question

Microevolution

answer

Change in allele frequencies over shorter time scales within a single population (typically observable within our lifetime)

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How we can use evolution to understand human health issues

answer

Antibiotic resistance, variation in virulence,(annoying to high mortality rates), myopia (short sightedness), breast cancer

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Antibiotic Resistance

answer

1. Evolving populations of pathogens 2. Evolving populations of humans Antibiotics kill bacteria by disrupting vital biochemical processes. Not a lot of new compounds coming into the market any more (maybe one a year at most). There used to be about 15 major pharmaceutical companies researching antibiotics - now one or two.

question

Why did resistance fall with decreased use of penicillin?

answer

If resistance comes at a cost, then sensitive bacteria will outcompete resistant bacteria.

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Is cost of resistance a solution to the problem of antibiotic resistance?

answer

No. Compensatory mutations can allow resistance bacteria to outcompete sensitive bacteria (even in the absence of antibiotics). There is no guarantee that an antibiotic will become effective again.

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Virulence

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the damage inflicted by a pathogen on its host

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Models of Evolution of Virulence

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1. Coincidental evolution hypothesis. Virulence is an accidental by-product. (ex: tetanus) 2. Short-sighted evolution hypothesis Long term best interest of pathogen is not relevant. (ex: polio) 3. The trade-off hypothesis Balance between costs and benefits of harming the host. Fundamental trade-off between transmission and rate of replication.

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Participation 1. According to this figure, what is the main difference between vectorborne and directly transmitted diseases with regard to death rate? 2. Do the data shown here support the trade-off hypothesis of virulence in pathogens? 3. Why do you think we see this difference in virulence between vectorborne and direct transmission pathogens?

answer

Vectorborne: needs a 'vector' like a mosquito to spread from one human to another human Direct: needs direct contact between hosts (humans) 1. Vectorborne diseases are more deadly. 2. Yes. If it is less deadly, it has higher transmission rate. 3. People who are a little bit sick go out (to class, to parties, shopping, etc.) which allow transmission. People who are really sick generally do not but vectorborne diseases can still spread through the 'vector'.

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Human Adaptation: Environment

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The environment to which we are adapted is very different from the environment in which we live. Until 10,000 years ago, human lived as hunter-gathers. Now over half out diet comes from processed foods. Think about: myopia and breast cancer

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Data we need to examine genetic diversity

answer

Sequencing data and phenotypic data

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Main mechanisms of evolution

answer

mutation, selections, drift, migration

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Mutation

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Any change in genome. Lead to all novel genotypes. Mechanism of evolutions.

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Drift

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Process where allele frequencies in population change by chance alone as a result of sampling error in each population. It can lead to large changes in population over time including fixation of alleles or genotypes in populations. Drift is stronger in smaller populations because alleles can become fixed or lost more easily.

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Directional Selection

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Favors individuals going in one direction from the mean; variation reduced, mean oves left or right. Example: size of Great Plains Cliff Swallows increased after 6 day storm

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Stabilizing Selection

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Favors average individuals; variation reduced because extremes are not selected for. means stays the same. Example: birth weight

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Disruptive Selection

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Favors extremes; variation increases and average stays the same. Example: beak length in black-bellied seedcreackers.

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Myopia

answer

Short-sightedness. A very large percentage of populations have myopia (some populations: 25% of individuals). Data from twins supports the claim that myopia is heritable. Identical twins have a much greater rate of being concurrent with each other than fraternal twins. It seems good eyesight would be critical to being successful hunter-gathers. Why is myopia so prevalent when it would have been disadvantageous? Perhaps the genetic predisposition to myopia only surfaces in our modern environment? Data from recent immigration of Inuit people into town shows that younger people had a much greater rate of myopia than older people. Younger individuals are growing up going to school in the city and reading and causing the strain leading to myopia.

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What is the likely reason for myopia?

answer

Disease of modern civilization.

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What is a mismatch with the environment?

answer

Disease of modern civilization. Health issues that appear because our environment changes very quickly. Example: myopia

question

What are two possible explanations of breast cancer? Explain them.

answer

1. Caused by a pathogen (coevolutionary arms race) 2. Disease of civilization

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Breast Cancer

answer

Breast cancer affects 1/8 North American women, sometimes resulting in death during child-bearing years. From on evolutionary standpoint, (on the surface) this pattern does not make sense. If cause is entirely genetic, natural selection should have eliminated the alleles from our ancestors' populations. If environmental causes were the same as those experienced by our ancestors, then natural selection should have favored immunity. So...why is the rate so high? Why is breast cancer still around?

