Terminology. Population Size and Extinction. Terminology. Population Size and Extinction. Population Size and Extinction

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1 Terminology Science is simply common sense at its best that is, rigidly accurate in observation, and merciless to fallacy in logic. Thomas Henry Huxley Locus Allele Gene Chromosome Homozygote Heterozygote Polymorphic Monomorphic Terminology Polygenic Epistatic Genotype Phenotype Quantitative trait Neutral Marker Population Size and Extinction Small populations are more likely to go extinct than large populations Genetics Demographic Population Size and Extinction Population Size and Extinction 1

2 Genetic Variation and Population Size Genetic Variation and Population Size Black-footed rock wallaby Genetic Variation & Population Size Genetic drift and heterozygosity Larger population sizes have more heterozygosity. Halocarpus bidwilli Picoides borealis Genetic drift results in a gradual loss of genetic diversity Follow an individual locus and allele frequency will drift until one allele becomes fixed Genetic drift Genetic Variation & Fitness 107 populations of Drosophila 16 individuals per population 2

3 Inbreeding &Population Size Inbreeding Inbreeding is related to population structure Consider (a) one large panmictic population (b) lots of small, discrete populations Identity by descent = Probabilities Probability of event A happening AND event B happening = P A x P B Probability of event A happening OR event B happening = P A + P B (if A & B mutually exclusive) assume every allele in initial population is different IBD = probability of this individual carrying two copies of the same allele Identity by descent Probability of black allele being passed down left hand side = 0.5 x 0.5 x 0.5 = 1/8 Probability of black allele being passed down right hand side = 0.5 x 0.5 x 0.5 = 1/8 Probability of individual at bottom getting two black alleles = 1/64 Same argument for yellow allele = 1/64 Probability of getting 2 copies of black or 2 copies of yellow = 1/64 + 1/64 = 1/32 Inbreeding in finite populations Previous examples showed inbreeding in known pedigrees through IBD What about in finite populations? In a finite population, there is some probability of mating with a relative This probability increases with subsequent generations 3

4 Inbreeding in finite populations Assume a population size of N, therefore 2N alleles in population Imagine eggs and sperm released randomly into environment (e.g. sea) Inbreeding in finite populations Assume a population size of N, therefore 2N alleles in population Imagine eggs and sperm released randomly into environment (e.g. sea) What is the probability of 2 gametes drawn randomly having the same allele? Why? Inbreeding in finite populations gen 0 gen 1 You already have one allele with which you started, thus you only need to pick 1 additional allele probability = 1/(2N) 2N alleles Therefore, after 1 generation the level of inbreeding is F 1 = 1 / 2N After t generations the probability is Why? More generally gen t-1 gen t 1/(2N) 1-1/(2N) Probability of picking 2nd allele Probability of picking 2nd allele & it is already inbred Genetic Drift F t = Probability that any 2 alleles drawn randomly from the population are identical by descent 4

5 Measures of Inbreeding 1. Inbreeding coefficient F Parents Unrelated Brother to sister, mother to so, etc Half sibs (half brother to half sister) First cousins Selfing (self-fertilization) Offspring F Extinction Factors Extinction Vortex Inbred individuals are less fit then outbred individuals Deleterious recessive mutations tend to become apparent in inbred individuals Inbred individuals may have lower reproductive success, lower survivorship or lower resistance to parasites Inbreeding and Survival Inbreeding and Survival Inbreeding increases juvenile mortality Inbreeding & Survival Inbreeding and Survival Inbreeding doesn t influence all species the same or does it? 5

6 Inbreeding and Survival Inbreeding and conservation genetics Inbreeding doesn t influence all species the same or does it? Inbreeding has greatest effects in small populations or populations that have suffered a bottleneck Loss of genetic diversity in the cheetah severe bottleneck in its past Inbreeding example 1 Keller et al Nature 372: Distribution of inbreeding coefficients for survivors/non-survivors Sparrows on Mandarte Is., BC Inbreeding associated with poor survivorship Paternities determined by genetic fingerprinting Population crash Survivors less inbred than those that die survivor non-survivor inbreeding coefficient Before crash After crash Adults (n=74) (n=7) Juveniles (n=132) (n=3) Inbreeding example 2: Soay sheep on St. Kilda (Coltman et al Evolution 53: ) Soay sheep subject to parasitism by intestinal nematodes Use markers distributed through the genome Heterozygous individuals appear best able to resist infection and to survive 6

