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Speciation

Speciation

Test Your Knowledge!

What Is a Species?

1. What is HGT?
  
2. Do you have to understand modern Linnaean taxonomy in order to accurately identify and distinguish different species?
  
3. True or false: there is general agreement among biologists that species are real biological entities.
  
4. True or false: there is general agreement among biologists as to what constitutes a species.
  
5. What does it mean to say that species delineations are congruent?

Species Concepts

1. What does "universal species concept" mean?
  
2. Which characteristic is more useful in determining whether two organisms belong to the same species: ecological similarity or potential to interbreed?
  
3. Why is individual morphology inadequate for defining species?
  
4. True or false: subspecies are considered distinct species.
  
5. In ring species, the first and last populations in the ring cannot hybridize. Why, according to the BSC, are they still considered the same species?

What's So Special About Speciation?

1. What do the nodes and branches represent on a phylogenetic tree?
  
2. Name one evolutionary process that might be occurring during periods of anagenesis.
  
3. Evolutionary biologists often refer to the nodes on a phylogenetic tree as "speciation events." Does this mean that speciation occurs instantaneously as a single event?
  
4. Are changes in gene frequencies expected during periods of anagenesis or cladogenesis?
  
5. What do the "tips" of a phylogenetic tree represent?

Reproductive Isolation

1. Quick! Name a type of prezygotic, post-mating reproductive isolation mechanism.
  
2. What is the difference between hybrid sterility and hybrid breakdown?
  
3. If two species have different mating calls, is this an example of an intrinsic or extrinsic isolating barrier?
  
4. Is there such thing as a pre-mating, postzygotic isolating mechanism?
  
5. Sterile hybrids are actually pretty common in the animal world. How many can you name?

The Geography of Speciation

1. We often describe speciation in terms of the geographical context in which it occurs. What are the major categories of geographic speciation?
  
2. What is the difference between allopatric and parapatric speciation?
  
3. Is geographic isolation (allopatry) a type of pre- or postzygotic isolation?
  
4. Name an example of a non-geographic isolating barrier.
  
5. True or false: Differences in individuals' microhabitat use can cause allopatric speciation.

Bring in the Reinforcements

1. Besides assortative mating, what are some other common mating patterns?
  
2. What type of mating would we expect to be advantageous if hybrids had higher fitness than parent species?
  
3. What evolutionary force determines the fitness of hybrid and parent species?
  
4. Is reduced hybrid fitness a result of intrinsic or extrinsic factors?
  
5. If two species successfully interbreed upon secondary contact, what does that tell us?

The Tempo of Evolution

1. True or false: species lineages are constantly undergoing anagenesis or cladogenesis.
  
2. In the Phyletic Gradualism vs. Punctuated Equilibrium debate, which do evolutionary biologists take more seriously?
  
3. What are incipient species?
  
4. What evidence would support a hypothesis that a species undergoing speciation?
  
5. Do periods of rapid speciation in one group of organisms tend to correspond to rapid speciation rates in other groups as well?

Adaptive Radiation

1. Adaptive radiations commonly follow mass extinctions. Is this more likely to be caused by evolutionary innovation or ecological opportunity?
   
2. What major generalization can we make about the speed of adaptive radiations?
  
3. Name one way in which scientists can test hypotheses regarding the speed and tempo of evolution.
  
4. If rapid speciation is occurring among many unrelated groups of organisms at once, is this an example of an adaptive radiation?
  
5. There are many great examples of organisms that arose through adaptive radiations. Can you think of some?

Hybridization vs. Hybrid Speciation

1. An organisms' "ploidy" refers to the number of…?
  
2. What factors are required for hybrid speciation?
  
3. Why is hybrid speciation more prevalent in plants than animals?
  
4. What is backcrossing?
  
5. Some fish, reptiles, and insects are tetrapoloid, meaning they have how many sets of chromosomes?

Possible Answers

What Is a Species?

1. What is HGT?  
Horizontal gene transfer is the sharing of genes without mating.
  
2. Do you have to understand modern Linnaean taxonomy in order to accurately identify and distinguish different species?  
No, in fact the species distinctions informed by indigenous biological knowledge are often the same as those described by Linnaean taxonomy.
  
3. True or false: there is general agreement among biologists that species are real biological entities.  
True, most scientists agree that species are biologically valid entities.
  
4. True or false: there is general agreement among biologists as to what constitutes a species.    
False, although some groups of organisms are fairly straightforward, there are many groups that still baffle scientists, and often a biologist's species concept will depend on which group of organisms is being studied.
  
5. What does it mean to say that species delineations are congruent?  
They are in agreement with another in recognizing the same species distinctions.

Species Concepts

1. What does "universal species concept" mean?  
A species definition that applies universally to all organisms.
  
2. Which characteristic is more useful in determining whether two organisms belong to the same species: ecological similarity or potential to interbreed?  
Potential to interbreed.
  
3. Why is individual morphology inadequate for defining species?  
Some organisms look very similar but do not interbreed, and some organisms look very dissimilar and do interbreed.
  
4. True or false: subspecies are considered distinct species.  
False, because subspecies can potentially interbreed with other subspecies, they're not technically distinct species.
  
5. In ring species, the first and last populations in the ring cannot hybridize. Why, according to the BSC, are they still considered the same species?  
Genes from one population can still be shared with the other population via hybridization with intermediate populations. Because gene flow is not completely cut off, they are still one species according to the BSC.

What's So Special About Speciation?

1. What do the nodes and branches represent on a phylogenetic tree?  
Nodes represent cladogenesis (speciation) and branches represent anagenesis.
  