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Evidence for pathogen cause of breast cancer

answer

Mouse equivalent of breast cancer is caused by a virus (MMTV) Cancer tissues have a much higher percentage of MMTV than normal tissue (almost 40% more). Countries that have the mice with MMTV have higher rates of breast cancer. Lacking specific evidence but have enough to suggest a general correlation. AKA: Incidence of breast cancer is correlated with prevelance of Mus domesticus (MMTV-carrying mouse). Evidence is suggestive of a link. Even if it is true, it would explain ;40% of breast cancer incidents.

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Evidence of disease of civilization cause of breast cancer

answer

Accumulated evidence suggests that continuous menstrual cycling increases the risk of breast cancer. Combination of estrogen and progesterone in post-ovulation stimulates cell division in the linking of milk ducts. More cell divisions means more opportunity for mutations. North American women have an increased risk of breast cancer - is this due to more menstrual cycles over a lifetime? Study of the Dogon women of Mali (northwestern Africa). Pre-modern society that does not use contraceptives. During menstruation they sleep in separate huts and the frequency of this was tracked. Number of menstruations was low during child bearing years. Rate of breast cancer among Dogon is not known, but incidence in urban West African women is ~1/12 of North American women.

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What is a compensatory mutation in bacteria?

answer

Antibiotic resistance

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Does correlation always equal causation? What do we mean by correlation - give an example.

answer

No. Poor eye sight is heritable. Families with poor eyesight are more likely to use nightlights to help see at night. There was a correlation between poor eyesight and nightlights but nightlights did not cause poor eyesight. The misunderstanding led many parents to not use nightlights. *Think carefully about what data is needed to make statements* Yeh's Joke: Old man in hospital. Wife was with him when he broke his life, when his business was failing, and now that he is in the hospital. "I think you are bad luck."

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What is evolutionary genetics?

answer

The study of the processes that generate and shape biodiversity at the genetic level. Begins with mutation as source of all novelty. Then studies how genetic diversity changes within species (i.e. microevolution). And how genetic diversity can give rise to novel traits such as adaptations and the reproductive barriers that can define species.

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What are common questions about genetic diversity?

answer

Why are some species genetically similar while others are diverse? How are some regions of the genome more diverse than others? (examples: human, tunicate, fruit fly, HLA-DRBI) How can genetic diversity affect the risk of species extinction? (example: hybrid vigor and corn - in this case, increase in genetic diversity results in a hybrid offspring that has a fast growth rate and is more successful; however, sometimes increase in genetic diversity leads to increase in harmful mutations *usually hybrid are not more successful*) What are sequencing data and phenotypic data used for?

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Genotype

answer

Genetic makeup of an individual, combination of alleles carried by individual at particular locus

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Phenotype

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Observable, measureable characteristic of an organism

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Locus

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Specific location of a gene on a chromosome

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Polymorphism

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The occurrence of two or more distinct phenotypes within a population

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Polymorphic locus

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Loci that are variable, multiple alleles in the population

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Allele

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One of several alternative forms of the DNA sequence of the same locus

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Nucleotide Diversity

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The average number of differences per base pair (bp) of two randomly sampled chromosomes from a population. Human nucleotide diversity = 1 difference each 1000bp. Tunicate, Ciona intestinalis = 1 difference each 100bp. Fruit fly, Drosophila melanogaster = 1 difference each 100bp.

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What are possible effects a mutation can have?

answer

No effect, increase fitness, decrease fitness.

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What is the evolutionary purpose of alternative splicing?

answer

Creates alternative options for proteins - on average there are 6 ways

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What are the different mechanisms of mutation?

answer

Point mutation - change in a base pair Insertion - insertion of several base pairs Deletion - deletion of several base pairs Gene Duplication - duplicate a gene twice Inversion - same number of genes present but in the wrong order Chromosome fusion - fusion of materials Genome Duplication - occurs less often but with interesting consequences

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How will mutations affect proteins?

answer

Most mutations in large genomes are silent. Can also be a loss-of-function or gain-of-function mutation. Both of these are fairly significant.

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What is a loss-of-function mutation? Gain-of-function mutation?

answer

Loss-of-function mutation: codes for a nonfunctional protein. Gain-of-function mutation: codes for a protein with a new function.

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How do mutations affect organisms?

answer

All eukaryotes are diploid: two copies of the genomes, split into chromosomes. One maternal copy and one paternal copy. Because we are diploid, we describe the genotype by specifying the two alleles an individual carries at a locus.

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What is the different between a simple trait and a quantitative trait?

answer

A simple trait: yes or no Example: Lactose tolerance/intolerance (due to lactase persistence) A quantitative trait: a continuous range of trait values Example: Finch beak height

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Are all mutations "bad" ?

answer

No. Most mutations are, but some have no effect, and some increase fitness.

question

Conclusions on the effects of mutation

answer

The outcome of a mutation on a phenotype may be: - A completely distinct phenotype - A slight shift in value of a quantitative phenotype - No effect on phenotype at all The outcome depends on: - Whether mutation is silent, loss-of-function, gain-of- function - Dominance/recessive relationships of alleles - Whether a trait is simple or complex - Whether a novel mutation has a fitness consequence, depends on how the trait is related to fitness

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Evolution

answer

The change in the frequency of an allele within a gene pool.

