Species, Speciation, and Variation

1. Watch these videos

1.1 Speciation

1.2. Variation

2. Study this summary

Biological Species Concept

Defines a species as a group of organisms that:
- Can naturally interbreed to produce viable and fertile offspring.
- Are reproductively isolated from other groups.
Limitations:
- Hybridization between closely related species (e.g., some plants, animals).
- Application to extinct, asexual, or prokaryotic species.

Reproductive Isolating Mechanisms

Prezygotic Barriers: Prevent mating or fertilization:
- Behavioral: Different courtship behaviors prevent mating.
- Temporal: Species breed at different times.
- Mechanical: Structural differences prevent mating.
- Habitat: Species live in different environments and don’t encounter each other.
- Gametic: Molecular incompatibilities prevent sperm from fertilizing the egg.
Postzygotic Barriers: Prevent viable or fertile offspring:
- Hybrid Inviability: Zygotes fail to develop into viable offspring.
- Hybrid Sterility: Offspring are sterile (e.g., mules).
- Hybrid Breakdown: First-generation hybrids are viable, but their offspring are inviable or sterile.

Modes of Speciation

Allopatric Speciation:
- Geographic isolation separates populations, preventing gene flow.
- Different selective pressures lead to genetic divergence.
- When the barrier is removed, populations remain reproductively isolated.
Sympatric Speciation:
- Occurs without geographic barriers.
- In Plants: Polyploidy creates reproductive isolation.
- In Animals:
  - Sexual selection (e.g., cichlids in Lake Victoria).
  - Adaptation to specific microhabitats (e.g., lice adapting to different parts of birds).

Adaptive Radiation

A single parent species gives rise to multiple descendant species with unique adaptations, filling different ecological niches.
Examples:
- 14 species of Galapagos finches, each adapted to a different ecological role.
Results in homologous and vestigial traits due to descent with modification.

Why Is Phenotypic Variation Important for Evolution?

Phenotypic variation is the raw material for evolution, enabling natural selection to act.
Key Points:
- Natural selection acts on phenotypes, not genotypes.
- Organisms with advantageous phenotypes survive and reproduce more successfully.
- Without phenotypic variation:
  - There is no natural selection or adaptation.
  - Species face an increased risk of extinction.

Examples of Phenotypic Variation and Its Adaptive Importance

Variation in Phospholipid Structure in Browsing Mammals:
- Phospholipids have saturated and unsaturated fatty acid tails, which vary based on temperature.
- Adaptation in snowy environments:
  - Core Body Tissues: More saturated fatty acids for optimal membrane fluidity.
  - Extremities: More unsaturated fatty acids to maintain membrane fluidity in cold temperatures, allowing oxygen diffusion into cells.
Variation in Hemoglobin in Mammals:
- Fetal vs. Adult Hemoglobin:
  - Both have two alpha chains, but:
    - Fetal Hemoglobin: Contains gamma chains, which have a higher oxygen affinity.
    - Adult Hemoglobin: Contains beta chains.
- Adaptive Importance:
  - Fetal hemoglobin facilitates oxygen transfer from maternal blood in the placenta to fetal blood.
  - After birth, beta chains replace gamma chains to optimize oxygen transport in the adult environment.
Variation in Chlorophyll Types in Green Plants:
- Types of Chlorophyll:
  - Chlorophyll a absorbs red light and is adapted to direct light.
  - Chlorophyll b absorbs blue light and is adapted to shaded environments.
- Adaptive Importance:
  - Plants with different proportions of chlorophyll a and b can thrive in varied light conditions.
  - Most plants use both types, maximizing light energy absorption for photosynthesis throughout the day or season.

3. Master these flashcards

[qdeck]

[h]Speciation and Variation

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cde6f0d83e38″ question_number=”44″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction”] What is the biological species concept, and what are some of its limitations?

[a] The biological species concept defines a species as a group of organisms that can naturally interbreed to produce viable, fertile offspring, and which is reproductively isolated from other such groups. The concept falters with closely related species (which can often hybridize), with extinct or asexual species (to which we can’t apply the criterion of reproductive isolation), or with most prokaryotic species (which don’t have sex in the way that eukaryotes do, but which frequently exchange genes through horizontal gene transfer). When the biological species can’t be applied, biologists designate species using morphological, phylogenetic, or ecological criteria.

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cdb3b7d2a638″ question_number=”46″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction”] Contrast the allopatric and sympatric models of speciation.

[a] Allopatric speciation involves a geographical barrier (1); sympatric speciation occurs without a geographical barrier (2).

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cd9c6f5bbe38″ question_number=”47″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction”] Explain the allopatric model of speciation.

Importance for the AP exam: High

[a] Allopatric speciation involves geographical isolation leading to genetic differentiation, which eventually leads to reproductive isolation. Imagine a species that’s spread out over a geographical range (stage 1). Some geographical barrier (“b”) splits the species into isolated subpopulations, with no gene flow (“a”) between them. Environmental differences lead to different selective pressures in each subpopulation, leading to genetic differentiation (stages 2 and 3). Eventually, the two populations become so different that when the geographic barrier is removed (stage 4), the populations can longer interbreed. They’ve become separate species.

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cd8526e4d638″ question_number=”48″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction”] Explain how sympatric speciation occurs in plants.

