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Midterm Summary Feb 2013.pdf

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Locke Rowe

Midterm Summary: 13-02-11 9:18 PM • The “nature- nurture fallacy” Dr. F Mustard • Early life effects development & late life outcomes • Genes, Environment and Behaviour • Genes and environment influence phenotypes including behaviours • Natural selection shapes behaviours • Environmental effects on tr ait values can be describes as “ plasticity”; these responses can be adaptive • The influence of genes and environment can be visualized with plots of the “reaction norm” • Natural selection shapes the reaction norm • Two classes of scientific questions : • How/what: proximate causes o How an individual carries out an activity? o What is the casual relationship between the animal’s genes and its behaviour • Why: ultimate causes o Why has an animal evolved this trait? o Why has this behaviour evolved and how has it changed over evolutionary time? • Drunken bees and wasps: • What: reaction to fermented ethanol • How: over ripe fruit • Why: an adaptation for locating ripened fruit • Genetic and environmental variation • Identical twins have same genetic makeup • Even slight differences in envir onment lead to variation in behaviours • Phenotypes reflect both genetic and environmental effects Z = G+ E (PHENOTYPE= GENES + ENVIRONMENT) • Within population - Variation in behaviour Rover-sitter polymorphism: • Rover: travels far distances as a larva Sitter: travels little from origin • Experiment: o Rovers move greater distances than sitters when food is patchy o This means that rovers are off food patches more often, also more likely to find new patches o Rovers and sitters move more often and for similar distances in absence of food • Natural variation in frequency of rovers and sitter larvae: sitter (black) = 30%, rover (white) = 70% Is this a genetic effect? Is this a behavioral effect? --What happens when they cross? • Results: F2 generation 3:1 ratio - means that one gene, two alleles and rovers are dominant • What do these foraging alleles produce? • PKG: - an enzyme involving cell signalling - located in the nervous system and the gut • What happens when we insert rover DNA into a sitter body o Behaves and has PKG levels of rover, even though the rest of DNA is sitter: indicates that this behavior arises from one gene • Evolution by natural selection • Variation in a trait • Variation in fitness for the trait • Genetic basis for the trait • Evolution of the behaviour • Behaviours have great variation • Different behaviours have different fitness • Behaviours have a genetic basis • Phenotypes reflect both genetic and environmental effects Z = G+ E (PHENOTYPE= GENES + ENVIRONMENT) • Environmental effects on foraging - Experiment: • Adults deprived of food for 4 or 24 hours • Evaluated for foraging behaviour in patchy environment o Rover is similar to sitter type, when it has been starved for a long time • Summary: • Single major genes underlies the rover/sitter polymorphism • The rover allele is dominant to the sitter allele • Both larval and adult behaviours are affected by these alleles • Elements of the environment (i.e. food deprivation) affect behaviour • Homologous genes occur in bees, mice, and humans (model gene) • Phenotypic plasticity: an environmental e ffect on the phenotype • Behaviour response to predators (plasticity) • Many organisms use refuges, which reduce predation risks • When there is no predator around, they have a different niche o Predators cause prey to use refuge niche • Morphological response to pr edators (plasticity): Daphnia • When prey is present water daphnia will acquire a spiked helmet • Same genotype creates two different phenotypes • Plasticity can be dramatic • Spade foot toad: depending on availability of shrimp, certain tadpoles will transform into the larger, more aggressive cannibal type • Can “taste” each other - will not eat similar cannibal types • Reaction norms: visualizing G and E • Environmental effects on trait values can be described as plasticity • The influence of genes and environment can be visualizes with plots of the reaction norm • The reaction norm describes the effect of some environmental variable on the phenotype of a single genotype • Reaction Norms: Visualizing G and E • Genetic difference; no environmental effect (x axis: environment, y axis: phenotype) • Genetic and environmental differences • - Large genetic effects, small environmental effects • - Small genetic effects, large environmental effects • - Complex gene environment interactions - one genotype will respond completely different ly to the other genotype • Evolution of reaction norms • Sexes & Differences 13-02-11 9:18 PM • How different are the sexes and why? • Two phenotypes • Sexually dimorphism quite apparent is many species • In humans 90% of autosomes (non-sex coding) is shared by sexes • Gene expression of shared genes in most tissues differs between the sexes • Most evident in gonads, but also in other tissues in body • 50-90% of all genes in the fly genome (~13,000) are expressed differently in the sexes • The evolution of sexual dimorphisms (differences) • Sexual dimorphism: conspicuous ornaments of the male species o Male widow birds: massive tails o What is the point of the ornaments? What are the big differences between species-> often time they are ornaments o Female types of widow birds are almost identical across species o Male types of widow birds are highly diverse (ornamentally) • Sexual dimorphism: conspicuous behaviours • Sexual dimorphism: armaments o Usually absent or reduced in females o Peacocks o Survival of the fittest? o Tail does not aid fitness, decreases it? o Tail is not good for survival, flight, etc. o If it is bad for survival, what is it used for? § Ornaments that increases mating success § Weigh (+) mating success with (-) survival (predation) • Sexual selection o Don’t think about it as a sense of beauty o I.e. frigget birds don't think, “Gee that's attractive”... o Sexually selected traits function to enhance mating success § Subset of natural selection • Sexual selection: o “Depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction” Darwin o Sexually selected traits function solely to enhance mating success o It’s a subset of natural selection but it can be useful to consider them separately o o Fitness in males and females § Females: # of eggs produced, and surviv al § Males: access to eggs, survival • The origin of sexual differences: • Why sexual selection? Why 2 sexes? • Anisogamy: unequal gametes • Sperm much smaller than egg o Males are class that produces small gametes § Inexpensive § Means they can produce A LOT o Females produce large gametes § Large, resource rich, loaded with energy • Parental Investment Theory • Robert Trivers (1972) • Sexes differ in the reproductive investment • Members of the sex that in vest little in offspring will compete amongst themselves to mate with members of the sex that invest more in offspring o Competition between males to access females who invest more; males restricted by access to mates o Females invest more, and female gametes also a limited resource, and females are therefore limited by access to res ources • Differences between the sexes: o Males: § Tiny, mobile gametes (sperm) § Fitness limited by access to fertilizable gametes § Competition: among males for mates o Females: § Large, resource, rich gametes (egg) § Fitness limited y access to resources § Choosing: among males for mates • Number of mates and number of offspring is a linear relationship (MALE) • Females, however, are limited by resources: weak relationship between number of mates and number of offspring • Hypothesis tested on flies: • Proved true for males (limited by number of mates) • Females: offspring is limited by resources • Flies stores sperm, use sperm everyday to fertilize o If they mated again, and stored more sperm, it doesn't affect the number of offspring produced o STD’s: cost of mating too frequently • Comparison of max number of offspring produced: • On average males produce way more offspring then females o Kittiwake gull (monogamous?) • Sexual selection • Intrasexual selection: male-male competition • Intersexual selection: female choice • Intra-sexual selection: male-male competition • Forms: o Pre-copulatory à number of copulations o Post-copulatory à success of copulations (sperm competition) • Manifestations of pre -copulatory (male-male competition): o Fighting behavior § Consequences of mating success: ú Variance in fitness ú Most dominant elephant seal has most offspring o Territory guarding o Social status o Sperm competition § Mate guarding ú Mate guarding in dragon and damselflies: • Sperm exits from bursa, curls abdomen and stores it in pocket • Female connects herself to pocket and takes sperm • Male guards her o Ensures other males won't interfere process ú § Sperm removal ú Sperm removal by damsel flies by using spikes and barbs § Copulation duration ú Post-copulatory: success of copulations ú The longer one copulates, the more sperm is released § Sperm plugs/ cement glands § Traumatic insemination § Anti- aphrodisiacs § Etc.