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5. cretaceous-tertiary (K-T) Extinction (65.6 mya)

(In paleontology, K is the abbreviation used for Cretaceous. C is used as an abbreviation for Cambrian.) This event defined the end of the Cretaceous and the beginning of the Tertiary CAUSE OF EXTINCTION: caused by impact of the Chixulub Comet (crater lies at the bottom of the ocean near Mexico's Yucatan peninsula) -- impact caused hot matter to warm in earth's atmosphere → earth's atmosphere to severally warmed CAUSE OF EXTINCTION: -- 75% of terrestrial plant and animal species → including the non-avian dinosaurs -- More than half of all marine species also died off A relatively recent theory about the immediate effects of the Chixulub comet is entertainingly presented here by the folks at Radiolab Dinopocalypse. Science as Performance Art.

4 modes of speciation

1. allopatric speciation 2. peripatric speciation 3. parapatric speciation 4. sympatric speciation

6 mass extinctions

1. late Ordovician extinction(~440 mya) 2. late Devonian extinction(365 mya) 3. permian-triassic extinction(252 mya) 4. late triassic extinction(201 mya) 5. cretaceous-tertiary (K-T) Extinction (65.6 mya) 6. The Anthropocene Extinction

evolution of the oxygen-rich atmosphere

1. the great oxygen catastrophe 2. saved by the plants

2. saved by the plants

600 million years ago: atmospheric O2 levels were only about 1% of Present Atmospheric Level (PAL) . At this point: 1. Cellular Respiration(aerobic metabolism) replaced fermentation(anaerobic metabolism) as the most common metabolic pathway. 2. An ozone (O3) layer started to form in the upper atmosphere → Ozone shielded microorganisms from lethal ultraviolet (UV) and gamma radiation 3. Oceanic shallows and wet terrestrial areas could now be colonized 400 million years ago: the earliest plants were established on land. -- Atmospheric oxygen levels were about 10% PAL, and continuing to creep upwards. Today: atmosphere is about 21% oxygen, thanks to photosynthesis.

character displacement

= Changes in the competing species' morphology to either: when competing species are sympatric: emphasizing the differences between species when competing species are NOT sympatric: minimization (or loss) of differences between species is a result of competition leading to resource partitioning (character = one ancestor species) (displacement = slightly different morphology)

competitive exclusion principle(Gause's Law)

= In a stable environment, 2 species cannot coexist if they occupy exactly the same ecological niche -- Species competing for the same resources must evolutionarily adapt to exploit different resources. This can lead to resource partitioning = dividing a common resource → each competing species uses only a portion of that resource -- so there is less competition (adaptive radiation can be a result of this)

-- EX: parametric speciation → ring species

= a geographically continuous series of neighboring demes, each of which can interbreed with neighboring demes, but for which there exist at least two "terminal" populations too distantly related to interbreed forms a "ring" around a specific geographical area

(systematists)

= a person who constructs or adheres to a fixed plan or system, especially a system of biological classification Modern systematists follow the rules of the Cladistic System Cladistic System = which states that the only quantifiable feature of evolution is cladogenesis

adaptive radiation

= differentiation of an ancestral species into multiple dissidents(daughter species) -- occurs over time over time living populations migrate and diversify -- Over time, such populations undergo repeated cladogenesis as lineages evolve(diversify) and "radiate"(migrate) into new ecological niches. diversification can be driven by: -- mutation -- migration -- assortative mating -- genetic isolation -- natural selection The end result is adaptive radiation

(photosynthesis)

= is the chemical process by which plants and some bacteria sequester atmospheric CO2 and use it to build carbohydrates waste product of photosynthesis is oxygen -- Oxygen is highly reactive and can be deadly if you're not evolutionarily equipped to use it

Macroevolution

= is the origin of populations becoming reproductively isolated from an ancestral population evolution of whole taxonomic groups over long periods of time

ecological niche

= of any given species includes: -- its role and position in its environment -- the ways it acquires food and shelter -- its survival mechanisms -- its reproductive strategies and natural history -- all of its interactions with biotic and abiotic factors in its environment Ecological interactions between species and their environment drive natural selection and speciation living and nonliving aspects of an organism's environment emprise this

patterns of speciation

= patterns that cause individuals of species to become separate species Anagenesis (= phyletic evolution) Cladogenesis (= diversifying evolution)

parametric

= refers to a geographic distribution that is continuous, but characterized by differences in habitat

allopatric

= species occupy different geographic regions

peripatetic

= species occupy overlapping ranges

sympatric

= species occupy the same geographic region they exhibit sympatry

Incipient species

= species that are on the verge of becoming separate species

Sister species (or taxa)

