats associate with each other daily?

They roost together and associate daily.

What was the average relatedness (r) between individuals in a study group of vampire bats in Costa Rica?

0.11

Why do vampire bats share blood meals?

Hunting is difficult and only successful 67-93% of the time.

Why is blood sharing important in vampire bats?

Without eating for three nights a bat will starve to death, both degree of relatedness and degree of association were significantly related to probability of regurgitating blood, blood sharing is not random and is based on relatedness and hope they will reciprocate in the future

What is manipulative altruism?

Altruism by donor may be manipulation by recipient, donors are tricked into behaving altruistically

What is mutualism?

2 or more individuals will each gain a net survival or reproductive benefit

How is mutualism different from reciprocity?

Different from reciprocity due to the lack of a time lag between the exchange of benefits, kin selection reciprocity and mutualism may be relevant

How does true sociality describe a social system?

- Overlap in generations

- Cooperative brood care

- Specialized castes of non reproductive individuals

What is eusociality?

One colony working towards the common goal of survival and reproduction

How do hymenopterans exhibit the most extreme form of eusociality?

Millions of individuals per colony but very few reproduce

Haplodiploidy

a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid

Why do hymenopterans use eusociality?

sisters share 75% genes and parent and offspring share 50%, females are better off rearing sisters than offspring

How was the haplodiploidy hypothesis tested?

Workers should favor 3:1 ssex reatio, queens are equally related to songs and daughters and should favor 1:1 rex ratio, their is a conflict of interest between queen and worker ants, workers selectively kill male eggs prior to hatching to win sex ratio battle

Findings of haplodiploidy study

In this case workers are not more closely related to sisters than offspring, if more than one queen founds nest some may not be related at all, many eusocial species are not haplodiploid

Best of a bad situation hypothesis

Building a complex nest and caring for many larvae would be impossible for a female to do herself, high predation rates and dependency of young, primary agent favoring eusociality is ecological

Polistes paper wasps

Wasps that are not completely eusocial the worker females may reproduce on their own to do so they either initiate their own nest, join a nest as a helper, or wait for a breeding opportunity

Why would females join a coalition to help care for offspring that aren't theirs? (paper wasps)

Indirect fitness gains since they are usually related to foundress, direct fitness gain if foundress dies and subordinate inherits the nest, costs and benefits depend on r coefficient and female body size

What do female paper wasps do if they do not help found a nest?

Wait and maybe be able to adopt an already constructed nest, they leave their nests in spring and enter dormant state until following season to try to take over a new nest

What is facultative sociality?

a species where individuals can choose to live in groups or independently, depending on the environment and resource availability

Where do naked mole rats live?

Underground in huge nests in Africa

How many members typically live in a naked mole rat colony?

70-80 members

What is a notable physical characteristic of naked mole rats?

They are hairless