Lecture 14 - Speciation/Extinction

Macro-Evolution

Evolution above the single species level.

Micro-evolution over very long time periods.

Phyletic Gradualism

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

Adaptive Radiation

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

Biological Species Concept

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

Genetic Variation

Refers to genetic differences within a species.

Genetic Divergence

Refers to fixed genetic differences between species.

Inbreeding Depression

Decreased fitness breeding individuals too closely related.

Reproductive Isolation

NO gene flow

Individuals can not breed and produce sterile or no offspring.

Heterosis

Increased fitness when breeding genetically different individuals.

Outbreeding Depression

Decreased fitness breeding individuals too genetically different. Epistasis and Pleiotropy cause poor allele interactions

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 met

Behavioral Isolation

Different mating behavior

Mechanical Isolation

Sometimes the parts just don't fit together

Post-Zygote Isolation

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

Genetic Architecture of Speciation

1.) Traits involved in RI are often quantitative (polygenic)

2.) May RI genes are under positive selection

3.) 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 the 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

Allopatric Speciation

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

Parapatric 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

Polyploid

New species formed when chromosome number in hybrids doubles

Extinct 

Does not exist ALIVE on Earth

Permian-Triassic

Extinction

About 250mya. The Biggest. Probably a comet or asteroid impact, but could have been caused by a large release of methane gas from the ocean bottom.

Around 95% of all marine species went extinct. So did about 70% of known plants, insects, and other land species.

Cretaceous-Tertiary Extinction

About 65mya. 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.

Primary Causes of Mass Extinction

a.) Extraterrestrial Impacts

b.) Climate Change

Law of Extinction 

Ancient species are not more extinction prone than younger species

Primary Causes of Modern

Species Extinctions

a.) Habitat Destruction

b.) Pollution

c.) Overharvesting/Poaching

d.) Introduced Species

Extirpate 

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

Endemic 

Found in restricted geographic area. Often in stable climate refugia