Summary Adaptation and Natural Selection - Summary of book chapters for the course PDF

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Summary of book chapters for the course...

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Chapter 1 “Adaptation by Natural Selection” Before Darwin there was no scientific explanation for the fact that organisms are well adapted to their circumstances People just though that adaptation were the result of divine creation On his charter on the Beagle Darwin’s observation of living and fossilized animals led him to stipulate that plants and animals changed slowly through time Darwin believed adaptation follows 3 postulates (Struggle for Existence)The ability of a population to expand is infinite, but the ability of any environment to support populations is always finite (Variation in fitness)-Organisms within populations vary, and this variation affects the ability of individuals to survive and reproduce (Variation is heritable) This variation is transmitted from parents to offspring natural selection- 1. Resources are limited; 2. Organisms vary in fitness; 3. Traits that influence survival and reproduction are transmitted from parent to offspring evolution by variation and selective retention are better names. Also non-random elimination Darwin observed finches in Galapagos Various finches had beak developments that correlated to the type of food they eat Morphology- an organisms size, shape, and composition Natural selection preserves the status quo when the most common type is the best adapted Traits in organisms evolve in such a that detrimental trait carriers die out and the beneficial trait carriers become the average When this occurs it is called equilibrium in the population and is caused by a stabilizing selection process in the environment Species (according to Darwin)- a dynamic population of individuals Characteristics of a particular species will be static over a long period of time only if the most common type of individual is consistently favored by stabilizing selection Adaptation results from the competition of individuals, not between entire populations or species Fecundity- the ability to produce offspring Evolution of Complex Adaptations

There are two categories of adaptation: continuous and discontinuous Continuous variation- phenotypic variation having a continuum of types; height in humans Essential for evolution of complex adaptations Small random, cumulative change Discontinuous variation- phenotypic variation where there are a discrete number of phenotypes with no intermediates; ex pea color in Mendel’s experiments No important for evolution of complex adaptations which don’t often occur in a single jump Complex adaptations can arise through the accumulation of small random variations by natural selection The evolution of complex adaptations requires that all of the intermediate steps be favored by selection Sometimes unrelated species have developed the same complex adaptation, implying that these adaptations are not mere chance Convergence- evolution of similar adaptations in unrelated species Rates of Evolutionary Change natural selection can cause evolutionary change that is much more rapid than we commonly observe in the fossil record Darwin was unable to prove his theory of evolution because he could not explain how variation is maintained Most people thought it occurred by blending inheritance- bother parents contribute hereditary substance that mixes

Chapter 2 “Genetics”

Gregor Mendel used garden pea plants to isolate traits with only two variants (forms) F0 generations parent population F1 first offspring F2 second offspring Mendel formulated two principles through his experiments 1. The observed characteristics of organisms are determined by particles (genes) from both the mother and father 2. Independent assortment- Each particles is equally likely to be transmitted when gametes are formed Mendel’s research was neglected until the discovery of the chromosome-small bodies replicated in cells during mitosis Diploid organisms- cells contain pairs of homologous chromosomes (similar shapes and staining patterns) inherited from each parent

Meiosis-cell division that produces gametes where only have the chromosomes are transmitted from parent to gamete These are haploid cells that forma diploid zygote Different varieties of a particular gene are called alleles Individuals with two copies of the same allele are homozygous Different copies are heterozygous Cross between homozygous dominant and recessive parents yields heterozygous F1 generation Genotype- particular combination of alleles of and individual Phenotype- observable characteristics Gene- segments of DNA in chromosomes Gene locus- the site of a particular gene on a chromosome If loci for different traits appear on the same chromosome they are called linked Crossing over- exchange of genetic material between homologous chromosomes during meiosis; causes recombination DNA is made up of four bases: adenine, guanine, cytosine, thymine A pairs with T C pairs with G DNA affects phenotype in two important ways Coding sequences signify the structure of protein Regulatory sequences determine the conditions under which the message encoded in a coding sequence will be expressed DNA is made up of codons- 3 base pairs grouped together * there was more stuff that we don’t need to know for the genetics chapter but look over the punnett square diagrams in the book to have an understanding of that

