BIO 370 Lecture Notes - Lecture 39: Alpheidae, Phenetics, Reproductive Isolation
What does allopatric speciation mean?
(Greek: allos – other; patris – fatherland)
In all allopatric speciation models, the processes of genetic drift, mutation, and natural
selection cause populations to diverge from one another (creating phenetic differences in
morphology and DNA sequence).
Coincidentally or later, novel characters (apomorphies) and breeding barriers may evolve.
In the long run, these processes may lead to multiple forms of reproductive isolation between
these populations and result in the formation of new species.
How does gene flow fit into all of this?
Gene flow b/w geographically isolated pops may be permanently gone when members of one
pop loses ability to breed successfully with members of the other pop bc diff in geographic
range, genetics, behavior, reproductive physiology.
Allopatric speciation is often subdivided into a dumbbell model (vicariance) and a peripheral
isolate model (dispersal and colonization).
Let’s take a look at the et slide ad ou a tell e aout each model.
How might the dumbbell model happen?
How might the peripheral isolate model happen?
What’s the iggest differee etwee the two odels?
Dumbbell: initially large pop subdivided into new pop that are themselves still large.
Peripheral: pop are geographically isolated, one large pop and one+ smaller pop.
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Allopatric Speciation – Dumbbell
An example of the dumbbell model is the separation of marine organisms on either side of
Central America after formation of the Isthmus of Panama.
A study analyzed a series of snapping shrimp populations from either side of the isthmus.
Based on the phenetic species concept, there appeared to be several closely related species
pairs (sister species) with one member of each pair found on each side of the land bridge.
There were 6 species on each side. Each had a very similar species on the other side. Scientists
gathered DNA from each and an outgroup species.
Here is a cartoon of what scientists think happened, and, if so, what the phylogeny
should look like.
Furthermore, when males and females of various species pairs were put together there was a
strong correlation between the degree of genetic distance between species pairs and how
interested the shrimp were in courting.
Also, none of the pairs that formed during the courtship experiments produced fertile clutches.
find more resources at oneclass.com
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Document Summary
What does allopatric speciation mean? (greek: allos other; patris fatherland) In all allopatric speciation models, the processes of genetic drift, mutation, and natural selection cause populations to diverge from one another (creating phenetic differences in morphology and dna sequence). Coincidentally or later, novel characters (apomorphies) and breeding barriers may evolve. In the long run, these processes may lead to multiple forms of reproductive isolation between these populations and result in the formation of new species. Gene flow b/w geographically isolated pops may be permanently gone when members of one pop loses ability to breed successfully with members of the other pop bc diff in geographic range, genetics, behavior, reproductive physiology. Allopatric speciation is often subdivided into a dumbbell model (vicariance) and a peripheral isolate model (dispersal and colonization). Let"s take a look at the (cid:374)e(cid:454)t slide a(cid:374)d (cid:455)ou (cid:272)a(cid:374) tell (cid:373)e a(cid:271)out each model. Dumbbell: initially large pop subdivided into new pop that are themselves still large.
