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evolution.docx

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Department
Psychology
Course
PSYCH 2TT3
Professor
Brett Beston
Semester
Winter

Description
January 21 , 2013 Psych 2TT3: Animal Behaviour Evolution Evolution - evolution by artificial selection - evolution by natural selection - a deeper look: genetic variation, heritability and inclusive fitness - a change over time of the proportions of individual organisms differing genetically in one or more traits Artificial Selection - nature isn’t always the driving force - ex.: artificial selection in dogs, vary in traits: size, loyalty, speed, friendliness - DNA studies have shown that all of the different dogs have derived from a common ancestor, the wolf - Hunting, herding abilities: taking an ancestral behaviour and turning it into something useful that humans can apply to a situation - Artificial selection: humans selecting for a certain variety of traits over others. Fitness is the key to control Artificial Selection for Small Poodles - each generation, the dog breeder allows only the smallest poodles to breed - if humans can select out the traits they desire they can increase the frequency of a certain trait - smaller poodles are more successful at reproducing - smaller poodles have higher fitness Fitness - the success of an individual in reproducing - simply the number of offspring you produce over your lifetime - how you change the frequency of a trait from one generation to the next Artificial Selection - the process by which humans selectively choose and breed animals with some preferred characteristics - we can and have selected for a large variety of traits in plants and animals we use for food (fruits, vegetables and grains; chickens, cows, pigs, etc.) - ex.: corn vs teosinte - chickens are treated as fast food on legs, bred to be fried and eaten within seven weeks of emerging from the egg: maturation has been accelerated - traditional Christmas turkey: a white-breat-meat robot with short legs and a small breastbone, the new turkey could barely stand or walk, never mind turkey trot or manage the intricate balancing act of mating - fitness: the individuals who are allowed to breed Evolution by Artificial Selection - the process by which humans using selective breeding change, over time, the proportions of individual animals differing genetically in one or more traits Artificial Selection for Phototaxis in Fruit Flies - phototaxis: movement towards or away from light - allowed fruit flies to navigate through a maze: a lot of corridors with T- junctions at the top, right towards light, left towards darkness - maze had 15 levels. Flies could score between 16 (all light) to 1 (all dark) - select for only fruit flies that had the most bias behaviour - by only allowing light flies to mate with each other they are setting up artificial selection - filled triangles: population of fruit flies that always navigated towards the dark - empty triangles: populations of fruit flies that always navigate towards the light - over successive generations, there is a population of fruit flies that always navigates towards the dark and one towards the light - can shape behaviour over successful generations - and can measure the degree to which the behaviour changes - what drives the traits is sub-selective pressure, if you take it away you drive away the differences Fruit Fly Fight Club - fruit flies brawl over mates and territory. Now some scientists are betting that these battles can help them unravel the genetic basis of aggression - why do male fruit flies fight? - Why select for increased aggression? Artificial Selection for Aggression in Fruit Flies - boxing, chasing, wing threat, charging, tussling Frequency of Fighting - after 10 (white bars) and 20 (grey bars) generations of selection (2 control, 2 selection lines) - neutral groups: no selective pressures - when aggressive behaviour is not selective for it can go down, not a prevalent part of their behaviour - aggressive behaviour being bred: upwards of 80%, huge jump in aggressive behaviour between when they are selected for these tactics and when they aren’t - what are the commonalities that differentiate these two groups: gene 11 and gene21 - humans have the same loci’s Evolution by Artificial Selection - artificial selection can succeed only with a trait that has heritable variation - heritability: the contribution of genes to observed variation in a trait Artificial vs. Natural Selection - artificial selection: the variation in reproductive success (fitness) of individuals is determined by humans, who decide which individuals reproduce - natural selection: the variation in reproductive success (fitness) of individuals is determined by survival, male choice Necessary Conditions for Evolution by Natural Selection - heritable individual variation that corresponds to variation in fitness The Importance of Fitness - fitness = lifetime reproductive success, which is a product of reproductive rate and the length of reproductive lifespan - example: female 1 lays 10 eggs per day and lives for 20 days. Female 2 lays 15 eggs per day and lives for 10 days. Female 1 has higher fitness (200 vs 150 eggs). We can image on average that the daughters of female 1 will also lay 200 eggs. Increasing the frequency of the trait Fitness Benefits and Frequency of Traits - fitness benefits and consequences can have dramatic effects Lifetime Reproductive Success in Female Red Deer - vast majority of females produce no offspring during their lifespan, reproductive success = 0 - average number of offspring seems to center around 8 - great amount of variation in reproductive success Lifetime Reproductive Success in Male Red Deer - 50% of all males never have an offspring - males compete to mate Fitness Consequences - many animal traits influence survival and reproduction - there is typically large differences in fitness among individuals - even a small difference in fitness (1%) can have strong effects on evolution Variation in Humans - exercise:  write down 5 behaviour or cognitive traits that vary among people:  theory of mind  introversion/extroversion  athleticism  anxiety  aggression  IQ  do you think the variation in that trait is heritable? (2 min)  all of the above traits show heritable variation. That is , they have a genetic basis - broad-sense heritability: scale of contribution of heritable traits Individual Variation - almost all traits show genetic variation - there is typically large variation among individuals - the variation is determined by genetic and environmental factors Genetic Variation - without genetic variation, some of the basic mechanisms of evolutionary change cannot