1. Reading: Chapter 12 pg. For all laboratory sections: Remember to complete problem set 1 (problems 1-15) for laboratory next week. Problems can be found on the last pages of the supplement. You should read the laboratory on demography (pg. 36 of the supplement) and, if possible, begin gathering data in your working groups from one or more cemetaries.

2. Why do most species live in groups? There are many reasons for species tending to occur in groups: increased chance of surviving - e.g. probability of being predated lower on average, most predation occurs on animals at the periphery of the group increased chance of finding a mate - higher density in groups than if scattered increased chance of finding food and feeding - some keep watch while others feed, jobs exchanged over time, everyone gets more time to feed There are costs, as well as benefits...

3. When each individual has to defend itself, it has to look around for predators frequently. When group defense occurs, each individual has to check much less frequently, even though the group as a whole has increased its defense. Therefore, each can spend more time feeding. Even with the limited range of flock sizes examined here, increased numbers mean more effort and time to find food resources.

4. This is one form of altruism that is seemingly easy to understand… It is called reciprocal altruism. In an unrelated group of birds, e.g. crows or the graphical example shown... One bird acts as a sentinel for the group. The remainder forage. There might be a small chance that a predator would find and attack the sentinel, since it ‘crows’ to warn others. The reciprocal benefit gained is the long stretches of time when this crow can feed while others act as sentinels.

5. Meerkats and the effect of groups on foraging and group defense

6. The advantage, measured by the presence of at least one sentinel first increases when flock size is small… but decreases again when flock size is large. The cause: rapid decrease in local food supply means more time the group spends searching for and moving between patches of food.

7. Effect on donor fitness --+ Effect on-- spitefulness selfishness recipient fitness+ altruism cooperation There are numerous observations of cooperation, both within related groups and among unrelated individuals. That’s logical from an evolutionary (fitness) perspective. There are no observations of spitefulness that I know of. That, too, is logical. So is selfishness. We can make a 2 x 2 table of the possible interactions of individuals in a group, measured by the effects of the interaction on the fitness of participants…

8. Altruism is a more difficult question. To understand altruism that is not reciprocal, you need to understand the idea of inclusive fitness. Evolutionary fitness is measured by the numbers of copies of ‘your’ genes in the subsequent generation compared to those of others. Note that it doesn’t matter whether you or a relative supplied those genes. An extreme example: You are one of 4 children of a family in a war zone. You are playing together when some- one throws a live hand grenade through your door. Would you achieve higher fitness by jumping through a window or jumping on the hand grenade?

9. The answer:If you survive, you leave behind one copy of your genes. Jump on the grenade! If you act in an altruistic way, each of your siblings shares (on average) ½ of your genes by descent from the parents. Saving 3 of them would leave 1½ copies of your genes, and give you a higher inclusive fitness. To assess the contribution to inclusive fitness made by a relative, you need to know the coefficient of relationship (the fraction of your genome shared by descent from ancestors in common).

10. Proportion shared Self100% father 50% mother 50% full sibling 50% half sibling 25% offspring 50% grandparents 25% niece/nephew 25% uncle/aunt 25% first cousin 12.5%

11. Again, cost/benefit ratios determine whether altruism should arise in the behaviour of an individual. Altruism should arise when the cost to the donor of the behaviour is less than the benefit to recipient(s), measured by the summed change in their individual fitnesses multiplied by their coefficients of relatedness (in other words their contribution to your inclusive fitness)… Or C <  Br where C is cost, B benefit, and r the relatedness of those who ‘receive’ the behaviour

12. Similarly, relatedness affects the likelihood of selfish behaviour. Since it has negative impact on recipients, if they are related, it reduces inclusive fitness…it should evolve only when benefits exceed costs (to the relatives)... or B > Cr rearranging… C/B < 1/r Selfish behaviour occurs only in this region Altruistic behaviour can evolve in this region

13. There is a name for the pattern of evolution indicated in these cost/benefit relationships… Kin Selection Hamilton’s definition of kin selection:...selection operating between closely related individuals to produce cooperation Closely related individuals are more likely to benefit from (pseudo)altruistic behaviour than distantly related ones.

14. Fisher, who has been critically important in the development of so much of modern population genetic theory, anticipated ideas about kin selection at least 30 years in advance of anybody else… Think of warning colouration in insects, e.g. the larvae of the monarch butterfly. It contains toxins poisonous to bird predators. The colouration warns them off… but how could this evolve? The first brightly coloured larvae would have attracted predators, and suffered total loss of individual fitness. Siblings (and they would be numerous) are ‘protected’ by bird learning. Inclusive fitness increases through kin selection.

15. Another example of kin selection is helping at the nest in white-fronted bee eaters in Kenya… These birds live in extended, multi- generational family groups of from 3 – 17 birds. Interactions among members of these families follow the predictions of theory closely. Siblings help each other, but cousins are unlikely to be helped, and are treated much like non-relatives.