Chapter 3 Population genetics Evolutionary change in a phenotype reflects change in the underlying genetic composition of the population Population genetics: the branch of biology dealing with the processes that change the genetic composition of genetics through time Genes in population Biologists describe the genetic composition of a population by specifying the frequency of alternative genotypes Genotypic frequency: The fraction of the population that carries that genotype. They must add up to 1 keep track of genotype frequencies instead of the number of

people who have the genotype because its easier to compare with different population sizes One goal of every evolutionary theory is to determine how genotypic frequencies change through time Number of “forces” act to change genotypes Most important are sexual reproduction, natural selection, mutation, and genetic drift How random mating and sexual reproduction change genotypic frequencies The event that occur during sexual reproduction can lead to changes in genotypic frequencies in a population Even though humans chose mate carefully, it is random because you cant chose mate based on particular allele at each locus The first step in determining the effects of sexual reproduction on genetic frequencies is to calculate the frequency of the PKU allele in the pool of gametes Gene frequency: the frequency of an allele The book gives a better description of this than I could ever make up, see page 54 The next step is to calculate the frequencies of al the genotypes among the zygotes. Probability of pick an a allele is .4, probability of picking an a allele from the sperm is .4 also. This means that .4 times .4 = .16 chance of getting aa allele. See chart 3.2 on page 55 When no other forces (such as natural selection) are operating, genotypic frequencies reach stable proportions in just one generation. These proportions are called the Hardy-Weinberg equilibrium. When no other processes act to change the distribution of genotypes f2 generation will have same distribution of genotypes as f1 generation Hardy-weinberg equilibrium: the unchanging frequency of genotypes that results from sexual reproduction and occurs in the absence of other evolutionary forces such as natural selection, mutation, or genetic drift. General view of equilibrium is: Freq (aa): q Freq (Aa): 2pq Freq (AA): p If no other process act to change genotypic frequencies, HW equilibrium will be reached after one generation and stay there How natural selection changes gene frequencies If different genotypes are associated with different phenotypes and

those phenotypes differ in their ability to reproduce, the alleles that lead to the development of the favored phenotype will increase in frequency Again, book describes this better than I can summarize, see page 58 The Modern Synthesis The genetics of continuous variation When Mendelian genetics was rediscovered, biologists at first thought it was incompatible with Darwin’s theory of evolution by natural selection Mendelian genetics and Darwinism were eventually reconciled, resulting in a body of theory that solved the problem of explaining how variation is maintained Before this two main objections to Darwin’s theory were: 1)the abscene of a theory of inheritance 2) the problem of accounting for how variation is maintained in populations modern synthesis: an explanation for the evolution of continuously varying traits that combines the theory of empirical eveidence Mendelian genetics and darwins theory continuously varying characters are affected by genes at many loci, each locus having only a small effect on phenotype environmental variation: phenotypic differences between individuals that exist because those individuals developed in different environments the more loci that have a small effect on phenotypes, the more the distribution of phenotypes will resemble a bell shaped curve Darwin’s view of natural selection is easily incorporated into the genetic view that evolution typically results from changes in gene frequencies Since ++ birds have bigger beaks than +-, and +- individuals have bigger beaks than --, assuming bigger beaks survive, + alleles would increase in frequency How is varitation maintained Genetics provides a ready explanations for why the phenotypes of offspring tend to be intermediate between those of their parents There is no blending of genes during sexual reproduction The only blending that occurs takes place at the level of the expression of genes in phenotypes, the genes themselves remain distinct physical entities Mutation slowly adds new variation Mutations: a spontaneous change in the chemical structure of

