Evolution final exam

chp 16,18,20

Species...What is a species?what is the best definition we have?

the grouping of organisms based on differences such as behavioral or morphological characteristics
Species are reproductively isolatedWhen closely related, can hybridize

what did Darwin struggle with?

Darwin struggled with how species originated

organisms tend to

name/recognize/groups/identify themselves

Darwin was surprised by what about species?

Darwin was surprised how very little different species were from each other. He figured out how species arose but now the question is what is a species and how do we differentiate between species

different species usually form what?

clusters of phenotypes

why did Darwin say we can't spend all of our time on one species?

because species are dynamic meaning they are always changing and it's a gradual process

species have unique combination of features

when features are similar, usually they are closely related, Linneus did this

almost all species are reproductively isolated

when they are closely related, they can hybridize. They have to be independent when they are reproductively isolated

how can we think of speciation?

Think of speciation as the splitting of one gene pool into two or more gene pools

what kind of population does population have?

A population has a whole and one continuous population

species concepts

* Morphospecies concept
* Phylogenetic species concept
* Biological species concept

why was the species concept created?

species concepts were created by humans to help us understand how these organisms are related to each other. instead of informal judgments of species physical similarity we need to use species concepts

what does a species have to be?

A species has to be a group of organisms that are revolutionary independent from another group
One group has its own little gene pool. with mutation, selection, genetic drift from another then that's two separate gene pools therefore it's two different populations.
Gene frequencies change in both independent gene pools. This means we have two populations that are independently evolving

morphospecies concept

this is how we determine whether they are independent or not
looking at morphology/shape of organism
careful analysis of shape of organism
widely applicable: can apply it to extinct or extant things or asexual and sexual EX: One dinosaur looks different from this dinosaur so they are different species

disadvantages/problems of the Morphospecies concept

- it's arbitrary. How can we say they are different from each other
- we need sufficient measurable characters. It doesn't apply to most species EX: bacteria there's no morphology because they are all round
- we cannot apply it to soft tissue on fossils because there are only bones to look at. maybe they have the same skeleton but they might differ dramatically and soft tissue and we would never know because we can't see it
- no behavior differences. One birdcall versus the other so they will never breed together because it is two different populations and two different species. EX: cryptic species = they look the same, can't tease them apart, they're cryptic/hidden. They are hard to find out what they are

cryptic species

a species that cannot be distinguished from similar species by easily identifiable morphological traits
Groups of organisms that are genetically distinct and do not interbreed, but are morphologically almost indistinguishable

phylogenetic species concept

most concerned with ensuring the groups you are looking at are shared common ancestor and it is the smallest group within the common lineage
A species is a monophyletic group composed of the smallest diagnosable cluster of individual organisms within which there is a Parental pattern of ancestry and descent
looking at separate phylogenetic species populations
populations have to have been evolutionary independent Long enough for these diagnostic traits to have evolved
if the populations cannot be clearly distinguished by synapomorphies, (there are no distinguishing characteristics to tease up) then they have to be considered the same species and they share the common ancestor. HOWEVER.... if they have evolved independently enough to have synapomorphies, that tells them apart, then we would see a split between species E1 and E2

disadvantages/problems of phylogenetic species concept

- how many synapomorphies does a group have to have before it's its own species?
- can't we just use genetics? No because genetic tech is so good it could tease apart so much and every individual can be its own species depending on where you draw the line. You end up with the same problem; where do we draw the distinction line?

biological species concept

species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups
they are not actually interbreeding because they are in different populations but they could if you put them together because they are still the same species
if you can reproduce successfully and produce viable offspring then you two are the same species
this concept is based on reproductive isolation which means gene pools are separate and they evolve their own way not in one direction

disadvantages/problems of the biological species concept

- can't apply to asexual organisms
- hybridization - Darwin had a hard time with it. If there's no strong barriers for intersexual breeding, then inter-species mating produces fertile hybrids. Not common but it does occur among plants and fungi mostly
EX: ligers . meet tigers and lions together in captivity but this would never happen in a natural environment

be aware of the Procrustes fallacy

Science creates a concept and we try to fit nature into that concept/framework but nature is far too diverse to be explained by a single concept.
we should accept natural diversity and apply concepts when applicable appropriately
we have to be careful we are not like Procrustes and create a concept and jam everything into it. Don't force nature to fit in concept

why do we need a reliable criteria for identifying species?