7 Heterozygosity & parasitism Heterozygosity & survivorship filled, low-density years open, high-density years (FEC = fecal egg count of strongyle nematodes) filled, low-density years open, high-density years (survivorship of lambs over winter) Factors acting against genetic drift No matter how big a population, genetic drift will eventually drive all loci to homozygosity (i.e. all alleles at all loci in all indvs. identical by descent) Mutation and migration counters genetic drift Analysis of effect of these processes identical. We see only what we know. Johann Wolfgang von Goethe It requires a very unusual mind to undertake the analysis of the obvious. Alfred North Whitehead EVOLUTIONARY PROCESSES AND PATTERNS Theories of species creations and diversity prior to evolutionary theory Theory of Special Creation Species are unchanged through time and are independent of one another All species were created independently by the Trinity on the October 26th 4004 B.C. at 9:00 in the morning Archbishop James Ussher EVOLUTIONARY PROCESSES AND PATTERNS Theories of species creations and diversity prior to evolutionary theory Theory of Spontaneous Generation New organisms (species) may suddenly appear wherever conditions are suitable Some new life-forms arise spontaneously from streams, soils, totting meat, and other nonliving materials; not all live arises directly from living organisms 7

8 VanHelmont s evidence for spontaneous generation for if you press a piece of underware soiled with sweat together with some wheat in an open mouth jar, after about 21 days the odor changes and the ferment coming out of the underwear and penetrating through the husks of the wheat, changes the wheat into mice. But what is more remarkable is that mice of both sexes emerge (from the wheat) and these mice successfully reproduce with mice born naturally from parents But what is even more remarkable is that the mice which came out were not small mice but fully grown s EVOLUTIONARY PROCESSES AND PATTERNS Theories of species creations and diversity prior to evolutionary theory Prior to Darwin and Wallace - Lamarck New simple life forms arise by spontaneous generation and change over time into more complex life forms Individuals change in response to their environment and the changes are passed to the next generation. EVOLUTIONARY PROCESSES AND PATTERNS Theories of Evolutionary Darwin and Wallace Species are related to one another, and they change over time, thus species existing today have descended, with modifications, from other preexisting species. Natural selection acts on individuals; individuals with certain favorable characteristics will produce more offspring. All natural selection results in evolution, but not all evolution is the product of natural selection. What is evolution? What is natural selection? What is an adaptation? All natural selection results in evolution, but not all evolution is the product of natural selection. What is evolution? Evolution is the change in allele frequencies (or traits) over time. Selection Natural Sexual Genetic drift Mutation Migration 8

9 All natural selection results in evolution, but not all evolution is the product of natural selection. What is evolution? Evolution is the change in allele frequencies (or traits) over time. What is natural selection? What is an adaptation? All natural selection results in evolution, but not all evolution is the product of natural selection. What is evolution? Evolution is the change in allele frequencies (or traits) over time. What is natural selection? Natural selection is the differential reproductive success resulting from an adaptation. What is an adaptation? All natural selection results in evolution, but not all evolution is the product of natural selection. What is evolution? Evolution is the change in allele frequencies (or traits) over time. What is natural selection? Natural selection is the differential reproductive success resulting from an adaptation. What is an adaptation? An allele (or trait) which provides superior reproductive success to an individual possessing it relative to an individual with a different allele (or trait). Sum it all up Natural selection for an adaptation results in evolution. What can selection do to a trait? If a trait is under selection, what are the possible results? 9

