7.1 microevolution megaset

Evolution

change over time

Microevolution

Changes within species

microevo → macroevo

• macroevolutionary differences are the result of microevo changes

Macroevolution

changes b/w species

microevo → macroevo

• macroevolutionary differences are the result of microevo changes

Lamarckism

Jean Baptiste Lamarck (1744-1829)

Acquired characteristics

• Offspring inherit characteristics acquired by parents thru use or disuse

Charles Darwin

1. natural selection

2. descent with modification (macro)

Survey expedition of the HMS Beagle (1831-1836)

On the Origin of Species 1859

Natural Selection (micro)

• traits that yield greater reproductive success will increase in freq in a population

• independently proposed by Alfred Russel Wallace

  • the threat of getting scooped by Wallace led Darwin to finally publish his book

Descent w Modification (macro)

species change over time as new traits appear and are passed down

Darwin’s Inspirations

1. Charles Lyell’s Principles of Geology

   1. Uniformitarianism

      1. Natural processes that happen today have always happened

2. Thomas Malthus’ An Essay on the Principles of Population

   1. Resources are limited

   2. Humanity is doomed to struggle

observe evolution today, which is the same evolution that happened in the past

BPQ

how does uniformitarianism relate to evolutionary theory?

Requirements for Natural Selection

1. Variation in a population

2. Selection (advantages over others)

3. Heritable traits

the dead male mantis bc he reproduced

BPQ

which male mantis will have higher fitness?

Artificial Selection

When humans do the selecting

e.g. dog breeds

Sexual selection

when mates are doing the selecting

e.g. peacocks, tropical birds

Convergent Evolution

when selection leads to unrelated species sharing the same (or similar) trait

without a common ancestor

e.g. Monarch and Viceroy butterflies

4 evolutionary forces

1. natural selection - non-random

2. mutation - random

3. drift - random

4. migration - random/non-random

think in terms of allele frequencies in a pop.

Natural Selection

certain traits/alleles lead to better reproductive success in certain environments

• traits/alleles that are selected for will incr in freq

• nat sel can affect traits influenced by a single gene or polygenic traits

Fitness

the measure of reproductive success given trait yields

appears late in life so you can still have lots of reproductive success

BPQ

why is there little selection against Huntington’s Disease?

Stabilizing Selection

intermediate phenotype is selected for

Directional Selection

one extreme phenotype is selected for

Disruptive selection

both extreme phenotypes are selected for (extremes are more fit)

disruptive selection → speciation

BPQ

which form of selection leads to speciation?

Frequency Dependent selection

rare traits are selected over common traits → rare traits become common

e.g. prey switching - predators focus on common traits

Mutation

the only evolutionary force that can create new traits

occurs very very very slowly

• mutation cannot make traits more common

• selection/drift makes traits more common

Genetic Drift

random change in allele frequencies

• changes in allele freq have nothing to do w reproductive success

more common in smaller pops, less likely in big pops

Founder Effect

• new pop is established by small # of indivs.

  • pop is small so genetic drift is common

  • if founder effect carries rare allele, it is no longer rare

  • not all alleles will be carried over from original pop

Bottleneck

drift that results from a dramatic loss in pop size

Migration

alleles are carried between pops

there would be type A in south/central america

bc european colonization

BPQ

This map represents allele frequencies of native peoples, how might Central and South America look different when all people are included.

Sexual selection

form of nat sel based on process of acquiring a mate

• intersexual selection - one sex chooses mates from other sex

  • females usually choose

• intrasexual selection - competition between members of the same sex for a mate

  • males usually compete

No bc there’s no selection of a mate

BPQ

conifers reproduce mostly by wind pollination and are more likely to be pollinated by nearby trees.

is this sexual selection?

Sexual dimorphism

Morphological (physical) differences b/w the sexes

2 main causes

• reproductive needs

• sexual selection

Sexual selection can lead to extravagant features in the non-limited sex (usually male)

No, this is purely reproductive, not caused by sexual selection

BPQ

which pelvis is male/female?

is this the result of sexual selection?

Males vs Females

females

• put more resources toward reproduction (typically)

• limited reproductive potential

• more selective

males

• put little resources toward reproduction (typically)

• unlimited reproductive potential

• more competitive

Female Choice - Good Genes Hypothesis

females are selecting traits in their male partners that are good signals of male fitness

females are not objectively picking males for good genes

• female preference is driven by nat sel - an innate instinct

the loud frog

bc its a good signal that he has good traits

BPQ

female frog A pref male with long loud calls. female frog B pref short soft calls.

Which female will likely have more offspring survive to maturity?

Mating Systems

1. Promiscuity

2. Polygamy

   1. Polygyny

   2. Polyandry

3. Monogamy

Promiscuity

a member of one sex mates with any indiv of the opposite sex

• female choice and male competition still present

Polygamy

Polygyny - Multiple females exclusively mate with one male

Polyandry - multiple males exclusively mate with one female

Polygyny

• one male multiple females

• alpha male prevents females from mating with other males

If you have two males, it’s harder to usurp the pride

Brothers have similar gene pool

BPQ

lions exhibit polygyny

However, sometimes a pride will have two or more males that are usually brothers.

What is the advantage of this?