[a] Sympatric speciation occurs without a geographical barrier subdividing a species into isolated populations. In plants, it can occur through polyploidy (shown at left) and allopolyploidy (polyploidy followed by hybridization, which is not shown). Because these processes change chromosome numbers, they cause instant, one-generation reproductive isolation between the newly emerged species and its parent species.

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cd6b8a620a38″ question_number=”49″] Explain how sympatric speciation occurs in animals.

[a] Sympatric speciation occurs without a geographical barrier subdividing a species into isolated populations. In animals, sexual selection can lead to reproductive isolation between subspecies, a process that has led to the evolution of hundreds of species of Cichlids (a type of fish) in Lake Victoria. Adaptation to specific habitats or microhabitats can also lead to reproductive isolation and speciation, such as the evolution of a variety of lice that inhabits different parts of birds (head lice, wing lice, etc).

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cd5441eb2238″ question_number=”50″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction”] What are reproductive isolating mechanisms? Compare and contrast pre and post-zygotic forms of isolation.

[a] Reproductive isolating mechanisms are processes or physical barriers that keep the gene pools of closely related species separate. Prezygotic isolating mechanisms prevent the formation of a zygote. Postzygotic barriers can exist between species that are close enough to mate and form a zygote. In this case, the formation of a zygote does not ultimately lead to the production of successful individuals who can survive and produce offspring themselves.

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cd3cf9743a38″ question_number=”51″ topic=”7.10-11.Speciation_and_Extinction”] List and describe 5 prezygotic isolating mechanisms.

[a] Prezygotic isolating mechanisms prevent the formation of a zygote. They can be

Behavioral (different mating rituals or courtship behaviors);
Temporal (breeding during different times of the day or different seasons);
Mechanical (structural barriers that prevent sperm or pollen from reaching an egg: think of long tubes in flowers or the structures that insects use for mating);
Habitat (imagine one species of wildflower that’s adapted to a wet environment, while a closely related one lives in drier areas); or
Gametic (the molecules on a sperm cell that induce an egg cell to allow fertilization are not complementary to receptors on the egg cell).

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cd25b0fd5238″ question_number=”52″ topic=”7.10-11.Speciation_and_Extinction”] List and describe 3 postzygotic isolating mechanisms.

[a] Postzygotic barriers can exist between species that are close enough to mate and form a zygote. These include

Hybrid inviability: hybrid organisms don’t develop.
Hybrid sterility: hybrid offspring are healthy, but can’t reproduce.
Hybrid breakdown: the hybrids are healthy and can reproduce, but the next generation (the F₂s) are inviable or infertile.

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4ccf277f7ba38″ question_number=”54″ unit=”7.Evolution_and_Natural_Selection” topic=”7.10-11.Speciation_and_Extinction”] What is adaptive radiation?

[a] Adaptive radiation occurs when one parent species produces several descendant species, each of which has unique adaptations and fills a different ecological niche. The 14 species of Galapagos finches, all of which are the descendants of a single species from the South American mainland, are an example.

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cc43d87bee38″ question_number=”61″ topic=”7.12.Variations_in_Populations”] Why is phenotypic variation important for evolution?

[a] Phenotypic variation is the raw material upon which natural selection acts. Natural selection selects for organisms with phenotypes that confer a selective advantage, allowing individuals with these advantageous phenotypes to survive and reproduce at higher rates than organisms with less advantageous phenotypes. With no phenotypic variation, there can be no natural selection and no adaptation.

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cc27e7ed3e38″ question_number=”62″ unit=”7.Evolution_and_Natural_Selection” topic=”7.12.Variations_in_Populations”] What’s the connection between a species’ genetic variability and its ability to adapt to environmental change?

[a] Species that lose their genetic variability become less resilient, losing their ability to adapt to changes in their environment. Loss of genetic variability can occur through a population bottleneck, and species that survive these bottlenecks are often at risk of extinction since they lack the genetic variability that would enable them to survive further environmental change.

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cc0e4b6a7238″ question_number=”63″ topic=”7.12.Variations_in_Populations”] Explain how variations in phospholipid structure can serve an adaptive function in browsing mammals that forage in snowy environments.

Illustrative example: Molecular diversity

[a]

In mammals such as elk that walk through the snow as they forage for food in winter, there’s a gradient of phospholipid structure in the cell membranes of their leg cells. Closer to the hoof, the phospholipids have more unsaturated fatty acids. Closer to the body’s core, they have more saturated fatty acids. That’s because the temperature in the extremities can be far below the temperature in the core (just like your hands are often colder than your torso). Having more unsaturated fatty acids in the membranes toward the hoof keeps those membranes fluid, despite the cold. By contrast, closer to the core the increased saturation of fatty acids maintains the right amount of membrane fluidity in those cells. Membrane fluidity, in turn, establishes conditions for the proper diffusion of substances across the membrane.

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cbeb5eb81638″ question_number=”64″ topic=”7.12.Variations_in_Populations”] Explain how variation in hemoglobin maximizes oxygen absorption in humans and other placental mammals at various life stages.

Illustrative example: Molecular diversity

[a] Hemoglobin is the protein that transports oxygen in red blood cells in almost all vertebrates. Before birth, humans and other mammals produce fetal hemoglobin, a hemoglobin variant that has a much higher affinity for oxygen than adult hemoglobin. Because of that, oxygen will diffuse from the mother’s red blood cells in the placenta to the red blood cells of the fetus. Within about six months after birth, the production of fetal hemoglobin is replaced by the production of adult hemoglobin.