operate - there are three primary sources of genetic variation:  mutation: changes in DNA itself  migration: movement of genes from one population to the next  Recombination Mutations - change in DNA - mutations are random: there’s no ultimate purpose, they can be beneficial, neutral or harmful - no actual function or purpose - not all mutations matter to evolution - somatic mutations: occurred in non reproductive cells and will not be passed down to generations - germ line mutation: only mutations that matter to large-scale evolution are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm: can be a big or small change that can affect survival - lethal mutations: cause death of an organism Causes of Mutations - DNA fails to copy accurately - External influences can create mutations: agents that cause DNA to breakdown in someway and copy inaccurately Migration - also known as gene flow - any movement of genes from one population to another - ex.: pollen being blown - genes are carried to a new population Sex and Migration - sex can introduce new gene combinations into a population and is an important source of genetic variation - genetic shuffling Genetic Variation - polygenic variation is caused by several many loci - a lot of natural traits tend to distribute themselves in a very organized fashion - normal distribution: occurs so frequently in a population - ex.: number of dermal ridges varies in a normally distributed pattern Sources of Variation - a given genotype has an average phenotypic value but individuals sharing this genotype vary because of environmental effects - genetic variance: average amount of variance among phenotypes - environmental variance: average amount of variance among individuals within the same genotype Components of Phenotypic Variation - phenotypic variance = genetic variance + environmental variance (V = V + p G V ) E 2 - heritability (broad sense) = h B = VG/(V G V ) E Just the Genes Please! 2 - heritability (narrow sense) = h N = VA/V P - the proportion of phenotypic variance that is caused by additive genetic variance - VA= additive genetic variance (V = cGnsists of additive and non additive components 9e.g. dominance and other gene interactions)) - VAdepends on both the magnitude of additive effects of alleles and allele frequency - Polygenic trait: many genes contributing to a trait - NSA: what proportion of a strait is accessible to natural selection Heritability of Beak Size (0.9) - narrow-sense heritability equals the slope of the regression (y=bx) - beak size from parents are quite as well passed down to offspring - we have to know:  what were selecting for  S = z s z p Selection Differential, S - the difference between the mean trait of selected parents and the population mean - S = z – z - s Response to Selection when Heritability is High - something that dissociates the two groups from one another - ex.: 13 – 10 = 3 - we want to see what happens in the next generation, how reliably are those genes passed on V Anables a Response to Selection - the additive effects of allele (V ) Are responsible for the degree of similarity between parents and offspring - response to selection (R): a change in the mean character state of one generation as a result of selection in the previous generation - R = Z –RZ , P3 – 10 = 3 - NSH = R/S, 3/3 = 1 - Response you see from offspring is consistent with selection criteria, you can say reliably all genes are passed on from parent to offspring Response to Selection when Heritability is High Response to Selection when Heritability is Low - 11 – 10 =1 - 1/3 Heritability of Phototaxis in Fruit Flies - mean parental score = 9 - mean of selected parents = 12 - mean offspring score = 9.27 - so h2N = 0.09 Conclusions - variation in biological traits typically has genetic and environmental factors - genes and environment always interact to create a phenotype - we can identify the heritability of a trait and predict its response to selection Genetic Refresher - chromosome: a long strand of DNA consisting of different genes - gene: the functional unit of heridety. A sequence of DNA that is transcribed into RNA mRNA: messanger RNA - locus: a site on the chromosome occupied by a certain gene - allele: one of several forms of the same gene (dominant vs. recessive, homozygote vs. heterozygote) - mutation: alteration of a DNA sequence Most Traits are Polygenic - many genes involved in the trait’s expression - quantitative trait loci (QTL’s): the gens that control polygenic traits - mapping of QTL’s: if the inheritance of a genetic marker is associated with the inheritance of a particular trait, the marker must be linked to the trait Psychiatric Genetics - my laboratory is investigating the genetic basis of psychiatric disorders, in particular the origins of stress related conditions, such a anxiety and depression, for which we have relatively ineffective treatments. Knowing more about the biological basis of these very common disorders is a starting point for developing better therapies and the more efficient use of those we already have QTL’s for Emotionality - open field arena - lelves of activity and defecation are heritable and negatively correlated - 2 QTL’s were identified on the mouse chromosomes 1 and 12 (correction) - these may be related to human genes affecting anxiety Evolutionary Value of Anxiety - certain levels of emotions such as anxiety, depression and love are adaptive Genes and Behaviour - genetic analysis using DNA microarrays, allow us to understand the genetic basis of some very complex behaviours - collect mRNA from two samples of bees - transcribe the mRNA to the more stable complementary DNA (cDNA) - mark each sample with a distinct fluorescent label DNA Microarrays - microarray contains in each spot numerous copies of single-stranded DNA representing a gene Genetics of Behavioural Development - two distinctions in behaviour - behaviour they take on depends on their age Genetic Activity in Bees’ Brains - analysis of ~5500 genes (out of ~14,000) - ~2000 genes showed distinct expression in nurses and foragers Genetics of Behavioural Development - yellow: high level of increased expression - blue: high level of decreased expression - opposite expressing profile - two reasons for differential expression:  age difference, not the age that’s the distinguishing factor but;  the behaviour that they are taking on Environmental Effects - colony needs affect the transition from nurse to forager - will this affect the genes that are active - over abundance of nursing bees if none adjust their behaviour - resident bees will change their behaviour and prematurely begin to forage when younger bees have been add
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