Infanticide

the intentional killing of the old alpha’s offspring by the new alpha

Polyandry

• one female multiple males

• less common

• eusocial colony nesters (has a queen)

  • bees

  • ants

  • naked mole rats

• infanticide avoidance

  • bank vole

males can’t tell if the offspring is theirs or not

BPQ

how do females use polyandry to avoid infanticide

Monogamy

• one male one female

• very common in birds

• often associated with bi-parental care

  • male and female raise the offspring

  • often necessary for offspring survival

• long-term monogamy (for life)

• serial monogamy (1 breeding season)

sexual selection decreases

male and female become similar (physically too)

female and male choice

BPQ

monogamy reduces male reproductive potential

parental care increases male reproductive costs

How may sexual selection be affected in monogamous species?

Male Choice

• roles begin to swap as males become the more limited sex

• females may show ornamentation

long-term monogamous males may select for neotenic (youthful) traits

• younger females will have more reproductive cycles

serial monogamous males may select for paramorphic (mature) traits

• older females will have more experience raising offspring

female is the top, bigger one bc it is ornamented

→ need to attract the male (who will care for the young)

BPQ

sex the pipe fish in the photo

Extra-pair copulation (EPC)

• cheating (in monogamy)

• one male gets extra offspring

• one female gets better genes for her offspring

• one male gets nothing

long-term monogamy

bc human skulls have lost sexual dimorphism

BPQ

what form of mating do humans have?

Hardy-Weinberg Equilibrium

A population in ___ is not evolving

Allele frequencies and genotype frequencies do not change over generations

Hardy-Weinberg Assumptions

1. Infinite population size

2. Random mating

3. No mutation

4. No gene flow (No migration)

5. No Selection

Big H-W Misconception

Traits not under selection do move to equal frequency (ex: 50% A, 50% a), they just do not change over time

Genetic drift

BPQ

What phenomena is eliminated when you assume an infinite population size?

In other words, what cannot occur in an infinite population?

NOTHING!!!!!!!

Evolution = Change

Only a change in allele frequencies can be interpreted as evolutionary change

BPQ

If an allele is found in high frequency in a pop, what does that tell us about that allele?

Note on Random Mating

Non-random mating DOES NOT affect allele frequencies

Non-random mating DOES affect genotype and phenotype frequencies

The Gene Pool

With infinite population sizes and random mating, the distribution of phenotypes in the parental generation does not affect the allele frequency of the offspring generation

Alleles can be treated as moving independently of each other from one generation to the next

Gene pool - “pool” of alleles that are randomly sorted into the next generation

Hardy-Weinberg Equation

p² + 2pq + q² = 1

p = A, q = a

Homozygous Dominant Probability - p²

Heterozygous Probability - 2pq (Aa or aA)

Homozygous Recessive Probability - q²

Tips - Assuming HW Eq.

• For Problems where you Assume HW equilibrium to find an unknown Frequency:

  • It is always easier to get allele frequencies from the recessive phenotype frequency (=q²)

    • If you are given the dominant phenotype frequency: recessive phenotype frequency = 1 – dominant phenotype frequency

• Once you have q you can get p (p = 1 – q)

• Once you have p and q you can get any genotype frequency (p², 2pq, q²)

H-W Chi Square Test

• Special Rule: HW df (degrees of freedom) =1

  • Because E is based on p & q (2-1=1)

• 16>>3.841

  • Statistically different

  • Not in HW equilibrium

Tips - Determining HW Eq.

• For problems where you are determining if a population is in HW equilibrium:

  • Never Never Never Never use HW to find p & q

    • You don’t know if the population is in HW.  That is your question

    • You must count the alleles in a population

      • HW gives you theoretical p & q.  These are the real p & q

• Once you have the real p & q you can determine what the population would look like if it was in HW equilibrium (p², 2pq, q²⁾

• Lastly compare the expected and observed population

Stabilizing selection

BPQ

If this population was under the influence of selection, what form of selection would this be?

Stabilizing

Directional

Disruptive

Random mating

BPQ
Other than selection, what other assumption could this population be violating?

Infinite population size (no drift)

Random mating

No mutation

No gene flow (No migration)

No Selection

H-W Uses

1. Find allele and genotype frequencies with only partial information

   1. You must assume H-W assumptions

2. Use expected H-W frequencies as a null hypothesis

   1. If observed frequencies differ than one of the assumptions is being broken

3. Model evolutionary forces to predict population evolution overtime

   1. Adds in variable for the various evolutionary forces

   2. Details are beyond the scope of this course

Inbreeding

mating of closely related individuals - bad

Outbreeding

mating of distantly related individuals - good

Inbreeding in a population

• Increases as populations size drops and becomes more sparse

• Effects on the population:

  • Increase in homozygosity

  • Decrease in heterozygosity

  • Inbreeding depression

    • Population becomes less healthy as more recessive conditions are expressed

• Does not affect:

  • Allele frequency

  • Genetic diversity

Inbreeding Coefficient

F statistic - measures how inbred a population is (0 - 1)

• F = 0 - no inbreeding

• F < 0.1 - acceptable level

• F > 0.1 - bad

• F < 0 - excess outbreeding

F = 1 - (ObservedFreq(Aa)/ExpectedFreq(Aa)) = 1 - (ObservedFreq(Aa)/2pq)