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Mechanisms of Evolution

answer

Natural Selection Genetic Drift Gene Flow Mutations

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Allele Frequency

answer

Number of copies of allele//total number of all copies of alleles

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Genotype Frequency

answer

genetic variation in population analyzed by allele frequency

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Gene Pool

answer

Stock of different genes in an interbreeding population (species)

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What are the components of the process of Natural Selection? How can it increase the frequency of an allele? What makes Artificial Selection possible? How is it different form Natural Selection?

answer

Process of natural selection: variation of traits -> differential reproduction (more offspring reproduced than will survive) -> heredity -> those that survive best and produce the most is not random -> outcome: those individuals are selected naturally If the alleles are advantageous to the species' survival and reproductive success, then it will be favored. Example: coral snake and king snake - nonpoisonous king snake is a very good mimic of poisonous coral snake Artificial Selection: humans artificially select for favorable traits Example: Diversification of wild mustard to various derived vegetables - ancestor has a diverse genotype

question

How does genetic drift cause allele frequencies to change?

answer

Genetic drift can cause loss and fixation of alleles due to chance. Example: flower color cartoon example - flower color has no effect on the average number of offspring of each individual but allele frequencies can still change due to randomness. Example: Buri experiment - flies evolved through genetic drift, random breeding led to loss and fixation of alleles. He did this for 19 generations. The random allele frequencies were drastically different from source population.

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Examples of evolution via genetic drift

answer

Segregating - both remain in population Lost - completely lost allele Fixed - completely fixed

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Does a neutral trait affect fitness?

answer

No.

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What is fitness?

answer

Success of an organism surviving and reproducing and thus contributing offspring to future.

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What is the effect of population size on strength of drift?

answer

The smaller the population, the more prominent the strength of genetic drift. Loss and fixation more frequent in small populations.

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What are population bottlenecks/founder effects, and what is their evolutionary significance?

answer

Population bottleneck effect: genetic drift at the extreme; number of individuals is drastically reduced which can cause loss of alleles -; population returns to original size but genetic variation remains low Example: Northern Elephant Seals - used to be very populous (thousands and thousands) until hunted down to about 20 individuals and has now repopulated to several thousand - Northern Elephant Seals have much lower genetic diversity than the Southern Elephant Seals that did not undergo this bottleneck effect. Founder Effect: Small group migrates out of the original group and interbreed. Genetic diversity decreases further away from original group, subset of bottleneck Example: Evidence for serial founder effect in humans and an origin in Africa - humans decrease in genetic diversity the further away from Africa you are

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What is gene flow?

answer

Individuals going into and out of a population that changes the allele frequency in the population. Example: Farmed vs. Wild Atlantic Salmon - farmed fish can escape and spread diseases and parasites to wild salmon; some also interbreed with the native fish which reduces the ability of their offspring to survive

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What is the Hardy-Weinberg model?

answer

With the absence of outside forces, allele frequencies of a population will not change

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What are the five assumptions for HWE?

answer

1. No natural selection 2. No genetic drift (i.e. an effectively infinite-sized population) 3. No mutation 4. Random mating 5. No gene flow (i.e. no contact with other populations)

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What is the use of HWE?

answer

HWE serves as a null hypothesis, with an explicit set of assumptions. If a population is not in HWE, then we know evolution is occurring and one (or more) of the assumptions has been violated. We can incorporate the assumption into the model one by one do figure out which of the evolutionary processes is actually occurring.

question

Calculate expected genotype proportions after one generation

answer

Frequencies: AA:Aa:aa=p^2:2pq:q^2 quick check: p = 1 - q

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Calculate expected allele frequency after one generation

answer

Allele frequency does not change - HWE!

question

What are the 4 antecedents to natural selections?

answer

1. More individuals in a population are born than survive and reproduce. 2. There is an inherent variation of traits in any population. 3. Traits are heritable (have a genetic component). 4. Survival and reproductive success is not random. It is determined by the traits exhibited by the organism.

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What do we mean when we say fitness?

answer

Success of an organism at surviving and reproducing and thus contributing offspring to future generations

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How do we understand adaptation as a trait vs. adaptation as a process?

answer

Natural selection is the differential survival and reproduction of individuals in a population based on variation in their traits if: 1. A trait has a genetic component 2. And the trait increases the survival and reproduction of individuals who carry it. Then: The trait's frequency in the population will increase through time. The trait is an adaptation. We also call this the process of adaptation.

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How can we classify natural selection acts on phenotypes?

