Evo Bio Ch. 12: Evolution of behavior

Fill in the blanks: "I would lay down my life for the sake of ..... brothers or ..... cousins"

"I would lay down my life for the sake of two brothers or eight cousins"

4 types of social interactions

1. Cooperation (or mutual benefit) 2. Altruism 3. Selfishness 4. Spite

2 conditions for reciprocal altruism to evolve

1. Cost to actor must be smaller than or equal to benefit to recipient 2. Individuals that fail to reciprocate must be punished

What are the 4 evolutionary explanations for how an allele that codes for altruism survive in the face of natural selection?

1. Kin selection 2. Reciprocity 3. Mutualism 4. Manipulation

What are 2 benefits that cannibalism provides?

1. Nutrition 2. Reduction of future competition

According to kin selection, when will altruism spread?

1. When benefits to recipient are great 2. When cost to actor is small 3. When participants are closely related

Simpson's Paradox

If cooperators provide sufficient benefit to their social groups, cooperation may increase in frequency in the population at large, even if it decreases in frequency within groups

Direct fitness

results from personal reproduction

Indirect fitness

results from reproduction by relatives (when genetic relatives reproduce more than they would have without aid by the actor)

How related are full siblings?

1/2

How related are parents to offspring?

1/2

How related are aunts/uncles to nieces/nephews?

1/4

How related are grandparents to grandchildren?

1/4

How related are half siblings?

1/4

How related are cousins?

1/8

How related are great-grandparents to great-grandchildren?

1/8

Evolutionary Stable Strategy

A strategy which, if most members of a population adopt it, cannot be bettered by an alternative strategy

Eusocial

Adjective to describe animals that (1) overlap in generations, (2) have nonreproductive individuals, and (3) cooperatively care for young.

What did Darwin mention was a "special difficulty" for his theory?

Altruism

Hamilton's Rule

Altruistic behavior will spread if Br - C > 0 B= benefit to recipient C= cost to actor

Weaning conflict

At the start of nursing, the benefit to offspring outweighs the cost to the parent. With time, that ratio declines: young demand more milk, increasing parental cost, and young can start finding their own food, decreasing their benefit. Mothes should stop producing milk when the ratio reaches 1. Offspring continue to try to nurse until benefit-cost ratio is 1/2. If half-siblings are produces then the ratio extends to 1/4.

Cooperation (or mutual benefit)

Both the actor and recipient enjoy fitness gains

Selfishness in cane toads

Cane toad tadpoles routinely eat cane toad eggs. The tadpoles are attracted to chemicals released by the eggs, called bufogenins, used to deter other predators. Reduction in population density that results from cannibalism enables tadpoles to grow faster, metamorphose more quickly, and survive at higher rates.

Cooperative breeding is a form of kin selection in birds

Cooperative breeding evolves most readily in bird lineages in which potential helpers and beneficiaries tend to be more closely related to each other and there is low female promiscuity. Promiscuity increases non-cooperative behavior because you don't know who the father is so you don't know who you're related to

Kin Selection in red squirrels

Female red squirrels defend a feeding territory that, except when mothers are caring for kittens, it occupies alone. In a study observing mothers and their litters, 34 out of 2230 litters were orphaned during lactation, from which a kitten could have been adopted and nursed to weaning by one or more lactating females nearby. 7 litters had had a genetic relative available to be the adoptive mother, 5 were actually adopted by a genetic relative, and the other 27 had no available adoptive relatives and were not adopted. The size of a litter affects the probability that any kitten will survive. When a mother adds a kitten, it reduces the chance that each of her existing offspring will survive. The probability that an adoptive kitten survives is a function of litter size and genetic relatedness. Females will adopt related kittens when the result is a net gain in the mother's inclusive fitness. (Benefit>Cost)

In Belding's ground squirrels, are males or females more likely to give alarm calls?

Females are more likely to give alarm calls. Mothers, daughter, and sister are more likely to assist each other chasing off trespassers compared to unrelated individuals. The closer in relativity, the more likely they are to help each other.

The greenbeard effect

Genetic explanation for kin selection recognized by Richard Dawkins that states, "If there is an allele that simultaneously causes its carriers to grow green beards, recognize green beards on others, and behave altruistically towards them, it will be favored by natural selection"

Cooperation in greater anis

Genetically unrelated couples nest together, typically in groups of 2 or 3 pairs. Before each female lays her first egg, she tosses out any eggs already laid by coalition partners.The first female to lay in a group nest therefore always loses at least one egg. Nonetheless, all females have higher reproductive success in large groups because more parents using the nest means better protection for the nest.

Altruistic behavior can be tricky to identify, as shown by Belding's ground squirrels

Give two kind of alarms when predators approach: trill in response to mammals approaching on foot and whistle in response to hawks attacking on the wing. When squirrels spot an attacking hawk and whistle, the whistling squirrel is captured only 2% of the time while nonwhistling squirrels are captured 28% of the time. The squirrel raising the alarm reduces its own chances of capture by calling -- a SELFISH act. When squirrels spot a stalking mammal and trill, however, the trilling squirrel is killed 8% of the time while non-trilling squirrels are killed just 4% of the time. The squirrel raising the alarm increases its own peril to the benefit of other squirrels nearby -- an ALTRUISTIC act.

Why is spite rare in nature, according to W. Hamilton?

If a spiteful actor removes a negatively-related recipient, all the remaining individuals benefit, not just the actor's kin, thus selection for spite is weak.

Ecology and life-history hypothesis

If life history or ecology make it easier to be a helper than reproduce, then eusociality is favored. Nest building and the need to supply larvae with a continuous supply of food make it difficult for a female to breed on her own. Also, when predation rates are high but young are dependent on parental care for a long period, then individuals who breed alone are unlikely to survive long enough to bring their young to adulthood.