[q json=”true” yy=”4″ unit=”7.Evolution_and_Natural_Selection” dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cbd1c2354a38″ question_number=”65″ topic=”7.12.Variations_in_Populations”] Explain how variation in chlorophyll types increases the efficiency of photosynthesis.

Illustrative example: Molecular diversity

[a] Chlorophyll is the key light-absorbing pigment in photosynthesis. Green plants have two main types: chlorophyll a and chlorophyll b. Their difference comes down to one functional group: chlorophyll a has a methyl group whereas chlorophyll b has an acetyl group. Whereas the peak absorption of chlorophyll a is in the red part of the spectrum, the peak absorption of chlorophyll b is in the blue portion of the spectrum. Having both types of chlorophyll thus increases the amount of light energy that plants can use during photosynthesis. Chlorophyll b is particularly prevalent in shade-adapted plants.

[q json=”true” yy=”4″ dataset_id=”Unit 7 Cumulative Flashcards Dataset|4cb978d0c0638″ question_number=”67″ unit=”7.Evolution_and_Natural_Selection” topic=”7.12.Variations_in_Populations”] How does a population’s genetic diversity enable it to survive in a changing environment?

[a] Genetic diversity is a key asset in a population’s ability to respond to environmental change. As the environment changes, a diverse population is more likely to contain individuals who can survive in the new conditions, and thus pass their genes on to future generations. Conversely, populations with little genetic diversity are less likely to be able to survive the selective pressure associated with environmental changes, putting them at higher risk for extinction.

[/qdeck]

4. Tackle these quizzes

4.1. Allopatric and Sympatric Speciation

[qwiz ] [h]

Allopatric and Sympatric Speciation

[i]

[q] Speciation that involves a geographical barrier is called [hangman] speciation.

[c]IGFsbG9wYXRyaWM=[Qq]

[f]IEV4Y2VsbGVudCE=[Qq]

[q] In the diagram below, which phase shows when a geographic barrier first subdivides a population into two isolated gene pools?

[textentry single_char=”true”]

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[c]IEVudGVyIHdvcmQ=[Qq]

[c]ICo=[Qq]

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[q]In the diagram below, which letter or number represents gene flow?

[textentry single_char=”true”]

[c]IG E=[Qq]

[f]IE5pY2Ugam9iLiBMZXR0ZXIgJiM4MjIwO2EmIzgyMjE7IHJlcHJlc2VudHMgZ2VuZSBmbG93Lg==[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[c]ICo=[Qq]

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[q]By stage 4, the two species can no longer [hangman].

[c]IEludGVy YnJlZWQ=[Qq]

[q]The basic idea of allopatric speciation is that ______________ isolation leads to genetic differentiation, which leads to reproductive isolation.

[hangman ]

[c]IGdlb2dyYX BoaWNhbA==[Qq]

[q]The basic idea of allopatric speciation is that geographical isolation leads to genetic differentiation, which leads to ___________ isolation.

[hangman ]

[c]IHJlcHJvZH VjdGl2ZQ==[Qq]

[q labels = “top”]

In the speciation model shown at left, the __________ size of the peripheral population allows for higher amounts of ________________. However, _____________ won’t occur until ______________ is cut off. By stage 3, the two populations are reproductively ____________ from one another.

[l]genetic drift

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]gene flow

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]isolated

[fx] No. Please try again.

[f*] Great!

[l]small

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]speciation

[fx] No, that’s not correct. Please try again.

[f*] Great!

[q]Because of its geographical distribution, species like E. eschscholtzii are called “ring species.” Based on what you know about natural selection, a reasonable prediction about subspecies 1 and subspecies 7 is that they might be unable to [hangman].

[c]aW50ZXJi cmVlZA==[Qq]

[q]In the E. eschscholtzii ring species complex shown below, if it weren’t for the gene flow between all of the adjacent subspecies, you could almost think of subspecies 1 and 7 as separate [hangman].

[c]c3BlY2 llcw==[Qq]

[q]In the diagram below, which letter represents a geographical barrier

[textentry single_char=”true”]

[c]WA ==[Qq]

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[c]IEVudGVyIHdvcmQ=[Qq]

[c]ICo=[Qq]

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[q]In the diagram below, which letter represents the moment in which mutations start to emerge in the gene pools of each subpopulation?

[textentry single_char=”true”]

[c]Qw ==[Qq]

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[c]IEVudGVyIHdvcmQ=[Qq]

[c]ICo=[Qq]

[f]IE5vLiBGaW5kIHRoZSBtb21lbnQgd2hlbiB0aGUgdHdvIHNlcGFyYXRlZCBwb3B1bGF0aW9ucyBzdGFydCB0byBiZSBkaWZmZXJlbnQu[Qq]

[q]If the environments experienced by the populations on the left and right sides are different, then another force causing the populations to genetically differentiate would be [hangman] [hangman].

[c]bmF0dXJhbA==[Qq]

[c]c2VsZWN0aW9u[Qq]

[q]In the diagram below, which letter represents the moment in which the two new species have become reproductively isolated?