= species that have diverged from a common ancestor

Anagenesis (= phyletic evolution)

= the conversion of an entire species to a morphologically different form, generating a new species → species formation without branching from the evolutionary line of dissent NO net increase in species diversity ancestral form gives rise to only 1 new form ^ not commonly "used" as an explanation for evolution

Cladogenesis (= diversifying evolution)

= the divergence of an ancestral species/taxon into 2 sister species/taxa The evolutionary line branches net INCREASE in species diversity ancestral form gives rise to 2 new forms commonly used

extinction

= the endpoint of evolution It is a natural process Most species that ever existed on earth are now extinct.

1. allopatric speciation

= the evolution of a new species from an ancestral species due to geographic division of the ancestral population that prevents gene flow between them also known as geographic speciation allopatric speciation steps: 1. physical barrier separates ancestor species into 2 populations(equal in size) that are isolated from one another(geographic isolation) 2. during isolation the one of the 2 population's gene pool changes → causing ancestor species to split into 2 different species 3. 2 populations rejoin and live in the same space as different species → reproductively isolated (both populations are equally adapted/fit) This may be the most common mode of speciation

4. sympatric speciation

= the evolution of a new species from an ancestral species while both continue to inhabit the same geographic region. can result from: -- a sudden genetic event (e.g., polyploidy) -- differential resource utilization (ecological) sympatric speciation steps: 1. sudden genetic event causes a population WITHIN a population to become (reproductively) isolated and branch off as a sister species OR population within a population utilizes different resources causing them to become ecologically isolated from the rest of the population 2. populations inhabit the same place but are genetically isolated -- usually starts with disruptive selection and assertive mating

3. parapatric speciation

= the evolution of a new species from an ancestral species without extrinsic geographic barriers to gene flow. -- The population is continuous. -- The population does not mate randomly -- Individuals are more likely to mate with neighbors than distant individuals. -- This creates a cline(gradients) of genotypes → fades into another species -- daughter species live in different but close areas → closer (geographically) daughter species can have gene flow with one another -- some daughter species are more isolated than other isolated species -- some daughter species are less isolated than other daughter species -- Individuals at opposite ends of the range are reproductively isolated → the farther away the 2 species populations are the more different they are -- It is sometimes considered a form of ecological speciationoug steps to parametric speciation: 1. large population covering a lot of geographic area 2. population members on opposite sides of geographic region do not mate(reproductive isolation), neighboring individuals mate with on another 3. This creates a cline(gradients) of genotypes between geographic sections within a population → fades into another species (hybrid zone) 4. with no deneflow between 2 opposite sides of a population soon 2 different gene pools form, resulting in 2 different species

2. peripatric speciation

= the evolution of a new species when an isolated peripheral deme/population (smaller part of population, not located near the "heart" of the population) undergoes reproductive isolation from its ancestral population due to reduced gene flow. (usually due to founder effect) peripatetic speciation steps: 1. smaller deme with in a population (not located at the heart but rather the edges of a population) becomes slightly geographically isolated(not as far) → thus small population is ecologically isolated 3. gene pool between 2 populations shift and differ 4. 2 separate populations have a chance of rejoining or breeding with one another(breed back) → are close relatives BUT they do not → small daughter species population stays separate 5. over time no gene flow could lead to reproductive isolation one species population is larger than the other → one species population is more fit than the other considered a special case of allopatric speciation

speciation

= the formation of new distinct species in the course of evolution -- a temporal process Populations exist in various stages of speciation at any given time current populations are now undergoing microevolutionary changes that may eventually give rise to a new species

EX: Character Displacement: Hawaiian Honeycreepers

An ancestral finch colonized Hawaii millions of years ago. From this ancestor, 51 species of Hawaiian Honeycreepers evolved. Each species is evolutionarily adapted for a specific foraging strategy. More than 30% are now extinct (Sadly, 15 since Europeans arrived)