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1. Directional selection: favors individuals that vary in one direction from the mean. Allele frequencies change in one direction. Variation is sometimes reduced (if strength of selection is strong). Mean value of trait increases or decreases. (example: Great Plains Cliff Swallows body size in 6 day storm - big body size meant larger fat reserves and could survive without a food source until storm passed and insects returned ) 2. Stabilizing selection: favors average individuals. Mean is going to stay approximately the same but two extremes aren't surviving or reproducing as well. Variation decreases. (example: human birth weight - high mortality for extreme birth weights) 3. Disruptive selection: favors individuals that vary in both directions from the mean. Opposite of stabilizing. Individuals in the middle have lowest fitness, begin to have bimodal peaks, mean roughly stays the same, variation increases - very interesting but also rare - can lead to speciation (example: Bill size in African black-bellied seedcrackers - long beaked individuals specialized on large seeds and short breaks on small seeds but intermediate sized beaks handled seeds inefficiently)

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How can we classify how natural selection acts on the levels of alleles?

answer

1. Positive selection: new mutant is advantageous (example: pesticide resistance in alleles) 2. Purifying selection: the selective removal of alleles that are deleterious -; can result in stabilizing selection

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What is the relationship between genetic drift and positive selection? What is the effect of population size? Why won't beneficial alleles always spread?

answer

Genetic drift can overpower selection in small populations (beneficial alleles do not always spread!). In large populations, genetic drift is less consequential.

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What is an adaptation?

answer

1. a trait that increases the ability of an individual to survive or reproduce compared with individuals without the trait. 2. a trait that increases an organism's fitness and that is a result of the process of natural selection for its present function. *Not all differences are adaptive. *Not all traits are adaptations. *Not all adaptations are "perfect" - evolution is ongoing.

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Under what circumstances does genetic drift overwhelm selection?

answer

In small populations.

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What is the molecular clock and how can it be used to predict divergence times between species?

answer

Two divergent populations will accumulate differences via the process of nucleotide substitutions. The molecular clock: Substitutions accrue over time. For many genes, the rate of substitutions is clock-like: a roughly constant rate of "ticking" as substitutions take place. Differences in DNA sequences between two species are proportional to the time elapsed since the divergence from their most recent common ancestor. But not all genes evolve in a clock like manner.

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How are some proteins, like histones or fibrinopeptides, not always good predictors of time of divergence between species?

answer

Histones and fibrinopeptides do not evolve in a clock like manner.

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Neutral Theory

answer

At the molecular level, the majority of variants in most populations are selectively neutral.

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How do neutral variants accumulate?

answer

Through genetic drift (not positive selection).

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Why does genetic variation not always produce fitness variation?

answer

Because of all the possibilities of synonymous mutations. Synonymous: get the same amino acid. Nonsynonymous: results in change. The neutral theory suggests that if a populations carries several different versions of a gene, odds are that each of those versions is equally good at performing its job - in other words, that variation is neutral: whether you carry gene version A or gene version B does not affect your fitness.

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How can we use the ratios of Synonymous to Nonsynonymous rate to understand what type of selection is operating (or whether selection is operating at all)?

answer

Positive vs. purifying selection Relative rate of SYN and NONSYN substitution differ among codons of protein coding genes as a function of selection. If the rates of SYN and NONSYN at a codon position are similar, the amino acid is likely drifting neutrally among states. If rate on NONSYN ; rate of SYN at a codon position, then selection accounts for change. If rate of SYN ; NONSYN, then purifying selection is likely resisting change in amino acid.

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Participation: If the rate at which a protein produces a metabolite is under stabilizing selection, then one would expect:

answer

Nonsynonymous mutations will be under purifying selection. Explain: Selection does not work on synonymous mutations. We can rule out options with synonymous mutations. That leaves non synonymous mutations under positive and under purifying selection. Because it is at stabilizing selection, we know the mean does not change. Positive selections means there is a beneficial mutation that would change the mean. Therefore, we know it must be nonsynonymous mutations under purifying selection.

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Explain the variation in genome size vs. proportion of genome encoding function genes.

answer

Some genomes are small and dense with functional genes. Others are large and have a low percentage of functional genes. Variation in size decreases if we only take into account the coding portions of DNA. No species has more than 100 times as many protein genes as E. coli.

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Does gene number correlate with organismal complexity?

answer

Not always. Rice has more genes than humans do.

