Ch 25.2: Mechanisms of Speciation
Section Summary:
This chapter was about the two different types of speciation. Speciation is the formation of new species, which is caused by genetic changes. The two causes of speciation include abrupt events such as changes in chromosome number and adaptation to different ecological niches. Cladogenesis is the splitting or diverging of a population into two or more species, and this would happen when gene flow becomes interrupted between members of different populations. The two types of speciation are allopatric and sympatric speciation.
Allopatric speciation is when some members of a species occupy a habitat that is isolated from other members, and may involve a geographical barrier, for example, a mountain range or a creeping glacier. Adaptive radiation is when a single ancestral species evolves into a wide array of descendent species that differ greatly in habitat, form, or behavior, such as the finches of the Galapagos Islands. Hybrid zones are areas where two populations can interbreed, and can cause diminishing gene flow.
Sympatric speciation is when members of a species are within the same geographical range but they don’t have a physical barrier. One example of this is polyploidy, which occurs most often in plants (40-70% plant species are from a result of polyloidy). What this means is basically organisms have more than two sets of chromosomes, and can be caused by complete nondisjunction of chromosomes or interspecies breeding. An alloploid organism consists of at least one set of chromosomes from two or more different species (usually closely related). They are usually not fertile because chromosomes cannot be evenly segregated.
Another type of sympatric speciation is adaptation to local environments, for example, with the introduction of new tree species, the apple maggot fly had two choices of food, the native hawthorn trees or the new apple trees. Since apple fruit have a different growing season than hawthorn fruit, there is a partial temporal isolation in the fly population; meaning one group would grow differently than the other.
The last example of sympatric speciation talked about in this section was sexual selection. It could separate one large sympatric population into smaller populations that become distinct species because they breed among themselves.
If you remember one thing from this section, make sure it is that allopatric speciation has a barrier, sympatric speciation does not.
Useful Links:
These two pictures explain the differences between sympatry and allopatry in fun and exciting ways. Not really, but it explains it really well. I like the fish because they look like Dory.
Anyways, sympatric speciation is when there are many varieties in one location, and they become different species while in the same location, as evidenced by the fat and skinny fish living in the same pond/lake/puddle whatever. Allopatric speciation is when a species becomes two or more species because of a geographical barrier, as shown by this lake body of water being separated into three, each having a different variation of the original population.
This podcast details the two types of speciation, allopatric and sympatric. It is a bit lengthy, but it does explain everything in this section with relevant examples.
This website explains the differences between allopatric and sympatric speciation pretty well, as well as going into the different types like adaptive radiation and geographical isolation.
This news article talks about how butterflies can become different species based on sexual selection because of wing patterns. This is a type of sympatric speciation.
My Prezi! http://prezi.com/kcnw1tzbf0ee/mechanisms-of-speciation-final/
Virtual Lecture! Sorry my voice skips a little, I'm not really sure what happened.
Poll Results: (You guys get credit for three of them!)