DNA Can be a result of ionizing radiation, and chemicals damage the DNA and alter the message Add variation very slowly by adding new alleles, some of which may produce new phenotypic effects that slecetion may assemble into adaptation Low mutation rates can maintain variation because a lot of variation is protected from selection If individuals with a variety of genotypes are equally likely to survive and reproduce, a considerable amount of variation is protected (or hidden) from selections Hidden variation explains why selection can move population far beyond their initial range of variation If big beaks are favored, and + allele is big beak, then over time hen little beaks die, it removes – alleles and so the ration of + to – alleles is greater. The greater the proportion of + alleles in an individual, the bigger the beak will be Natural Selection and Behavior the evolution of mate guarding in the soapberry bug illustrates how flexible behavior can evolve Mate Guarding: a form of mating in which the male defends his mate after copulation to prevent other males from mating with her This increases the males reproductive success Cost: male cannot reproduce with other mates while he is guarding Sex ratio: relative number of males to females When not a lot of females, mate guarding is a good idea, when a lot of females, males benefit from looking for more mates Behavioral plasticity allows male soapberry bugs to vary their mateguarding behavior adaptively in response to variation in the local abundance of females Canalized: showing same trait in wide range of environments Plastic: adjusting the trait with the different environments Soapberry bugs from Oklahoma are plastic and change their mating patterns depending on the sex ration Evidence suggests that the soapberry bug has evolved in response to the variability in conditions in Oklahoma Most soapberry bugs live south of Oklahoma, so he took bugs from florida keys These bugs did not change their mating patterns

Reason for this are: Flexible males must spend time and energy figuring out sex ratios Sometimes make mistakes Probably requires a more compelx nervous system In a stable environment, makes more sense not to be flexible A comparison of the mate-guarding behavior in two different populations of soapberry bugs indicates the behavioral plasticity evolves when the nature of the behavioral response to the environment is genetically variable Why did Oklahoma bugs evolve: by the slective retention of beneficial genetic variants For any character to eveolve: 1)character must vary 2)variation must affect reproductive success 3)variation must be heritable Constraints on Adaptation Correlated Characters When individuals that have particular variants of one characteristic also tend to have particular variants of a second character, the two characters are said to be correlated Correlated: traits that are statistically associated in a population correlated characters arise when particular genes affect multiple characters Positively correlated Example: deep beaks tend to have wide beaks Negatively correlated Example: deep beaks tend to have narrow beaks Correlated characters occur because some genes affect more than one character Pleiotropic effects: they are created by genes that influence multiple characters When two characters are correlated, selection that changes the mean value of one character in the population also changes the mean value of the correlated character Correlated response: an evolutionary change in one characteristic caused by selection on a second, correlated character. A correlated response to selection can cause other characters to change in a maladaptive direction Maladaptive: detrimental to fitness

Depending on which effect on selection is stronger, selection can lead to maladaptive traits Disequilibrium Selection produces optimal adaptations only at equilibrium Example: 5000 years ago, people couldn’t always eat sugar fat and salt so when they could, they ate as much as they could Now a days, it is readily available to us and too much of these things lead to unhealthy lifestyles. Genetic Drift When populations are small, genetic drift may cause random changes in gene frequencies Sampling variation: the variation in the composition of small samples drawn from a large population Genetic drift: random changes in gene frequencies due to sampling variation that occurs in any finite population The rate of genetic drift depends on population size Genetic drift causes more rapid change in smaller populations than in large ones because sampling variation is more pronounced in small samples Genetic drift causes isolated populations to become genetically different from each other Genetic drift leads to unpredictable evolution because the change in gene frequency caused by sampling variation are random Fixation: a state that occur when all of the individuals in a population are homozygous for the same allele at a particular locus Smaller populations differentiate rapidly while larger ones are more slow Populations must be quite small for drift to lead to significant maladptation local versus Optimal Adaptations Natural selection may lead to an evolutionary equilibrium at which the most common phenotype is not the best possible phenotype Reason for this is natural selection is myoptic This means that it favors small improvements to the existing phenotype, but it does not take into account the long-run consequences of these alterations Camera type eyes: ex. Humans. There is a single opening in front of a lens, which projects an image on photoreceptive tissue Compound eyes: ex. Insects. There are many different small photoreceptors build up an image composed of a

