BIO 188 Evolution-CH12 Kin Selection and Social Behavior slides

natural selection that favors the spread of alleles that increase reproduction by related individuals.

kin selection

Behavior that is beneficial to the actor, and costly to the recipient.

selfish behavior

Behavior that is costly to both actor and recipient.

spiteful behavior

Hamilton's rule formula = Br > C "I would give my life for two brothers or 8 cousins"-- JBS Haldane

-B: benefit to recipient -r: relatedness (0-1) -C: cost to actor Simplest case, identical twins (r=1) then, B>C

Kin selection...

-favoring an increases in fitness of relatives. Personally costly behavior can evolve if the benefit to kin is sufficiently high.

Parent-offspring conflict (Trivers, 74) Relatedness and competition often positively correlate. Weaning conflict •Parents want to maximize their lifetime F1 output. Imagine they have one F1 at a time, feed it only until it is time to have a 2nd offspring. •Parents are equally related to all F1, therefore... •B>C... • B/C > 1... As the F1 ages, this reverses. When B (current F1) / C (of future F1) = " " <

...ignore r. ...Benefit to current offspring > Cost (loss of future offspring) ...If B to the current F1 / C to the parent (delay of future offspring) >1, then continue feeding. When current F1 is young, it is cheap and very dependent therefore B/C is great. ...=1 the pay off to the parent is neutral. ...< 1, the current F1 should be weaned and a new •F1 created (from the parents perspective) but not from the current F1's perspective. •From the current F1's perspective: r = 1 to self, and ½ to full sibling. Therefore, conflict over when parent stops investing in one F1, in favor of another F1.

•Most alleles favored by kin selection rise to high frequency by... •Greenbeard alleles would rise to high frequency by...

...inducing altruism toward individuals likely to be carrying copies of the same allele. ...inducing altruism toward individuals certain to be carrying copies of the same allele.

Inclusive fitness...

1. Direct fitness: one's own RS 2. Indirect fitness: RS of related individuals prediction: altruism should be proportional to relatedness

Which of the following statements describe a "greenbeard" allele?

A theoretical evolutionary mechanism proposed by Richard Dawkins that may occur in slime molds. An allele that causes development of a trait, recognition of the trait in others, and altruistic behavior toward others that carry the trait. A theoretical evolutionary mechanism that could drive an allele for altruism to high frequency without the involvement of organism-level kin selection or reciprocal altruism. Richard Dawkins proposed this concept long before the Dictyostelium slime mold example was discovered. The "greenbeard" name comes not from the slime molds, but from Dawkins' original, hypothetical, example of an allele that causes the growth of green beards in men.

Calculation (r) probability of identity by descent with grandparent to grandchild, aunt/uncle to niece/nephew.

Each • ½ x ½ = 1/4 = r

Now consider weaning conflict in more mathematical terms. Choose the correct ratio in the following description of weaning conflict: When B and C are calculated from the mother's perspective, weaning conflict for families of full siblings should begin when B/C ratio is [1/4, 1/2, 1, 2, 4] and end when B/C ratio is [1/4, 1/2, 1, 2, 4]. Weaning conflict for families of half siblings should begin when B/C ratio is [1/4, 1/2, 1, 2, 4] and should end when B/C ratio is [1/4, 1/2, 1, 2, 4].

Full siblings: Start at 1, end at 1/2. Half siblings: Start at 1, end at 1/4. Note that mothers always initiate the period of weaning conflict when B/C (from their perspective) is 1; that is, benefit and cost are equal.

Choose the correct ratio in the following description of weaning conflict: When B and C are calculated from the offspring's perspective, weaning conflict for families of full siblings should begin when B/C ratio is [1/4, 1/2, 1, 2, 4] and end when B/C ratio is [1/4, 1/2, 1, 2, 4]. Weaning conflict for families of half siblings should begin when B/C ratio is [1/4, 1/2, 1, 2, 4] and should end when B/C ratio is [1/4, 1/2, 1, 2, 4].

Full siblings: Start at 2, end at 1. Half siblings: Start at 4, end at 1. Note that offspring should finally accept the end of weaning when B/C (from their perspective) is 1; that is, benefit and cost are equal.

What is Hamilton's rule? What are its three mathematical terms, and how are they calculated?

Hamilton's rule states that an allele for altruistic behavior should spread if Br - C > 0. B is the benefit to the recipient, and C is the cost to the actor, both measured as number of surviving offspring. r is the coefficient of relatedness; it is the probability that two homologous alleles in actor and recipient are identical by descent. (Equivalently, it is also the percentage of the genome that the actor and recipient are likely to share.) r is calculated by tracing each possible pathway of relatedness between two individuals; every step between parent and offspring represents a 0.5 probability of any allele being shared. The probability for a whole path is (0.5)<n where n is the number of steps. Finally, the probabilities for each separate path are summed. (See pp. 2-4 for a review of this topic.)