[textentry single_char=”true”]

[c]Rg ==[Qq]

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[q multiple_choice=”true”] Among the multicellular, eukaryotic kingdoms, speciation through chromosome number changes is least common in

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[c]ZnVuZ2k=[Qq]

[f]Tm8uIFNwZWNpYXRpb24gdGhyb3VnaCBwb2x5cGxvaWR5IGlzIGZvdW5kIGluIGZ1bmdpLg==[Qq]

[q] In the diagram below, which letter refers to (abnormal) meiosis?

[textentry single_char=”true”]

[c]IG E=[Qq]

[f]IE5pY2Ugam9iIQ==[Qq]

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[c]ICo=[Qq]

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[q] In the diagram below, which letter indicates fertilization?

[textentry single_char=”true”]

[c]IG I=[Qq]

[f]IEV4Y2VsbGVudCE=[Qq]

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[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[q] The diagram below represents speciation through a doubling in chromosome number. Multiplication of chromosome number is also known as [hangman].

[c]IHBvbHlwbG9pZHk=[Qq]

[f]IEdvb2Qh[Qq]

[q] Because it involves changes in chromosome number, polyploidy can result in [hangman] speciation,

[c]IGluc3RhbnQ=[Qq]

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[q] Polyploidy involves changes in [hangman] number.

[c]IGNocm9tb3NvbWU=[Qq]

[f]IEV4Y2VsbGVudCE=[Qq]

[q]When females assess a male’s attractiveness as a way of choosing whom they’ll mate with, it’s known as [hangman] selection.

[c]aW50ZXJzZXh1YWw=[Qq]

[q multiple_choice=”true”]Intersexual selection can lead to

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[c]bW9yZSBpbnRlcmJyZWVkaW5nIGFuZCBtaXhpbmcgYmV0d2VlbiBzdWJncm91cHMgb2YgYSBzcGVjaWVzLg==[Qq]

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[q] Female mate choice can lead to [hangman] isolation between populations. This can set the stage for [hangman] speciation.

[c]cmVwcm9kdWN0aXZl[Qq]

[c]c3ltcGF0cmlj[Qq]

[x][restart]

[/qwiz]

4.2. Species, Speciation and Variation

[qwiz style=”min-height: 450px !important;” random=”true”]

[h] Species, Speciation, and Variation

[q json=”true” multiple_choice=”true” unit=”7.Evolution” topic=”7.10-7.12.Speciation,_Variation,_Extinction” dataset_id=”Unit 7 Cumulative MC Dataset|20ed08e3bbbeeb” question_number=”15″] The apple maggot fly, Rhagoletis pomonella, is a plant parasite that is native to North America. Its original host was the fruit of Hawthorn trees. Females lay their eggs on Hawthorn fruit. The eggs develop into maggots, which consume the fruit as they grow.

In the 1600s, when European colonists introduced apples into North America, some Rhagoletis flies started to parasitize apple trees. Over time, two Rhagoletis variants have emerged: one with a preference for apples, and the other with a preference for Hawthorns. Hybridization experiments between the two populations show that they’re still capable of successfully interbreeding.

The table below summarizes the difference between the two variants.

Which reproductive barriers appear to be emerging between these two sub-populations?

[c]IGNocm9tb3NvbWFsIGRpZmZlcmVuY2VzIGFuZCBnYW1ldGljIGJhcnJpZXJz[Qq]

[f]IE5vLiBUaGUgdHdvIHZhcmlhbnRzIGNhbiBpbnRlcmJyZWVkLiBUaGlzIHdvdWxkIGJlIGltcG9zc2libGUgaWYgdGhlcmUgd2VyZSBnYW1ldGljIGJhcnJpZXJzLg==

Cg==

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[c]IG1lY2hhbmljYWwgYW5kIGJlaGF2aW9yYWwgYmFycmllcnM=[Qq]

[f]IE5vLiBUaGUgdHdvIHZhcmlhbnRzIGNhbiBpbnRlcmJyZWVkLiBUaGlzIHdvdWxkIGJlIGltcG9zc2libGUgaWYgdGhleSB3ZXJlIG1lY2hhbmljYWxseSBpc29sYXRlZCwgYSBjb25kaXRpb24gaW4gd2hpY2ggYW5hdG9taWNhbCBkaWZmZXJlbmNlcyBwcmV2ZW50IGZlcnRpbGl6YXRpb24u

Cg==

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[c]IHRlbXBvcmFsIGFuZCBtZWNoYW5pY2FsIGJhcnJpZXJz[Qq]

[f]IE5vIChidXQgeW91JiM4MjE3O3JlIHJpZ2h0IGFib3V0IHRlbXBvcmFsIGJhcnJpZXJzKS4gVGhlIHR3byB2YXJpYW50cyBjYW4gaW50ZXJicmVlZC4gVGhpcyB3b3VsZCBiZSBpbXBvc3NpYmxlIGlmIHRoZXkgd2VyZSBtZWNoYW5pY2FsbHkgaXNvbGF0ZWQsIGEgY29uZGl0aW9uIGluIHdoaWNoIGFuYXRvbWljYWwgZGlmZmVyZW5jZXMgcHJldmVudCBmZXJ0aWxpemF0aW9uLg==

Cg==

VGFrZSBhbm90aGVyIGxvb2sgYXQgdGhlIGltYWdlIGFuZCBzZWUgaWYgeW91IGNhbiBpZGVudGlmeSB0d28gdGhpbmdzIHRoYXQga2VlcCB0aGVzZSB2YXJpYW50cyBhcGFydC4=[Qq]