EX: Character Displacement: Darwin's Finches

An ancestral finch colonized the Galapagos millions of years ago. From this ancestor, 16 different species comprising five genera evolved. The bill size and shape of each species reflects a specific foraging strategy

Anagenesis vs. Cladogenesis

Anagenesis = gradual transformation of an ancestral lineage into successive, morphologically distinct descendant lineages -- ancestor species turns into next ancestor species → linear Cladogenesis = sequential, side by side divergence of ancestral taxa into two sister taxa over evolutionary time -- shows that not every species turns into an ancestor species -- also shows that once species becomes an ancestor it is extinct -- ancestor species branches into a current species and an ancestor species Any speciation event one could explain by invoking anagenesis can more accurately be explained by invoking cladogenesis and extinctions Remember: by definition, an ancestral taxon becomes extinct when it splits into 2 new taxa -- all ancestors are hypothetical→ their dissidents are the endpoints on the phylogenetic tree

EX: Anolis spp.

Anolis distichus group in the West Indies share a common ancestor -- The ancestor arrived on the islands millions of years ago The ancestral population gave rise to at least 16 different species Each species occupies a distinct ecological niche -- Body morphology depends on the specific habitat the species occupies -- Dewlap color displacement results from competition for mates. Both sexual selection and natural selection have modified Anolis characters. the specific niche of each ancestor is influenced onto each of their off spring and linages

EX: allopatric speciation → contiental drift

As Pangaea split into Laurasia (north) and Gondwanaland (south), and then into the continents of today, species living on split with them. Differences in -- mutation -- climate -- natural selection ... drove their divergence from their common ancestral forms

1. the great oxygen catastrophe

Before photosynthesis evolved, earth's atmosphere contained little free O2 2.8 billion years ago: rise of photosynthetic bacteria/prokaryotes(cyanobacteria) cyanobacteria = first photosynthetic organisms -- contained chlorophyll a = the most primitive form of chlorophyll -- conducted Photosynthesis, → began producing O2 For 1.2 billion years: photosynthetically produced O2 reacts with exposed iron in the ocean and earth's crust → forming iron oxide (rust) = rust sink after 1.2 billion years: rust "sink" was filled → O2 began to enter/fill the atmosphere → organisms at the time were not used to O2, and were killed by it → resulted in a mass extinction called The Great Oxygen Catastrophe. -- anaerobic organisms died -- aerobic organisms started to appear

2. late Devonian extinction(365 mya)

CAUSE OF EXINCTION: The causes are still controversial, with candidates including -- asteroid impact -- global anoxia -- plate tectonics -- sea level change -- climate change -- expansion of tropical, terrestrial plants MAIN THEORY OF CAUSE: expansion of tropical, terrestrial plants (Massive shale deposits from this period indicate large-scale organic detritus buildup. Terrestrial plant matter may have caused eutrophication and anoxia in tropical shallow waters.) -- massive increase in plant competition may have caused a massive increase in decomposition → causing massive loss of O2 WHAT BECOME EXTINCT: -- 20% of all animal families -- 70-80% of all animal species -- benthic invertebrates jawless fishes, and placoderm fishes living in shallow water ecosystems, primarily in the tropics

4. late triassic extinction(201 mya)

CAUSE OF EXTINCTION: is also controversial, but includes: - gradual climate change - asteroid impact - massive volcanic eruptions resulting in: → breakup of Pangaea → severe climate change → ecological disruptions WHAT BECOME EXTINCT: -- 30% of marine genera -- 42% of all terrestrial tetrapods This extinction may have contributed to the rise of the dinosaurs.

