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Unformatted text preview: Introductory Biology II: EEMB 2 Ecology of Evolution Basic Concepts of Adaptation, Fitness, and Natural Selection Introduction to Evolution Genotype The hereditary material or set of genetic instructions that partly determine an organism's structural, physiological, and behavioral characteristics Phenotype The physical expression of the genetic instructions in the genotype In a general sense, they phenotype must provide three things: 1. Secure raw materials for growth and reproduction (G) 2. Protection from enemies (P) 3. Produce offspring (F = fecundity) Why this allows us to strip away all unnecessary complexity and focus on the process rather than the details Consider a hypothetical plant: To keep analysis simple, make three simplifying assumptions 1. Annual life cycle 2. Asexual reproduction 3. Entire phenotype coded by a single gene Suppose we plant five different genotypes (A,B,C,D,E with 10 seeds of each) into a natural meadow: We will describe the phenotypes in terms of a resource budget This phenotype has equal investment in all 3 functions This phenotype invests mainly in fecundity Reflects tradeoffs of energy, minerals, etc., put into growth, protection, and fecundity If more resources are put into one function, then there is less left over for the other functions 50 = Total Total = 61 1. Does the population reproduce itself? Yes 50 seeds --> 61 seeds so population growing by >20% / gen. 2. Does each genotype reproduce itself? No, this concept is best answered by developing concept of the gene pool Gene pool: abstract assemblage of all genes in a population. 3. What is the measure of the biological "success" of Ecology of Evolution 1 a genotype? Darwinian Fitness is abbreviated Fitness Fitness: the number of genome copies an organism places into the next generation 4. Which phenotypes will ultimately predominate within the population? Why? D & E will increase in frequency each generation until all other genotypes are eliminated 5. Suppose a new herbivore was introduced into the meadow so that the level of damage produced by herbivory was raised, but only slightly. Which phenotype has highest fitness now? E Note: This example indicates that fitness is not an intrinsic characteristic of an organism, but rather a measure of the match between the characteristics of an organism and the prevailing demands of the environment. 6. Does any one attribute (G,P,F) determine fitness? No, it is the combination relative to the demands of the environment. 7. In general terms, what is the function of the phenotype? To be an effective gene transport machine Generalized task of the phenotype: To transport as many gene (genome) copies as possible from one generation to the next. (i.e., to be a good gene transport machine) 8. Why can we conclude that organisms are designed to be good gene transport machines? Because those genotypes that code for phenotypes that transport more gene copies from generation to generation will eventually predominate within a population. Process of Natural Selection Changes in the relative frequencies of different genotypes (genes) due to difference in the associated survival and fecundity of their phenotypes Suppose that a population of asexual plants was fixed (100%) for a genotype that produced cooperation against competitors (other species). It released an energetically expensive toxin into the air that poisoned competitors in its neighborhood 100% genotype-A producing Phenotype = altruist Next a mutant genotype-C appears that does not produce the costly toxin but benefits from the toxin produced by its neighbors (Phenotype = cheater). Which phenotype is best for the species (altruist or cheater)? Which genotype will have highest fitness (A or C)? Which phenotype will eventually predominate in the species? Do phenotypic traits evolve because they are good for the species or because they are good for individuals within species? How can altruistic cooperation evolve in species? Usually altruistic cooperation only evolves between close relatives, as we will see later Some evolutionary geneticists consider phenotypes like you and me to be "throw-away survival machines" used by genes to transport themselves from one generation to the next. Do sexual organisms reproduce themselves? No Do genes reproduce themselves? Yes, 99.9% of the time Genes potentially live forever by jumping through time within organisms (throw-way gene transport machines) Microevolution Definition: evolutionary change that occurs on a time scale of a few to 100's of generations Ecology of Evolution 2 ...
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This note was uploaded on 09/01/2009 for the course EEMB eemb2 taught by Professor Rice during the Winter '09 term at UCSB.
- Winter '09