[c]IGhhYml0YXQgYW5kIHRl bXBvcmFsIGJhcnJpZXJz[Qq]

[f]IEV4YWN0bHkuIFRoZSBmcnVpdCBwcmVmZXJlbmNlIGNhbiBiZSB0aG91Z2h0IG9mIGFzIGEgaGFiaXRhdCBiYXJyaWVyLiBUaGUgYnJlZWRpbmcgdGltZSwgd2hpY2ggY29pbmNpZGVzIHdpdGggZnJ1aXQgcmlwZW5pbmcsIGlzIGEgdGVtcG9yYWwgYmFycmllci4=

Cg==

[Qq]

[q json=”true” multiple_choice=”true” unit=”7.Evolution” topic=”7.10-7.12.Speciation,_Variation,_Extinction” dataset_id=”Unit 7 Cumulative MC Dataset|20ecf19b44d6eb” question_number=”16″] The soapberry bug (Jadera haematoloma) lives in the southeastern United States. It uses a needle-like beak to pierce the outside skin of the fruit of the soapberry bush, C. corindum. After piercing the skin, the soapberry bug pierces the seed coat of seeds within the fruit. Enzymes liquefy the seeds, and the bugs suck up the liquified seed contents.

Over the past 150 years, the soapberry bug has adapted to an introduced plant species from Eurasia, K. elegans. K. elegans, has a fruit structure in which the seeds are much closer to the skin of the fruit than in C. corindum.

In a study in the 1990s, measurements were made of the beak length of soapberry bugs feeding on C. corindum compared to those feeding on the introduced species, K. elegans.

A researcher has noted that the bugs feeding on C. corindum are more likely to breed with one another than with bugs feeding on K. elegans.

Which of the following is most likely the first barrier to gene flow to have emerged between soapberry bugs feeding on C. corindum and those feeding on K. elegans?

[c]IGhhYml0YXQgaX NvbGF0aW9uLg==[Qq]

[f]IFllcy4gVGhlIHR3byBwb3B1bGF0aW9ucyBhcmUgaXNvbGF0ZWQgYnkgZGlmZmVyZW50IG1pY3JvaGFiaXRhdHMgKHRoZSB0d28gZGlmZmVyZW50IHBsYW50IHNwZWNpZXMpLiBPdGhlciBkaWZmZXJlbmNlcyBtaWdodCBlbWVyZ2UgbGF0ZXIsIGJ1dCB0aGlzIGRpZmZlcmVuY2UgaW4gaGFiaXRhdCBpcyBtb3N0IGxpa2VseSB0aGUgaW5pdGlhbCBiYXJyaWVyLg==[Qq]

[c]IG1lY2hhbmljYWwgaXNvbGF0aW9uLg==[Qq]

[f]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[Qq]

[c]IHRlbXBvcmFsIGlzb2xhdGlvbi4=[Qq]

[f]IE5vLiBUZW1wb3JhbCBpc29sYXRpb24gb2NjdXJzIHdoZW4gc3ViLXBvcHVsYXRpb25zIGJyZWVkIGF0IGRpZmZlcmVudCB0aW1lcy4gVGhpcyBjYW4gYmUgc2Vhc29uYWwgKGZhbGwgdi4gc3ByaW5nKSBvciBldmVuIGFjcm9zcyB0aW1lIG9mIGRheSAoZGF5dGltZSB2LiBuaWdodHRpbWUpLiBUaGVyZSYjODIxNztzIG5vIGV2aWRlbmNlIHRoYXQgYW55IHRlbXBvcmFsIGlzb2xhdGlvbiBpcyBhdCB3b3JrLg==[Qq]

[c]IGJlaGF2aW9yYWwgaXNvbGF0aW9u[Qq]

[f]IE5vIGJlaGF2aW9yYWwgaXNvbGF0aW9uIG9jY3VycyB3aGVuIHN1Yi1wb3B1bGF0aW9ucyBldm9sdmUgY291cnRzaGlwIHJpdHVhbHMgdGhhdCBhcmUgbm8gbG9uZ2VyIHJlY29nbml6ZWQgYnkgYW5vdGhlciBwb3B1bGF0aW9uIGFuZCBkb24mIzgyMTc7dCBsZWFkIHRvIG1hdGluZy4gV2hpbGUgdGhlc2UgZGlmZmVyZW5jZXMgbWlnaHQgdWx0aW1hdGVseSBldm9sdmUgYmV0d2VlbiB0aGUgdHdvIHBvcHVsYXRpb25zLCB0aGVyZSBhcmUgb3RoZXIgYmFycmllcnMgdGhhdCB3b3VsZCBldm9sdmUgZWFybGllci4=

Cg==

[Qq]

[q json=”true” xyz=”2″ multiple_choice=”true” dataset_id=”Unit 7 Cumulative MC Dataset|20ecda52cdeeeb” question_number=”17″ unit=”7.Evolution” topic=”7.10-7.12.Speciation,_Variation,_Extinction”] Entomologists thought that two populations of insects were different species. Recent studies suggest that these populations are the same species. Which of the following observations best indicates that the two populations of insects are the same species?

