Lecture 32 - Speciation and Species Extinction

What are the three types of speciation?

1. Allopatric

2. Sympatric

3. Single Gene

Allopatric speciation

speciation where populations are isolated through different geographies

What type of selection is associated with allopatric speciation?

Directional selection

Directional selection

Adaptation to a different habitat or genetic drift. Can lead to sufficient phenotypic change that reproductively isolates a population

Sympatric speciation

No geographical isolation. Disruptive selection or physical incompatibility can result in this

The Wallace effect

Individuals that avoid hybrid mating would have an advantage

Describe the process of disruptive selection

1. A population of organisms inhabits a territory

2. Subpopulations form in the absence of geographical barriers and differ genetically

3. Genetic differentiation leads to reproductive isolation and the subpopulations become distinct species

What are two ways hybridization is facilitated between species?

1. Nondisjunction at meiosis

2. Genome duplication

Single gene speciation

When a mutation affects a single gene and disrupts the mating process

Are species becoming more complex over evolutionary time?

Directional selection does NOT imply that cellular or physiological complexity increases. Mutation is random and has no direction

How is simplicity advantageous?

Simpler organisms CAN have other strengths like faster multiplying, producing more offspring, and requiring fewer resources for reproduction

How does genetic drift remove complexity in a population?

If a trait provides no selective advantage, it can be lost to genetic drift

How does complexity arise from evolution?

Co-evolution or co-operation between genes or organisms

What is an example of co-evolution?

Increased complexity of pathogens and hosts increase the complexity of the immune system and mechanisms of pathogen resistance

Barcoding

A standardized approach to identifying plants and animals by minimal sequences of DNA called DNA barcodes

DNA Barcode

Mitochondrial cytochrome oxidase I gene used for identifying species

What are characteristics of Mitochondrial DNA?

1. Inherited through eggs (maternal inheritance)

2. Fast mutation rate

What are the advantages of mtDNA?

1. Greater sequence differences between species

2. There are 100-10,000 more copies of mitochondrial than nuclear DNA per cell which makes it easier to purify and sequence

3. Relatively few differences within species

4. No introns

What are disadvantages of mtDNA?

1. Poor resolution of recently diverged species

2. Nuclear COI pseudogenes complicate sequencing analysis