reliable criteria for identifying species are essential for preserving biodiversity
EX: IUCN, World wildlife fund - they need to be able to define what a species is if they are going to try and preserve biodiversity
Ex: case history - elephants2 different species of elephants; Indian elephant and African elephant but then a new species appeared the African forest elephant and now it is hard for conservationist because now they don't know who to donate money to

when is a population considered a separate gene pool?

as long as two or more populations are diverging and evolving independently then they are considered separate gene pools. Evolution is changes in allele frequencies and its frequencies change independently which means there are two different populations/species

Speciation

Formation of new species

process of Speciation (steps)

isolation (1st stage) 1 pop. becomes isolated - physically separated - Temporal - mutation
divergence (2nd stage) separate gene pools. This is how species form
secondary contact (3rd stage) not always necessary only in some cases when 2 pops are in capable of reproduce

More on Speciation Mechanisms

\*Speciation classically three step process:1) Isolation of populations2) Divergence of traits-Ex. Mating system or habitat use3) Reproductive isolation-Traditionally thought takes place over time while populations are geographically isolated

\-BUT, speciation can occur at the same time & place

Also, in many cases, 3rd time never happens

Mechanisms of Isolation: DISPERSAL -physical

\- populations can become geographically isolated when individuals colonize a new habitat

\- similar to founder effect = Limited number of alleles from parent pop that are represented in New population

EX: crickets in Hawaiian islands. As new habitats (new islands) became available, the crickets would colonize them. Colonized diversified and became different from initial island and different species

Mechanisms of Isolation: VICARIANCE - physical

\- pops can become geographically isolated when a species' former range is split into two or more areas

\- something vicarious has come between them and created 2 populations (mountains river etc)

\- allopatric speciation/geographic speciation

EX: this example of vicarious event that result in 2 allopatric speciation : bonnet head sharks. 2pops: West Atlantic and east pacific. used to be one species but the abscess of panama popped up in between and physically isolated the Caribbean basin from the east tropical Pacific. Now 2 separate populations diverge and now morphologically difference between

Mechanisms of Isolation: TEMPORAL - time

EX: Japanese winter moths \n North Japan population and south Japan population. North is cold south is warm. In the north are two genetically isolated populations blue and pink.

Blue reproduces during early winter but pink does early spring. Blue and pink will never reproduce together because they are temporarily isolated and reproduce at different times. Temporally distinct adult populations

Mechanisms of Isolation: MUTATION

EX: polyploidy \n produce gametes same quality as parent, makes them reproductively isolated from parent. Instantly you're a different species because you can't reproduce with your parental population.

Some mutation causes them to be sufficiently different basically immediately and prevents them from reproducing

allopatric speciation

phenomenon where biological populations are physically isolated by some extrinsic barrier and evolve intrinsic genetic reproductive isolation

when does the speciation process begin?

when gene flow is disrupted and populations become genetically isolated

what does it mean if populations are freely exchanging genes?

this means that they are conspecifics, they are the same species even if they are morphologically differentEX: Chihuahua and a great Dane are morphologically very different but they share the same genes so therefore they are the same species

reproductive barriers to gene flow

1. Pre-mating (prevents mating)2. pre-zygotic (prevent actual formation of zygote)3. post-zygotic (reduces fitness of hybrid zygote)

Pre-mating barriers

1. potential mates do not meet/breed/reproduce
isolating barriers that impede gene flow before sperm or pollen can be transferred to other species
EX: temporal isolation - there is seasonal mating in different insects (Japanese moths) - out of sync with mating cycle
EX: habitat isolation - Lady bugs stay on one plant for most of their lives so they will never reproduce/meet with the lady bug that lives on a different plant right next to it because they live in different habitats - physically separating in different habitats even if synchronous mating cycles



2. Behavioral isolation - most common
2 organisms might be in the same place at the same time but they have different behaviorEX: courtship display may not stimulate female enough to meet with the male.-Chemical or pheromone interferenceEX: Green lacewings- there are different species of lace wings that look identical but have different colored sounds. So mating only occurs if female answers the call back. hybrids discriminated because of their intermediate call

pre-zygotic barriers

once you get past the first step this factor comes into play. before this I got his form so you actually get a chance to try and mate
mechanical isolation (mostly plants and pollinators)there is copulation occurring but no transfer of male gametes because genitalia are differently shaped so they don't fit
gametic incompatibilitygamete transfer occurs but egg isn't fertilized and gametes aren't compatibleEX: Broadcast spawning - corals release sperm's/gametes simultaneously into water. we don't get a weird combo mix because very specific coding in the head of the sperm which is species specific coding, so sperm of one species will not penetrate coating of the egg of another species

