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How does the equation b > c relate to the probability of a supposedly "altruistic behavior evolving?
- The benefit provided by the altruistic behavior must exceed the cost.
- For example, if a mother is to lose her life then cost would be 1, her entire genome is lost. The only way this makes sense is if the benefit is to save three children (1.5>1)
What is inclusive fitness? How do direct benefits differ from indirect benefits?
Inclusive fitness: fitness of individual bearing specific allele (direct) and fitness of other individual that carry copies of the same allele (indirect)
What is kin selection? Provide an example. Consider Hamilton's equation rb > c. How does the inclusion of the r term influence the likelihood of a supposedly "altruistic" behavior evolving?
- Kin selection: selection based on inclusive fitness where "other individuals" are bearer's relatives (kin)
- *your alleles increase in the next generation with the increased fitness to you OR your family
- The r term indicates the degree of relatedness (a child is r=.5, a sibling is r=.25)
- Parental care is simplest case of a trait evolving by kin selection. If altruistic trait A is to continue a mother will only sacrifice herself if 3 children are saved (rb >c = (.5)(3)>1)
- Indiscriminate altruism cannot evolve by NS, because only
Under what circumstances would parental care evolve? Consider this in terms of Hamilton's equation.
- The benefit would have to be greater than (not equal to) the cost.
- If altruistic trait A is to continue a mother will only sacrifice herself if 3 children are saved (rb >c = (.5)(3)>1)
Expand your consideration to include 2nd degree relatives such as nieces/nephews. Under what circumstances would kin selection for these relatives be favored?
- The relatedness factor for a 2nd degree relative would be much lower than a direct offspring (.25 vs .5)
- In this case it would require more than 4 nieces saved (not equal to 4) to equal the cost of a death (fitness -1)
What is an ESS? How does a fiddler crab claw display behavior fit the requirements of an ESS?
- ESS = Evolutionary Stable Strategies
- A strategy such that, if all the members of a population adapt it then NO mutant strategy could invade under the influence of NS
- The claw is used to fight males and attract females
- A regenerated claw is an effective bluff, although it is actually much weaker than the original claw
Cooperation among unrelated individuals is, on the surface, altruistic. How does the example of the cuckoo contradict this surface assessment? How does the example of the pied kingfisher contradict this surface assessment? How does the example of the vampire bat contradict this surface assessment? In all of these cases, why is the cooperation not really altruistic?
- Cuckoo: Manipulation- a brood parasite who manipulates its host into providing aid to its young
- Kingfisher: Individual advantage- helps non-relatives rear children to make themselves more attractive
- Vampire bat: Reciprocation- feed regurgitated blood to roost members if no others were successful, this will be reciprocated in the future
- The cost is not larger than the benefit to the host
How is eusociality the most extreme case of kin selection? What species of mammal is eusocial? What insects are eusocial?
- Sterile workers rear the kids of their mom
- The only eusocial mammal is the naked mole rat
- Termites and many hymenoptera
How does a haplodiploid genetic system in the social Hymenoptera pre-dispose these species for eusociality? What evidence exists to support the hypothesis that haplodiploidy is the driving force behind eusociality in these insects?
- females are from fertilized eggs (diploid)
- males are from unfertilized eggs (haploid)
- In diploids r=.5 btwn parent/offspr and ~.5 btwn siblings
- Queens typically mate with a single male, so that all females inherit the males chromosome
- Thus a female is more closely related to her sisters (.75) than her daughters (.5) or her brothers (.25)
- Queen's fitness is maximized by equal investment in daughters and sons, because r=.5 to both, but fitness of workers is maximized if 3/4 of siblings are sisters and 1/4 are brothers
- In colonies with 1 queen- sex ratios 3:1 because kin selection shapes worker behavior
- In colonies with >1 queen sex ratios ~1:1 because workers may not be full sisters
How is infanticide by males who are not the father of the infant (as in lions or langurs) an example of a genetic conflict between males and females? How do females make the best of a bad deal in such conflicts?
Infanticidal males cause females to go into heat faster and thus can father their own children faster
Under what circumstances would infanticide by parents be selectively favored? Provide an explicit example
- Parents can kill/abort offspring as a way to adaptively regulate brood size or sex ratio
- Great tit populations in Oxford, England show that a clutch size of >8.5 eggs results in too much competition, and the rate of survival decreases
- Easier to kill than neglect and cause issues amongst entire brood
Under what circumstances would siblicide by siblings be selectively favored? Provide an explicit example.
- In some eagle and boobie species, larger kids in broods may kill smaller siblings
- Brown booby: survivors of sibling competition depends on food supply
- Shark siblings eat eachother in the uterus
How can genetic conflict exist at the level of individual genes? Provide an explicit example.
- A gene that adjusts the sex ratio of kids toward females would be in conflict with a gene that adjusts the ratio toward neutral or males
- EX: Cytoplasmic male sterility in thyme
- Mitochondrial loci (CMS) inherited through eggs; nuclear loci (r) inherited through both eggs and pollen
- CMS+ mutation stops pollen production and increases seed #, allocates energy and resources from pollen to eggs. Plants lack anthers making them "male sterile" or female
- NS favors "restorer" gene (r+) which counteracts the effects of CMS+ (plants have hermaphroditic flower w/ male stamens and female pistils)
Consider endosymbiotic parasites. Their genome is in direct conflict with the genome of the host. Under what circumstances would extreme conflict (ie. using all the host's resources and killing the host quickly) be favored? Under what circumstances would reduced conflict (ie. reduced virulence) be favored?
- If endosymbionts are passed horizontally within a host population than NS favors genotypes with high reproduction rate, even if the host dies
- If endoysmbionts are passed vertically from parent to offspring then the RS of the symbiont depends on host fitness
Consider an endosymbiotic mutualist, such as the ancestral mitochondria which was engulfed by the ancestral eukaryote. Why did this cooperative relationship evolve? What must be the foundation of all mutualistic or symbiotic relationships? (think b>c)
This relationship evolved because it was mutualistic. The mitochondria gained a stable environment and safety while the eukaryote gained an abundance of energy. All mutualistic and symbiotic relationships must be thought of in terms of the benefit vs the cost to BOTH organisms
Human homosexual behavior on the surface appears to be unnatural and mal-adaptive. What adaptive benefits might homosexual behavior have in other species? Is there evidence for a genetic component to homosexuality in humans? Why has homosexuality not been under much negative selection in past generations? What experimental evidence suggests a potential genetic benefit to maintaining a "gay" gene in a population?
- Social benefits: dominance, friendships
- reproductive benefits: practice with mating and parenting behavior
- There is a large genetic component in homosexual behavior that appears to be greater in men and in butch women
- Gays have tended to engage in reproduction (no negative NS) AND there has been evidence to support that the low RS of a gay male is balanced by high fecundity of female relatives