eemb 2 evolution

evolution

change within species through time

descent with modification

benoit de maillot

thought earth was billions of years old

life evolved from sea creatures

georges buffon

earth at least 75,000 years old

life is changeable w/modification influenced by the enviornment

erasmus darwin

charles darwins grandpa

competition leads to speciation

all life descended from one filament

speciation

change in respose to the enviornment

georges cuvier

studied comparative anatomy and vertebrate paleontology

catastophism theory

catastrophism theory

extinctions caused by catastrophes

extant species are survivors not new

lamarck

inheritance of acquired characteristics:

physiological changes develop over the life of an organism are trasnmitted to offspring

charles lyell

wrote priciples of geology

geologic processes occur at the same gradual and uniform rates: slowly

malthus

wrote essay of the principle of population

populations can grow exponentially and produce more individuals than the enviornment can support

beagle voyage observations

species compositions change with the enviornment

fossils are related to current species but can also look different

galapagos island species are related to mainland species but have different forms and functions

alfred wallace

independantly works out the pricipals of natural selection: survival of the fittest

presented paper along with darwin to the linnaean society in 1858

gregor mendel

father of genetics

inheritance via discreet units (genes/alleles) with 2 units per individual

devries

theory of mutation

mutation as a source of variation and new speciaiton

neodarwinism

combines genetics with natural selection

gould and eldredge

punctuated equilibrium

long periods of no change w/ short bursts of rapid change

modern theory of evolution

incorporates neodarwinism, population biology and puctuated equillibrium

modifications in descent can occur, rapidly, gradually, or in combination

microevolution

small scale change

involves changes in allele frequency and/or genotype frequency

major mechanims = natural selection

macroeovolution

large scale change

involves speciation or higher level changes

genotype

an individuals genetic (allelic makeup)

phenotype

an individuals physical appearance or observed characteristics

determined by genotype and enviornment

gene pool

collection of all genes and alleles in a populatio

genome

all the genes and alleles in a species

allele (gene) frequency)

relative proportion of an allele w/in the population

how common is A vs a

freq of A = #A/total alleles

hardy weinberg equillibrium

a state of non evolution for the population

no changes in allele frequency are occuring

criteria for hardy weinberg equilibrium to be established

population is large with no migration or mutation

mating between individuals is random

there is no natural selection occuring

sexual reproduction generates a hardy-weinberg equilibrium meaning:

gene frequencies wont change between generations

we can preduct what genotype frequencies should be

hardy weinberg eq. equation

p² + 2pq + q²

p = freq A

q= freq a

p + q = 1

p² = AA

2pq = aa

q² = aa

no evolution

expected HW eq values are observed and equilibrium is stable

evolution is occuring

expected HW eq values are NOT observed equibibrium is unstable

gene flow

genetic drift

natural selection

possible mechanims that HW equilibrium is undergoing evoolution (unstable)

gene flow

changes due to migration

genetic drift

random changes due to sampling error

natural selection

changes due to differing fitness/adaptiveness

the process by which certain inherited characteristics leading to more offspring increase in a population over time

original synthesis of natural selection by darwin

1. populations can grow geometrically, but are actually limited by resources

   1. high level of intraspecific competition

2. variation within a species may be inheritable and affect survival and reproduction

   1. certain types survive better reproduce more and increase in the population

3. new variations appear

   1. evolution continues

3 types of variation

continuous

discrete

along a gradient ecogeographical

mutatuon

sexual reproduction

sources of variation

mutation

inheritable change in DNA sequece

ultimate source of all NEW alleles (variation)

Rare and random often egative or neutral sometimes beneficial.

can change with environment

sexual reoproduction

• during meiosis

  • crossing over

  • independent assortment

• during fertilization

  • gametes from differen parents combine to form new genotype combos

spatially varying enviornment

frequency dependent selection

heterozygote advantage

maintaining variation

spatially varying enviornment

different alleles favored in different places/habitats

frequency dependent selection

• positive: most abundant form increases

  • tends to decrease variation

• negative: slection favors the rarer form/allele

  • tends to maintain variation

  • a form of balancing selection (balaned poymorphism)

