To see if you’ve mastered the key concepts in this module, take the quiz below.

Some of the questions are free response, so grab a pencil and some paper (because you’ll learn more if you write out your best explanation before looking at the answer).

[qwiz random = “false” qrecord_id=”sciencemusicvideosMeister1961-speciation and extinction, cumulative quiz”] [h]

Speciation and Extinction: Cumulative Quiz

[i]

[q] Part 1: What type of speciation process is most connected to ecoclines?

Part 2: Explain.

[c*] Show me the answer

[f]

Part 1: The type of variation most connected to clinal variation is parapatric speciation.

Part 2: An ecocline (or cline) is a shift in genotype frequency that correlates with an environmental variable (which is itself shifting along a geographical axis). The result is that allele frequencies within a population become geographically differentiated. These differences set the stage for parapatric speciation. During parapatric speciation, a parent species becomes geographically differentiated. A hybrid zone develops between the two differentiated sub-populations. As differences progress, hybridization becomes less frequent, eventually resulting in the emergence of two distinct daughter species.

[q multiple_choice=”true”] The table to the right shows 8 species of bird lice, their hosts, and the part of the bird where the lice can be found. Which species is most closely related to species 5?

[c*] Species 2

[f] Excellent. DNA analysis indicates that the different species of lice that parasitize the same type of bird (such as the various species of lice that parasitize parrots) are more closely related to one another than species of lice that live on the same parts of different birds (such as the various species that live on the wings of different types of birds). The morphological similarity between species that live on the same parts of the birds is a convergent feature.

[c] Species 3

[f] No, but here’s a hint: use either the morphological or phylogenetic species concept.

[c] Species 6

[f] No. It looks like you used the morphological species concept. Think phylogenetically.

 

[q multiple_choice=”true”] How would you explain the similarity between species 1, 2, and 3?

[c] allopatric speciation

[f] No. Bird louse evolution is an example of sympatric speciation.

[c*] convergent evolution

[f] Way to go. DNA analysis indicates that the different species of lice that parasitize the same type of bird (such as the various species of lice that parasitize parrots) are more closely related to one another than species of lice that live on the same parts of different birds (such as the various species that live on the wings of different types of birds). The morphological similarity between species that live on the same parts of the birds is a convergent feature.

[c] adaptive radiation

[f] No. While the various species of bird-lice did evolve from a common ancestor that parasitized different species of bird and different parts of birds, that doesn’t explain why the three species of bird head-lice look so similar. What process can elicit morphological similarity in unrelated organisms?

[c] horizontal gene transfer

[f] No. While horizontal gene transfer is a powerful force for sharing adaptations in bacteria (which can, for example, share plasmids for antibiotic resistance with one another), it’s not at work in these eukaryotic species, and doesn’t explain the morphological similarity between species 1, 2, and 3. What process can elicit morphological similarity in unrelated organisms?

[c] genetic drift

[f] No. While genetic drift was probably a factor in bird-louse speciation, it wouldn’t explain the morphological similarity between species 1, 2, and 3. What process can elicit morphological similarity in unrelated organisms?

[q multiple_choice=”true”] In the diagram below, which letter represents allopatric speciation?

[c*] A      [c] B       [c] C     [c] X      [c] Y

[f] Excellent. With its geographical barrier at X, it’s clear that A represents allopatric speciation.

[f] No. B looks like parapatric speciation. The hint is the hybrid zone shown at Y. Here’s a hint: look for a geographic barrier.

[f] No. For allopatric speciation, you need a geographic barrier.

[f] No, but you’re close. X represents a geographical barrier, and that’s a key part of allopatric speciation.

[f] No. Y represents a hybrid zone, which is connected with parapatric speciation. Look for a geographic barrier, and then you’ll be able to find allopatric speciation.

[q multiple_choice=”true”] In the diagram below, which letter represents parapatric speciation?

[c] A    [c*] B [c] C    [c] X   [c] Y

[f] No. With its geographical barrier at X, it’s clear that A represents allopatric speciation. Here’s a hint: Parapatric speciation involves hybrid zones.

