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Lecture 14 - Announcements Tutorial 3 running this week...

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Unformatted text preview: 3/8/2011 Announcements Tutorial # 3 running this week Midterms marks posted on Blackboard & exams returned in tutorial Genetic Drift Biodiversity Average 62% Last day to drop courses: March 13th day to drop courses: March 13th Final Exam: – Tuesday April 26, 2-5pm – A-Sc: EX200 – Se – Z: EX100 March 8, 2011 ENV200H1S 1 2 Review Outline Evolution is “survival of the fittest” – Fitness defined as number of offspring that survives to the next generation Adaptations that improve fitness are selected for Adaptations possible because of genetic diversity Mutation is one source of genetic diversity Mechanisms capable of changing gene frequency (evolution) – Natural selection – Sexual selection – non-random mate choice non– Genetic drift – Founder Effect Genetic drift – Founder effect Biodiversity – Definition – Benefits & Importance 3 Fitness and Genetic Load Each of us carries 5 to 8 lethal alleles which, if homozygous, would likely cause death. The more lethal alleles found in a population, the greater its genetic load (The difference between the theoretical fittest genotype of a population and the average fitness of that population) Inbreeding Inbreeding among individuals carrying a genetic load will will increase the frequency of 2 individuals with similar deleterious alleles mating – increasing homozygosity of deleterious alleles As homozygosity rises through inbreeding, a positive feedback loop known as inbreeding depression sets in - characterized by reduced survival of offspring, low birth weights, and infertility among other things. (Anybody who breeds dogs, cats or fancy goldfish 5 already knows this!) e.g. hemophilia in european royal families Queen Victoria arranges marriages for her children and grandchildren with royal families of Europe (to strengthen political ties). In Spain and Russia, the plan backfires leading to political unrest as the royal children are discovered to be hemophiliacs antianti-British sentiments are fueled as the blood of Britain is fueled as the blood of Britain is considered considered “tainted.” (In Russia, Rasputin is believed to have come to power primarily because Czarina Alexandra was so unhinged over her hemophiliac son, Alexis.) Interestingly, this particular mutation seems to have started with Victoria as hemophilia was unknown in her ancestors. 1 3/8/2011 In small populations, gene frequencies can change randomly in a process known as genetic drift Reach into a pile of pennies and pull out six. If there were five heads and one tail or 4 heads and 2 tails, you would not be particularly surprised However if you pulled out 600 pennies, we would expect the results to be closer to 300 heads, 300 tails (e.g. we really don’t expect 400 heads and only 200 tails) In a small sample, chance can cause a departure from the expected result In the next generation . . . This process of random fluctuation continues generation after generation, because the population has no "genetic memory" of its state Each generation is an independent event. However as an allele’s frequency decreases, it could become less likely to be sampled and a positive feedback process sets in where the allele continues to spiral down in frequency (assume a population of 100). – – – – – 50 heads/50 tails (pull out 10: 6 heads/4 tails) (p Next generation: 60 heads/40 tails (pull out 10: 6 h/4 t) Next generation: 60 heads/40 tails (pull out 10: 7 h/3 t) Next generation: 70 heads/30 tails (pull out 10: 8 h/2 t) Next generation: 80 heads/20 tails (pull out 10: 9 h/1 t) It is possible that an allele could disappear completely simply as the result of random chance. 7 Why might we care if drift changes allele frequencies in small populations (particularly why should we worry about the risk of allele loss)? It’s genetic diversity that allows organisms to adapt to change If environmental conditions change, the population may not have any significant ability to “respond” (evolutionarily) to the changed conditions (if they have no underlying diversity for natural selection to work on). Concern wrt genetic drift helps us understand the definition of a minimally viable population (MVP) - 50 breeding pairs and 500 individuals - is the minimum population size that is statistically “immune” to genetic drift for about 100 years (depending on generation time). To protect extant genetic diversity in perpetuity, populations need to have between 2500 and 5000 individuals. 8 Small populations (subject to drift) can arise from founder effect – particularly of concern when we try to rere-constitute a population from just a few individuals (or when only a few individuals survive some severe impact) Imagine that you and 9 other people are the only survivors of the human race (or the 10 of you end up traveling to Mars). traveling to Mars). Your group cannot possibly contain the full genetic diversity of all humans on the planet Nevertheless (assuming the group has both sexes), you could form a breeding population. After many generations there might be millions of people. But this second human race would be substantially genetically different from our current human race reflecting the genetics of the “founding” individuals. 