Chapter 24: Speciation

Objectives-Importance of reproductive isolation in the biological species concept-Speciation can take place with or without geographic separation-Importance in hybrid zones when studying reproductive isolation-Speciation can happen quickly or slowly with many or few genetic changes

Species means A group of populations whose members have the potential to interbreed in nature and produce viable offspring but do not produce viable offspring with other groups.

Earnst Mayr

Eastern and Western meadowlarks are not same species due to differences in songs and behaviors that would prevent them from mating in the wild

People are same species due to ability to interbreed. Is physical appearance the only species determinant?

Organisms are classified into discrete units called species based on:

1. Morphology (physical traits)2. Physiology (living systems like organs)3. Biochemistry4. DNA Sequences

Speciation: -The process in which one species splits into two or more species-Bridge between microevolution and macroevolution

Reproductive Isolation-Species is based on success in reproduction-Reduction in Gene flow based on reproductive barriers is the focus of speciation p. 490

Create a foldable of your choice that describes the prezygotic and postzygotic barriers that isolate species from reproducing with other species.

Biological Species differs from

1. Morphological Species

2. Ecological Species3. Phylogenetic

Species

Allopatric Speciation

-Caused by geographical barriers-Depends on species ability to move-Mutations, Genetic Drift or Natural Selection can cause the populations to separate genetically

Sympatric Speciation

-Speciation that occurs in populations that live in same area

Mechanism 1. PolyploidyMuch more common in plants then animals

Type 1: Autopolyploid

Type 2: Allopolyploid

Mechanism 2. Habitat Differentiation-Tree frogs colonized a different tree which formed a reproductive barrier.

Mechanism 3. Sexual Selection

Hybrid Zones-Areas where two species converge with the possibility of mating-Living genetics experiment

Possible Outcomes1. Reinforcement of reproductive barriers = maintain two species2. Weakening of the reproductive barriers = fusion of gene pools into

one species3. Stability = Hybrid individuals persist and thrive (not common)

Time and Patterns Associated with

Speciation

Strata shows fast change when actually it may have been much slower

Punctuated patterns suggest rapid change after speciation startsSpeciation Rate

Conclusions-No speciation time clock (Fast or slow)-Speciation only occurs after gene flow within a population is interrupted. -Genetic divergence needs to happen before gene flow starts again. (Fusion in a hybrid zone)

How many genes need to change to make a new species?

-One or many genes-Minimum requirement = genetic changes that leads to reproductive isolation p. 503

Many Speciation events can collectively lead to Macroevolution