Transcript PPT
Altruism What is altruism? Benefit another at a cost to yourself. Fitness is lost! Does altruism exist? Best examples come from eusocial insects Bees, termites, ants Suicide in bees, etc. Non-breeding workers Theories to explain altruism 1. Group selection. 1962, Wynne-Edwards. Altruism costs the individual but helps to perpetuate the species. Ants who are workers do not reproduce but without their sacrifice the ants would not be successful. Lemmings migrate away when food is scarce, risking their lives, so resources would be available for others of the species. Why doesn't group selection work? Prone to invasion by Selfish gene. Natural selection acts on the individual Which would have higher fitness, a suicidal lemming or one who was selfish? Fitness would be higher in the selfish individuals and they would pass on their genes. -G.C. Williams Spelled the end of group selection! Theories to explain altruism 2. Inclusive Fitness W.D. Hamilton (my academic grandfather!) Altruism actually increases fitness by helping related individuals. Need to know something about genetics… Hamilton's rule r=coefficient of relatedness, B=benefit, C=cost rB>rC Relatedness You share ½ of your genes with your offspring so r=.5. Same with full siblings. The child of your sibling has ½ x ½ of the genes in common. r=.25 If you raise 1 child that is the same benefit to your fitness as helping your parents raise 1 more full sibling then they could raise otherwise (helping behavior)! Which increases your fitness more? Raising 1 child of your own or 3 nieces? Definitions Direct fitness: reproductive success based on your own reproduction. Indirect fitness: reproductive success based on the helping of related individuals (above what they otherwise would have raised). Inclusive fitness: total fitness due to both direct and indirect fitness. So is altruism selfish? Yes. You are increasing your own genetic fitness by helping, even if your own direct fitness suffers. Natural selection favors these genes, and is known as indirect or kin selection. Return to the insects Helping is one thing, not reproducing at all is different! What is unique about ants, bees and wasps? Haplodiploid! Terms Diploid-cells with 2 copies of each chromosome, like most of our body. Haploid-cells with 1 copy of each chromosome. Gametes-egg and sperm, sexual reproduction. Explains the r=.5 for your offspring Haplodiploid insects Females are diploid, males are haploid What is the r for each sex of offspring? And between siblings? Between sisters and brothers? Among sisters? Compare A queen is related to a daughter by .5 and a son by 1.0 A drone is related to a sister by .75 and a brother by .25 A conflict? What happens if the queen mates with more than one male? So does haplodiploidy favor Eusociality? Eusocial: individuals fill different roles in a group, such as workers, breeders, soldiers and most don't breed. There are lots of examples with workers that are females in this group (Hymenoptera). Predict that these workers will favor sisters over brothers. Don't see this. Alternate hypothesis: monogamy favors eusociality. Hymenoptera phylogeny Monogamy in black, Probably ancestral in all these groups. Supports the hypothesis! Some are polyandrous? Workers cannot mate. They are stuck! Chapter 3 Being Social Is there a reason to be social? What are the benefits of sociality? 1. Cooperation, both benefit 2. Postponed cooperation (delayed resource) 3. Reciprocity (delayed benefit) 4. Altruism Any problems with being social? What are the costs of being social? Maladaptive altruism Spite Manipulation and deceit Not to mention disease and parasites 1. Cooperation Many examples: hunting, defense. Need to show that both benefit from the relationship. Example: Lazuli bunting males in 3 plumages Cooperation Bright males allow brownish males to have neighboring territories. Advantage to brownish: get to father a few offspring. Advantage to bright blue: get to mate with second female, father additional offspring. Loser, the intermediate form gets little success at all. 2. Delayed Cooperation Long-tailed manakins https://www.youtube.com/watch?v=Z1zOmOfsy2Q One male gets all the matings. Why cooperate? Second male? He might inherit the perch in the future. 3. Reciprocity Similar to previous but benefit comes directly from first recipient. Grooming in primates. Pied Flycatchers and mobbing behavior of predator. Most birds help neighbors who have previously helped them. The Prisoner's Dilemma So when do you cooperate? Vampire bats-share their blood meals. Need to eat regularly or die. But who are you helping? Need to look at DNA to know. Cost of cooperation Belding's Ground Squirrels: alarm call results in higher rate of predation on caller. So why call? Cost of cooperation Sherman found callers are more likely to be females, who don't migrate. She is more likely to call if living near other relatives. Therefore, supports indirect or kin selection. Helping at the Nest Pied Kingfisher males. First year have 3 strategies: 1. Help your parents (primary) 2. Help an unrelated pair (secondary) 3. Do nothing. Eusocial Mammal The naked mole rat. https://www.youtube.com/watch?v=eHi9FvUPS dQ Very unusual mammal. Alexander, mid-70's, predicted the characters of a eusocial mammal and was correct! Underground, rodent, safe, expandable territory, food large and scattered, defendable, hard ground, Africa. Caste System Roles within the group Only 1 female reproduces and she enforces sterility by keeping stress hormones high. Dispersal is very difficult Lack pain receptors, resist cancers, don't thermoregulate, and live a long life. Not inbred.