BIOLOGY 152 1st Edition Lecture 23 Outline of Last LectureI. Natural Selection a. Types of Selection for Phenotypes II. Other Mechanisms a. Gene Flow b. Genetic Drift Outline of Current Lecturei. Bottleneck Effect ii. Founder Effect III. SpeciationCurrent LectureSpeciation IMore on Evolution**Clicker Question**The goldenrod gall fly lays eggs on terminal buds of goldenrod plants. Larvae chewthrough buds where their saliva induces the plant to generate a gall. They are preyto both parasitoid wasps and to birds (wasps prey on larva inside smallest galls, birds prey on larva inside largest galls) what kind of selection is this?- Stabilizing selection (directional would be selecting for one end or the other anddisruptive is selecting for both sides, and that is the opposite of what ishappening here) Genetic drift = when genetic variability (loss of allelic diversity) is reduced because of RANDOM chance- can still contribute to evolution/change in a speciesComputer simulations of genetic drift -top population = 20-middle population = 200 -bottom population = 2,000These 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.if we have random mating, then what would the next population look like?- in a small population, you often get fixation (some of the alleles are presentall of the time) or in some cases you lose alleles. - so allele frequency changes dramatically - in 200 individuals none of them goes to fixation but the allele frequency changesa lot - in the 2,000 population it becomes much more stable (closer to Hardy-Weinberg equilibrium) *small population, you’re more likely to get drift**2 types1. Bottleneck effect : if you take a bottle and filled it with marbles of differentcolors, then shook it out into a beaker, you will randomly lose some colors ofmarbles - have reduced population from how many were in bottle to however manyin beaker, so in the next generation some alleles are lost Example: Greater Prairie Chicken - population in early 1900s there were 25,000 inIllinois - in 1993 there were less than 50(dramatic reduction) **Clicker Question**So what is likely to be true about the alleles in the 1994 generation?- it is a much smaller population, so some alleles may become fixed(equilibrium won’t happen because the population is so small) - C is not true: in genetic drift, no alleles are more common in the populationbecause of fitness, you’re just losing a chunk of the population for noparticular reason What would be the best way to combat genetic drift in the prairie chicken? -import more prairie chicken from out of state to reintroduce allelic diversity**Clicker Question**Silvereyes bird originally lived in Australia and migrated to Tasmania, then from Tasmania to New Zealand and finally to Norfolk Island. Each of these jumps was made by a smaller group. What would happen to genetic variation in each subsequent population?- would decrease - if you assume you have millions at the beginning and at each jump you havea subset of that population (so a population bottleneck at each step) and thisdecreases the allelic diversity - if a larger population moves you will have less genetic drift - this is called the founder effect = some alleles are over-represented becauseof a small starting population 2. Founder effect:- Ellis-van-Crevald syndrome in the amish population is more common because of200 people, 2 had this syndrome. You see this trait much more frequently in thissubset Wild pigs can be hairy or have smooth skin. Hair skin is much less delicious to its predators. Over time, there will be more hairy skinned pigs. This is an example of:- Natural selection!**Clicker Question**Soon after the island of Hawaii rose above the sea surface, the evolution of life on this new island should have been most strongly influenced by what?- the founder effect will substantially reduce number of organisms that are there(you have such a tiny group that shows up that it will affect the geneticdiversity) - once they get there they must go through genetic radiation and there willbe lots of different environments which will lead to differentiation in theflies Be sure you understand why a mechanism has a certain effect on variation (and average fitness)**Clicker Question**Question about the worm with the mutation in the insulin growth factor receptor live longer. WT and mutated worms grown together in a large culture. Worms were sampled after each generation and tested for the mutant allele. What is the likely explanation for these data?- This is selection. Why? - if it were genetic drift you would need to have a small population, and therewere many thousands of worms (so a large population) so you shouldn’t belosing it by chance - gene flow would mean that the 2 populations of worms were mating and there were no selection and you have a large population, you would see themin Hardy-Weinberg equilibrium (it should be steady but the line drops) - there are mutations involved but if there were some reasons that mutations were happening in that population then it would be in the WT AND mutants, not just mutants. - so there was selection AGAINST this trait because when you grow them with WTworms they disappear from the population. SpeciationWhat is a species?You can have a population (species) that evolves/changes but remains a single species Example of this = average temperature anomaly of a stream/lake in Alaska and data drawn from pink salmon in the area and shows their average migration time. Salmon wait until it warms up to head up the stream.-Starting to head up the stream earlier and earlier because the stream is starting to warm up earlier — the alleles leading to this migration are being selected for (selection over the course of 40 years for this kind of migration)- they’re not spectating but they are changing (evolution without speciation) Evolution with speciation = creation of a new lineageexample = Lake Baikal Seal (only wholly fresh water pinniped) vs. Ringed Seal — they started as one type of seal and then splitSo what is a species?- a collective group of organisms that share common traits and canproducing fertile offspring - traits can be genetic or morphological - genetically similar Biological