ENVIR ST 260 1st Edition Lecture 3 Outline of Last Lecture I Populations A What Controls Size and Growth B Impact of Competition and Density C What We Learn from Studying Populations II Evolution A Definition B Observation of Genetic Changes Outline of Current Lecture I Evolution A Working Definition B Null Model II Natural Selection A Requirements B Examples Things to Think About III Information about Files on Moodle Current Lecture Evolution Definition of Evolution Working Definition Change in the genetic makeup of a population overtime Changes in DNA These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute We have to have the whole population individuals can have changes but it doesn t really matter And then there s the time component generational time Example from Tuesday If there are flowers of two different colors and if a pollinator has a preference to one flower color the purple flower we can look at how the allele frequencies change in this population There would be a greater proportion of purple flowers Null Model 5 criteria that if in place will lead to a population that is static and not evolving No Selection You can select for a trait or against a trait Predators Predators can select against slow easy to spot individuals Climate One trait as cold tolerant or not cold tolerant If it gets colder you ll be selecting for the cold tolerant genotype and against the genotype that is not cold tolerant Resistance to disease Antibiotic resistance is a huge problem in health care You re selecting for antibiotic resistant bacterial strains No Mutation These occur in the background all the time They re not necessarily bad they can be good A gene can mutate and give an individual an advantage But if it s not occurring you don t see evolution No gene flow This is individuals moving from one population to another This is either immigration joining a population or emigration leaving a population Clicker Question What do mutation and gene flow have in common Correct Answer These events can introduce new genotypes Mutation rate generally mutations are rare but that s what we see and experience in a day to day basis Typically organisms with big genomes have slow mutation rates while those with smaller genomes mutate a lot faster Random Mating The idea that all individuals have an equal opportunity to mate and produce offspring An example of nonrandom mating would be sexual selection which happens in peacocks Males with big flashy tales get all the ladies Nonrandom mating takes place with most organisms that have males and females There s some sort of mate selection going on Large Population Size Large populations buffer against random events So if you had some sort of disturbance introduce a predator disease fires floods and you have thousands or tens of thousands of individuals a lot will stay alive in comparison to a population with around 10 individuals Genetic drift happens with small populations It s a random occurrence If you have a big population and you reduce it you get a skewed subset of the population From these individuals you may have more of one genotype than another so surviving individuals can really change the genotype of the population over time when they start to breed This is still evolution but there s no selection pressure that s making these individuals more fit As you can see ALL of these assumptions are violated in the real world Natural Selection Requirements for Natural Selection Variation in traits If you have a population of flowers that are all the same color there s no variation in the trait so there s nothing that s going to be selected for or against Having a lot of variation is a good thing from an evolutionary perspective If you have species that lack genetic differences and key traits ability to avoid predator no variation in color they are doomed to go extinct Differences in fitness of genotypes You might have insects with two different phenotypes of color but they re both easy to spot so there s no difference in fitness Fitness isn t about strength it s about being able to breed and pass on genetic material Heritability of traits These traits have to be inheritable If you have a great genetic make up but no offspring the population doesn t benefit Examples Things to Think about Population of beetles If the predator bird prefers green beetles that trait is selected against The preference for pray changes how the population looks By the end it s all brown beetles Once we have a bunch of brown beetles the birds might change and eat brown beetles or if the predator won t change they ll die out Properties of natural selection speeding it up artificially corn example Ancestral corn people saw it was good and tasty to grow and started selecting for good traits So they take the good seeds out of the harvest and harvest those with the trait for more kernals It s not a natural selection in that it s human intervention but it s still an example of a species that s evolving Modern corn We ve completely altered what the species looks like over time Same thing can be said for what animals humans have domesticated Evolutionary arms race Futurama video clip Two species Every time one adapts to have the upper hand there s some individuals of another species that can adapt and outsmart the one with the upper hand They re not adapting these traits consciously Clicker Question Does selection act upon the genotype or phenotype Phenotype the expressed trait Example population of mice AA long legs fast mice Aa long legs fast mice aa short legs slow mice Predator he s going to catch the slow mice We re selecting against a slow trait What happens if a fast mouse has a slow day He s got long legs and the right genotype so he s supposed to have a higher fitness However if the cat catches him he eats him anyway In the rare circumstances where the genotype and phenotype don t match natural selection goes towards the phenotype It s all about the expressed traits Chapter 8 Intersection of Ecology and evolution An ecologist na ve about natural selection would have a dilemma to solve Chili Peppers in Arizona example Clicker Question What if seeds were deposited in the sun Sun tolerant seeds would be selected for That s a likely outcome Just because you have a population where seeds were mostly deposited in the shade doesn t mean that there aren t some seeds that are sun tolerant If