… • Alternative Reproductive strategies & satellite and sneak males • Bluegill sunfish • Large males can guard areas that females lay eggs • Externally fertilize, other females can use the ne st • Males take care of eggs • Males that resemble females can sneak up on large male’s territory to “sneakily” fertilize eggs • Another male type is a “drive -by sperm shooter” • Alternative male reproductive strategies & frequency dependent selection • Side-blotched lizards o Orange, blue, and yellow types • Rock, paper, scissors in nature • Each type employs a different strategy, which have a genetic basis • They vary in frequency over time • Prediction: o Success of each strategy in obtaining copulations dependent on fre quency of other strategies in the population § If blue is high, orange will increase § If orange is high, yellow increases § If yellow is high, blue will increase • Results suggest that there is a dynamic rock, paper, scissors game, where selection is frequency dependent Sexual Selection & Female Choice 13-02-11 9:18 PM Examples of Female Choice • Satin bowerbird • Male builds a “bower” (stick structured, covered in ornaments) • Blue and yellow colours attractive to females • Males will steal things from people, or other birds • Females observe the bowers o Most decorated/more attractive wins the female o Female enters bower, male sneaks around and mates with her • Lek =group of males that try to attract females • Males perform in groups • Females inspect males and pick the most attractive • Fitness for most males is 0 o Causes strong selection, large variation of fitness • Female choice: • Any female trait (behaviour, morphology) that biases the mating success of males towards the preferred type • We will use mating bias, female preference, female choice to mean the same thing • No implied sense of beauty • Male choice is simply the reverse • Examples: • Visual stimulation o Scorpion-fly o Barn swallow o Long-tailed widowbird o Cichlid fish o Field cricket o Jungle fowl • Tactile stimulation o Sierra dome spider • Acoustical stimulation o Field cricket o Woodhouse’s toad o Great reed warbler o Tungara frog • Olfactory (scent/smell) Stimulation o Mouse o Cockroach o Moth • Widow birds • Tail manipulation experiment o Question: are long tails preferred by females o Experiment: manipulate tail length § Natural length (N) § Reduced length (R) § Elongated (L) § Sham Surgery (S) à cut tail off, glued it back on o Results: § No difference between natural and sham (no glue bias) § Long tails more successful • Female preference of eyespots in peacock tails • Experiment: reduction of eyespot number • Results: fewer eyespots meant way fewer copulations • Female preference of complex calls in tungara frog • Whining attracts females • Once female arrives, she seeks the most complex “chucking” call • Females prefer complex calls o Why don’t all males have a “chucking ability”? § Frog-eating bat § Bats prefer complex calls too § Two modes of selection (predators reduce chuck phenotype, female choice increases male chuck phenotype) ú Evens out the ratio of who gets to actually mate! • The problem of female choice: • Why are male elaborations common? o Females prefer them o Therefore creating selection for elaboration • Why do females prefer certain traits? o One of the biggest problems in evolutionary biology • Hypotheses for female choice (non -exclusive) • Direct benefits: involve direct natural selection on t he female o Female preferences are a side effect of other forces shaping female behaviour § I.e. females are sensitive to sound- male exploits that o Selection of resources (PI) rather than male attributes § I.e. nutritious spermatophores, larger males give more r esources to females à crickets, katydids § Hanging fly: female is attracted to pheromone, if he has a lot of food she will mate with him (eats while mates!), more food means longer period of copulation o Male trait is indicator (or badge) of parent investment (PI) § Selection for male traits as indicators of PI or other direct benefits: ú Territory quality ú Parental care ú Defense ú Lack of parasites (STI’s) ú Traits that serve as indicators that male will help female and baby. These ornaments will say that the male will have a good quality territory, parental care...etc. • Indirect benefits: involve genetic benefits to her offspring o Females prefer male traits that indicate high genetic quality (good genes) o If so, offspring from copulation with preferred males should have h igher fitness o Is peacock display size an indicator of good genes? Yes à large display sixe correlates to higher % chick survival • Parental investment (PI) theory • Robert Trivers 1972 • Sexes differ in their reproductive investment • Members of the sex that inv est little in offspring will compete among themselves to mate with members of the sex that invests more in offspring • Expectations and examples • High male PI o Giant water bugs o Pipefish • Male choice o Katydids o Spotted sand piper • Female/female completion o Plover? • High male PI • Pipefish sex roles and mating system: o Male reproductive success limited by size of their brood pouch o Female reproductive success limited by access to males o Females compete for access to males o Sexual selection on female size and ornamentation o Sexual dimorphism in pipefish § Males resemble water grass § Females colourful, ornamented • Experimental evidence of sex role reversal o Question: do males exercise mate choice? o Prediction: males will prefer large highly fecund females o Results: do males actually prefer these ornamentations? § Males prefer long, ornamented females! • Katydids: • Relative PI and flexible sex roles in Katydids • Females get pollen form male spermatophores, males collect it from flowers o As ambient resource level s decline: § Male availability d eclines (resource limited) § Female need for male’s resources increases o Predictions at low resources § Male choice of females § Female/female competition § Results: food abundant § When lots of food males can make spermataphores and call for females § When lots of food females can eat pollen and don't mate as much but when no pollen they want males for food Food scarce § When males are common and call females and females come males can reject them • So what about selection in humans • Females preferring symmetry in mates • Mate choice in mice and humans: the MHC • what is MHC: o major histocompatibility complex o called HLA in humans o MHC loci coded for the antigen recognition system of the immune response o Lots of genetic variation at the MHC is good § improves immunity and avoid inbreeding o do mice choose mates based on MHC? § image you could see the loci ,then you'd avoid MHC that are the same as you because could be a relative o why would this evolve? § To avoid inbreeding § To increase he genetic variation at MHC in their offspring o House mice prefer to mate with individuals of a different MHC -type § They can smell the loci § mate choice is based on differences in odor that correspond with differences in MHC Social Behaviour 13-02-11 9:18 PM • alarm calls: ground squirrel • live in groups • if a female sees a predator it will stand u p and sound an alarm call • even though it risks its own livelihood, the rest of the group can escape • altruistic behaviour decreases fitness for group’s benefit • co-operative behaviour- one reproduces, the others help raise the offspring • some individuals reduce their own fitness by helping others raise their offspring – helps maximize the fitness of the other adult/parent • eusocial behaviour- complex social castes • hymenopterans • naked mole rats • Social behaviour: • The interaction with, and response to other indivi duals of the same species • Altruistic: o Behaviour increases another individual’s reproductive success at the cost to one’s own reproduction • Cooperative: o behaviour that, if adopted by 2 (or more) individuals, will benefit both • are there cheaters that exploit the system? • Cooperation and natural selection • Troubled Darwin: If genes are truly selfish (genes that have been replicated and past on to next generation at the cost of other genes) how can cooperative social behavior work? • How then can cooperative genoty pes spread in an environment of selfish genes? • Game theory • Developed during the cold war • Explanation: o Some number of players o Set of possible strategies o Some pay-off schedule for playing A against B, for all A and B (co -relates to fitness) • Hawk-dove game o Contest between two individuals over obtaining a resource o Two strategies can be used: § Hawk- fight aggressively § Dove- resolve contest peacefully DOVE’S PERSPECTIVE § Dove verses dove: they work it out and split the resource (R/2) § Dove verses hawk: hawk takes resource, dove gets 0 HAWK’S PERSPECTIVE § Hawk versus dove: hawk takes resource (R), dove gets nothing § Hawk verses hawk: gets maybe half the resource, but there is a cost to fighting • Which strategy will prevail? o If the resource is more than twice the cost : If R>2C, i.e. R=4, C=2 Always best to play hawk o If the resource is less than twice the cost: R=2, C=6 - if there are many doves, playing hawk will yield the most resources - if there are many hawks, then playing a hawk is a risk (H vs. H has cost of -5), so it is better to play a dove § You might expect a mixture at equilibrium fitness is frequency dependent § in this case, there would be a mixture in terms of population of hawks/doves (they balance each other) • Social Behaviour • Reciprocity o Given multiple encounters, perhaps it does not pay to be selfish o Can examine this possibility using iterated Prisoner’s Dilemma o The evolution of Reciprocity (with repeated encounters) § Why does cooperation occur? § Iterated Prisoner’s Dilemma best strategy is “tit for ta t” 1. Cooperate on the first encounter 2. Copy your opponents last move thereafter § Elements of the tit for tat strategy: ú Nice- start by cooperating ú Retaliatory- stop if partner stops ú Forgiving- if partner has cheated in past but “changes”, then cooperates § Example: predator inspection ú fish in shoals: few individuals inspect for predators ; who "decides" who does this? ú Predator