Transcript Slide 1
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. Eastern and Western meadowlarks are not same species due to differences in songs and behaviors that would prevent them from mating in the wild Earnst Mayr Organisms are classified into discrete units called species based on: 1. Morphology (physical traits) 2. Physiology (living systems like organs) 3. Biochemistry 4. DNA Sequences Speciation: -The process in which one species splits into two or more species -Bridge between microevolution and macroevolution People are same species due to ability to interbreed. Is physical appearance the only species determinant? 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 Species 3. 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 Mechanism 1. Polyploidy Much more common in plants then animals -Speciation that occurs in populations that live in same area Mechanism 2. Habitat Differentiation -Tree frogs colonized a different tree which formed a reproductive barrier. Mechanism 3. Sexual Selection Type 1: Autopolyploid Type 2: Allopolyploid Hybrid Zones -Areas where two species converge with the possibility of mating -Living genetics experiment Possible Outcomes 1. Reinforcement of reproductive barriers = maintain two species 2. Weakening of the reproductive barriers = fusion of gene pools into one species 3. Stability = Hybrid individuals persist and thrive (not common) Time and Patterns Associated with Speciation Speciation Rate Conclusions -No speciation time clock (Fast or slow) -Speciation only occurs after gene flow within a population is interrupted. Punctuated patterns suggest rapid change after speciation starts Strata shows fast change when actually it may have been much slower -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