Chapter 24 - Orgin of Species and Macroevolution

Macroevolution

Evolutionary changes that produce new species or groups of species.

How many different species are on Earth?

Currently about 2 million however a vast number of species have yet to be classified which is particularly true among bacteria and archaea.

The most commonly used characteristic for identifying species are?

Morphological traits.

The ability to interbreed.

Molecular features

Ecological factors

Evolutionary relationships.

Reproductive isolation mechanisms fall into which 2 categories

Prezygotoic isolating mechanisms and Postzygotic isolating mechanisms

Prezyogotic Isolating Mechanism

A mechanism that blocks interbreeding by preventing the formation of a zygote.

Postzygotic Isolating Mechanism

A mechanism that prevents interbreeding by blocking the development of a viable and fertile individual after fertilization has taken place.

Interspecies Hybrid

The offspring resulting from the interbreeding of members of 2 different species

Reproductive Isolating Mechanisms

These mechanisms prevent successful breeding between different species. They can occur prior to fertilization (prezygotic) or after fertilization (postzygotic).

Habitat Isolation

A way to prevent interbreeding is for members of different species to never come in contact with each other when breeding. This occurs because different species occupy and/or breed in different types of environments.

Temporal Isolation

Species happen to reproduce at different times of the day or year.

Behavioral Isolation

Mating behavior plays a key role in promoting reproductive isoaltion.

Mechanical Isolation

Occurs when morphological features such as size or incompatible genitalia prevent 2 species from interbreeding.

Gametic Isolation

Occurs when two species attempt to interbreed but the gametes fail to unite in a successful fertilization event.

Hybrid Inviability

Operates when an egg of one species is fertilized by a sperm from another species but the fertilized egg may not develop past the early embryonic stages.

Hybrid Sterility

When interspecies hybrid may be viable but sterile.

Postzygotic isolating mechanisms tend to be _____ in nature compared with prezygotic mechanisms.

Uncommon

Why are postzygotic mechanisms rare?

One explanation is that they are more costly in terms of energy and resources used.

Speciation

Formation of a new species typically caused by genetic changes in a particular group that make it different from the species from which it was derived.

What can contribute to the formation of new species?

Interspecies breeding.

Changes in chromosome number

Horizontal gene transfer

What is the underlying cause of speciation?

The accumulation of genetic changes that ultimately promote enough differences that a population can be reorganized as a unique species.

Cladogenesis

The splitting or diverging of one species into 2 or more species.

Allopatric Speciation

A form of speciation that occurs when a population becomes more geographically isolated from other populations and evolves into one or more new species.

Hybrid Zone

An area where 2 populations can interbreed.

Sympatric Speciation

A form of speciation that occurs when members of a species that initially occupy the same habitat within the same range diverge into 2 or more different species even though there are no physical barriers to interbreeding.

How can sympatric speciation occur?

Although it is believed to be less common than allopatric speciation, particularly in animals, it can occur in Polyploidy, hybrid speciation, adaptation to local environments, and s*xual selection.

Polyploidy

The condition in which a cell or organism has three or more sets of chromosomes.

Gradualism

A concept suggesting that species evolve continuously over long spans of time.

Hox Genes

Found in nearly all animals, indicating that they originated very early in animal evolution.

They are homeotic genes that specify the fate of a particular segment or region of the body.

Macroevolution comprises evolutionary changes that?

Produce new species and groups of species.

The ecological species concept classifies a species based on?

The niches the organism occupies in the environment.

The large number of honeycreeper species on the Hawaiian Islands is an example of?

Adaptive Radiation

The key difference between allopatric and sympatric speciation is?

Whether the speciation process involves geographic separation.

Researchers suggest that an increase in the number of Hox genes?

Facilitated the evolution of more complex body patterns in a animals.