Chapter 6 Evolution and Ecology PDF

Methods Sections Common errors: Mention of groups Mention of “Used excel to calculate” Failure to mention two sites Incorrect site names - irrelevant land features (oil changes) Listing supplies - this isn’t written the same as a chem lab report Test Statistics Average: 72....

Methods Sections Common errors: Mention of groups Mention of “Used excel to calculate” Failure to mention two sites Incorrect site names - irrelevant land features (oil changes) Listing supplies - this isn’t written the same as a chem lab report Test Statistics Average: 72.6 SD: 18.7 Chapter 6 Evolution and Ecology Trophy Hunting and Inadvertent Evolution: A Case Study Bighorn sheep populations have been reduced by 90% by hunting, habitat loss, and introduction of domestic cattle. Trophy hunting removes the largest and strongest males— the ones that would sire many healthy offspring. The average size of males and their horns decreased over 30 years of study. Not just sheep…  Common theme This is also being observed in other species: Cod: By targeting older, larger fish, commercial fishing has selected for genes that result in maturation at earlier ages and smaller size. mature earlier can reproduce before they are caught; but small fish produce fewer eggs. African elephants poached for ivory the The proportion unintended of the effects of population human harvestingthat onhave thesetusks is decreasing. animals illustrate how populations can change, or evolve, over time.  Ecology & Evolution Humans have a large impact on the environment—pollution, land use change, climate change, etc. We are just beginning to realize that we also cause evolutionary change and the consequences of this. Ecology and evolution are strongly interconnected. Define the following terms: Genotype Phenotype Gene Locus Allele Remember genetics? Genes are the basis of an organism’s traits Variation in DNA sequences = variation in traits among species Genotype are the genes that organism possesses Different forms of the same gene = alleles AA is a genotype – it inherited an A allele from mom and dad Aa is another genotype, this time the offspring for an A allele from one parent and an a from another Genotype vs phenotype Genotype = the particular set of alleles an individual has Phenotype = the physical manifestation of the genotype Remember Genetics? Homozygous = same alleles Homozygous dominant = AA Homozygous recessive = aa Heterozygous = different alleles Aa Mendel’s pea plant experiments Revealed predictable patterns of inheritance between parents and offspring What alleles was Mendel studying?  What Is Evolution? Evolution is change in allele frequencies (proportions) in a population over time. Example: if the frequency of a in a population is 0.4 or 40%, the frequency of A is 0.6 or 60%. If the frequency of a changed to 71%, the population would have evolved at that gene. Alleles in Populations Population = an interbreeding group of individuals of the same species in some particular area Together, all the genes of a population comprise a pool of genetic resources or gene pool The proportion of one allele relative to other copies of genes in a population is the allele frequency  Calculating Allele Frequencies The frequency or relative proportion of each allele determines possible genotypes and phenotypes in a population How do we figure out the allele frequencies in a population? Step 1: figure out the total # of alleles in the population Step 2: figure out relative # of genotypes in the population Step 3: math! (And make sure everything totals to 100%) Example: You have a diploid population (i.e. 2 copies of each chromosome/gene) There are 100 individuals in the population Half of the individuals are homozygous dominant, ¼ of the individuals are heterozygous, and ¼ of the individuals are homozygous recessive Allele frequencies will remain constant over time if: 1. No mutations 2. No natural selection 3. Random mating 4. No genetic drift 5. No gene flow The Hardy-Weinberg equilibrium is a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors. Genetic Equilibrium Hardy-Weinberg principle Assume “p” is the frequency of your dominant allele in the population Assume “q” is the frequency of the recessive allele in the population The frequency of your alleles must total 1.0 (100%) p + q = 100% (1.0) To accurately calculate allele frequency we have to consider all possible allele combos (genotypes) Homozygous dominant (or p x p) Homozygous recessive (or q x q) Heterozygous (or p x q) p2 + 2pq + q2 = 1.0 Hardy-Weinberg Example Practice Question: In a population of turtle, the allele for ninja fighting (F) is dominant over the allele for apathy (f). In a survey of 500 turtles, you find that 180 turtles are apathetic. Assuming the population is in Hardy-Weinberg equilibrium, calculate the following: a) The frequency of the apathy allele (f) in the population. b) The frequency of the ninja allele (G). c) The expected number of turtles with each genotype (GG, Gg, gg). Shifting Frequencies = Microevolution Generation 1 BB = 0.49 bb = 0.09 S Bb = 0.42 H Generation 2 I F BB = 0.52 T bb = 0.10 Bb = 0.38 H Generation 3 A BB = 0.55 P P bb = 0.12 E Bb = 0.33 N Generation 4 S BB = 0.61 bb = 0.12 Bb = 0.31 Shift in allele frequency over time = microevolution Evolution = change over time Descent with modification Descent = shared ancestry, genetic inheritance Modification = changes accumulated over time This happens at the population level not the individual level! Individuals die or survive…survivors pass on the genes they have Populations evolve, individuals do not Strong selection against recessive allele  What Causes Shifting Frequencies? Shifting frequencies = evolution What are some reasons you might see allele/genotype frequency shifts? Think back to HWE Assumptions!  1. Mutation—the original source of new alleles 3 types of mutation 1. Neutral (most common)- no effect on survival or reproduction Easily passed on to offspring 2. Lethal – changes phenotype so drastically that the mutation results in death. Never passed on to offspring 3. Beneficial- changes phenotype in a way that enhances fitness Becomes more common in a population over time even if it conveys *Mutations are onlyrare. actually very a slight advantage In a generation, a mutation occurs in every 10,000 to 1,000,000 copies of a gene Selection pressure! 