10 Inlet Midcavity Outlet Chimp Lucy Human m2 Female Mimicry a - unpaired male (m) assumes female coloration and posture while approaching the female (f) as the consort male (c) fights with an approaching male (m2) b - the female accepts a mating by the female mimic while the consort continues fighting with the approaching male c - The consort male allow the female mimic to finish mating without interruption, even when he is not distracted by the other male 10

11 Seeds Ticks off of iguanas etc. Tools use to get insects Leaves and fruit Insects, spiders, nectar Is there variation about a trait? Is the variation heritable and not the result of maternal effects? Is there an excess of individuals so that only some animals live to reproduce? Is there an excess of individuals so that only some animals live to reproduce? Is reproduction nonrandom? The drought of 1977 eliminated seed set by most of the plants producing small soft seeds. Tribulus cistoides seeds are large and hard and became the dominant food item. Only large birds with deep beaks could defend resources and access the resources 11

12 Is reproduction nonrandom? Did evolution occur? The El Niño of 1983 produced 1359 mm of rain and lavish seed set by the small soft seeded plants. Birds with shallow beaks harvest these seeds more efficiently and thus reproduced better than birds with deep beaks, undoing the selection shown here. Fluctuating environmental conditions maintain both phenotypes. At what level does selection occur? Gene for the good of the gene. Individual for the good of the individual. Group for the good of the group. Population for the good of the population. Species for the good of the species. THE INDIVIDUAL NOT THE GROUP!!! * *In silico (computer simulations) do show specific conditions where group selection can work but This has never been seen in nature NEVER THE SPECIES!!! 12

13 P.S. THERE IS NO ALTRUISM! 13

14 Why does it appear that some animals help others at a cost to themselves? Hamilton s inclusive fitness Direct Fitness Personal reproduction Indirect Fitness Relatives reproduction Br - C > 0 What are the units of B and C? Fitness must be in addition to that which you would have gotten from the relative regardless of the behavior! Who will you save from a fire? Brother Cousin 1 Cousin 2 Father Friend Mother Sister Spouse Who will you save from a fire? Brother - Age 21 Cousin 1 - Age 19 Cousin 2 - Age 20 Father - Age 65 Friend - Age 23 Mother - Age 63 Sister - Age 22 Spouse - Age 25 Who will you save from a fire? Brother - Age 21 Cousin M - Age 23 Father - Age 65 Mother - Age 63 Sister - Age 22 Cousin F - Age 19 Spouse - Age 25 Cousin F - Age 20 14

15 Who will you save from a fire? Brother - Age 21 Cousin M - Age 23 Father - Age 65 Mother - Age 63 Sister - Age 22 Cousin F - Age 19 Spouse - Age 25 Cousin F - Age 20 Who will you save from a fire? Brother - Age 21 Cousin M - Age 23 Father - Age 65 Mother - Age 63 Sister - Age 22 Cousin F - Age 19 Spouse - Age 25 Cousin F - Age 20 Who will you save from a fire? Brother - Age 21 Cousin M - Age 23 Father - Age 65 Mother - Age 63 Sister - Age 22 Cousin F - Age 19 Spouse - Age 25 Cousin F - Age 20 Who will you save from a fire? Brother - Age 21 Cousin M - Age 23 Father - Age 65 Mother - Age 63 Sister - Age 22 Cousin F - Age 19 Spouse - Age 25 Cousin F - Age 20 The Modern Synthesis Combines genetics, geology, and natural selection Gradual evolution results from small genetic changes acted upon by natural selection Speciation and macroevolution can be explained by microevolution given the age of the earth Modern Synthesis - Darwin s postulates restated Mutation is the ultimate source of all variation, segregation and independent assortment create novel combinations of alleles Alleles are passed between generations More offspring are produced than can survive Individuals with the most advantageous allelic combination for the current situation produce more offspring. 15

16 God does not play dice with the universe. Albert Einstein Who are you to tell God what to do? Neils Bohr Not only does God play dice, but he throws them where we cannot see them. Stephen Hawkings Happy is he who gets to know the reason for things. Virgil 16