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How are prokaryotic vs. eukaryotic genomes different?

answer

Prokaryotic genomes: -Small: 160 kilobases - 12 megabases -Circular genome -Carry plasmids (small circular pieces of DNA) -No introns (spacer material within genes) Eukaryotic genomes: -Large: Mammalian genomes ~ 3 gigabases -Linear DNA broken up into chromosomes -Lots of non-coding DNA and regulatory sequences -Lots of repetitive DNA

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What are relationships between number of genes and prokaryotes vs. eukaryotes, animals and plants vs. microbial species?

answer

Eukaryotic genomes typically have more genes than prokaryotic. Animals and plants tend to have more genes relative to microbial species.

question

Big genomes tend to be found in species with smaller population sizes. Smaller population sizes equals stronger genetic drift. Is there a connection?

answer

In small populations, genetic drift can overpower selection, so that counterintuitively: deleterious variants can be fixed. If having extra DNA is weakly deleterious, the on average mutations creating extra DNA should be lost. However, in small populations, it may occasionally fix in the population, and thus increase genome size. The fixation of deleterious "junk" by genetic drift might explain the bloated genomes of species with small population sizes.

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Sexual Selection

answer

Differential reproductive success resulting from competition for mate.

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How is sexual selection different from natural selection?

answer

Sexual selection is not for viability/survival but for success in mating. (A subset of natural selection.)

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Intra-sexual competition

answer

within a sex e.g. male-male competition

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Intersexual competition

answer

among the sexes e.g. finding a mate - males are competing for a female to choose them

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Anisogamy

answer

Sexual reproduction involving fusion of two gametes, individuals producing the larger gamete are defined as female and smaller as male

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Sexual Dimorphism

answer

Difference in form between male and female

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Why is the female investment in reproduction generally larger than males?

answer

When female investment in reproduction is greater: Favors "choosy females" Leads to competition amongst males

question

Explain direct and indirect benefits of female choice.

answer

Direct benefits: benefit the female directly (e.g. food, nest sites, protection) Example: Male gifts: female katydids choose males who give more spermataphores (protein/lip rich food item) - Number eaten has direct benefits on number of eggs laid and mean egg weight. Extreme male gift: sexual cannibalism - male literally consumed by female after mating (praying mantis, male redback spiders). Indirect benefits: benefits that affect the genetic quality of the female's offspring

question

Explain male-male competition

answer

Males may develop elaborate armaments. Example: Harlequin beetles defend patches below fig trees where sap falls - females come to these spots to find a mate. Males with long forelegs are better able to defend their territory and get a mate. Example: Pseuodscorpions ride on the back of harlequin beetles to reach fig sap patches and mate with females along the way. Males that have enlarged claws have higher reproductive success.

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Good Genes

answer

indirect benefit

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Sensory Bias

answer

Female preferences may arise from preexisting sensory bias. Example: Female guppies prefer males with bright orange spots. Sensory bias tested by counting number of pecks at orange discs. Males may display elaborate ornaments. Ornaments may often reflect general health ("good genes", and indirect benefit) or simply exploit an inherent sensory bias.

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Runaway Selection

answer

Positive feedback loop: (Fisher's hypothesis) ornaments or signals get bigger, louder and females keep preferring them. What stops the runaway is when the trait becomes a threat to the survival of the male. There is a limit.

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Can sexual selection and natural selection work in opposite directions?

answer

Yes. What happens: better fitness can survive with more sexually desirable trait (ex: red-collared widowbird tail). Ornaments can reflect body condition and attract mates. In long run, ornaments can be harmful.

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Question: In a species in which males invest more for parental care of the offspring, one would expect sexual selection:

answer

to become an even stronger force of selection on males ?

question

How can we examine adaptations - what are the three main methods?' Hypotheses Testing

answer

Hypothesis Testing 1. Experiments: Most powerful method for testing hypotheses. A well-designed experiment limits the difference between study groups to a single variable (hold everything else constant). 2. Observational studies: The most valuable observational studies seek circumstances that mimic an experiment. Observation is used when experiments are impractical. 3. Comparative method: Hypotheses are evaluated by testing for patterns across species. Used to confirm or refute prediction but must take into account shared evolutionary histories.

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Explain what is needed to show adaptation.

answer

1. Determine function of the trait. 2. Show that the individuals possessing the trait leave more offspring than those that do not. 3. Show that trait was "shaped by natural selection to serve the same primary function that make it beneficial today".

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Explain: oxpeckers and mammals (Hypothesis testing)

answer

Oxpeckers ate ticks off of mammals - thought to be a mutualistic relationship. Observation: oxpeckers only infrequently eat ticks. Birds spend >85% of their time feasting on blood from open wounds, probing for ear wax, and harvesting dead skin. Cattle tried 1-2x per minute to swat the birds away. Conclusion: there was no clear direction in how the birds affected tick load. Without birds, cattle had much fewer open wounds and much more earwax. Traditional explanation appears incorrect - they are parasites and not mutualists. It is possible that in other environments a sufficient number of ticks are consumed to be of benefit. Not all differences are adaptive. Example of experimental hypothesis testing. Critical: everything but interaction with birds held constant.