Test Experiment: 1. Captive bats 2. Withheld food from different individual each night 3. Observe who is more likely to feed whom

If reciprocal altruism, then individuals should preferentially feed those they are likely to see in the future (who can return the favor). Predictions: 1. non-random association (in wild) Association = (times seen together) / (times seen total) There is substantial variation in association 2. Preferential feeding of associates

What is the evidence that whistling is selfish and trilling is altruistic in Belding's ground squirrels? Was similar evidence presented for the black-tailed prairie dogs? What patterns in the data from the black-tailed prairie dogs suggest that alarm-calling is altruistic in that species too? How could you verify whether alarm-calling truly is altruistic in the black-tailed prairie dogs?

In Belding's ground squirrels, observations of actual attacks by predators documented that trilling doubles the squirrel's risk of being killed by the predator, while whistling decreases the squirrel's risk. Therefore trilling is definitely altruistic, and whistling is not, in this species. (It is important to note that not all alarm-calling behavior is automatically altruistic.) Similar data was not presented for black-tailed prairie dogs, and thus we cannot say for sure that this behavior is altruistic in this species. However,the patterns of the data shown in Figures 12.2 and 12.3 show that squirrels are more likely to alarm-call when they have kin nearby. This strongly suggests (but does not prove) that alarm-calling is altruistic.

Menopause is an unusual feature seen in humans and some whales that have matrilineal social systems (family groups led by older females), such as pilot whales and orcas. Menopause involves a complete and sudden cessation of reproduction function relatively early in a healthy female's life. In humans and in these whales, females completely cease reproduction about one-half to two-thirds of the way through their life spans, but continue to assist siblings, offspring, and grand-offspring for the rest of their lives. (In most other animals, females continue to reproduce as long as they are alive.) Part I: Refer to the information above regarding menopause to answer these questions. What must B and C be for an older female to cease reproduction and instead care for her grand-offspring? Part II: Refer to the information above regarding menopause to answer this question. Can menopause in these two species be considered a form of eusociality - i.e. can the older females be considered a caste of nonreproductive workers? Part III: Refer to the information above regarding menopause to answer this question. What traits of a species might favor evolution of menopause?

Part I: Females are related to grandoffspring by r = 1/4 and to offspring by r= 1/2. For menopause to evolve, the benefit in helping grandoffspring must be twice as high as the cost in foregoing the chance to produce more offspring. This can occur if (1) an older female's chances of raising offspring to independence are fairly low, and (2) the female can offer valuable care to her grand-offspring that substantially increases their chances of survival. If menopause evolves, the age at which it should occur is: average female lifepsan minus the average age for young to attain independence. Part II: Many answers are possible. Both species do have the other two requirements for eusociality - shared care of young, and overlapping generations. Menopause has not traditionally been considered as eusociality. However, evolutionary biologists differ about whether the sterile caste must be sterile for their whole lives. Some consider that being reproductively sterile for part of ones' life is good enough to be called eusociality, and that humans should be included in the list of eusocial vertebrates. Part III: Many answers are possible. Evolution may favor evolution of menopause in other long-lived species in which (a) the young have an extremely long period of care, and (b) older individuals can make a large difference in survival of younger kin, which seems to be the case in certain intelligent species with complex social systems. Other species with some of these traits include African elephants and certain desert antelopes in which only the older individuals know the locations of very distant food and water sources.

Should sibling rivalry be more or less common in species that are monogamous or polygamous? Why?

Sibling rivalry should, in theory, be more common in species that are polygamous, since most litter-mates or nest-mates will be only half-siblings instead of full siblings.

Calculation (r) probability of identity by descent with full siblings.

Same as before s(hares ½ of genes w/ parent) except genes are also shared through 2 parents, so • ½ x ½ x 2 = 1/2 = r Father ½⇠Actor ⇢½ Mother ↳½ Recipient ½↵

Calculation (r) probability of identity by descent with half siblings.

Shares ½ of genes w/ parent • Parent gives ½ of genes to other F1 • ½ x ½ = 1/4 = r Actor ½➤Shared Parent➤Recipient ½

Summarize the logic behind the haplodiploidy hypothesis of eusociality. What is the evidence in favor of and against this hypothesis? Describe two other hypotheses for the evolution of eusociality.

The haplodiploidy hypothesis is based on the proposition that females are more closely related to sisters than to their own potential offspring. In this case, natural selection should favor the evolution of sterile female workers who raise sisters rather than raising their own young. In favor of this hypothesis, eusociality is particularly common in haplodiploid taxa, and female workers do manipulate colonies toward a female-biased sex ratio. However, not all haplodiploid species are eusocial, and many eusocial species are not haplodiploid. The major evidence against the hypothesis, however, is experimental evidence that relatedness among females is actually much lower than the hypothesis assumes. Because most colonies have multiple fathers and often multiple queens, most worker females are not more closely related to sisters than to their own offspring. Two alternative hypotheses are (1) eusociality may represent the best option for females in taxa that build complex nests and in which young require extended care. If solitary females have very little chance of establishing a viable nest on their own, raising siblings is probably the next best option. (2) Eusociality may evolve in taxa that live in extremely inbred colonies, such as naked mole-rats. (Note that this is similar to the haplodiploid hypothesis in its essential logic, i.e., r among colony members is proposed to be very high.)

