How do _____ evolve?
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How do _____ evolve?. microevolution. populations. allele frequencies. - genetic drift - natural selection - migration. How do _____ evolve?. microevolution. populations species. over time, populations can diverge & produce two or more daughter species from one

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Populations

How do _____ evolve?

microevolution

populations

allele

frequencies

- genetic drift

- natural selection

- migration


Populations

How do _____ evolve?

microevolution

populations species

over time, populations

can diverge & produce

two or more daughter

species from one

ancestral species

each species must be

reproductively isolated

each species becomes

adapted to its niche by

natural selection

allele

frequencies

reproductive

isolation

- genetic drift

- natural selection

- migration

adaptation


Populations

How do _____ evolve?

microevolutionmacroevolution

populations specieslineages

(clades of species)

allele

frequencies

reproductive

isolation

diversification

- genetic drift

- natural selection

- migration

why do some groups

have more species

than related groups?

adaptation


Populations

one common

ancestor

clade of 3 surviving (modern)

species

1 surviving species

2 daughter lineages,

of equal age

Evolutionary success = number of living species

 Why does one lineage diversify into many more species

than its less-successful sister lineage?


Populations

2 living species

of Bosellia

- flat sea slugs

- eat one algal

genus

- tropical only

134 species

in sister clade

Plakobranchidae

- sides rolled up

- eat >20 algal

genera

- tropics to poles


Populations

Some lineages undergoadaptive radiations, filling all

available ecological niches and diversifying into many species

1) opportunity: ancestor colonized an empty habitat with

many unoccupied niches...

- went from marine into freshwater or terrestrial habitat

- got into a new lake, or onto a new island

- survived mass extinction of dominant competitors

2) specialization: when related species exploit different

ecological niches (i.e., food or host), many related species

can co-exist in one place without competing

3) key innovation: evolution of a trait that allows exploitation

of new niches, or greater competitive ability


Populations

Adaptive radiation

When an ancestor colonizes a new habitat, its offspring may

undergo an adaptive radiation

- descendents diversify (get different) and occupy all the

available ecological niches

- each lineage adapts, becomes phenotypically differentiated

by natural selection (= ecological speciation in action)

May follow colonization of islands, newly-formed lakes

- could provide opportunities for sympatric speciation

Often follows mass extinction events that remove previously

dominant competitors


Populations

Adaptive radiation via natural selection

Example: cichlid fishes in volcanic crater lakes in Africa

- monophyletic assemblage of fishes arose in sympatry by

descent from common ancestor that colonized new lake

- each species maintains its differences by assortative mating:

depends on ecological differences and mating preferences


Populations

Evidence for sympatric speciation in cichlids

All fishes from Lake Mbo

are each other’s closest

relatives

All fishes from Lake

Bermin also group

together

Suggests they arose in

sympatry, following an

initial colonization event


Populations

Adaptive radiation 1: Disruptive selection

Lake Victoria was completely dry 12,000 years ago

- now contains 500 species of cichlid fish

An adaptive radiation happened after an ancestral fish got washed into the empty lake when a river flooded

Most species pairs have different feeding behaviors, due to the

adaptive evolution of their jaws

- by occupying different ecological niches, species avoid

competing with each other (necessary for co-existence)

Disruptive selection on feeding specializations can

drive adaptive radiation, by promoting species divergence


Populations

Disruptive selection on feeding: Cichlid jaws

(1) Diversification: each species feeds something different,

due to adaptive evolution of their jaws

front jaws -

catching food

back jaws -

processing food


Populations

Adaptive radiation 2: Sexual selection

Within a “feeding type,” there are often several sister species

(each other’s closest relatives) that differ only in color

All weird predators group

together (sponge-eaters)

All plankton-feeding species group together

All normal predatory species group together


Populations

Adaptive radiation 2: Sexual selection

Females with eye pigment alleles that see blue better prefer

bluer males; females that see red better like redder males

Sexual selection: female preference for color keeps different

species from hybridizing reproductive isolation

End up with a blue, a yellow, and a red sponge eater;