inspection in guppies: • Two fish approaching a predator can be views as an iterated prisoner’s dilemma • At each point in time, each indi vidual can: a) continue towards the predator (cooperate) b) hold back (defect) • Question: do guppies play tit for tat during predator inspection? • Experiment: examine predator inspection behavior with cooperating and with defecting partner • Results: With ‘defective’ partner, guppy will not approach, with cooperating partner guppy will approach • Group Selection o “bad” o alleles can become fixed or spread in a population because of the benefits they bestow on groups. This theory explains traits that are not b ased on natural selection acting on individual alleles or the fitness of individuals within that group o group selection can be invaded by cheaters and rendered useless? o Example: crows are extremely intelligent and have unique dialects § Individual selection on alarm calling ú call when owls near ú attracts attention to caller while sparing the rest (altruistic) ú after selection (owls) you'll see that non callers live ú callers paid a cost thus altruism is hard to understand • if there is a reduction of callers, is that gene reduced? § Experiment: 3 roosts: - group 1 has few callers - group 2 has a ton of callers - group 3 has an intermediate amount - then they interbreed later in the year ú in the breeding season they all mix up and then reassemble in the roosts (roosts will now vary in frequencies of callers) § results: low à high mortality rate, no warning for predators high à low/no mortality rate, callers all warn each other int. à most benefit from caller behaviour when they reassemble the frequency of non -callers is low o Evidence for group selection? § Large plants out compete small plant, yet small plants still very common § Question: Why don’t large plants take over the population? § Hypothesis: groups with many large “selfish” plants do worse than groups with many small “cooperative” plants (too many large plants leads to over shading) § Results: - large individuals in well spaced groups tended to have high fitness - groups consisting of many small individuals tended to have high fitness ú These two tended to cancel each oth er out • Kin Selection “the difficulty…is lessened, or as I believe disappears, when it is remembered that selection may be applied to the family, as well as to the individual, and thus may gain the desired end” - Charles Darwin 1859 o altruists allele gives benefits to other alleles o altruist allele pay a cost when working with non -altruist o all recipient get benefits of altruism o communities of only altruists share the benefits, it might spread therefore (as it is successful) o interactions of altruists amongst themselves, in this case altruists might do best (if benefit is higher than the cost) o Hamilton’s rule: § b R >c § c= cost of altruism to the actor § b= benefit of altruism to the recipient § R= genetic coefficient of relatedness (i.e. probability that the recipient carries the altruist gene) - therefore as relatedness increases, altruism becomes more common o Alarm calling in ground squirrels § Observation: individuals give predator alarm calls ú Callers are at high risk (cost) ú Group benefits from warning (benefit) § Question: ú Do squirrels with close relatives nearby give more calls than those without? ú Results: ú Altruism is therefore a result of passing the alarm calling allele, therefore increasing the fitness of their offspring Parent-Offspring Conflict 13-02-11 9:18 PM Parent-Parent Conflict • Who will care for the offspring? • Parent-Offspring (PO) conflict • Offspring begs for food • Parents provide the food • Question 1: how much should offspring try to acquire? Question 2: How much should the parent provide • Important to consider siblings, and the effect of no t sharing • The trade-off o Provisioning= p § p increases the fitness of the current offspring, decreases the fitness of future offspring o (+) à B(p) fitness of current offspring o (-) à number of future offspring C(p)= number of future offspring “given up” • Offspring (benefits-cost) o Siblings are genetically related, r= ½ o A gene that causes an offspring to take more resources will reduce its own replication through future siblings o Offspring should maximise B(p) – ½ C(p) • Parent (benefits – cost) o All offspring are gene tically related to parent by R=1/2 o Parents should maximize ½ B(p) – ½ C(p) • In general we expect an evolutionary conflict between parents and offspring over the level of care • Parent-Parent (PP) conflict • Ma/pa both equally related to offspring, who should ta ke care of them? • Costs of desertion: reduced quality of each offspring (lower probability of survival) • Benefits of desertion: increased quality of offspring • Thought experiment: o Females are restricted by resources and thus few benfits