populations microevolution - genetic drift - natural selection - migration allele frequencies how do...

populations

microevolution

- genetic drift- natural selection- migration

allelefrequencies

How do _____ evolve?

populations species

microevolution

- genetic drift- natural selection- migration

allelefrequencies reproductive

isolation

How do _____ evolve?

adaptation

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

populations species lineages(clades of species)

microevolution macroevolution

- genetic drift- natural selection- migration

allelefrequencies reproductive

isolation

How do _____ evolve?

adaptation

diversification

why do some groupshave more species

than related groups?

one commonancestor

2 daughter lineages,of equal age

clade of 3 surviving (modern) species

1 surviving species

Evolutionary success = number of living species

Why does one lineage diversify into many more species than its less-successful sister lineage?

2 living species of Bosellia

- flat sea slugs

- eat one algal genus

- tropical only

134 speciesin sister clade Plakobranchidae

- sides rolled up

- eat >20 algal genera

- tropics to poles

Some lineages undergo adaptive 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

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

Adaptive radiation

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

Adaptive radiation via natural selection

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

Evidence for sympatric speciation in cichlids

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

Adaptive radiation 1: Disruptive selection

(1) Diversification: each species feeds something different, due to adaptive evolution of their jaws

Disruptive selection on feeding: Cichlid jaws

front jaws - catching food

back jaws - processing food

Within a “feeding type,” there are often several sister species (each other’s closest relatives) that differ only in color

Adaptive radiation 2: Sexual selection

All weird predators group together (sponge-eaters)

All plankton-feeding species group together

All normal predatory species group together

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

Adaptive radiation 2: Sexual selection

males can be red, yellow, or blue with different markings

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

Adaptive radiation 2: Sexual selection

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

Adaptive radiation 3: end of cichlid diversity?

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

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

2) Specialization: why are there so many beetles?

evolution.berkeley.edu

other beetles are: - fungus-eaters - predators - aquatic

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)

2) Specialization: why are there so many beetles?

When a plant speciates, so may its pollinators and specialized herbivores

2-A) Plant-insect coevolution

pollinator(butterfly)

herbivore(beetle)

When a plant speciates, so may its pollinators and specialized herbivores

2-A) Plant-insect coevolution

Desertspecies

Rainforestspecies

Pollinators and herbivores may also form new species when their host plant speciates coevolution promotes speciation

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

2-B) Specialization and “inordinate fondness”

Farrell 1998

Farrell (1998) proposed that beetle diversity resulted from their associations with flowering plants: as plants diversified, so did their beetle pests

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)

aquatic eat fungus

herbivory predation

14,000 35,000

Hunt et al. (2007) argued the radiation of beetles was due to: A) specialization on different plant parts B) frequent ecological shifts among major feeding strategies

aquatic eat fungus

herbivory predation

23,000 14,000 48,000 35,000 35,000

Hunt et al. (2007) argued the radiation of beetles was due to: A) specialization on different plant parts B) frequent ecological shifts among major feeding strategies C) partly just because beetle lineages rarely go extinct

aquatic eat fungus

herbivory predation

23,000 14,000 48,000 35,000 35,000

Some lineages undergo adaptive 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

3) key innovation: evolution of a trait that allows exploitation of new niches, or greater competitive ability

9 species, non-Antarctic (no anti-freeze)

123 species, Antarctic - anti-freeze glycoproteins

For instance, one group of fish diversified in the Antarctic after evolving anti-freeze glycoproteins, allowing them to survive water temperatures below freezing

- within Antarctic, species also diversified into benthic and pelagic forms, like lake fish

‘Big 5’ mass extinction eventsDuring 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

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

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 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

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

Mackenzie 2003

Seedlessplants

Gymnospermsdominate

Angiosperms dominate

First gymnosperms

Plant Evolution following Mass Extinctions

# of

fam

ilies

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

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 biogeographically widespread – more likely to survive mass extinctions

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