[f] Way to go! B, with its hybrid zone at Y, is a good model of parapatric speciation.

[f] No. C looks like sympatric speciation. For parapatric speciation, you need a hybrid zone.

[f] No, X represents a geographical barrier, and that’s a key part of allopatric speciation. For parapatric speciation, you need a hybrid zone.

[f] No, but you’re close Y represents a hybrid zone, which is connected with parapatric speciation. Which letter would represent the entire process?

[q multiple_choice=”true”] In the diagram below, which letter represents sympatric speciation?

[c] A    [c] B [c*] C [c] X [c] Y

[f] Excellent. With its geographical barrier at X, it’s clear that A represents allopatric speciation.

[f] No. B, with its hybrid zone at Y, is a good model of parapatric speciation.

[f] Terrific! C, with its lack of any geographical factors, looks like sympatric speciation.

[f] No, X represents a geographical barrier, and that’s a key part of allopatric speciation. Sympatric speciation occurs without any geographic boundaries.

[f] No, Y represents a hybrid zone, which is connected with parapatric speciation. Sympatric speciation occurs without any geographical separation.

[q multiple_choice=”true”] In the diagram below, which letter represents a hybrid zone?

[c] A [c] B [c] C [c] X [c*] Y

[f] Excellent. With its geographical barrier at X, it’s clear that A represents allopatric speciation.

[f] No. but you’re very close. B includes a hybrid zone, and that makes it a good model of parapatric speciation.

[f] No. C, with its lack of any geographical factors, looks like sympatric speciation.

[f] No, X represents a geographical barrier, and that’s a key part of allopatric speciation. You’re looking for a hybrid zone.

[f] Nice job! Y represents a hybrid zone, which is connected with parapatric speciation.

[q multiple_choice=”true”] The image below represents a model of

[c] allopatric speciation

[f] No. Allopatric speciation involves a geographical barrier.

[c] peripatric speciation

[f] No. Peripatric speciation looks more like this. Notice the small peripheral population that gest separated from the main population, and then differentiates into a separate species.

[c] parapatric speciation

[f] No. Parapatric speciation involves geographical separation (though often not a complete barrier) with a hybrid zone between the emerging species.

 

[c*] sympatric speciation

[f] Awesome. The model of speciation shown above represents sympatric speciation, which you can tell because of the lack of any geographical separation.

[q multiple_choice=”true”] The image below represents a model of

[c] allopatric speciation

[f] No. Allopatric speciation involves a geographical barrier. Here’s a hint: notice how the newly emerging daughter species is on the periphery of the parent species.

[c*] peripatric speciation

[f] Excellent. Peripatric speciation involves speciation in a small population at the periphery of its parent species’ geographical range.

[c] parapatric speciation

[f] No. Parapatric speciation involves geographical separation (though often not a complete barrier) with a hybrid zone between the emerging species.

 

[c] sympatric speciation

[f] No. In sympatric speciation, speciation occurs without any geographical separation, as shown below.

[q multiple_choice=”true”] The image below represents a model of

[c] allopatric speciation

[f] No. Allopatric speciation involves a geographical barrier. Here’s a hint: the hybrid zone in the diagram above (at 3) is the key feature of this mode of speciation.

[c] peripatric speciation

[f] No. Peripatric speciation involves a small peripheral population that evolves into a new species, as shown below

 

[c*] parapatric speciation

[f] Fabulous. Parapatric speciation involves geographical separation (though not a complete geographical barrier) with a hybrid zone between the emerging species.

[c] sympatric speciation

[f] No. In sympatric speciation, speciation occurs without any geographical separation, as shown below.

[q multiple_choice=”true”] The image below represents a model of

[c*] allopatric speciation

[f] Yes. Allopatric speciation involves a geographical barrier, as is shown above.

[c] peripatric speciation

[f] No. Peripatric speciation involves a small peripheral population that evolves into a new species, as shown below. For allopatric speciation, you need a geographical barrier.

[c] parapatric speciation

[f] No. Parapatric speciation involves geographical separation (though not a complete geographical barrier) with a hybrid zone between the emerging species. For allopatric speciation, you need a geographical barrier.