2. Name one evolutionary process that might be occurring during periods of anagenesis.  
Possible answers: genetic drift, mutation, selection
  
3. Evolutionary biologists often refer to the nodes on a phylogenetic tree as "speciation events." Does this mean that speciation occurs instantaneously as a single event?  
No. While the rates of speciation may vary, generally speciation is a process that takes place over geological (very long) timescales.
  
4. Are changes in gene frequencies expected during periods of anagenesis or cladogenesis?  
Both.
  
5. What do the "tips" of a phylogenetic tree represent?  
The taxa of interest; usually species.

Reproductive Isolation

1. Quick! Name a type of prezygotic, post-mating reproductive isolation mechanism.  
Gametic isolation.
  
2. What is the difference between hybrid sterility and hybrid breakdown?  
Hybrid sterility occurs when two parents produce sterile or inviable offspring; hybrid breakdown produces fertile, viable offspring, but the offspring's offspring are sterile or inviable.
  
3. If two species have different mating calls, is this an example of an intrinsic or extrinsic isolating barrier?  
Intrinsic.
  
4. Is there such thing as a pre-mating, postzygotic isolating mechanism?  
No: if there's no mating, there can be no zygote.
  
5. Sterile hybrids are actually pretty common in the animal world. How many can you name?  
Ligers, mules, hinnies, zeedonks, beefalos, wholphins, lijagulep.

The Geography of Speciation

1. We often describe speciation in terms of the geographical context in which it occurs. What are the major categories of geographic speciation?  
Parapatric, allopatric, and sympatric.
  
2. What is the difference between allopatric and parapatric speciation?  
Allopatric populations are completely separated from each other, whereas parapatric populations are connected and often include regions where hybridization is common (hybrid zones).
  
3. Is geographic isolation (allopatry) a type of pre- or postzygotic isolation?  
Prezygotic.
  
4. Name an example of a non-geographic isolating barrier.  
Lots of possible answers: ecological isolation, behavioral, temporal, pollinator, gametic isolation, etc.
  
5. True or false: Differences in individuals' microhabitat use can cause allopatric speciation.  
False: allopatric speciation occurs on larger spatial scales, whereas differences in microhabitat use could contribute to sympatric speciation.

Bring in the Reinforcements

1. Besides assortative mating, what are some other common mating patterns?  
Non-assortative mating and random mating.
  
2. What type of mating would we expect to be advantageous if hybrids had higher fitness than parent species?  
Non-assortative.
  
3. What evolutionary force determines the fitness of hybrid and parent species?  
Natural Selection.
  
4. Is reduced hybrid fitness a result of intrinsic or extrinsic factors?  
Extrinsic, as an animal's fitness is determined relative to its environment.
  
5. If two species successfully interbreed upon secondary contact, what does that tell us?  
That they were never two separate species, just two geographically separated populations of the same species.

The Tempo of Evolution

1. True or false: species lineages are constantly undergoing anagenesis or cladogenesis.  
False, the fossil record suggests that periods of evolutionary stasis are quite common for many lineages. Of course small changes in genes and gene frequencies are always occurring, but they don't have a major effect on phenotype during periods of stasis.
  
2. In the Phyletic Gradualism vs. Punctuated Equilibrium debate, which do evolutionary biologists take more seriously?  
Punctuated Equilibrium.
  
3. What are incipient species?  
Organisms that technically belong to the same species but are suspected to be in the process of diverging into distinct species.
  
4. What evidence would support a hypothesis that a species undergoing speciation?  
Evidence for reproductive isolation among individuals of that species, such as differences in mating cues or ecology.
  
5. Do periods of rapid speciation in one group of organisms tend to correspond to rapid speciation rates in other groups as well?  
In general, speciation in one group of organisms occurs quite independently from other groups, so no. However, there are known periods (for example, the Cambrian Explosion) where many groups of organisms were undergoing rapid speciation at the same time.

Adaptive Radiation

1. Adaptive radiations commonly follow mass extinctions. Is this more likely to be caused by evolutionary innovation or ecological opportunity?  
Probably ecological opportunity, as the recently extinct organisms have left a lot of empty niches to be occupied by new species.
  
2. What major generalization can we make about the speed of adaptive radiations?  
They're fast. Really fast.
  
3. Name one way in which scientists can test hypotheses regarding the speed and tempo of evolution.  
Look at the fossil record to see if evolutionary patterns of previous organisms support the proposed hypotheses.
  
4. If rapid speciation is occurring among many unrelated groups of organisms at once, is this an example of an adaptive radiation?  
No, adaptive radiations refer to rapid speciation of a group from a common ancestor.
  
5. There are many great examples of organisms that arose through adaptive radiations. Can you think of some?  
Cichlids in the East African rift lakes, Darwin's finches in the Galapagos, Hawaiian Honeycreepers, and Heliconius butterflies in the New World Tropics, to name a few.

Hybridization vs. Hybrid Speciation

1. An organisms' "ploidy" refers to the number of…? 
Chromosome pairs in the cell.
  
2. What factors are required for hybrid speciation?  
Increased hybrid fitness relative to parent species and reproductive isolation between hybrids and parent species.
  
3. Why is hybrid speciation more prevalent in plants than animals?  
Hybridization can be limited by the number of chromosome sets (ploidy), and since plants are more tolerant of polyploidy (which is fatal to most animals) there is more opportunity for distinct species to successfully interbreed.
  
4. What is backcrossing?  
When a hybrid mates with an individual from one of its parent species.
  
5. Some fish, reptiles, and insects are tetrapoloid, meaning they have how many sets of chromosomes?  
Four.

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