Speciation Flashcards
Speciation
The formation of new and distinct species in the course of evolution
Morphological Species
Different species can be distinguished anatomically. Most species described this way.
Biological Species
Different species distinguished based on breeding patterns. Populations of 1 species breed only among them selves and are reproductively isolated from other populations. Rarely used to describe species
Phylogenetic Species
Different species distinguished based on genetic differences. Usually done through DNA analysis. Very rarely used, but it is growing in popularity
Reproductive Isolating Mechanisms (RIMs)
Evolutionary mechanisms and behaviors that prevent interbreeding among different species
Prezygotic RIMs
Prevent gametes from uniting (mating doesn’t occur)
Habitat Isolation
A type of prezygotic RIM. When two species have different habitats and don’t meet. (e.g., plants that grow in different types of soil)
Temporal Isolation
A type of prezygotic RIM. Species don’t meet because they live during different times of the year. (e.g., insects that emerge in different seasons)
Postzygotic RIMs
Prevent the formation of fertile offspring even if mating does occur (e.g., offspring of a horse and a donkey is a mule. Mules are infertile and can’t reproduce)
Problems with Biological Species
Cannot be used with fossils. (Fossils show morphological differences nothing about reproduction).
It’s also hard to use where hybridization (breeding) between different groups is normal
Allopatric Model
Speciation can ONLY occur when there is some sort of physical barrier that prevents gene flow between two populations.
Allopatric Model steps
1) A geographic/physical barrier that prevents gene flow occurs
2)During isolation, evolution causes population to become different
3)The differences become so great that if the barrier is removed they couldn’t breed.
4) After re-establishing contact, prezygotic isolating mechanisms would occur
Barriers effectiveness depends on…
the size and mobility of the species (a barrier for a snail won’t be a barrier for a butterfly)
Sympatric Speciation
Two species emerge without physical separation
Polyploidy
Example of sympatric speciation where different incompatible chromosomes occur. Tetraploid and diploid organisms meet and cannot produce fertile offspring, so the two species become reproductively isolated
Autopolyploid
Chromosome duplication in a single species. Can occur when cells accidentally make 4 sets of chromosomes instead of 2 (called a tetraploid)
Allopolyploid
Combining of chromosomes from two different species.
Fruit fly and sympatric speciation
Flies deposited their eggs on hawthorn fruits. Once apple orchards emerged, some laid eggs on apples not hawthorns. The offspring only lived in apple trees rather than hawthorne trees, and these two types of flies are becoming different species
African Rift Chiclids and Speciation
Large lakes in the east African Rift Valleys have many species of chichlid fish. The cichlids have evolved with no physical barriers. We don’t know why they have evolved, but can’t be described from the allopatric model.