[c] sympatric speciation

[f] No. In sympatric speciation, speciation occurs without any geographical separation, as shown below. For allopatric speciation, you need a geographical barrier.

[q multiple_choice=”true”] Which of the following processes does not promote speciation?

[c] genetic drift

[f] No. Genetic drift causes genetic differentiation, especially in small, isolated populations. That genetic differentiation can lead to speciation. What’s on this list that keeps emerging populations from becoming genetically distinct?

[c] Natural selection

[f] No. Natural selection can promote sub-populations to become genetically (and phenotypically) different from one another, which can lay the groundwork for speciation. What’s on this list that keeps emerging populations from becoming genetically distinct?

[c] geographical isolation

[f] No. Geographical isolation, by allowing populations to genetically differentiate, can promote speciation. What’s on this list that keeps emerging populations from becoming genetically distinct?

[c*] gene flow

[f] Excellent. Gene flow, by moving alleles between adjacent populations, keeps them from becoming genetically different, and thus works against speciation.

 

[q multiple_choice=”true”] Rhagoletis flies parasitize fruit trees. Some Rhagoletis flies lay their eggs on apples, which produce fruit in early summer. Others lay their eggs on hawthorns, which produce fruit in early fall. After the eggs hatch, maggots emerge, which grow to maturity as they eat the fruit. Adults tend to mate and lay eggs on the same type of tree where they themselves developed. This creates which kind of reproductive barrier?

[c] pre-zygotic; hybrid breakdown

[f] No. First, hybrid breakdown is a post-zygotic barrier, not pre-zygotic one. Second, based on what’s above, all you know is that the flies parasitize and reproduce on fruit from plants that develop at different times of the year. What kind of reproductive barrier involves time?

[c*] pre-zygotic; temporal

[f] Good job. The difference in host fruiting season is an example of a temporal, pre-zygotic reproductive barrier.

[c] post-zygotic; hybrid sterility

[f] No. Based on the information above, there’s no evidence about hybrid sterility. All you know is that the flies parasitize and reproduce on fruit from plants that develop at different times of the year. What kind of reproductive barrier involves time?

[c] post-zygotic; gametic

[f] No. Based on the information above, there’s no evidence about gametic incompatibility. All you know is that the flies parasitize and reproduce on fruit from plants that develop at different times of the year. What kind of reproductive barrier involves time?

 

[q multiple_choice=”true”] Which species concept is based on reproductive isolation?

[c] the phylogenetic species concept

[f] No. The phylogenetic species concept defines a species as a tip on branch of a phylogenetic tree: “the smallest set of organisms that share an ancestor and can be distinguished from other such sets.” (Understanding Evolution, UC Berkeley)

[c*] the biological species concept

[f] That’ correct! The biological species concept defines a species as a group of organisms that can interbreed to produce fertile offspring, and which is isolated from other such groups.

[c] the morphological species concept

[f] No. The morphological species is based on phenotype or appearance. It’s most commonly used with extinct species, or species that reproduce asexually).

 

 

[q] Explain how peripatric speciation works.

[c*] Show me the answer

[f] Peripatric speciation involves formation of a new species from a small, somewhat isolated sub-population at the periphery of a parent species’ range. Because the sub-population is on the periphery of the parent species’ range, it will be subject to the most different environmental conditions, and therefore more natural selection. Because it’s a small population, it will be more subject to genetic drift. Both of these factors enhance genetic differentiation, contributing to speciation.

 

[q] In the Ensatina eschscholtzii complex of salamander subspecies, adjacent subspecies (such as 1 and 2 below) can successfully interbreed, but subspecies 1 and 7 cannot. Part 1: Identify the phenomenon. Part 2: Explain.

[c*] Show me the answer

[f] Part 1: The Ensatina eschscholtzii subspecies complex makes up a ring species.

Part 2: The E. eschscholtzii subspecies complex can be thought of as a cline that has folded in upon itself, so that the extreme ends are touching. If the cline were spread out over a geographic axis, we’d expect the subspecies at the extreme edges of the species range to be the most differentiated, and to possibly have difficulty interbreeding.