Siblicide

In certain bird species, it is common for young siblings to kill each other while parents look on passively, even though they are related by r=1/2. Females normally lay a two-egg clutch with one chick hatching 2-10 days before the other. Masked boobies push 2nd egg from nest immediately. In blue-footed boobies, the older chick will eat less during food shortages to provide extra for their sibling. But if famine continues, the older chick attacks and kills the younger one. Blue-footed booby parents intervene but masked do not.

Hymenopterans (ants, bees, wasps) exhibit the most extreme form of eusocialty

In these animals, there are millions of individuals per colony yet very few reproduce. Because of haplodiploidy, sisters share 75% of genes while parents and offspring share 50%. Works invest in sisters over brothers 3:1. Queens are equally related to sons and daughters and favor them 1:1, lays equal numbers of male and female eggs. Workers selectively killed male eggs prior to hatching, winning the sex ratio battle.

Why would females join a coalition and help rear offspring that are not theirs?

Indirect fitness gains because usually related to foundress. Direct fitness gains if foundress dies and a subordinate inherits the nest.

Will people leave a greater share of their wealth to their spouse or to kin?

Kin

Eusociality in naked mole rats

Live underground in huge nests in Africa with colonies of 70-80 members. They are hairless, ectothermic, and digest cellulose. There is a single queen, 2-3 reproductive males, and male and female workers. Workers first tend to their young, later they excavate tunnels, and the oldest defend the nest. They are not haplodiploid but they are highly inbred, with the highest coefficient of relatedness to ever exist for siblings at r=0.81. The queen shoves slow workers with her head to increase their work pace but more often directs her shoves towards more distant relatives.

Haplodiploidy

Males (haploids) grow from unfertilized eggs Females (diploids) grow from fertilized eggs

What are the most common social interactions?

Mutual benefit and selfishness

Are all eusocial species haplodiploid?

No

Does true altruism really exist in nature?

No

Kin selection

Occurs when natural selection favors the spread of alleles that increase indirect fitness; Explains many cases of apparent altrusim

Will people leave a greater share of their wealth to offspring or siblings?

Offspring, because most people are about the same age as their siblings, money left to offspring is more likely to encourage the production of another grandchild than money left to a sibling is to encourage the production of another niece or nephew.

Coefficient of relationship, r

Probability that a particular allele in 2 individuals is identical by descent

How do animals know their relatedness/cost vs. benefit?

We don't know! We hypothesize that they can tell by how similar they are

Manipulation

Recipients trick donors into behaving altruistically

"Selfish gene" model

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

There's not many good examples of spite, but bacteriocins is one of them.

Some bacteria produce chemicals called bacteriocins that are lethal to other members of the same species. The makers are immune to their own poison but because they require energy and materials to make, strains that produce them grow more slowly than those that do not. In an experiment to investigate whether spiteful interactions among bacteria occur in nature, two soil samples were taken from an Illinois forest and were separated by a distance of just 4 meters. When in contact with strains from its own sample, no strain inhibited the growth of bacteria on the recipient strain. But all strains were deadly to bacteria from the other sample. That naturally occurring bacterium can make costly poisons that are deadly to members of the same species living just a few meters away suggests that wild bacteria indeed behave spitefully to each other.

What is the rarest social interaction?

Spite

Why would selection favor spite, according to E.O. Wilson?

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

Selfishness

The actor benefits at the expense of the recipient

Altruism

The actor makes a sacrifice on behalf of the recipient

Spite

The actor suffers a loss in order to impose a penalty on the recipient

Inclusive fitness

The sum of an individuals direct and indirect fitness

Mutualism

Two or more individuals gain a benefit, without the time lag between the exchange of benefits

Reciprocal altruism

Unrelated individuals will act altruistically if that favor is later returned

Evolutionary Game Theory

Used to analyze cooperation and conflict using a payoff system -- similar to economics

Slime mold example of the greenbeard effect

When free-living amoebae aggregate to make fruiting bodies, the cells that form the stalk sacrifice themselves on behalf of the cells that form spores. csA allele= protein that sits on surface of amoebae and is recognizable by adhesion. Experiments mixed csA wild-type cells and csA loss-of-function cells together. On agar plates, wild-type cells are more adhesive so they form the stalk and the others make the fruiting body so most spores are csA loss-of-function. In soil, wild-type cells could aggregate and form the fruiting body while loss-of-function cells were left behind. In agar, the wild-type cells were altruistic and in soil they were greenbeard altruists.

Blood-sharing in vampire bats

Without eating for 3 nights, a bat will starve to death. Depending on degree of relatedness, bats will regurgitate blood and share with others, in hopes of future reciprocity.

Facultative eusociality in Polistes paper wasps

Workers are not sterile. Each female reproduces on her own and pursues one of three strategies: (1) initiate their own nest, (2) join a nest as a helper, (3) wait for a breeding opportunity. Single foundress nests are less successful. Multifoundress nests are more likely to be rebuilt if destroyed and grow fastest if there is a large size difference of dominant female and subordinate helpers.

Harassment in White-fronted bee eaters

Young adults forgo breeding to help their parents raise their siblings. Fathers coerce sons into helping by harassing sons as they attempt to set up their own territories and prevent them from breeding. The coefficient of relatedness determines if they will help. Sons are equally related to their siblings and their own offspring. Parents are more closely related to their offspring than to their grandchildren. For helpers, your siblings are nearly the same as your own offspring, therefore it's worth it to avoid harassment from your father.

Cooperative breeding

Young that are old enough to breed on their own instead remain and help their parents rear their brothers, sisters, or half-siblings