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Lecture 3

Evolution - Week 3 Notes

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Psychology 3229A/B
Scott Mac Dougall- Shackleton

Week 3 - Sexual Selection Unit 3.1 - Behaviour Genetics ● Behaviour genetics - types of gene variation that result in behavioural variation ● Single gene variations ● Chromosomal variations ● Quantitative variation (polygenism) ● Methods: ● Inbreeding ● Artificial selection ● Hybridization ● Mutation and screening studies ● Genetic engineering ● Single gene variations ● Allelic variation at single gene results in variation in behaviours ● Simplest relationship between genes and behaviour ● Mendelian inheritance patterns (traits that depend upon 1 or 2 loci) ● Punnett Square ● Round and wrinkled peas ● R=allele for round pea (dominant) ● r=allele for wrinkled pea (recessive) ● Two heterozygous parents: Offspring will be 3/4 round; 1/4 wrinkled ● Fearfulness in Basenji hounds ● Basenji hound puppies - fearful, retreat from strangers ● Fearful (FF) ● Cocker spaniel puppies - bold, approach strangers ● Bold (ff) ● F1 generation - all fearful (Ff) ● F2 generation - 3/4 fearful (FF, Ff, fF); 1/4 bold (ff) ● Human single genes ● Sickle-cell anemia - anemia, but increased malarial resistance ● Lactase production - lactose intolerance ● Tongue rolling ● Single gene effects ● Usually determined through controlled breeding experiments (or study of family trees) ● Pattern of inheritance suggests number of genes and alleles involved ● Determination of molecular aspects of gene requires further study to identify gene and its regulation ● Chromosomal variations ● Chromosome number - change in number of chromosomes ● Trisomy 21 (extra chromosome 21; Down's syndrome) ● Sex differences - XX vs XY ● Various sexual disorders (XO, XXY) ● Quantitative variations (polygenism) ● Polygenism - idea that trait depends upon lots of genes that contribute in a lot of ways to the trait ● Eg. Height is influenced by several factors ● Phenotype depends on effects of many genes ● Different genes for different components of trait ● Additive and subtractive effects of many genes ● F1 offspring exhibit intermediate trait ● Many genes, each gene sorts independently ● Additive effect intermediate ● Nest-building in mice ● Artificial selection for large or small nest ● Each generation, study how much cotton is used to make a nest; researchers then select for large and small nest, and never crossed them ● Over generations, became big differences in nest size ● Control line (random mating) ● After 15 generations, large difference ● Fact that nest size responded to selection, shows that ● Single locus or polygene? ● When crossed once, mice were building average sized nests (back to natural wild genes) ● When artificial selection was done, genes changed; different genes changed in different lines ● Crosses of different large nest strains result in average size nests ● Different strains have had different genes affected ● Maze-running mice ● Tryon successfully artificially selected for maze-running ability ● Maze 'bright' and maze 'dull' ● Learning to run a maze has inherited factors ● Can be subject to selection ● Artificially selected mice that were really smart (aka could solve mazes) ● Maze-solving ability appeared to have genetic basis ● After selection of generations, 'maze brights' had less errors than 'maze dulls' ● New researchers then raised rats in different environments (but otherwise same study) ● Genetic difference was apparent ● In enriched condition, no difference between groups ● In impoverished environment, both groups did poorly ● Highlights fact that traits which clearly have genetic basis, how phenotype is expressed and influenced by environment ● Quantitative traits include ● Gene-gene interactions ● Gene-environment interactions ● Most traits are polygenic ● Most genes are pleiotropic ● The Modern Synthesis ● Both evolutionary theory and genetics have advanced tremendously since the 'modern' synthesis ● Provides a robust and detailed understanding of evolution and selection Unit 3.2 - Sexual Selection Theory ● Sexual selection - selection of traits relating to reproduction, rather than survival ● Traditionally divided: ● Intrasexual selection- male-male combat ● Intersexual selection - female choice ● Mechanisms: ● Intrasexual selection: 1. Scrambles ● Early search and swift location of mates (get to females quickest) ● Well-developed sensory and locomotory organs ● Many insects: males have larger eyes, antennae, and locomotory organs than females ● Occurs in species where mates are available for a short period of time and location 1. Endurance rivalry ● Ability to remain reproductively active for long portion of breeding season ● Antechinus(insect-eating marsupial) remains at breeding site until it starves ● Males who can last the longest without eating will have the most success 1. Contests ● Traits that improve success in fights ● Interference with mating success of rivals ● Alternative mating tactics of smaller competitors (sneaker males) ● Another type of male, who is small and mimics females to sneak into female grounds can mate with them while other males are competing ● Men sheds sperm and stays and cares for eggs ● Other males dump load of sperm then swim away 1. Sperm competition ● Contest following copulation (LOOK ALL THESE UP) ● Mate guarding ● Sequestering ● Mating plugs - observed in insects and some mammals; blocks reproductive tract of female so no other males can fertilize their eggs ● Frequent copulation ● Sperm displacement ● Infanticide ● New males kill offspring, or sometimes induce abortion (rodents - Bruce effect) ● Lions, tigers, primates, birds… ● If male lion takes over pride of another female, will try to kill off infants in pride ● Male frees up females to have his own offspring ● Female infanticide in sex role reversed species (wattled jacanas) ● Reproductive strategy ● Evolution of female groups ● Highlights importance of levels of analysis ● Ultimate - reproductive strategy, product of sexual selection ● Proximate - overcrowding, aberrant behaviour ● Intersexual selection: 1. Mate choice ● Members of one sex compete amongst each other to be chosen by opposite sex ● Choosiness increases as parental investment increases (usually female > mate choice) ● Results in behaviour and morphology that attracts and stimulates females ● If you have females who are gestating, lactating, and caring for infants for years, should be more choosy about who the other parent is because there's more on the line ● Mate choice criteria ● Material benefits ● Nuptial gifts, sexual cannibalism ● Territory ● Sperm quality ● Parenting ability ● Non-material benefits ● 'Good genes' ● Evolution of mate choice ● Honest advertising vs arbitrary signals ● Runaway selection ● Genetic basis for an initially arbitrary female preference ● Advantage to females to have sons with that trait (sexy sons) ● Trait and preference co-evolve because they are genetically linked ● Can lead to very rapid evolution ● Positive feedback, random directions ● Great divergence between closely related species ● May produce large or small sex differences ● Dependent on mutual mate choice ● Female mate choice - exaggerated male ornaments ● Mutual mate choice - 'species recognition' features ● Indicator mechanisms (honest advertising, handicaps) ● Handicap principle ● Offspring viability, good genes ● Immune function ● Traits are costly to produce ● Only high quality males can afford the cost ● Signal is therefore an honest indicator of quality ● Cost of producing a signal ● Energetic cost ● Roaring of red deer ● Increased risk of predation ● Bright colours, long tails ● Cost of maintaining trait ● High testosterone levels (more likely to show aggression) ● Depress immune function (increased risk of cancer) ● Suppress parental and other behaviour ● Genetic compatibility ● Preference for compatible genes rather than 'good' genes ● Eg. MHC locus-immune function ● Idea of good MHC complex is diverse ● Want lots of variations so it can react to lots of different pathogens ● You want to mate with somebody who has completely different
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