post zygotic barriers

once you have gotten past the first and second step and actually get a chance to meet this third a factor comes
zygote mortalityzygote dies soon after fertilization and is unable to keep dividing
hybrid inviabilityeven if a zygote continues to divide and create hybrid... the hybrid is inviable
hybrid sterility in F1 or F2 (1st or 2nd generation)hybrids maybe physically strong but they are in capable of reproducing themselves; they are sterileEX: Horse + donkey = mule. Mules are always sterile they cannot reproduce

when does hybridization occur?

when offspring are produced by interbreeding between genetically different populations (2 diff gene pools)

when would a hybrid population be more fit than the parent population?

in intermediate or transitional habitats, hybrid populations may be more fit than either parental population
EX: Sage brush-found at different elevations either in the mountains or basin. Hybrids form in between those two elevations. The basin only has a high fitness in its basin elevation. Mountain only has a high fitness in the mountain elevation. However the hybrid has the highest fitness at the intermediate elevation and therefore has the highest fitness of all three because the other two only have a high fitness at one place

hybrid zones

regions in which members of different species meet and mate, producing at least some hybrid offspring

HYBRID ZONES
when hybrid's fitness is less than the parents fitness....

The hybrid zone is narrow, short-livedThe outcome is a reinforcement of parental population

HYBRID ZONES
when hybrid's fitness is equal to the parents fitness....

The hybrid zone is wide, long livedThe outcome is coalescence. hybrid acts as a bridge between parents and there is one continuous population of the basin mountain and intermediate sage brush pops

HYBRID ZONES
when hybrid's fitness is greater than the parents fitness....

The hybrid zone dependsThe outcome is a stable zone or speciation. The hybrid either becomes its own zone or create its own new species. typically happens if hybrids are found outside the range of their parents

mechanisms of divergence

1. genetic drift2. natural selection3. sexual selection
drives A wedge to further separate species/populations and maintain it

genetic drift mechanism of divergence

can produce rapid, genetic divergence and small, isolated populations. Result in fixation or loss of alleles

natural selection mechanism of divergence

can produce genetic divergence in populations subjected to different pressuresEX: Apple fly versus Hawthorne fly fruits look the same but they are isolated by the host species. Natural selection acts to maintain their population separately. Apple flies hatch at one time while the hawthorn flies hatch at another time and their time period of hatching matches up with the season of fruit

sexual selection mechanism of divergence

acts on characters involved and mate Choice
females prefer one trait
can cause pre-mating or pre-zygotic barriers
changes in sexual selection may isolate populations and cause rapid divergence
EX: lacewings don't like mating call
EX : mediterranean cricket versus Pyerenees mountain cricket. have a different mating call. Females prefer a single chirp in the Mediterranean. Females prefer five chirps in the mountains
EX: sympatric speciationpopulations evolve in geographic proximity. same place but still forming different species

Reinforcement

leads to assortive mating and the pre-zygotic isolation of population

secondary reinforcement

keep species separate even if they come back together.
natural selection works hard so reproduction is beneficial
EX: flycatcher birds. pied vs collared. pied has two colors brown and black & white. when both species live together, Brown males preferred so no mistake is made. when the two species are not mixed the black is preferred when only the pied species is present. When only the collared is present the black and white is favored.

ring species

populations that can interbreed with neighboring populations but not with populations separated by larger geographical distances
can interbreed with neighbor/closely related populations but and populations can interbreed with each other
is it one species or a bunch or is it a continuous population?
EX: herring gulls

What does each layer of the Grand Canyon tell us?

each layer of rock represents different time periods. The deeper you go the further back in time you go. Different color strata is each layer of rock

how much of earth's history does the Grand Canyon represent?

despite its size it represents only a tiny fraction of life on this planet.
Hadean time period = no life just rocks and volcanos. 1 billion yearsarchean time period = first single celled life. 1 billion yearsproterozoic = Single celled life started to produce oxygen and it went from reducing atmosphere to oxidizing atmosphere. 2 billion years spanthen the Grand Canyon made an appearance

The archaen and Proterozoic periods combined is called what?

pre-Cambrian = there was life but it was single celled

linear scale versus logarithmic scale

.... in notes

what are the three different measurements of time we talk about?

eons eras and periods

how many eons have there been?