of abandonment • • Consider: a pop of plovers in turkey where male care predominates o Can we account for pattern of male care in terms of costs, benefits? o Experiment 1 (benefits of desertion) § Caught parents ú One parent remove ú Measured time to re-mate § Low re-mating time = incentive to abandon § High re-mating time = no incentive § Results: females re-mated quickly (B+), males did not (C-) o Experiment 2 (costs of desertion) § Manipulated number of parents and measured brood survival § Results: males provide much of the resource, without males survival rate decreases. also females have little impact on survival • Combined PO and PP conflict Perspectives on Evolutionary Medicine and an Introduction to Aging 13-02-11 9:18 PM • Evolution and medicine • Aging: proximate and ultimate causes • Costs of reproduction • The evolutionary theories of aging • Mutation accumulation • Antagonistic pleiotropy • Evolutionary medicine • Definition: application of evolutionary principles to the problems of health • Approach: asks why (ultimate), rather than how (proximate) questions • Utility: better understanding = better prevention, or treatment • Questions in evolutionary medicine: • Is this response (fever, resistance, virulence) adaptive, and for whom? • When do we expect resistance to evolve? • When do we expect the evolution of ext reme virulence? • Are there multiple origins of disease? • Will vaccines lead to evolution of pathogens? • Why do we age? • Three reasons why we are vulnerable to disease: • Trade-offs: structures and systems must balance conflicting demands o Defences: systems buil t for defence against pathogens and degradation come at some cost • Environmental change: environments change at a rate that exceeds out rate of evolution o if the environment was slowly changing, our phenotypes would match the environment more often • pathogen evolution: pathogens evolve faster than we do o generation time is extremely rapid, 10,000 generations during a single infection allows for rapid evolution • Aging • What is aging or senescence • Definition: progressive decline in somatic function reflected in red uctions in fertility as well as survivorship • How/Proximate causes: progressive degeneration of the soma • Manifestations of aging • General degeneration of the soma (non sex cells) o Impaired function (speed, strength, sight, etc.) o Increases disease (cancer, organ failure) • Mortality rate increases with age (age specific fitness decreases over time) • Evolutionary mystery • Observation: why have we evolved to age and die? • Explanation: appears to be non -adaptive in the extreme • Aging at different rates: humans and fulma rs • George Dunnit and buddy the fulmar meet over the years. George ages over time and his reproductive rate decreases, but Buddy’s reproductive rate has not changed over the years. • Mayfly lives for 1 day • Bristlecone pine lives 5000 years • Headlines: • Vitamins that extend you lifespan • Exercising • Eat healthy • Be rich • But why has aging evolved? • Free radicals and vitamins • Molecules containing at least on unpaired electron • Attack and modify macromolecules o Oxidation of DNA, proteins, lipids • We have our own defences ( various amino acids that act as antioxidants) o Also vitamin A and C • We also have repair mechanisms o Why doesn’t repair occur throughout life, and into old age? • Life without constraints • Darwinian demon? o The ideal organism would maximize all fitness component s simultaneously § Would begin reproducing at birth § Reproduce at an infinite rate since it lives forever • But.., o Biological systems are constrained o Constraints often take the form of trade -offs • Trade-offs affect the evolution of all traits Examples: • Display size (morphological trait ) (i.e. evolution of peacock tail comes at a cost of longevity) • Foraging rate (behavioural trait) increases foraging ability comes at a cost of increased mortality rate • longevity (life history trait) • Trade offs may govern the evol ution of DNA repair mechanisms? • DNA repair à (+) longevity o as you increase DNA repair, you decrease fecundity o DNA repair is resource costly, which detracts from reproduction à (-) Fecundity • (-) Costs of reproduction • High reproductive rates accelerates agin g and thereby shortens the lifespan • More offspring you have, the greater the reduction in longevity • Reproductive costs in water striders o Males do a little bit of eating, and mostly chasing around water surface looking for females o Females collect food, av oid males, and use resources to produce eggs o Can you induce a higher reproductive rate and cause reduced longevity? o Prediction: females induced to reproduce at a high rate will have reduced longevity o Hypothesis: high reproductive rate accelerates aging and thus shortens
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