    • ex. predator concentrates on common form

heterozygote advantage

• heterozygotes are the most fit (favored by selection)

• leads to balanced polymorphism (both alleles maintained)

• another form of balancing selection

  • ex. sickle cell trait

natural selection

gene flow

genetic drift

non random mating

agents of evolution

non random mating

changes due to preferential mating patterns

agents of evolution: natural selection

differences in phenotype leading to differential survival and reproduction

fitness

a relative measure of reproductive success

• related to the # of genome copies contributed to the next generation

• depends on the match between the individuals phenotype and the present enviornment

• higher fitess implies possessing more or better adaptations than others in the population

forms of fitness

• evolutionary (individual fitness (W*)

  • W* = sirvival x fecundity

    • can use # offspring as estimate

• relative fitness (W)

  • individual fitness/highest individual fitness

    • W = W*/W*_max

    • normalizes genotype comparison range: 0-1

3 forms of natural selection (based on polygenic/continuous variation)

stabilizing selection

directional selectio

disruptive selection

stabilizing selectio

• favors the intermediate

• remvoes extreme (reduces variation)

• occurs in stable enviornments

  • ex. clutch size in birds

  • human birth weight

directional selection

• favors 1 extreme

• average shifts over time

• occurs in changing enviornmets

  • ex. peppered moth

  • antibiotic resistance

  • pesticide resistance

disruptive selection

• favors both extreme

• intermediates selected against

• results in bimodal distribution

• occurs in habitats patchy or shifting in time or space

  • ex. mice in the desert

  • seed cracker finches

agents of evolution: gene flow

changes due to migration between populations

• may counter and slow local adaptation

• immigration may introduce new alleles

agents of evolution: genetic drift

changes due to random events

• important in small groups → sampling error

• may result in loss of alleles → remaining allele becomes fized (freq=1)

• when many harmful alleles all become fixed → mutational meltdown

founder effect (genetic drift)

small number of individuals start a population in a new location

ex. colonization of islands

bottleneck effect (genetic drift)

population declines to small size

ex. cheetahs

agents of evolution: non random mating

• preferential mating patterns

• changes genotype frequencies but not allele frequencies

positive assortative

negative assortative

inbreeding

types of nonrandom mating

positive assortative

between like types

• decreases variation; increases homozygotes

negative assortative

between unlike types = disassortative mating

• increases variation; increases heterozygotes

inbreeding

between relatives

similar to + assortative mating

sexual selection

differeing fitness within one sex due to competition for mates

arises because the 2 sexes maximize their fitness differently

• male fitness by having a large quantity of mates → small mobile gametes

• female fitness by choosing a quality male → large well provisioned gametes

leads to sexual dimophism

extremely ornamented males have higher fitness so extreme male traits increase

sexual dimorphism

male and females look different; males often w/ extreme traits

intrasexual selection

intersexual selection

types of sexual selection

intrasexual selection

within 1 sex (usually males)

involves male vs male competition

may include:

• fighting and aggression

• intimidation displats

• sperm competition

intersexual selection

between sexes

involves female choice of the male based on trait

models

• fishers runaway (sexy sons)

• good genes hypothesis

• sensory exploitation hypothesis

fisher runaway (sexy sons)

females choosing attratcive male will also hae attractive sons → attractive sons will have high mating success

good genes hypothesis

male trait is an indicator of superior quality (longevity/good health)

sensory exploitation hypothesis

female is reacting to pre existing sensory preference for the trait

coevolution

when 2 species or genes interact and evolve in response to each other

interspecific coevolution

when 2 SPECIES interact and evolve in response to each other

intraspecific (intergenic) coevolution

when 2 GENES interact and evolve in response to each other

Antagonistic coevolution

mutualistic coevolution

major forms of coevolution

antagonistic

a perpetual cycle of defense and counter defense

aka RED QUEEN

interspecific examples:

• predator prey

• Parasite Host

• Between competitors

intraspecific example

• sperm vs egg matrix thickness

mutualistic

system where both parties benefit

interspecific examples

• plants and their pollinators

itraspecific examples

• hormones and receptors

species (ernst mayers biological species definition)

groups that have gene pools and therefore do not freely exchange genes-they are reproductively isolated

• morphology

  • if extinct (via fossils)

• genetic aalysis

  • microbes

reproductive isolating mechanisms (RIMS)

act as barriers to successful interbreeding and free gene exchange between species

two types of RIMS

pre-zygotic RIMS

post-zygotic RIMS

pre-zygotic rims

preventing interbreeding: no hybrids are formed

ex.