.. a blue, a yellow, and red clam eater... etc

males can be

red, yellow, or

blue with

different

markings


Populations

Adaptive radiation 2: Sexual selection

sexual selection thus splits one group in two

Mate choice is determined by coloration

- strong assortative mating quickly leads to isolation of

different color morphs

- different species can interbreed without loss of fertility, but

normally they are pre-zygotically isolated by mate choice

Disruptive selection on feeding fueled diversification of sister species; sexual selection provided reproductive isolation

one-two punch that drove the most explosive speciation

in the history of vertebrates


Populations

Adaptive radiation 3: end of cichlid diversity?

Recently, pollution has clouded Lake Victoria so badly, fish are

unable to see color differences

- species barriers are collapsing, as different species start

hybridizing with each other

Human activities that cloud the water are thus destroying cichlid

biodiversity

- unravels the mechanism of reproductive isolation by relaxing

sexual selection

- loss of evolutionary novelty, due to human disruption of

the environment


Populations

2) Specialization: why are there so many beetles?

~25% of described living species are beetles (flying insects)

- more than 135,000 species of beetles feed only on angiosperms (flowering plants)

other beetles are:

- fungus-eaters

- predators

- aquatic

evolution.berkeley.edu


Populations

2) Specialization: why are there so many beetles?

2 factors may favor diversification in herbivorous beetles

2-A) Co-speciation

- when one plant speciates (evolves into 2 new species), its

pollinators and the herbivores that eat it may also speciate

2-B) Ecological specialization + host-shifting

- specialization = eat one species of host plant

(or animal, if you are a parasite)

- many related species can co-occur without competing,

which allows greater diversity of species in an area

- speciation can occur by host-shifting (as in Rhagoletis flies)


Populations

2-A) Plant-insect coevolution

When a plant speciates, so may its pollinators and specialized

herbivores

herbivore

(beetle)

pollinator

(butterfly)


Populations

2-A) Plant-insect coevolution

When a plant speciates, so may its pollinators and specialized

herbivores

Rain

forest

species

Desert

species

Pollinators and herbivores may also form new species when their

host plant speciates coevolution promotes speciation


Populations

2-B) Specialization and “inordinate fondness”

Each time a lineage of beetles started to feed on angiosperms

(flowering plants), it quickly evolved into many more species

than did its sister lineage that did not eat flowers

- its rate of speciation increased, suggesting the association

with flowering plants in turn promoted beetle biodiversity

Farrell (1998)

proposed that

beetle diversity

resulted from their

associations with

flowering plants:

as plants diversified, so

did their beetle pests

Farrell 1998


Populations

Hunt et al. (2007) argued the radiation of beetles was due to:

A) specialization on different plant parts in some groups

(roots, flowers, fruit, leaves)

14,000 35,000

 herbivory

 predation

 aquatic

 eat fungus


Populations

Hunt et al. (2007) argued the radiation of beetles was due to:

A) specialization on different plant parts

B) frequent ecological shifts amongmajor feeding strategies

23,000

14,000 48,000 35,000

35,000

 herbivory

 predation

 aquatic

 eat fungus


Populations

Hunt et al. (2007) argued the radiation of beetles was due to:

A) specialization on different plant parts

B) frequent ecological shifts amongmajor feeding strategies

C) partly just because beetle lineages rarely go extinct

23,000

14,000 48,000 35,000

35,000

 herbivory

 predation

 aquatic

 eat fungus


Populations

Some lineages undergoadaptive radiations, filling all

available ecological niches and diversifying into many species

1) opportunity: ancestor colonized an empty habitat with

many unoccupied niches...