Coefficient of relatedness, r...

The probability that homologous alleles are identical by descent.

Heinsohn and Packer found that territory defense in female African lions defied the simple predictions of both reciprocity and kin selection theory based on which of the following?

The willingness of pride females to assist the "leader" in pride defense was independent of the degree of relatedness to other pride members. Some females always led and some always lagged in defense. Although the behavior of leading females suggested that they recognized the laggards, they did nothing to threaten laggards or to withhold benefits.

List the three features of true eusociality. Name two types of insects, and two types of non-insects, that have true eusociality.

True eusociality includes: (1) overlap in generations between parents and offspring, (2) cooperative care of offspring, and (3) specialized castes of nonreproductive individuals. Eusociality is found the Hymenoptera (bees, ants, etc.), termites, and a few other orders such as plant bugs and one family of beetles. It also occurs in at least two non-insects: snapping shrimp and naked mole-rats.

Reciprocal altruism (among unrelated individuals) (Trivers '71). Sequential cooperation is...

altruism now for altruism returned later. 1. B-C (benefit to recipient - cost to actor) 2. Cheaters must be punished These conditions tend to be met to the extent that- a. individuals interact b. opportunities for altruism are frequent in both directions (similar social position, paupers cannot help kings) 3. score can be kept (memory) Probably frequent in primate and some other vertebrate societies

Behavior that is costly to the actor, and beneficial to the recipient.

altruistic behavior

Hamilton's rule:

an allele for altruistic behavior will spread when the benefit to recipient is greater than the cost to the actor, after devaluing the benefit by the degree of relatedness.

Behavior that is beneficial to both actor and recipient.

cooperative behavior

fitness resulting from personal reproduction.

direct fitness

a social system involving overlap in generations, cooperative care of young, and nonreproductive individuals.

eusociality

a theoretical model of a type of allele for altruistic behavior that could spread through a population via recognition of similar traits, without the involvement of kin selection or reciprocal altruism.

greenbeard effect

total reproductive success of an individual, including reproduction by the individual and also reproduction by related kin.

inclusive fitness

fitness resulting from reproduction of kin.

indirect fitness

Which of the following correctly complete the statement, "Reciprocal altruism directed toward non-kin may evolve when _______________"?

individuals can recognize and remember other individuals

Prairie dogs are more likely to give alarm calls when...

relatives are nearby.

Female red squirrels adopt related kittens when the ...

result is a net gain in the mother's inclusive fitness.

Blood sharing in vamp bats • Hypothesis: Is this altruism kin-based, reciprocal, or neither?

• Live in groups of mothers and dependent offspring ~ 200 individuals per roost • Feed on horse and cattle at night • 33% of young and 7% of adults fail to find food each night • 3 consecutive failures = starvation • Individuals often regurgitate a meal to another • If kin selection, then feeding should positively correlate with relatedness

Kin selection - empirical evidence. Frequency of assistance in chasing trespassers in Belding's ground squirrels.

• Males disperse • Therefore, females within a group are more closely related than males

Cannibalistic tiger salamander tadpoles (same life-history characteristics) • br>c; is the benefit to the kin of not being eaten, devalued by relatedness, greater than the cost to the cannibal of missing a meal? • What are the values of b and c?

• Some cannibals avoid eating kin (discriminators) and some don't • Placed 18 cannibal tadpoles, in separate cages in artificial lakes, each with 24 non cannibal tadpoles: 6 siblings and 18 non kin. • cannibals sibs that survived,b= 4-2=2 c=0 c=0 br>C; 2(0.5)>0; 1>0, true, therefore altruistic behavior should be selected

Levels of selection: Group Selection Group selection: hypothesis that... • Quantitative situation • Groups tend to go extinct...

• adaptations may reduce the fitness of the actor, but increase the fitness of the group. • less often than individuals favoring individual interests more than groups. •This doesn't mean that selfish behavior is always beneficial to individuals. •If a selfish behavior drives a group to extinction then individuals may respond with adaptations to protect the group (e.g., punishment of selfishness, rewards for altruism, etc.)

Calculation (r) probability of identity by descent with cousins.

• ½ x ½ x ½ = 1/8 = r

Levels of selection: C-value paradox • Size of genome doesn't correlate strongly with organismal complexity among multi cellular organisms. Only 2% of human DNA is protein coding; most of the rest is dead or parasitic

•Transposable elements (transposons, retro elements, etc.) may explain much of the paradox •Sequences that can make copies of themselves that insert elsewhere in genome. Insertion constitutes a mutation and is often deleterious. Transposase protein causes transposition •6% of human genome is Alu sequence (300bp, codes for nothing) Parasitic DNA analogous to functionless mitochondria except selection is very weak. Replication speed is of the essence in microbes, but not mammals

The four basic kinds of social interaction...

☀Mutually beneficial where both the actor and the recipient benefit. ☀Selfish where the actor benefits at the expense of the recipient. ☀Altruistic where the actor make a sacrifice on behalf of the recipient. ☀Spiteful where the actor suffers a loss in order to impose a penalty on the recipient.