Lab 6 - Kin Selection PDF

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Name Oyinda Adeyemo

LAB EXERCISE 6:

Kin Selection and Hamilton's rule Introduction Basic evolutionary theory struggles to explain altruistic behavior. Altruism is defined as animal behavior where an animal sacrifices their own fitness (sometimes their own life) for the benefit of a different individual. Although altruism is rare in nature, there exist many examples, ranging from the sacrificial stings delivered by honey bees to the protective behavior of a mother grizzly. One theory put forward to explain altruism is the theory of Kin Selection. Kin selection proposes that since evolution acts on genes and not individuals, that an individual can help pass on their genes without reproducing themself. This is because related individuals share many of their genes, therefore, fitness can be achieved altruistically by helping a related individual pass on those shared genes. This concept of an animal's fitness extending to other related animals is called inclusive fitness. The best support for kin selection theory comes from the insect order Hymenoptera. These animals, which include bees and ants, demonstrate some of the most extreme altruistic behaviors in nature. They are also (as Kin Selection would predict) always made up of individuals that are closely related, with most hives being made up of sisters. We likewise find closely related communities in other animals which demonstrate altruistic behavior including wolves, human beings and naked mole rats. Materials Your brain, your imagination, and your wits. Thought Experiment 1 Imagine that you are a wolf. Your pack has just brought down a caribou. Although all the members in your pack are related, some are closer relatives than others. While feeding on the kill you see your cousin, Whitefang, and your sister, Black Tooth, waiting for their chance to eat. You decide to give up your position on the kill to one of your relatives so that they can feed.

1. In your own words, how would you define kin selection? Kin selection is a type of selection in which an individual can pass down its genes without reproducing itself.

2. According to Kin Selection which wolf should you choose to maximize your inclusive fitness? Sister wolf – black tooth

3. Explain your choice for number 2 in evolutionary terms. I decided to use altruistic behavior to save my sister wolf by giving up my position for her so she could eat.

Calculating Relatedness Sometimes it can be challenging to determine how much two individuals are related. When calculating relatedness simply remember from basic biology that each parent contributes half the chromosome number to their offspring. This means that offspring are share half their genes with their parents (see A & B). Likewise, siblings will only share half their genes with each other (see B &C). This percentage of relatedness between individuals is called their coefficient of relatedness (r). The easiest way to calculate it is to draw a genealogical tree as below and simply multiply the coefficient (usually 1/2) for each link separating the two individuals.

For example, we can calculate how related C is to their nephew E by counting the links (1/2, 1/2) between them and then multiplying them together resulting in a coefficient of relatedness of 1/4

Thought Experiment 2 Let's return to the wolves again but make things more complicated. Your pack has just brought down another caribou. This time you must choose between your grandfather, Two Socks, and your cousin, Ghost. Make sure to draw a genealogical tree as above to help in your calculations.

4. What is the coefficient of relatedness between you and Two Socks? ¼

5. What is the coefficient of relatedness between you and Ghost? 1/16

6. According to Kin Selection which wolf should you choose to maximize your inclusive fitness? Grand dad wolf

7. Explain your choice in evolutionary terms. I chose grandad wolf because we both share same genes and can pass on said genes altruistically from one generation to the next

Hamilton's Rule

Hamilton's rule is a theoretical equation meant to determine whether evolution will select for a particular cooperative or altruistic behavior. It uses the coefficient of relatedness (r) we already discussed. Hamilton's Rule: rB>C Here B represents the fitness benefits of cooperation and C represents the fitness costs. Hamilton's Rule is still a controversial equation with some evolutionary biologists swearing by it, while others claim it rarely reflects reality. Example: A bear with two cubs can share her den with her sister but there is a 50% chance she will lose one of her cubs. Bears of her species have an average of six cubs during their lifespan. Her sister has already had 4 cubs. r=0.5, B=2 (the # of additional cubs the sister will likely have should she survive), C=0.5 (the 50% chance of the mother losing a single cub) .5*2>.5 1>.5 So, in this case the Rule predicts the behavior would be selected for. 8. If C represents individual fitness then what does rB represent? (hint: we discussed this in the introduction) r represents the relatedness between individuals and B represents the benefits of the selection to the individual. 9. Name an altruistic behavior in nature that you think would verify Hamilton's Rule? Explain why. Donating a kidney for a friend who needs a kidney transplant. The probability of donating one of your kidneys and surviving is a 75% chance. 0.75 x 2 > 0.25 1.5 > 0.25. The rule predicts that the behavior of donating a kidney can be selected for.

10. Name an altruistic behavior in nature or humans that you think would violate Hamilton's Rule? Explain why. Donating a heart for a child who needs a heart transplant. The probability of donating your heart and surviving is 10% Probability of not surviving is 90% 0.1 x 1 > 0.90 0.1 > 0.9. The rule predicts that the behavior of donating a heart cannot be selected for.

11. Referring to the example above, would Hamilton's rule still predict evolution to select for altruism if the bear needing a winter den was a niece rather than a sister? Show your calculation and interpret the answer. 0.125 x 2 > 0.5 0.25 > 0.5 The rule predicts that the behavior of allowing a niece rather a sister cannot be selected for....