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Explain: the tephritid fly and jumping spider

answer

Example of experimental hypothesis testing. Tephritid fly wing waving resembles the territorial threat display of jumping spiders. Question: why does the fly have the wing-waving and distinct marking? Potential explanations: 1. The fly mimics the spider to evade other predators. 2. The fly mimics the spider to intimidate the same species of spider (which is the fly's main predator). A. Untreated tephritid fly. B. Cut off the wing and reglued it. C. Cut off the wing and glued on a wing of a house fly (no markings). D. Cut off the wing of a house fly and glued on a tephritid fly's wing. E. Untreated house fly. Trying to differentiate between marking and behavior. Hypothesis 1: The flies do not mimic jumping spiders. Hypothesis 2: The flies mimic jumping spiders to evade other predators. Hypothesis 3: The flies mimic jumping spiders to deter predation by the jumping spiders themselves. Experiment: 20 jumping spiders from 11 different species were starved for 2 days to make sure they were hungry. One fly form each of the five groups (A-E) was presented in random order to each spider. Most aggressive response during a five-minute interval was recorded for each spider/fly combination. Most flies waving marked wings survived. Most flies lacking markings or waving were attacked and many were killed. Need both. Flies from groups A, C, and E were presented to a selection of other predators and all flies were quickly attacked and eaten. Conclusion: Third hypothesis is correct.

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Explain: thermoregulation in ectotherms

answer

Observational Study Nighttime retreat in garter snakes Ectotherms - in the lab prefer temperatures in the range of 28-32*C (82-90*F) Tracked and measured body temperature of using radio transmitters that had been implanted in snakes. Found that the snakes stayed fairly close to the range found in the lab. Snakes do remarkably well at staying the this optimal range. Strategies of thermoregulation: 1. Use of rocks for shake (in the day) and insulation (in the night). 2. Moving up and down a burrow. 3. Moving back and forth from sunshine to shade. Prediction: At night, underneath a medium rock is best.

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Explain: testes size in bats

answer

Comparative Method Species of bats vary in relative testes size. It was hypothesized that testes size is an adaptation for sperm competition. Sperm competition occurs when females mate with more than one male per mating cycle. Sperm competition should be more prevalent in bats with large social groups Concluded that sperm competition hypothesis is consistent with testes size/social group size correlation. Later study found a negative association between testes size/brain size (correlations do not show cause!).

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What are the advantages and disadvantages for: morphological species?

answer

Phonetic (morphological) species concept: Based on traditional concept of identifying species using morphological species (how they look) Advantage is that is widely applicable: - Living or extinct organisms (can get information from fossils) - Sexual or asexual organisms Disadvantages: -Difficult to apply to organisms lacking measureable morphological characters -Organisms that vary according to environment (phenotypic plasticity) may be misidentified -Lack of consistency (dependent on the judgment of the investigator) -Difficult to apply to organisms lacking measureable morphological characters -Problematic for species with sexual dimorphism

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What are the advantages and disadvantages for: phylogenetic species?

answer

Criterion for species identification is monophyly. (Monophyletic group: lineages descended from a common ancestor) Rationale is that monphyletic groups will possess a number of unique traits. These traits (synapomorphies) are only likely to exist if reproductive isolation has occurred. Advantages: -Widely applicable (sexual/asexual, living/extinct(?)) -Relatively objective (?), species are named based on statistically significant differences Disadvantages: -To some extent classification is arbitrary -Likely to result in a large number of new species and require substantial revision of traditional classification schemes

question

What are the advantages and disadvantages for: biological species?

answer

"Species are groups of interbreeding natural populations that are reproductively isolated from other such groups." - Ernst Mayr Geographic isolation is not sufficient, reproductive isolation must be caused by genetic differences. Not a species if: -Organisms do not mate regularly in nature OR -Mating results in infertile offspring Advantage: -Object test of reproductive isolation Disadvantage: -Only relevant for living (no fossils) and sexually reproducing organisms -Can be difficult to apply (e.g. if two population do not overlap geographically, would they mate if the geographic barrier was removed?)

question

Postzygotic: intrinsic

answer

Hybrid inviability and sterility, reflecting genetic make-up -e.g., aborted embryos; malformed and inviable offspring -e.g., A mule is the F1 hybrid of a female horse and a male donkey. They are almost always sterile

question

Postzygotic: extrinsic

answer

Hybrids have low viability and/or mating success in their environment -e.g., Heliconius butterflies: Hybrids have low fitness due to high predator attack (aposematic warning coloration not recognized by predators). -e.g., low mating success due to intermediate sexually selected traits

question

Reproductive Barriers

answer

Speciation an occurs when there is a barrier to gene flow (two populations that don't interbreed).