- went from marine into freshwater or terrestrial habitat

- got into a new lake, or onto a new island

- survived mass extinction of dominant competitors

2) specialization: when related species exploit different

ecological niches (i.e., food or host), many related species

can co-exist in one place without competing

3) key innovation: evolution of a trait that allows exploitation

of new niches, or greater competitive ability


Populations

3) key innovation: evolution of a trait that allows exploitation

of new niches, or greater competitive ability

For instance, one group of fish diversified in the Antarctic

after evolving anti-freeze glycoproteins, allowing them to

survive water temperatures below freezing

9 species, non-Antarctic

(no anti-freeze)

123 species, Antarctic

- anti-freeze glycoproteins

- within Antarctic, species also

diversified into benthic and

pelagic forms, like lake fish


Big 5 mass extinction events

‘Big 5’ mass extinction events

During 5 mass extinctions, 50-90% of species disappeared

over a period of one million years

- the ‘big 5’ eliminated 20-60% of families of plants + animals

(whole families, or kinds of organisms)

end Permian extinction: 90% of marine

species gone

end Cretaceous K-T extinction,

65 Mya ago: bye-bye dinosaurs

Triassic-Jurassic boundary, 215 Mya


Mass extinctions vs background extinctions

Mass extinctions vs. background extinctions

Despite their immediate impact, the Big 5 mass extinctions only

account for 4% of total extinctions over the last 500 million yrs

- 96% of species suffer background extinctions

- they just die out, or differentiate into new species

Episodic mass extinctions are important because they clear the

way for new adaptive radiations

(1) what causes them?

(2) why do some species survive them?


Causes of mass extinction deep impact

Causes of mass extinction: Deep Impact

Many forms of evidence support asteroid impact theory of K-T

mass extinction, possibly others as well

(1) iridium layer in rocks at the K-T boundary

- rare on earth, common in meteors

(2) microtektites also found in rocks at K-T boundary

- little glass particles formed when minerals melt at impact

- cool while flying through the air

(3) huge crater found off Mexican coast, 180 Km diameter,

dating to K-T boundary

(4) extraterrestrial origin suggested for noble gases trapped in

“buckey balls”, carbon spheres found at extinction boundaries


Causes of mass extinction deep impact1

Causes of mass extinction: Deep Impact

K-T Impact likely had numerous environmental consequences

(1) injected SO2 and water into atmosphere, producing acid rain

(2) global cooling as dust blocked sunlight

(3) huge wildfires

(4) massive earthquake and tidal wave, supported by geological

evidence

(5) massive die-off in ocean phytoplankton

(photosynthetic plankton) disrupted marine food chains


Survivor s guide to mass extinction

Survivor’s guide to mass extinction

Studies on marine snails (good fossil record) indicate that the

lineages which survived mass extinctions had member species

scattered in many different biomes, or environmentally

different regions of the world

- surviving lineages had some species in the deep sea,

some in the tropics, some in cold water, etc

In other words, more biogeographically diverse lineages were

less likely to be wiped out by asteroid impact

- hedges against the total wipeout of any one niche or region

following a deep impact


Plant evolution following mass extinctions

Plant Evolution following Mass Extinctions

Gymnosperms

dominate

Seedless

plants

# of families

Angiosperms dominate

First

gymnosperms

First

angiosperms

Lineages are often around, but not very successful, until a mass

extinction event wipes out the dominant competitors

 clears the way for adaptive radiation

Mackenzie 2003


Populations

What makes a lineage an evolutionary “winner”...?

1) specialization to exploit different niches

(co-existence without competition)

2) something that promotes rapid speciation:

- sexual signaling

- strong host association

- tendency to get allopatrically isolated (dispersal)

- fast-evolving gamete recognition proteins

3) key innovation (trait) allowing exploitation of new niches

or greater competitive ability

4) in the long run, being biogeographicallywidespread –

more likely to survive mass extinctions


Populations

Why only 2 Bosellia

but 134 plakos?

- flat sea slugs

- eat one algal

genus

- tropical only

134 species in clade

Plakobranchidae...

- have sides of body rolled up, which

protects stored chloroplasts from sun

(key innovation?)

- each species feeds on just one of >20

kinds of algae (specialized)

- species live and mate on their host

- colonized cold water habitats


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