2. Natural selection – traits that increase chances of survival and reproduction will be passed on to the next generation Acts on phenotype to influence genotype Directional selection – the end of a trait’s range is adaptive and passed on Stabilizing selection – the intermediate form of the trait is adaptive and passed on Disruptive selection – forms of a trait at both ends of the spectrum are adaptive and the intermediate form is selected against Classic Examples in Ecology Classic Examples in Ecology African seedcrackers (Pyrenestes ostrinus) Mutation and Natural Selection in Real Time https://www.youtube.com/watch?v=plVk4NVIUh8  3 miles above sea 2. Natural Selection level! Natural selection can result in populations in which all individuals have the favored allele: Andean geese have evolved a type of hemoglobin with a very high affinity for O2, an advantage at high altitudes. Live at 3000 m (~2 miles ASL); can fly as high as 6000m (20,000 ft; 3.7 miles ASL)! The allele frequency for this trait is 100% (it has reached fixation). 3. Non-random Sexual selection – survival of the sexiest mating Some individuals out re-produce others because they are better at securing mates Can sometimes be at odds with natural selection (runaway selection)! Non-selective processes! 4. Genetic drift – change in allele frequency due to chance alone, not on the merit of genotype! Fixation (remember) happens when the allele frequency becomes fixed because only one allele is present in the population Only way to readjust frequency is to introduce more alleles Bottlenecks, Founder effects, and inbreeding can all also lead to fixation Exacerbated by small population sizes (b/c statistitics!) Genetic Drift (con’t) Non-selective processes 5. Gene flow – movement of alleles between populations (immigration and emigration) Be able to differentiate between microevolution and macroevolution  Microevolution vs Macroevolutio n An issue of scale Remember….evolution = changes over time Microevolution is defined as a change in allele frequency over time within a population Macroevolution is also change over time but in higher taxa Example: land plants Anagenesis is a process where a species gradually changes over time without Anagenesis is the evolution with the lineage. Cladogenesis is the splitting into new species. In the context of microevolution, it means small, slow evolving from green evolution changes due within happen to theasplitting of the population due lineage. to things It is natural like a slow transition of one selection, mutations, orspecies genetic to another. Over a The long species are rapidly separated can makeinto two or more algae groups. behave drift. period, these changes the population differently than it did before, but it's still considered the same species. look or Speciation events  Speciation Speciation = splitting of one lineage into two new species Every time speciation occurs, it happens in a unique way, which means that each species is a product of its own evolutionary history BUT, there are recurring patterns… 1. Reproductive isolation – end of gene flow between populations that can result in divergence over time 2. Pre-zygotic isolation Ecological isolation Behavioral isolation Mechanical isolation 3. Post zygotic isolation Non-viable, sterile, or less fit offspring Flavors or Speciation Different processes for speciation (reproductive isolation) Allopatric speciation = geographic barrier Sympatric speciation = no geographic barrier (ecological, behavioral barrier)  Patterns and terms of Macroevolution Stasis – very little change in a lineage over time Exaptation- trait that has been “evolutionarily repurposed” *Extinction – disappearance of a species/lineage *Adaptive radiation – one lineage rapidly diverges into many Key innovation – adaptive trait that allows bearer to exploit a habitat more efficiently in a novel way (e.g. lungs) Coevolution – one species acts as an agent of selection on the other and each adapts to changes in the others (e.g. angiosperms/pollinators)  Patterns and terms of Macroevolution Stasis – very little change in a lineage over time Exaptation- trait that has been “evolutionarily repurposed” *Extinction – disappearance of a species/lineage *Adaptive radiation – one lineage rapidly diverges into many Key innovation – adaptive trait that allows bearer to exploit a habitat more efficiently in a novel way (e.g. lungs) Coevolution – one species acts as an agent of selection on the other and each adapts to changes in the others (e.g. angiosperms/pollinators) Explain how ecological interactions and evolutionary could have joint effects. In other words, how does each affect the other?  Evolution and Ecology Ecological interactions can drive evolution Ecological success determined by: Eat Don’t get eaten Pass on your genes Results in web of ecological interactions (trophic and non-trophic!) Interactions can drive changes in populations over time  Evolution and Ecology Evolution can alter ecological interactions Appearance of new adaptations will impact interactions with other organisms Short term predator/prey interactions The duel of escalating adaptations between parasites and hosts is known as an evolutionary arms race. The Red Queen Hypothesis “Now, here, you see, it takes all the running you can do, to keep in the same place” from Through the Looking Glass (Alice in Wonderland) Long term: origin and diversification of early plants altered soils —literally built today’s habitats!  Evolution and Ecology Evolution can happen quite rapidly and influence ecosystem function Example: Remove guppy predator from streams Selective pressure gone, population of guppies shifts to larger body sizes Increased population of larger guppies adds more nitrogen to system Nutrient cycling has been impacted! But this change is an example in a change of life history