9 founder effect can be important when a small group of individuals leaves to “found” a new population in a new environment but it can also be important when a catastrophic event reduces a population to a few survivors (a sub-set of original genetic diversity): the subevent is termed a genetic bottleneck From a laboratory exercise designed by Bill Armstrong 11 10 Examples of species that have passed through genetic bottlenecks Lions of Ngorongoro Crater, Tanzania – In 1962 a plague of biting flies killed almost all the lions in the park (leaving 9 females and 1 male) – This population is geographically restricted to the Crater which cuts res th off emigration/immigration – While the population has rebuilt to approximately 125 individuals, their allelic diversity is different and much lower than that of lion populations in other locations The concern – from a biodiversity perspective - is the ability of this population to respond to environmental change! 12 2 3/8/2011 The elephant seal was hunted almost to extinction in the 1800s By the 1890s only about 20 survived. Elephant seals breed in harems, with a single male mating with a group of females, so one male may have fathered all the may have fathered all the offspring offspring at the extreme bottleneck point. The population today has expanded to about 30,000, but biochemical analysis shows that all elephant seals are virtually genetically identical. Conservation of Biological Diversity The concern – from a biodiversity perspective - is the ability of this population to respond to environmental change! 13 Biodiversity BIODIVERSITY Biodiversity – number of Earth’s organisms - richness of biological variation Possible partly because the earth has many different combinations of environmental conditions Range of environmental types can be classified into broad categories: BIOMES Biodiversity – richness of biological variation. Genetic Diversity - Measures variety of different different versions of same genes. Species Diversity – Species richness Measures number of different kinds of organisms within a community. Ecological Diversity - Measures richness and complexity of a community. 15 High levels of genetic diversity is generally desirable More likely to be adaptable to changes in environmental conditions More likely to survive, have enhanced fecundity, greater resistance to diseases fecundit Conversely small populations with low genetic diversity at risk of inbreeding and low adaptability to environmental changes 17 16 Species Diversity Number of different kinds of species within individual communities or ecosystems 18 3 3/8/2011 Species Richness Species Richness Number of different species in a community Varies greatly Depends on available niches Species Evenness How Many Species? (dominance) The extent to which number of individuals of different species are equal or skewed 5 species with 50 individuals 10/10/10/10/10 46/1/1/1/1 Inversely related to: Geographic isolation Environmental stress Greater at edges of adjacent communities: why? Ecotone: transitional zone Ecotone: Edge effect Geologic history also important: why? Reduced when one species is dominant Currently 1.7 - 2 million species of plants, animals and microorganisms identified. 35% known species live in tropics 59% in temperate zones Remaining 6% in boreal or polar latitudes Invertebrates make up 70% of all known species, and probably most of yet to be discovered species. Estimates of total species richness can range between 3-100 million (best est of ~5-30mill). 3~5 With 90% living in the tropics, particularly rainforests 21 22 Ecological Diversity Measures richness and complexity of a community. 23 Includes number of niches, trophic levels, and ecological processes that capture energy, sustain food webs, and recycle material material 24 4 3/8/2011 Why Should We Care? Value and Importance of Biodiversity natural landscapes contain species and communities that have evolved together Examples of ecosystem level biodiversity losses losses in Canada Only 0.2% original area of tall-grass prairie tallremains Virtually all Carolinian forest of SW Ontario destroyed Old growth forests in coastal BC Wetlands throughout southern Canada 25 Benefits of Biodiversity Food Security Drugs and Medicines Ecosystem services Maintenance of ecosystem function Biological processes Organisms are interdependent Aesthetic, recreational and Cultural Benefits Environmental Monitoring biomimicry Intrinsic value 26 Medicinal Value Food Security Genetic diversity infers potential for disease resistance As many as 80,000 edible wild plant species could be utilized by humans. ld Drugs and Medicines 25% of all pharmaceuticals in the US contain ingredients originally derived from native plants Pharmaceutical companies actively prospect tropical countries for products. Species provide many medicines Rosy periwinkle: childhood leukemia AZT Treat AIDS Derived from a sponge 20 best selling prescription drugs in U.S. 27 Ecosystem Services Free of Charge 29 Processes by which the environment produces resources or provides services that we often take for granted but granted, but upon which we are dependent. dependent. 30 5 3/8/2011 Estimates of Ecosystem Services (trillion $US) Ecosystem Services Provides food, fuel, and fibre Provides shelter and building materials Purifies air and water Detoxifies and decomposes wastes Stabilizes and moderates Earth’s climate Moderates floods, droughts, wind, and droughts wind and temperature temperature extremes Generates and renews soil fertility and cycles nutrients Pollinates plants, including many crops Controls pests and diseases Maintains genetic resources as inputs to crop varieties, livestock, and medicines Provides cultural and esthetic benefits Gives us means to adapt to change Estimates that annual value of 17 of these ecosystem services range from: $16 $16 trillion to $54 trillion trillion per year 31 32 6 ...
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