3. permian-triassic extinction(252 mya)

CAUSE OF EXTINCTION: after a series of massive volcanic eruptions (in what is now Siberia) -- Lava and ash directly caused die-offs. -- Excess CO2 caused global temps to rise ~ 6 degrees F -- More uniform temp across the globe caused reduced ocean water cycling, reducing oxygen content (ocean anoxia) -- Anaerobic bacterial overgrowth in oceans may have increased concentrations of toxic, ozone-destroying hydrogen sulfide (H2S) → Ozone depletion may have contributed to extinctions Over the course of about 60,000 years WHAT BECOME EXTINCT: 96% of all animal and plant species

EX: Peripatric Speciation → Ursus spp

Ecological factors may play a major role in peripatric speciation If a subset of a larger population migrates to an area at the periphery of the original population's range where ecological features are different, the new deme's ecological niche may change as the populations diverge Polar bears (Ursus maritimus) and Brown bears (Ursus maritimus) share a common ancestor with the extinct Eurasian Brown Bear (Ursus arctos) that once lived in Europe. As the ancestors of polar bears dispersed northward from their original range, glaciation may have made movement southward difficult, isolating them from the more southern populations.Contributing to speciation: -- genetic drift -- new mutations -- reduced gene flow -- new selective pressures As climate change allows Brown Bears to disperse farther north,hybridization has been documented between Brown and Polar Bears Among bears, this may not be as uncommon as was once thought.

Anagenesis is not a quantifiable aspect of macroevolution

Fossils are endpoints in a clade, just as ancestor species are -- they are hypothetical because they are dead and gone -- we can't fully be sure what they gave birth to All ancestors are hypothetical because -- They are dead and gone -- They cannot be directly observed -- Ancestor status cannot be assigned to a particular fossil with any degree of certainty

EX: Allopolyploidy in a Desert Flower(Gilia, Polemonaceae)

Gilia minor, Gilia clokeyi and Gilia transmontanaare all native to the Mojave Desert in the southwestern U.S. Chromosomal analysis reveals that Gilia transmontana is the product of hybridization between Gilia minor and Gilia clokeyi. Gilia transmontana has two sets of chromosomes from each parent species, making it allotetraploid. It is reproductively isolated from its two parent species.

EX: Hawthorne Flies and Apple Maggot Flies

Hawthorne flies (Rhagoletis pomonella) are native to the U.S. Before European settlers arrived, the flies laid their eggson hawthorne fruit, which are related to apples. When European settlers brought and planted apples,a subset of R. pomonella began laying eggs on apples. The flies will lay eggs only on fruit typein which they spent their maggothood. Not surprisingly, there is now a R. pomonella populationreproducing only on apples. Gene flow between this new populationand the original population is highly reduced. Genetic divergence between the incipient species can already be seen

EX: Anagenesis vs. Cladogenesis: Evolution of the Modern Horse

If Horses Had Undergone Anagenesis... An anagenetic view of horse evolution would hold that - Hyracotherium evolved into -- Mesohippus and [Miohippus ---> extinct] -- Mesohippus evolved into ---- Merychippus and [Parahippus ---> extinct] ---- Merychippus evolved into -------- Pliohippus and [Hipparion ---> extinct] -------- Pliohippus evolved into Equus In this scenario, Hyracotherium is considered a direct ancestor of Equus If Horses Had Undergone Cladogenesis... An original ancestor gave rise to (1) Hyracotherium and (2) Ancestor x. - Ancestor x gave rise to (1) Mesohippus and (2) Ancestor y -- Ancestor y gave rise to (1) Merychippus and (2) Ancestor z ---- Ancestor z gave rise to (1) Pliohippus and (2) Equus Thus, Equus did not evolve from Hyracotherium All five horse genera share the same common ancestor All but Equus went extinct Equus is the only surviving genus of the original ancestor

life is ancient

Life on earth originated at least 4 billion years ago ever since it has been diversifying and expanding BUT as new species arise, existing species may go extinct.

New species evolve from pre-existing species

New species remain nested in the ancestry of their predecessors Parents do not give rise to offspring drastically different from themselves

what drives extinction?

species interactions local ecosystem changes (habitat loss) natural disasters climate change -- glaciation -- changes in sea level

mass extinctions

Phanaerozoic = the eon encompassing all time including: -- the Cambrian (~ 540 → 485 mya) -- to present time fossil records contains evidence that there must have been at least 5 past global extinction cycles

MODES OF SPECIATION

Physical, ecological, and genetic factors often interact to drive populations to evolve and undergo cladogenesis.