16. These birds nest colonially. Helpers tend to assist close relatives more often than distant relatives or unrelated birds. Breeders coeff. of relatedness% cases to a particular offspring father x mother 0.5 44.8 father x stepmother 0.25 9.8 mother x stepfather 0.25 9.2 son x nonrelative 0.25 10.3 uncle x nonrelative 0.125 1.1 grandmother x nonrelative 0.125 0.6

18. From the occurrence of kin selection and the occurrence of unrelated groups living together arose the notion of group selection. The usual, commonsense view has a fatal flaw… “Robins (or any other bird) lay fewer eggs in a drought year because competition for limited food supplies would be detrimental to the group…” but under those conditions in such a group, a cheater who laid more eggs would have a higher fitness. The simplistic view of group selection does not make evolutionary sense, since it works in the opposite direction as individual selection.

19. There are two recent approaches to group selection that could work: 1) a population exists as a set of groups. Among those groups, isolated, selfish subgroups must go extinct faster than selfishness arises among initially altruistic subgroups. Most newly founded subgroups must be altruistic. Classical Darwinian selection says that eventually selfishness will develop. 2) Populations come together and separate into subgroups. Some subgroups have different rates of survival and/or reproduction. More successful groups contribute larger numbers to the population at re-coalescence.

20. Group selection is controversial because conditions that lead to cooperation among unrelated individuals are very restrictive in evolutionary terms. Self-interest is the dominant force in Darwinian selection. Ricklefs uses game theory, and the hawk-dove game to demonstrate this. Hawks always behave selfishly in conflicts. Doves never compete for resources, instead sharing them evenly with other doves. Now consider the costs and benefits in this system when individuals must share or compete for resources.

21. The payoff to a ‘contestant’ depends on the behaviour of the other individual… 2 hawks fight over resources - each will end up with half the benefits less the cost of the physical conflict, or 1/2B - C when a hawk and a dove conflict, the hawk gets it all, the dove gets nothing, or the hawk gets B when 2 doves share a resource, there is no physical conflict, so each gets half at no cost, or 1/2B

22. Who is better off? It depends on the proportions in the population. If the population is all hawks, then each gets 1/2B - C If the population is all doves, each gets 1/2B, a higher reward and doves have the advantage. If the population is a mixture of hawks (proportion p of the total) and doves (proportion (1 - p), then the reward to a hawk is: p (1/2B - C) + (1 - p) B and to a dove: 1/2 (1 - p) B

23. You can try to solve this for equilibrium, and you will fail. Why? Try thinking about the rewards to a single hawk in a population otherwise comprised of doves. All its encounters will be with doves, giving a reward of B, while doves will almost always encounter other doves, and get a reward half as large, 1/2B This sort of result indicates that selfish behaviour ultimately wins, and a mixed population is an evolutionarily unstable system. Dovish behaviour is an evolutionarily unstable strategy. The text demonstrates this graphically...

25. Is there any circumstance that can lead to persistence of a mixed strategy? Yes. If the cost of the contest to hawks is very high. Hawkishness is advantageous unless the cost is greater than 1/2B. If B < 2C then doves can invade an all hawk population…an equilibrium mixture exists as an evolutionarily stable strategy.

26. A last form of group/society structure - the eusocial insects Almost all eusocial species are hymenoptera. They have certain characteristics in common: 1) adults live together in groups (e.g. hives) 2) the group includes overlapping generations (parents & offspring) 3) there is cooperation among members of the group in efforts supporting reproduction 4) there is reproductive dominance by (at most) a few individuals (frequently one individual) What makes this remarkable is the sacrifice of individual fitness by whole sterile castes. This can be explained only by kin selection.

27. As an example, the structure of a bee colony… There is one queen, only she is reproductively active as a female. She only mates once, gathering enough sperm to continue producing fertilized eggs through her lifespan. A) Some of her eggs undergo the equivalent of partheno- genetic development - no fertilization and a haploid genome. They become ‘male’ drones. B) Some eggs are fertilized, but exudates produced by the queen arrest their development prior to sexual maturity. They are ‘female’ workers. C) Some (only a few) are specially fed and allowed to mature. They will disperse to found new colonies as queens.

29. Why should drones be dispersed, and a female biased sex ratio (by weight) occur in a colony? Kin selection… The queen has a coefficient of relatedness of 0.5 to offspring of either sex. A female worker has a coefficient of 0.25 with male siblings, but a coefficient of 0.75 with female siblings (sperm is produced by mitosis, therefore all sperm are genetically identical.). She is more closely related to female siblings than she would be to her own offspring. Kin selection is, therefore, the logical result.

31. Parent-offspring conflict… A parent would maximize its fitness by producing as many surviving offspring as possible (and considering both current and future reproductive value)… but the offspring is best served (in the selfish sense) by being given more resources, and having what is available divided up among as few offspring as possible. Think about this and consider what’s happening between a plant parent and the offspring (seeds, fruits, nuts, …) it’s producing simultaneously. What control does a parent have? What might an offspring do to get a larger share of resources?