Similarly, in the ring species above, subspecies 1 and subspecies 7 are the most genetically different from one another, and can be considered to be reproductively isolated from one another. However, because gene flow is possible between all the other adjacent subspecies in the ring, the complex as a whole is still considered to be one species.

 

[q] Create a model and write out an explanation of how allopatric speciation works.

[c*] Show me the answer

[f] Allopatric speciation is speciation that involves geographic isolation, followed by genetic differentiation, followed by reproductive isolation. Imagine a species spread out over a geographic range. Gene flow (a) between various subpopulations within this species prevents genetic differentiation. When a geographical barrier (b) arises, it splits the population into isolated subspecies. In each population, natural selection (which can result from environmental differences caused by the barrier itself) and genetic drift cause each population to genetically differentiate. If this differentiation continues, then when the barrier is removed and the two subpopulations come back into contact (stage 4) they might have differentiated to the point where they are now reproductively isolated from one another.

 

[q] Explain 1) how sympatric speciation is different from allopatric speciation and 2) how sympatric speciation might come about in plants and animals

[c*] Show me the answer

[f] Part 1: Sympatric speciation is speciation that arises without geographical separation between sub-populations.

Part 2: Because of their ability to survive chromosomal changes, sympatric speciation in plants can involve processes like polyploidy and allopolyploidy. In polyploidy, errors in meiosis lead to chromosomal doubling, which can result in instant speciation. In allopolyploidy, meiotic errors that increase the number of chromosome sets are combined with hybridization, instantly creating new hybrid species.

In animals, three mechanisms can result in sympatric speciation. The first, seen in Lake Victoria cichlids, is sexual preference. Female mate preference for males with a specific phenotype can keep closely related species from hybridizing, reducing or eliminating gene flow between closely related species. Disruptive selection can split a population into two phenotypes, each of which has a high degree of fitness, while hybrids between these populations can have low fitness. This type of selection regime, continued for enough time, is thought to be capable causing one species to diverge int two. Finally, habitat selection (such as that seen in bird lice), can isolate gene pools. Subsequent natural selection and genetic drift can generate the genetic differentiation that can lead to speciation, even in the absence of any geographical separation between evolving populations.

 

[q multiple_choice=”true”] The evolution of multiple descendant species from a single ancestral species is known as

[c] genetic drift

[f] No. Genetic drift involves random genetic change in small, isolated populations. Genetic drift can be involved in the process above, but there’s another name for the entire process. Here’s a hint: it looks like this:

[c] natural selection

[f] No. Natural selection can be a key part of the process described above, but there’s another name for the entire process.

Here’s a hint: it looks like this:

[c*] adaptive radiation

[f] Excellent. Adaptive radiation is the evolution of multiple descendants from a single ancestral species.

[c] allopatric speciation

[f] No. The process can definitely involve allopatric speciation, but there’s another name for the process itself.

Here’s a hint: it looks like this:

[q]What evolutionary process best explains why the forelimbs of all vertebrates are built from the same bones?

[c]sympatric speciation

[f]No. Sympatric speciation is speciation that arises without geographical separation. While some of the groups above might have arisen by sympatric speciation, there’s a better explanation for why all of their forelimbs are built from the same bones.

[c]disruptive selection

[f]No. Disruptive selection involves selection against the mean phenotype in a population, and for the extremes. While some of the groups above might have arisen by disruptive selection, there’s a better explanation for why all of their forelimbs are built from the same bones.

[c]convergent evolution

[f]No. Convergent evolution occurs when similar selective pressures produce superficially similar phenotypes in distantly related organisms. What’s shown above is actually the opposite of convergent evolution.

[c*]adaptive radiation

[f]Excellent. The reason why all of the tetrapod (four-limbed) vertebrates represented above have forelimbs composed of similar bones is because of adaptive radiation. Deep in evolutionary time, all of the tetrapods had a common ancestor. Through innumerable branchings, that ancestor gave rise to all of the tetrapod species existing today. The evidence is in the shared bone structure, despite the fact that the evolutionary niches in which these forelimbs are deployed are widely divergent.

[/qwiz]

What next?

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