[c]IFRoZSBwb3B1bGF0aW9ucyBhcmUgcGh5c2ljYWxseSBzaW1pbGFyLg==[Qq]

[f]IE5vLiBQaHlzaWNhbCBzaW1pbGFyaXR5LCBvbiBpdHMgb3duLCBkb2VzbiYjODIxNzt0IGVuc3VyZSB0aGF0IGRpZmZlcmVudCBwb3B1bGF0aW9ucyBhcmUgcGFydCBvZiB0aGUgc2FtZSBzcGVjaWVzLiBUaGluayBhYm91dCB3aGF0IGRlZmluZXMgYSBzcGVjaWVzLCBhbmQgbWFrZSBhIGRpZmZlcmVudCBjaG9pY2UgdGhlIG5leHQgdGltZSB5b3Ugc2VlIHRoaXMgcXVlc3Rpb24u[Qq]

[c]IFRoZSBwb3B1bGF0aW9ucyBvY2N1cHkgdGhlIHNhbWUgaGFiaXRhdC4=[Qq]

[f]IE5vLiBCZWluZyBpbiB0aGUgc2FtZSBoYWJpdGF0IGRvZXNuJiM4MjE3O3QgZW5zdXJlIHRoYXQgZGlmZmVyZW50IHBvcHVsYXRpb25zIGFyZSBwYXJ0IG9mIHRoZSBzYW1lIHNwZWNpZXMuIFRoaW5rIGFib3V0IHdoYXQgZGVmaW5lcyBhIHNwZWNpZXMsIGFuZCBtYWtlIGEgZGlmZmVyZW50IGNob2ljZSB0aGUgbmV4dCB0aW1lIHlvdSBzZWUgdGhpcyBxdWVzdGlvbi4=[Qq]

[c]IFRoZSBwb3B1bGF0aW9ucyBjYW4gaW 50ZXJicmVlZCBpbiB0aGUgd2lsZC4=[Qq]

[f]IEFic29sdXRlbHkuIFRoZSBiaW9sb2dpY2FsIHNwZWNpZXMgY29uY2VwdCBkZWZpbmVzIGEgc3BlY2llcyBhcyBhIHBvcHVsYXRpb24gb2Ygb3JnYW5pc21zIHRoYXQgY2FuIGludGVyYnJlZWQgaW4gdGhlIHdpbGQsIGFuZCB3aGljaCBpcyByZXByb2R1Y3RpdmVseSBpc29sYXRlZCBmcm9tIG90aGVyIHN1Y2ggZ3JvdXBzLg==[Qq]

[c]IFRoZSBwb3B1bGF0aW9ucyBhcmUgc2VwYXJhdGVkIGJ5IGEgZ2VvbG9naWNhbCBiYXJyaWVy[Qq]

[f]IE5vLiBHZW9ncmFwaGljIGJhcnJpZXJzIGNhbiBiZSBhbiBpbXBvcnRhbnQgcGFydCBvZiB0aGUgc3BlY2lhdGlvbiBwcm9jZXNzLCBidXQgc2VwYXJhdGlvbiBieSBhIGdlb2dyYXBoaWMgYmFycmllciB3b3VsZG4mIzgyMTc7dCBlbnN1cmUgdGhhdCBkaWZmZXJlbnQgcG9wdWxhdGlvbnMgYXJlIHBhcnQgb2YgdGhlIHNhbWUgc3BlY2llcy4gVGhpbmsgYWJvdXQgd2hhdCBkZWZpbmVzIGEgc3BlY2llcywgYW5kIG1ha2UgYSBkaWZmZXJlbnQgY2hvaWNlIHRoZSBuZXh0IHRpbWUgeW91IHNlZSB0aGlzIHF1ZXN0aW9uLg==[Qq]

[q json=”true” multiple_choice=”true” unit=”7.Evolution” topic=”7.10-7.12.Speciation,_Variation,_Extinction” dataset_id=”Unit 7 Cumulative Multiple Choice Quiz 2|2137c93d7ccc07″ question_number=”15″] Researchers on Corsica, a large island in the Mediterranean Sea, have proposed that small lizards on that island might be undergoing speciation. Which of the following conditions would be most favorable to speciation?

[c]IE11bHRpcGxlIHBvcHVsYXRpb25zIG9mIGxpemFyZHMgb24gZGlmZmVyZW50IHBhcnRzIG9mIHRoZSBpc2xhbmQgcHJleSBvbiB0aGUgc2FtZSB0eXBlIG9mIGluc2VjdC4=[Qq]

[f]IE5vLiBTcGVjaWF0aW9uIGludm9sdmVzIHRoZSBzdWJkaXZpc2lvbiBvZiBhIHBhcmVudCBwb3B1bGF0aW9uIGluIGEgd2F5IHRoYXQgdWx0aW1hdGVseSBsZWFkcyB0byByZXByb2R1Y3RpdmUgaXNvbGF0aW9uLiBJZiB0aGUgcG9wdWxhdGlvbnMgcHJleSBvbiB0aGUgc2FtZSB0eXBlIG9mIGluc2VjdCwgdGhlcmUmIzgyMTc7cyBubyBkeW5hbWljIGF0IHdvcmsgdGhhdCBsZWFkcyB0byByZXByb2R1Y3RpdmUgaXNvbGF0aW9uLg==

Cg==

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Cg==

[Qq]

[c]IFRoZSBsaXphcmRzIGhhdmUgYSBicmVlZGluZyBjeWNsZSBpbiB3aGljaCBicmVlZGluZyBvY2N1cnMgbW9yZSBkdXJpbmcgdGhlIHJhaW55IHNlYXNvbiB0aGFuIGR1cmluZyB0aGUgZHJ5IHN1bW1lciBtb250aHMu[Qq]

