Speciation/ extinction BIOL 1102

Macro-Evolution

Evolution above the single species level(e.g. genus,Family, order, etc.) Microevolution over long periods of time.

Phyletic Gradualism

New species evolve by accumulating many small changes over long time periods.

Punctuated Equilibrium

Speciation is rapid and followed by long periods of stasis(no change).

Adaptive radiation

One species evolves into many species in a short time period.

Biological Species Concept

Species are groups of interbreeding natural populations reproductively isolated from other groups.

genetic variation

refers to genetic differences within species

genetic divergence

refers to fixed genetic differences between species

Me: GCTGCTACGT

You:GCAGGTACCT

3/10 variable sites

30% sequence

variation

Human: ACCTGCTTAT

Chimp: AGCAGCTAAT

3/10 fixed differences

30% sequence

divergence

Inbreeding depression

Decreased fitness breeding. individuals too closely related.

Reproductive isolation: = NO gene flow(different species)

Individuals cannot breed and produce sterile or no offspring “this is where speciation occurs.

________ between different chicken ________ produce the fastest growth rates and most meat(Broilers)—often reaching 10 pounds in only 10 weeks.______ protein problem causes giant muscle growth in broiler chickens.

Hybrids,Breeds, Myostatin

The _______ and the_______ are hybrids between __________,________, and __________. Both hybrids grow larger than coyotes but not as large as a Gray Wolf.

Pre-zygotic Isolation

Mating and fertilization are prevented. (no zygote formed).

Temporal Isolation

Species do not breed at the same time

Ecological/Habitat Isolation

If species live in different environments they never meet.

Ecological/habitat isolation

if species live in different environments they never meet

behavioral isolation

different mating behaviors

mechanical isolation

sometimes their parts just don’t fit together

Post zygotic Isolation

mating occurs(zygote is made), but offspring are sterile or die early

Some different ways that organisms can become reproductively isolated…

Pre-zygotic isolation, temporal isolation, ecological/habitat isolation, Behavioral isolation, mechanical isolation, and post-zygotic isolation

Genetic architecture of speciation

Traits involved in RI are often quantitative(polygenic)

many RI genes are under positive selection

many RI genes are transcription regulators.

Haldane’s Rule

If in the offspring of two different animal species one sex is absent, rare, or sterile, that sex is heterogametic sex( e.g, In birds, females are the heterogametic sex…ZW).

Geographic speciation models

How geography can block gene flow and lead to speciation

allopathic speciation

geographic ranges do not touch. No gene flow between populations. Probably most common in animals

Parametric speciation

Ranges touch but do not overlap significantly, hybrid zone forms where ranges meet. Gene flow usually small.

Sympatric speciation

ranges overlap significantly geography does not prevent gene flow.

Sympatric speciation is probably just ________ speciation at smaller spatial scales. = __________.

Allopatric, Mircoallopatric speciation

Pre-zygotic Isolating mechanisms

are probably often at work in cases of Sympatric speciation

speciation by Polyploidy

New species formed when chromosome number in hybrids doubles, allowing polyploid hybrids to mate with other polyploid hybrids, but not with either parent species; thus creating new hybrid species that is reproductively isolated from either parent species.

Artificial polyploidy is used to overcome inbreeding depression example

wheat and rye are hybridized to form triticale which has desirable traits of both parent species, BUT THE HYBRIDS ARE STERILE. This is the desierable traits of both species but does not reproduce. Then researchers use chemicals to block microtubule formation during cell division casing non disjunction and polyploidy in the gametes; then can mate two polyploid hybrids together successfully.

Extinct

Does not exist Alive on earth

how many large scale extensions have happened?What does this cause

at least 20; loss of diversity followed by adaptive raadiation

Permian–Triassic extinction

250 MYA . The biggest, probably a comet or asteroid impact, but could heavee been caused by a large release of methane gas from the ocean bottom. around 95% of all marine species went extinct. As well as about 70% of known plants, insects, and other land species.

Cretaceous-Tertiary extinction(K-T)

about 65 mya. caused by asteroid impact in the Gulf of Mexico. 52% of marine genera went extinct, 18% of land vertebrate families, including the dinosaurs went extinct.

What are the primary causes of Mass extinctions?

a. Extra terrestrial impacts

b. climate change

which strikes the earth more frequently Asteroids or comets?

Asteroids: 70%;Comets: 30% However there is evidence that comets shower the earth and cause extinction on average every 26 million years.

Law of extinction

ancient series are not more extinction prone than younger species.

Extinction is natural, it occurs at a natural “ background rate of about ______ species per year scientists estimate we’re now losing species at more than ______ times the background rate.

1-5;1000 times

As many as ____ percent of all species could be extinct by the end of the century, including most _____ animals.

20-50; mammal

Primary causes of modern species extinctions … 

a.Habitat destruction

b. pollution

c. over harvesting/poaching

d.introduced species

Extirpate

(locally extinct) does not exist in location but still present in others

endemic

found in restricted geographic area. often in stable climate refuge