3 - Sexual Selection.docx

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Western University
Psychology 3229A/B
Scott Mac Dougall- Shackleton

UNIT 3  Behaviour Genetics o Types of gene variation that result in behaviour variation o Single gene variations o Chromosomal variation o Quantitative variation (polygenism)  Methods o Inbreeding o Artificial selection o Hybridization o Mutation and screening studies o Genetic engineering  Single Genes and Behaviour o Allelic variation at single gene results in variation in behaviour o Mendelian inheritance patterns o Two heterozygous parents  Offspring ¾, ¼  Fearfulness in Basenji hounds o See slide  Human Single Genes o Sickle-cell anemia  Anemia, but increased malarial resistance o Lactose production  Lactose intolerance o Tongue rolling  Single Gene Effects o Usually determined through controlled breeding experiments (or study family trees) o Pattern of inheritance suggests number of genes and alleles involved o Determination of molecular aspects of gene requires further study to identify gene and its regulation  Chromosomal Variations o Chromosome number  Change un number of chromosomes  Trisomy 21 (Down’s syndrome)  Sex differences, XX vs. XY  Various sexual disorders (XO, XXY)  Quantitative Genetics o Phenotype depends on effects of many genes o Different genes for different components of trait o Additive and subtractive effects of many genes  Quantitative Traits o F1 offspring exhibit intermediate trait o Many genes, each gene sorts independently o Additive effect intermediate  Nest Building in Mice o Artificial selection for large or small nest o Control line (random mating) o After 15 generations, large difference o Crosses of different large nest strains result in average size nests  Different strains have had different genes affected  Maze Running o Tryon successfully artificially selected for maze-running ability  Maze bright and maze dull o Learning to run a maze has inherited factors  Can be subject to selection  Quantitative Traits o Gene-gene interactions o Gene-environment interactions o Most traits are polygenic o Most genes are pleiotropic  Modern Synthesis o Both evolutionary theory and genetics have advanced tremendously since the modern synthesis o Provides a robust and detiled understanding of evolution and selection Sexual Selection Theory  Selection of traits relating to reproduction, rather than survival  Traditionally divided o Inrasexual selection: male-male combat o Intersexual selection: female choice  Mechanisms o Intrasexual selection  Scrambles  Endurance rivalry  Contests  Sperm competition o Intersexual  Mate choice  Scrambles o Early search and swift location of mates o Well-developed sensory and locomotory organs o Many insects  Males have larger eyes, antennae and locomotory organs than females  Endurance Rivalry o Ability to remain reproductively active for long portion of breeding season o Antechinus (insect eating marsupial) remains at breeding site until it starves  Contests o Contest following copulation  Mate guarding  Sequestering  To remove mate or segragte  Mating plugs  Vaginal plug  Frequent copulation  Sperm displacement/interference  Infanticide  Infanticide o New males kill offspring, or sometimes induce abortion (rodents – Bruce effect: females terminate pregnancy at scent of unfamiliar male)  Lions, tigers, primates, birds o Female infanticide in sex role reversed species (watted jacanas) o Reproductive strategy o Evolution of female groups o Highlights importance of levels of analysis o Ultimate  Reproductive strategy, product of sexual selection o Proximate  Overcrowding, aberrant behaviour  Mate choice o Members of one sex compete amongst each other to be chosen by opposite sex o Choosiness increases as parental investment increases (usually female>male choice) o Results in behaviour and morphology that attracts and stimulates females  Mate Choice Criteria o Material benefits  Nuptial gifts, sexual cannabilism  Territory  Sperm quality  Parenting ability o Non-material benefits  ‘good genes’  Evolution of Mate Choice o Honest advertising vs arbitrary signals o Runaway selection o Indicator mechansisms ( honest advertising, handicaps) o Sensory bias  Pre-existing preference for a trait  Runaway Selection o Genetic basis for an initially arbitrary female preference o Advantage to females to have sons with that trait (sexy sons) o Trait and preference co-evolve because they are genetically linked o Can lead to very rapid evolution  Positive feedback, random directions o Great divergence between closely related species o May produce large or small sex differences  Dependent on mutual mate choice o Female mate choice  Exaggerated male ornaments o Mutual mate choice  ‘species recognition’ features  Indicator Mechanisms o Handicap principle  Offsprings that can handle the costs (i.e. survive) of these traits show  Offspring viability, good genes  Immune function o Genetic compatibility  Mens t-shirt study  Better odors related to compatible genes  Handicap Principle o Traits are costly to produce o Only high quality males can afford the cost o Signal is therefore honest indicator of quality o Costs of Producing a Signal  Energetic cost  Roaring of red deer  Increased risk of predation  Bright colours  Long tails  Cost of maintaining a trait  High testosterone levels  Depress immune function  Suppress parental and other behaviour  Genetic compatibility o Preference for compatible genes rather than ‘good’ genes  i.e. MHC locus – immune function  increase heterozygosity of offspring  Male and Female Reproductive Strategies o Males and females differ in reproductive strategy as a result of differences in  Reproductive potential  Parental investment  Reproductive potential o Females limited by number of eggs o Males limited by number of fertilization  Reproductive Investment o Ansiogamy  Different gamete size  Females have greater investment of conception o Additional investment  Gestation, lactation o
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