[f]IE5vLiBTcGVjaWF0aW9uIGludm9sdmVzIHRoZSBzdWJkaXZpc2lvbiBvZiBhIHBhcmVudCBwb3B1bGF0aW9uIGluIGEgd2F5IHRoYXQgdWx0aW1hdGVseSBsZWFkcyB0byByZXByb2R1Y3RpdmUgaXNvbGF0aW9uLiBJZiB0aGUgbGl6YXJkIHBvcHVsYXRpb25zIGFsbCBicmVlZCBhdCB0aGUgc2FtZSB0aW1lLCB0aGVyZSYjODIxNztzIG5vIGR5bmFtaWMgYXQgd29yayB0aGF0IGxlYWRzIHRvIHJlcHJvZHVjdGl2ZSBpc29sYXRpb24u

Cg==

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Cg==

[Qq]

[c]IEEgbGF2YSBmbG93IGJldHdlZW4gdGhlIG5vcnRoZXJuIGFuZCBzb3V0aGVybiBwYXJ0cyBvZiB0aGUg aXNsYW5kIGhhcyBjcmVhdGVkIGEgem9uZSB0aGF0IGxpemFyZHMgYXJlIHVuYWJsZSB0byBjcm9zcy4=[Qq]

[f]IFdheSB0byBnby4gVGhlIGxhdmEgZmxvdyB3b3VsZCBzZXQgdGhlIHN0YWdlIGZvciBhbGxvcGF0cmljIHNwZWNpYXRpb24sIHdoaWNoIHJlcXVpcmVzIHNvbWUgdHlwZSBvZiBnZW9ncmFwaGljYWwgYmFycmllci4=

Cg==

[Qq]

[c]IFRoZSBsaXphcmRzIGNhbiBwcm9kdWNlIGJvdGggc2V4dWFsbHkgYW5kIGFzZXh1YWxseSB0aHJvdWdoIHBhcnRoZW5vZ2VuZXNpcy4=[Qq]

[f]IE5vLiBTcGVjaWF0aW9uIGludm9sdmVzIHRoZSBzdWJkaXZpc2lvbiBvZiBhIHBhcmVudCBwb3B1bGF0aW9uIGluIGEgd2F5IHRoYXQgdWx0aW1hdGVseSBsZWFkcyB0byByZXByb2R1Y3RpdmUgaXNvbGF0aW9uLiBOb3RoaW5nIGFib3V0IGEgbWl4IG9mIHNleHVhbCBhbmQgYXNleHVhbCByZXByb2R1Y3Rpb24gd291bGQgc2V0IHVwIGEgZHluYW1pYyB0aGF0IHdvdWxkIGxlYWQgdG8gcmVwcm9kdWN0aXZlIGlzb2xhdGlvbi4=

Cg==

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Cg==

[Qq]

[q json=”true” multiple_choice=”true” unit=”7.Evolution” topic=”7.10-7.12.Speciation,_Variation,_Extinction” dataset_id=”Unit 7 Cumulative Multiple Choice Quiz 2|2137b1f505e407″ question_number=”16″] The soapberry bug (Jadera haematoloma) lives in the southeastern United States. It uses a needle-like beak to pierce the outside skin of the fruit of the soapberry bush, C. corindum. After piercing the skin, the soapberry bug pierces the seed coat of seeds within the fruit. Enzymes liquefy the seeds, and the bugs suck up the liquified seed contents.

In a study in the 1990s, measurements were made of the beak length of soapberry bugs feeding on C. corindum compared to those feeding on the introduced species, K. elegans.

A researcher has noted two things related to soapberry bug breeding.

Soapberry bugs feeding on C. corindum are more likely to breed with one another than with bugs feeding on K. elegans.
Matings between soapberry bugs feeding on C. corindum and those feeding on K. elegans result in hybrid offspring that have a normal lifespan. However, matings between these hybrids result in eggs that successfully hatch less often than matings between males and females adapted to feeding on C. corindum and males and females that are adapted to feeding on K. elegans.

What isolating mechanism is at work?

[c]IE1lY2hhbmljYWwgaXNvbGF0aW9u[Qq]

[f]IE5vLiBNZWNoYW5pY2FsIGlzb2xhdGlvbiBpbnZvbHZlcyBjaGFuZ2VzIHRoYXQgbWFrZSBpdCBpbXBvc3NpYmxlIGZvciBmZXJ0aWxpemF0aW9uIHRvIG9jY3VyLiBJbiBhbmltYWxzLCB0aGlzIGNhbiBpbnZvbHZlIGFuIGluY29tcGF0aWJsZSBmaXQgaW4gdGhlIHN0cnVjdHVyZSBvZiB0aGUgZ2VuaXRhbHMgdGhhdCBwcmV2ZW50cyBzcGVybSBmcm9tIHJlYWNoaW5nIHRoZSBlZ2cuIFNpbmNlIGluZGl2aWR1YWxzIGZyb20gdGhlIHR3byBwb3B1bGF0aW9ucyBjYW4gZm9ybSBoeWJyaWRzLCB0aGV5JiM4MjE3O3JlIGNsZWFybHkgbm90IG1lY2hhbmljYWxseSBpc29sYXRlZC4=[Qq]