2 major eons

what were the 2 major eons?

pre-cambrian and phanerozoic eons

How many eras were there?

5

what are the names of the 5 eras?

The Precambrian eon had 2 eras : archaen and proterozoic
The Phanerozoic eon had 3 eras : Paleozoic, Mesozoic, and Cenozoic

how many periods were there?

11

what are the names of the 11 periods?

The only eon that had periods was the Phanerozoic eon

The Paleozoic era had 6 periods : Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian
The Mesozoic era had 3 periods : triassic, Jurassic, and Cretaceous
The Cenozoic era had 2 periods : tertiary and quaternary (Pleistocene - Recent)

earths history in order

1. Pre-Cambrian Eon
- archaean era
- Proterozoic era
2. Phanerozoic Eon
- Paleozoic Era (Ancient) • Cambrian period • ordovician periodEND-ORDOVICIAN MASS EXTINCTION EVENT • Silurian period • Devonian periodEND-DEVONIAN MASS EXTINCTION EVENT • carboniferous period • permian periodEND-PERMIAN MASS EXTINCTION EVENT (this ended the paleozoic era)
- Mesozoic Era (Dinosaurs) • triassic periodEND-TRIASSIC MASS EXTINCTION EVENT • jurassic period • cretaceous periodEND-CRETACEOUS MASS EXTINCTION EVENT (this ended the Mesozoic era - no more dinos)
- Cenozoic Era (Recent) • tertiary period • quaternary period (Pleistocene - Recent)

what and when were the mass extinction events that happened?

there were five mass extinction events
1. END-ORDOVICIAN MASS EXTINCTION EVENT2. END-DEVONIAN MASS EXTINCTION EVENT3. END-PERMIAN MASS EXTINCTION EVENT (this ended the paleozoic era)4. END-TRIASSIC MASS EXTINCTION EVENT5. END-CRETACEOUS MASS EXTINCTION EVENT (this ended the Mesozoic era - no more dinos)

why are mass extinction events important?

they are important because extinction often goes hand-in-hand with speciation
taxa with high levels of speciation often are the same taxa that have high levels of extinction - this is called species and extinction correlation

species and extinction correlation

speciation goes hand-in-hand with extinction

reasons/explanations for speciation extinction correlation

1. ecological specialization2. population dynamics3. Geographic range

ecological specialization

this is the first reason for speciation extinction correlation
there's lots of speciation with a niches. environment changes and niches disappear. Species goes extinct because their niche dies. - this is the price you pay for specialization; the risk of extinction

population dynamics

this is the second reason for speciation extinction correlation
if you are in a small size population or in a fluctuating population size, then you are vulnerable to extinction because you don't have a lot of members in your species - therefore you can be wiped out quickly

geographic range

this is the third reason for speciation extinction correlation
if a population of species are distributed over a broad range, you might have relatively low rate of speciation because you are widely dispersed - however this is also an advantage because it is good for unfortunate incidents EX: if a population in one area gets wiped out we still have another population in another area somewhere else
broad range = less susceptible to extinctionnarrow range = species goes extinct

what are the type of species that have high rates of species and extinction?

they are volatile, they fluctuate greatly in diversity, and they are prone to extinction

after a mass extinction event...

not only is it about the individuals background levels of extinction (the speciation extinction correlation) but also it's about multiple taxa around THE WORLD going extinct in huge numbers

Permian mass extinction

before : diverse Rich marine habitatafter : hardly any species left

what causes mass extinction events?

varies

how do we know a mass extinction event happened?

- we look for fossils and compare fossils from 2 time periods - however there are constraints by fossil record- if it's a bad fossil, it's hard to tell what happened- Darwin was the first to realize this; we have a spotty fossil record

why do we have a spotty fossil record?

because when we look at the Grand Canyon for example there are layers of rocks but because the rate of deposition is not constant then we have spotty fossils but even if it is constant there's also erosion that happens.
what we can do is go back through rocks and recognize different layers have distinct fossils in them. we don't see the same fossils found throughout all the layers. - This is how we are able to piece together this geological column from all around the world

how do we know the fossil record is spotty?

because the fossil records are imperfect

Imperfection of fossil record

1. Many time periods represented by few sedimentary layers - we have a little info about it
2. Many lineages represented over long time periods with no fossils in between - Scientist found one fossil and then never found another in a long time. But then found the same exact fossil years later. They were missing this whole time. And will never disappear they just never found the fossil from that time
3. Many extinct species of large organisms represented by only a few fossils - we know these huge animals were everywhere but we have little to no fossil record of them
4. New taxa continue to be discovered - we are still finding new fossils this proves we have an imperfect fossil record

we have a pretty good understanding but not thorough enough because there are gaps

example of a imperfect fossil record

stickleback fossils
110,000 year time period We can look at
because the lake had an annual deposition of debris on the bottom of the lake, they were able to get very fine scale resolution fossils - they could sample back every 5000 years interval and found fossils of the fish. they found very little change but then all of a sudden a huge change occurred
this is important because how well are we able distinguish what actually happened and what is true and evolutionary history?