grid of dots, something like a television image. Come local adaptations are called “developmental constraints” Development: process of growth and differentiation Lactate: produce milk for young Males don’t develop lactate because while it would help, it would also make them sterile so its not good Other Constraints on Evolution Evolutionary processes are also constrained by the laws of physics and chemistry Example is there is no elephant that can run fast and climb trees because he is too big, not physically possible.

Chapter 8 “The

Evolution of Social Behavior”

Kinds of Social Interactions Social interactions are behaviors that affect the fitness of more than one individual When two individuals interact in competition over resource or in cooperative defense of valuable food items, the individual of one behavior directly affects the fitness of the other Dyadic- describing an interaction that contains two individuals Actor- the individual performing the behavior Recipient- the individual affected by the behavior beneficial (+) act if it increases fitness costly or detrimental (-) if it reduces fitness Selfish- +/Mutualistic- +/+ Altruistic- -/+ Spiteful- -/Technical deifitions of these words may differ than how they are used in biology slightly It is extremely difficult to measure the effects of particular behavioral acts on the fitness of individuals, particularly for long-lived animals like primates However, we can make inferences about the immediate cost and benefits of acts on the basis of more general considerations Altruism: a Conundrum Altruistic behavior cannot evolve by ordinary natural selection Altruism is a puzzle because it decreases fitness for the individual performing the act While altruistic behavior might arise by accident or as side affect of other behavior, it seems impossible for complex altruistic behavior to be assembled by natural selection Logically, it would be selected against over time due to decrease in fitness Primates perform altruistic behavior in nature This problem wouldn’t exist if altruistic behavior was rare or unimportant, but it occurs often Grooming other member, giving an alarm call of a predator, forming alliances, and sharing food are all examples that decrease own fitness and increase others Altruistic behaviors cannot be favored by selection just because they are beneficial to the group as a whole

Example is a group of monkeys, if one forth are alarm callers and three fourths are non-callers. Calling reduces the risk of mortality for the group, but all share the benefits so change the frequency of callers. Since calling actually decreases fitness because it gives away position, calling gene will actually be selected against and non calling gene will be selected for. Kin Selection Natural selection can favor altruistic behavior if altruistic individuals are more likely to interact with each other than chance alone would dictate Same example as before, but now species live in groups composed of full siblings If an individual is a caller, the by mendellian genetics, sibling has 50% chance of having same gene for calling behavior Frequency of genes for calling will be more than one fourth in groups with callers. Thus when an individual makes a call, benefiting other callers also, increasing the average fitness of callers to non callers When non caller doesn’t call, lowers average fitness of non callers to callers because more non callers in group Hamilton’s Group Hamilton’s theory of kin selection predicts that altruistic behaviors will be favored by selection if the costs of performing the behavior are less than the benefits discounted by the coefficient of relatedness between actor and recipient Kin selection- a theory stating that altruistic acts will be favored by selection if the product of the benefit to the recipient and the degree of relatedness (r) between the actor and recipient exceeds the cost of the actor Hamilton’s Theory- rb>c r=the average coefficient of relatedness between th actor and the recipients b= the sum of the fitness benefits to all individuals affected by the behavior c= the fitness cost to the individual performing the behavior (measures the genetic relationship between interacting individuals) r is basically the average probability that two individuals will acquire the same allele through decent from a common ancestor Hamilton’s rule leads to two important insights: (1) altruism is limited to kin, and (2) closer kinship facilitates more costly altruism Evidence of Kin Selection in Primates

Primates may use contextual cues to...