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Pre-mating Isolation

answer

Organisms occur in the same area but don't mate. Potential mates don't meet: - different habitats - different mating seasons/times Potential mates meet but don't mate: - different mating behavior in animals - different pollinators in plants

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Post-mating isolation (prezygotic)

answer

Potential mates try to mate but can't form a zygote. Incompatible genitalia Incompatible gametes

question

Postzygotic isolation

answer

Hybrids are formed but have low fitness. "intrinsic" mechanisms: - hybrid lethality - hybrid sterility (physiological or behavioral) "extrinsic" mechanisms - ecological: hybrids don't fit into either ecological niche - mate recognition: mating behavior not appropriate for either species

question

Classify different scenarios by their reproductive barrier:

answer

Prezygotic barriers • Habitat isolation • Behavioral isolation • Temporal isolation • Genital incompatibility (post-mating) • Gamete incompatibility (post-mating) Postzygotic barriers- intrinsic vs. extrinsic • Reduced hybrid viability (intrinsic) • Reduced hybrid infertility (intrinsic) • Ecological (extrinsic) • Mating behavior (extrinsic)

question

Allopatric Speciation

answer

Populations evolve isolating barriers in geographic isolation.

question

Sympatric Speciation

answer

Speciation occurs within a freely interbreeding population. Difficulty with sympatric speciation: Disruptive selection on phenotype has to be very strong (i.e. selection against intermediates has to be strong) AND Individuals must mate assortatively with others of similar phenotype. The loci underlying both the phenotype and mating preference must be the same or tightly linked. (ex: if people with blue eyes only prefer to mate with people with blue eyes: genes controlling blue eyes are closely linked to mating preference)

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What is more common in speciation - allopatry or sympatry? Why?

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Allopatry Allopatry is "easy." Sympatry requires very strong disruptive selection which is not common in natural populations.

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Classify scanarioes as either allopatric or sympatric.

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Allopatric: a physical barrier: a river, a mountain range, etc. comes up and over time the populations evolve differently. When the populations come back together, they have a difficult time interbreeding (or don't interbreed). Evolutionary mechanisms (causes): drift, mutations, selection Example: If a mountain range divides population, the climates on either side might be very different which will result in very different selection pressures. Sympatric: a population can freely interbreed but don't. Example: Cichlids that prefer different water depths.

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Isolating mechanisms Examples

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Coral polyps temporal divergence -Ecological: temporal (some coral polyps follow a full moon - won't interbreed with the those that don't) Divergence in habitat of Apple Maggot Fly -Ecological: habitat use (Rhagoletis are found on both apple trees and hawthorne trees. The trees are intermixed. Some of the maggot flies feed and mate on apple trees and some on hawthorne trees. The ones on apple trees are only mating with those on apple trees; the ones on hawthorne trees are only mating with those on hawthorne trees) Mating rituals in bowerbirds (Satin bowerbirds and MacGregor's Bowerbird have very different mating rituals.) Postmating divergence in snake hemipenes -Post-mating: incompatible genitalia (Mechanistic differences between genitals makes successful fertilization impossible) European blackcaps -Extrinsic postzygotic isolation: hybrids (one parent migrates southwest, one parent migrates northwest - hybrid not as well suited in either destination) -Also a little bit prezygotic because less likely to mate with birds in the other migration pattern (Changed migration patterns. New population established In UK that had shorter migration path and will get to destination at a different time.) Mules and hybrid sterility Hummingbird hybrid courtship behavior Migration patterns diverge European Blackcaps

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What is necessary for sympatric speciation to occur? Why is it theoretically possible, but difficult to find empirical evidence for? (Only very few cases)

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Disruptive selection Assortative mating Tight connection with phenotype and mating preference

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Why is allopatric speciation easier to document and explain?

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No interbreeding due to geographic barriers Barriers to reproduction are more likely to accumulate more gradually over time Speciation is a passive consequence of population divergence This may happen rapidly of ecology of the populations differs

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How does the ecology of a population contribute to the rate of speciation?

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Ecological divergence can accelerate the process of speciation. Ecological divergence has a passive consequence Speciation may occur rapidly if ecology greatly differs due to different selection pressures.

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What is reinforcement the icing on the proverbial speciation cake?

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During period of allopatry: postzygotic barriers to reproduction have arisen. If species spread back into sympatry: alleles that reduce the degree of interbreeding can be favored. BUT: If that does not happen fast enough, the species may collapse back together. Reinforcement is selection against individuals that mate and form hybrids. Natural selection is acting to increase the amount of reproductive isolation (because hybrids usually have much lower fitness).