• incompatible anatomy or physiology

• differing habitats locations or breeding seasons

• differing mating courtship behaviours

  • lions and tigers

    • never mate in nature due to different habitats

post-zygotic rims

interbreeding occurs but hybrids show lower fitness relative to pure parental types

ex.

• decreased hybrid fertility

• decreased hybrid survival

• hybrid breakdown (F2 offspring w/ low fitness)

  • horses and donkeys are 2 spp

    • hybrid offspring (mule) is sterile

reinforcement (decreased interbreeding) can evolve if hybrid fitness is very low

speciation

development of rims between groups/populations

3 main modes of speciation

allopatric

sympatric

parapatric

allopatric speciation

genetic divergence occurs while 2 poplations are geographically seperated (too far apart for gene flow, dispersal or migration)

• due to mutation, genetic drift or natural selection

  • can lead to the pops becoming genetically and or behaviorally incompatible

special case: peripatric speciation → occurs in small isolated peripheral populations

• colonization of nearby islands = founder events

allopatric model secondary contact 3 possible outcomes

• the 2 populations do not interbreed (+ assortative mating only)

  • pre zygotic RIM → 2 spp.

• the 2 populations interbreed, but the hybrid offspring are inferior (have lower fitness)

  • post-zygotic RIM → 2 spp. (reinforcement may occur)

• the 2 populations freely interbreed and produce viable and fertile offspring

  • random matting is occuring

  • no RIM developed → still 1 sp. (fusion will likely occur)

sympatric speciation

speciation occurs when the populations overlap

can occurs via

• resource partitioning and specialization

  • ex. 2 extremes of an insect population eating, living, and mating on different species of tree may eventually become 2 species

    • hawthorn flies utilizing different fruits - hawthorn berries vs apple etc.

• polyploidy (chromosome duplication)

  • common in plants (rare in animals)

  • due to cell division mistakes in meiosis or mitosis

    • notation A=1 complete set of chromosomes from species A

    • autopolyploid: involves 1 parental sp.

      

    • allopolyploid: duplication after hybridization of 2 spp.

      

parapatric speciation

speciation occurs while maitaining a common border

neighboring populations adapting to local enviornments

• reuslts in a hybrid zone (narrow border where hybrids are produced

macroevolution: large scale change (species level and higher)

can be difficult to track due to incomplete and biased fossil record

patterns change with dispersal and vicariance

rates depend on speciation (alpha) and extinction (omega)

standing diversity

= (total diversity) = diversity_t0 + alpha - omega

turnover

= # speciations + # extinctions = alpha + omega

possible mechanisms for macroevolution

gradualism

punctuated equilibrium

gradualism

slow steady rate of change w/ gradual accumulation of small changes over long time periods

punctuated equilibrium

short periods of rapid change followed by long periods of little or no change (stasis)

adaptive radiation

high level and rapid speciation to fill new or open niches (alpha» omega)

processes that increase speciation rates

• vacant niches

• new mutations

• evolution of key innovations/novel traits

  • wings

  • bilateral symmetry

  • animal pollination

ex.

• hawaiian honeycreeper birds

• cambrian explosion

mass extinction

omega is much greater than baseline/background levels

• at least 75% marine spp disappear

causes

• climate change

• volcanis action

• change in sea level

• asteroids

phylogeny

the evolutionary hisotyr of organisms

involves cladistics

clade

taxa that descend/diverge from 1 common ancestor

• monophyletic

• paraphyletic

• polyphyletic

phylogenetic tree

summary of relatedness on a branching diagram

monophyletic

includes ALL descendants of a common ancestor

paraphyletic

excludes some descendants of a common ancestor