EX: Peripatric Speciation → grass tolerance to heavy metals

Populations of Vernal Sweet Grass, Anthoxanthum odoratum, living around strip mines have undergone selection for tolerance to heavy metals in the soil. -- Original population is not tolerant of heavy metals -- Incipient daughter species is tolerant of heavy metals -- Natural selection removes metal-intolerant hybrids from contaminated soil -- Over generations, further divergence is likely to occur.

EX: Peripatric Speciation → California Channel Islands

The California Channel Islands form an archipelago of eight islands along the coast of southern to central California. Like the mainland, the habitat is primarily coastal chapparal. endemic species = a species that is native and restricted to a particular geographic location In the California Channel Islands, several unique, endemic species and subspecies share common ancestors with their mainland sister taxa. - Torrey Pine (Pinus torreyana insularis) - Island Tree Mallow (Malva assurgentiflora ) --- closest relative is a Mexican Tree Mallow - Island Night Lizard (Xantusia riversiana) --- sister species: Bolson Night Lizard (Xantusia bolson) (Mexico) - Island Scrub Jay (Aphelocoma insularis)sister species: California Scrub Jay (Aphelocoma californica) San Clemente Loggerhead Shrike (Lanius ludovicianus mearnsi) San Clemente Sage Sparrow (Artemisiospiza belli clementeae) Channel Islands Spotted Skunk (Spilogale gracilis amphiala) Island Fox (Urocyon littoralis)sister species: Gray Fox (Urocyon cinereoargenteus) Species (and incipient species) evolving from small founder mainland populations arise via peripatric speciation.

EX: allopatric speciation → isthmus of Panama

The Isthmus of Panama formed(rose above the ocean) 2.8 million years ago, separating the Atlantic and Pacific Oceans and generating the Gulf Stream Populations all species living on either side of the isthmus were separated, and proceeded to evolve in isolation from one another

6. The Anthropocene Extinction(TODAY)

The current extinction rate has been estimated at 24 - 150 species lost per day -- This is 1,000 times higher than "normal" extinction rate -- The current extinction rate is similar to that of previous mass extinctions. CAUSE OF EXTINCTION: anthropogenic, 5 factors caused by humans are causing this extinction: Habitat loss Invasive exotic species Pollution Population Explosion Overexploitation -- the most recent threat is anthropogenic climate change (global warming causes climate change)

Sympatric Speciation: Polyploidy

Unlike most animals, plants can generate polyploid zygotes that grow into viable individuals -- Usually larger and more robust than their their parents -- Usually cannot back-cross with their parents due to chromosomal differences -- They can often self-pollinate or cross-pollinate with polyploid siblings -- Instant reproductive isolation! autopolyploidy = chromosomes come from 1 parent species -- chromosome sets coming from one species allopolyploidy = chromosomes come from 2 related species. -- chromosomes sets coming from 2 different species

side by side modes speciation

all end up with 2 different species but the way they get there is different

ecological aspects of speciation

ecological speciation = process where natural selection operates on ecological characters, resulting in reproductive barriers between populations -- natural selection effects the way organisms interacts with environment + each other → leading to speciation modes of speciation we have discussed so far and ecological speciation are by no means mutually exclusive -- forms of speciation can occur at the same time or can cause one another

3 main mechanisms that drive speciation

geographical isolation → physically separated ecological isolation → use different resources genetic isolation

chapter 254

http://www.bio.miami.edu/dana/160/160S21.html

1. late Ordovician extinction(~440 mya)

life during the Ordovician period: Biodiversity expanded tremendously -- fossil records reveal being rich in marine invertebrate fauna, early fish, and macro algae. CLIMATE: -- relatively mild climate -- northern hemisphere was mostly ocean, with shallow water conducive to life CAUSE OF EXTINCTION: during late Ordovician Gondwanaland (the largest land mass) occupied the south pole -- Massive glaciation and sea level drop caused shallow seas to dry up, with devastating ecological effects WHAT BECAME EXTINCT: -- About 60% of all marine invertebrate genera and 25% of all marine invertebrate families went extinct.

EX: poison dart frogs

the Strawberry Poison Dart Frog (Dendrobates pumilio) exhibits different color morphs in different regions of Panama The more brightly colored the frog, the more toxic it is Females significantly prefer individuals of their own color morph (assortative mating) Frogs mate assortatively, based on coloration This reinforces the ecological signal that warns predators of toxicity