Types of Speciation

1. gradualism 2. saltation

Gradualism

- first type of speciation
- large changes in phenotypic characters have evolved through many slightly different INTERMEDIATE states
- slow continuous movement on graph
- two different taxa that may have evolved gradually from a common ancestor

example of gradualism

ancestral yellow butterfly gradually changed to a brown butterfly and an orange butterfly

what is the argument for gradualism?

it can be advantageous

how is gradualism advantageous?

slightly different intermediate states are advantageous because if we all of a sudden had a major change in our physical characters/morphology it would be difficult for us and it would be just advantageous.
we can only handle small morphological change
having a major change would be a mutation

mutation of major change in morphology

It would be deleterious effect that outweighs any advantage and we have a large scale change
but it's not always harmful
we can't assume a large scale change is deleterious but a small scale change is it not because even something small can be detrimental

Saltation

- Second type of speciation
- A DISCONTINUOUS mutational change in one or more phenotypic traits, usually of considerable magnitude - sudden appearance of new forms
- punctuated equilibrium (the time when species keeps same morphology)
- Constant and then a sudden jump when graphed
- no large number of intermediates along the way
- gets it from a single mutation that has a large affect in producing this gap between different forms

example of saltation

yellow ancestral butterfly and all of a sudden a brown and orange butterfly pop out of this yellow butterfly = it would be a punctuated equilibrium model

arguments for saltation

transformation of many characters from a single mutational event rapidly
Goldschmidt came up with the term hopeful monster
hopeful monster said you can have a major mutation that could result in a dramatic change in organism and leads to a monstrosity. The monstrosity can either become deleterious and die but it may not be deleterious and die and it could just be OK and live
hopeful monsters result from small mutations during development that have a large affect later on in the adult EX: One gene turns on or off and now the lamb is super long and different from the ancestor but they are OK and do just fine - hammerhead shark - normal shark head and then all of a sudden the head start to grow laterally

hypothesis for a gradualism graph

stable environment : no selective pressure because they are doing just fine and as a result morphology stays the same

hypothesis for a saltation graph

rapidly changing environment : A lot of selective pressure happens and moving from one form to another and result in lots of change = punctuated equilibrium

which is easier to explain gradualism or saltation?

gradualism, which is slow change, it's hard to explain but rapid change, saltation, is not hard to explain because we know why it does because there's lots of pressure

stasis

Long periods of geological time with little change in form

hypotheses for stasis

1. Genetic/developmental constraints
2. Stabilizing selection for constant optimum phenotype
3. ephemeral local divergence

genetic/developmental constraints - hypothesis for stasis

if you lack genetic variation then you cannot evolve. If nothing changes then you stay the same

stabilizing selection for constant optimum phenotype - hypothesis for stasis

environment might change but organisms don't have to, organisms can move to remain in a constant environment... this is called habitat tracking

example of stabilizing selection for Constant optimum phenotype - stasis hypothesis

ephemeral local divergence - stasis hypothesis

Do you have a very brief period or something has changed but it's too brief to be represented in the fossil record (spotty) OR it could be local and the change only happens in one hour

example of ephemeral local divergence - stasis hypothesis

characters/morphology might change for the glaciers to the new climate but when the climate changes back to the original climate, the characters revert back to where they were right before - adaptations are locally advantageous

what is mass extinction typically followed by?

mass extinction is typically followed by periods of rapid speciation
this is because many species are being wiped out and now a bunch of niches open up for new ones
diversification of taxa is rapid

What are wiped out taxa/species replaced with?

wiped out species are replaced often by unrelated but ecologically similar taxa
ancestral taxa are more morphologically similar and ecologically generalized - descendants can be more different than the ancestor

competitive displacement

One group may have caused extinction of another group OR extinction may have vacated some ecological niche space permitting second taxa to radiate