The Origin and Diversification of Life on Earth (ch.12)

Diversity of life

Microevolution

Speciation

Macroevolution

What is Macroevolution:

The accumulated effect of microevolution over a long period of time

What is a microevolution?

A change in allele frequencies over one or a few generations

Fact about microevolution:

• Microevolution changes in allele frequencies in a population over time can lead to macroevolution, changes on a grand scale including vast diversification of species

Classification of species

• Systematics and Taxonomy

• Every species has a two-part scientific name: Genus species

• Hierarchical Classification:

Genera= Relates species are grouped together

Families= groups of genera

What is a species?

• Carl linnaeus invented a system for classifying species based on shared traits

• Hybrids were difficult to classify

• Dawin laughed at these difficulties and argued that varieties were in the process of evolving to become different species

• species are the products of evolution

Biological Species Concept:

• Coined by Ernst Mayr in 1942

• A group of “actually or potentially interbreeding populations which are reproductively isolated from other such groups”

• focuses on the process of how species form, not just recognizing a species once it is already present

• Also provided info on how populations might be kept apart

Barriers- stops gene flow

• A species divides into 2 when a geographical or behavioral barrier between populations prevents interbreeding

Reproductive Isolation:

1) Before sex barriers (prezygotic)

2) After Conception Barriers (postzygotic)

Habitat Isolation

• Elk (N.America) and Red deer (Europe, Russia)

• Considered 2 Populations of a single species

• They can interbreed when put into zoos

• Should they be considered 2 different species?

Temporal and Gamete Isolation

• Interbreeding is not separated geographically but by time or biology

• These coral species are mass spawners

• they release gametes at different times

• minimizing changes of interbreeding between species

Behavioral Isolation:

• male fireflies use flashes of light for courtship

• females respond only to signals from males of their own species

• Flash behavior by males and recognition from females creates a barrier to prevent interbreeding

Mechanical Isolation

• Egg producing and sperm producing parts of different species are anatomically incompatible

Reproductive Barriers after conception

1. Hybrid Embryos between 2 different species may fail to develop

2. Hybrids sometimes are deformed or healthy but steriles

• Mules are hybrid between horses and donkey

• Mules are viable but sterile

• Keep horses and donkeys separate species

1. Hybrids live and are fertile but their offspring are not

Other speciation concepts:

• Phylogenetic species concept

• Morphological species concept

Mechanisms of Speciation

• Allopatric Speciation

• Sympatric speciation

Allopatric speciation

• A river poses a geographical barrier to interbreeding

• mutations accumulate

• reproductive barriers evolve which minimize interbreeding when/if geographical barrier is removed

• Anoles

Example of evidence of allopatric speciation

• Atlantic and Pacific shrimp are more closely related to each other than they are to shrimp in the same ocean

Sympatric speciation

• Fly selection for different fruits helps isolate the populations, allowing them to diverge in sympatry