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Evolutionary Medicine

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Putting it all together: selection, random genetic drift, population genetics, changing environments, variation among populations

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Human and Societies (time, transitions, species)

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Human lifestyles and societies have changed dramatically. Major transitions/ perspective of time: 2,000,000 YA: first hominid ancestor (Homo habilis) 200,000 YA: first Homo sapiens in fossil record 12,000 YA: early agricultural revolution 100 YA: penicillin discovered Main Points 1. As a species, we have spent most of our time in an environment that was entirely different from the one most of us currently experience. 2. Many of our current traits and behaviors will have shaped by those past environments. 3. Some traits that were advantageous in a past environment may no longer be beneficial.

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What are some ways that modern environments differ from the environments our ancestors lived in?

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Food availability and compositions -; obesity and related health problems The pathogens and parasites to which we are commonly exposed -; allergies, asthma (we used to be exposed to much more pathogens and parasites because people used to have more kids, live in closer proximity to farm animals, etc. which may be leading to a significant increase in allergies and asthma)

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Evolutionary Medicine: Obesity Diet

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Ancestral diet: 46% carbs, 33% protein, 21% fat Ancestral carbs: almost entirely vegetables and fruit, some cereal grains, no refined flour Modern diet 46% cabs, 12% protein, 42% fat Modern carbs: only 23% fruit and vegetables - lots of sugars and refined flours Artificial additives (mostly after 1950) Highly processed food (mostly after 1800) Potatoes (after 1750) Cereal grains, cow's milk (~10000 years ago)

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Why do we care about obesity when we think about evolutionary medicine?

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Obesity increases the risk of: -cardiovascular disease (heart disease and stroke) -diabetes -musculoskeletal disorders -some cancers The WHO estimates that 2.8 million adults die every year as a result of being overweight or obese

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Study: is there a difference between the Pima that live in the US and the Pima in Mexico?

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Pima in US: high fat, highly processed food (typical American diet) Pima in Mexico: traditional diet of beans, corn, potatoes, and high physical activity Percentage of Type 2 diabetes: non-Pima Mexican, Mexican Pima, US Pima Shows a striking difference. Level of type 2 diabetes in US is MUCH higher. Genetics fairly similar. Evidence that diet plays a rule.

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What is the Thrifty hypothesis? What assumptions are needed?

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Thrifty hypothesis: certain genes evolved to regulate efficient intake and utilization of food in unpredictable environments (fluctuations of feasts and famines). More thrifty storage means more likely to survive through next famine/activity phase until next feast. You would have an advantage if genes allow you to uptake nutrients and hold on to them efficiently and use them when needed. These same genes could lead to obesity and diabetes in modern environments. (Many people now have access to a constant stream of food - i.e. supermarkets). In other words, the current prevalence of obesity and diabetes is the result of positive selection for their underlying genes in a past environment. Debate against: 1. We should all be obese (or, possibly, none of us should) 2. Famines don't actually increase mortality enough to act as a particularly strong selective pressure

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Thrifty hypothesis counterargument: Why aren't we all obese?

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The A allele should reach a frequency of 99% in 16500 generations. With a generation time of ~20-30 years, there have been at least 70000 generations since our hominid ancestors. We should all have inherited these 'thrifty genes' by now. But: evidence suggests that famines may not have been important before humans lived in sedentary agricultural societies. In this case, selection has only been acting for ~400-600 generations. An allele conferring an advantage of only 0.1% would have no chance of spreading in this time. We should all be thin.

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Thrifty hypothesis counterargument: Too few people die of starvation in famines.

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To get the A allele to increase from 1% to 30% (approximately current incidence of obesity) in 600 generations, it needs to provide a fairly substantial advantage in survival or fecundity. Selection would have to be very strong. The difference in mortality during famines required to explain current levels of obesity is between 15-20%. Actual estimates of mortality during famines rarely exceeds 10%.

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What is the Drifty hypothesis? What assumptions are needed?

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Hypothesis: In the past, we were always being chased or chasing somethign, so selection favours slimness to be quicker. In modern environments, that selection pressure has been relieved. We're no longer running from tigers or running after bunnies for food. Our body size can now drift because there is no longer a selection pressure either way. There is no advantage of being slim. In other words, the current prevalence of obesity and diabetes is the result of genetic drift (and relaxation of selection) in current environments, rather than selection for their underlying genes in past environments.

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Think about: Is the current prevalence of obesity and diabetes really the result of selection in a past environment and mismatch with the current one (i.e., is it due to a Thrifty Genotype)?

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Still a matter of debate. Both require assumptions. Both evoke selection. Only Drifty evokes drift.

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What are the six explanations for why we get sick/why we are vulnerable?

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(selection is slow) 1. Mismatch with modern environments: fitness landscape has changed 2. Pathogens are coevolving with their hosts (What selection can do is limited:) 3. Constraint on what selection can do 4. Tradeoffs (We misunderstand what selection shapes:) 5. Selection maximizes reproduction, not health 6. Defenses, while unpleasant, are useful

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