Chapter 17: Speciation and Macroevolution

Marcoevolution

Evolution on a large scale.

Best observed within the fossil record.

Involves the origin of species, also called speciation.

Speciation

Splitting of one species into two or more species.

Final result of changes in the gene pool’s allelic and genotypic frequencies.

Species

A group of organisms that can interbreed and produce fertile offspring in nature. 

Morphological Species Concept

Based on the analysis of diagnostic traits distinguishing one species from another.

Species can be distinguished anatomically by one or more distinct physical characteristics.

This method was used by Linnaeus.

Evolutionary Species Concept

Distinguishes species from one another based on morphological (structural traits).

It was used to explain speciation in the fossil record.

It implies that members of a species share a distinct evolutionary pathway.

Since fossils don’t provide information about color, soft tissue anatomy, or behavioral traits, they are of limited use.

Phylogenetic Species Concept

Is used to identify species based on a common ancestor.

It is based on a single ancestor for two or more different groups.

For you and your cousins, your shared female grandparent is a common ancestor.

Biological Species Concept

Populations of the same species breed only among themselves.

They experience reproductive isolation from other such populations.

A group of birds collectively called flycatchers all look similar but do not reproduce with one another, so they are different species.

What are the two general types of reproductive isolating mechanisms?

Prezygotic isolating mechanisms.

Postzygotic isolating mechanisms.

Prezygotic isolating mechanisms

Prevent mating attempts or make it unlikely that fertilization will be successful.

What are the 5 prezygotic mechanisms?

Habitat, Temporal, Behavioral, Mechanical, and Gamete Isolation.

Habitation Isolation

Species occupy different habitats.

Temporal Isolation

Each reproduces at a different time.

Behavioral Isolation

courtship patterns for recognizing mates differ.

Mechanical Isolation

incompatible animal genitalia or plant floral structures.

Gamete Isolation

Gametes that meet do not fuse to become a zygote.

Postzygotic isolating mechanisms

prevent hybrid offspring from developing or breeding

(POST) Hybrid Inviolability

The hybrid zygote is not viable and may die.

(POST) Hybrid Sterility

Hybrid zygote may develop into a sterile adult.

What are the two modes of speciation?

Allopatric speciation and Sympatric speciation.

Allopatric speciation

Microevolutionary processes such as genetic drift and natural selection alter the gene pool of each population independently.

When differences become large enough, reproductive isolation may occur, and new species are formed.

Sympatric Speciation

One population develops into two or more reproductively isolated groups.

There is no prior geographic isolation.

Example: Midas and arrow cichlid fish; the arrow cichlid evolved from a population of Midas cichlids adapted to living and feeding in an open water habitat.

Polyploidy

In plants, sympatric speciation often involves polyploidy (several chromosomes beyond the diploid [2n] number).

Adaptive Radiation

It occurs when a single ancestral species rapidly gives rise to a variety of new species as each adapts to a specific environment.

Convergent Radiation

Occurs when a similar biological trait evolves in two unrelated species as a result of exposure to similar environments.

Gradualistic Model (Macroevolution)

Evolution at the species level occurs gradually.

Speciation occurs after populations become isolated.

Each group continues its own evolutionary pathway.

Suggests that it is difficult to indicate when speciation occurred.

Slow & Steady.

Punctuated Equilibrium Model (Macroevolution)

This model states that periods of equilibrium are punctuated by speciation.

A long period of time without change.