[c]IGh5YnJpZCBi cmVha2Rvd24=[Qq]

[f]IE5pY2Ugam9iLiBIeWJyaWQgYnJlYWtkb3duIGlzIHdoZW4gdGhlIEY=_MSA=aHlicmlkcyBhcmUgdmlhYmxlIGFuZCBoZWFsdGh5LCBidXQgdGhlIG5leHQgZ2VuZXJhdGlvbiAodGhlIEY=_Mg==cykgYXJlIHN0ZXJpbGUgb24gdW52aWFibGUu[Qq]

[c]IHByZXp5Z290aWMgaXNvbGF0aW9u[Qq]

[f]IE5vLiBQcmV6eWdvdGljIGJhcnJpZXJzIGFyZSB0aG9zZSB0aGF0IHByZXZlbnQgaW50ZXJicmVlZGluZyBiZXR3ZWVuIG1lbWJlcnMgb2YgZGlmZmVyZW50IHBvcHVsYXRpb25zLiBJZiBwcmV6eWdvdGljIGlzb2xhdGlvbiB3YXMgYXQgd29yaywgdGhlbiBoeWJyaWRzIHdvdWxkIG5ldmVyIGJlIGZvcm1lZCBpbiB0aGUgZmlyc3QgcGxhY2Uu[Qq]

[c]IGdhbWV0aWMgaW5jb21wYXRpYmlsaXR5[Qq]

[f]IE5vLiBJbiBhbmltYWxzLCBnYW1ldGljIGluY29tcGF0aWJpbGl0eSBvY2N1cnMgd2hlbiBhIHNwZXJtIGZyb20gYW4gaW5kaXZpZHVhbCBpbiBvbmUgcG9wdWxhdGlvbiBjYW4mIzgyMTc7dCBmZXJ0aWxpemUgdGhlIGVnZyBmcm9tIGFuIGluZGl2aWR1YWwgaW4gYSBzZWNvbmQgcG9wdWxhdGlvbi4gVGhlc2UgdHdvIHBvcHVsYXRpb25zIGNhbiBwcm9kdWNlIGh5YnJpZCBvZmZzcHJpbmcsIHNvIGdhbWV0aWMgaXNvbGF0aW9uIGNhbiYjODIxNzt0IGJlIGF0IHdvcmsu

Cg==

[Qq]

[q json=”true” xyz=”2″ multiple_choice=”true” dataset_id=”Unit 7 Cumulative Multiple Choice Quiz 2|21379858831807″ question_number=”17″ unit=”7.Evolution” topic=”7.10-7.12.Speciation,_Variation,_Extinction”] The climate in Australia has become more arid in the last million years. This change in climate is causing decreased forest and woodland areas. Scientists collected data on the mitochondrial DNA in distinct species of spiders from various Australian forests. The data suggest that all of these species of spiders evolved from a common ancestor that lived approximately one million years ago. Which of the following evolutionary mechanisms best explains the Australian spider study results?

[c]IGdlbmUgZmxvdw==[Qq]

[f]IE5vLiBHZW5lIGZsb3cgbWVhbnMgYW4gaW5mbHV4IG9mIGdlbmVzIGZyb20gb25lIHBvcHVsYXRpb24gaW50byBhIG5laWdoYm9yaW5nIHBvcHVsYXRpb24uIEl0JiM4MjE3O3Mgbm90IGEgbWVjaGFuaXNtIHRoYXQgd291bGQgbGVhZCB0byB0aGUgZW1lcmdlbmNlIG9mIHNldmVyYWwgZGlzdGluY3Qgc3BlY2llcyBmcm9tIGEgY29tbW9uIGFuY2VzdG9yLg==[Qq]

[c]IFNleHVhbCBzZWxlY3Rpb24u[Qq]

[f]IE5vLiBTZXh1YWwgc2VsZWN0aW9uIGNhbiBsZWFkIHRvIGRpZmZlcmVuY2VzIGJldHdlZW4gbWFsZXMgYW5kIGZlbWFsZXMgd2l0aGluIGEgc3BlY2llcywgYnV0IGl0IHdvdWxkbiYjODIxNzt0IGFjY291bnQgZm9yIHdoYXQmIzgyMTc7cyBkZXNjcmliZWQgYWJvdmUu[Qq]

[c]IGNvbnZlcmdlbnQgZXZvbHV0aW9u[Qq]

[f]IE5vLiBDb252ZXJnZW50IGV2b2x1dGlvbiB3b3VsZCBleHBsYWluIHdoeSBzcGlkZXJzIGluIGRpZmZlcmVudCBwYXJ0cyBvZiBBdXN0cmFsaWEsIG9jY3VweWluZyBzaW1pbGFyIGhhYml0YXRzIGFuZCBuaWNoZXMsIG1pZ2h0IGV2b2x2ZSBzaW1pbGFyIGFwcGVhcmFuY2VzIG9yIGJlaGF2aW9ycy4gQnV0IGl0IHdvdWxkbiYjODIxNzt0IGFjY291bnQgZm9yIHdoYXQmIzgyMTc7cyBkZXNjcmliZWQgYWJvdmUu[Qq]

[c]IGFsbG9wYXRyaWMg c3BlY2lhdGlvbg==[Qq]

[f]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[Qq]

[/qwiz]

What’s Next?

Please proceed to the next tutorial: Extinction