chapter 17 opener. figure 24.5 a summary of reproductive barriers between closely related species

Chapter 17 Opener

Figure 24.5 A summary of reproductive barriers between closely related species

Figure 24.6 Two modes of speciation

Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon

Figure 24.8 Has speciation occurred during geographic isolation?

Figure 24.9 Ensatina eschscholtzii, a ring species

Figure 17.1 Members of the Same Species Look Alike—or Not

Figure 17.1 Members of the Same Species Look Alike—or Not (Part 1)

Figure 17.1 Members of the Same Species Look Alike—or Not (Part 2)

Figure 17.2 Cryptic Species Look Alike but Do Not Interbreed

Figure 17.2 Cryptic Species Look Alike but Do Not Interbreed (Part 1)

Figure 17.2 Cryptic Species Look Alike but Do Not Interbreed (Part 2)

Concept 17.1 Species Are Reproductively Isolated Lineages on the Tree of Life

A ring species the name given to a ring of populations that encircles an area of unsuitable habitat. Ring species provide a unique glimpse into one way in which new species arise.

Ring species acquire new traits as the distance from their ancestral home increases; when the “head” of the ring meets the “tail,” they have become two distinct species. A ring species is therefore a ring of populations in which there is only one place where two distinct species meet.

At one location within the ring, two distinct forms coexist but do not interbreed. Around the rest of the ring, the traits of one species change gradually through intermediate populations, eventually changing so much that it they are considered a separate (second) species.

Ring species allow us to examine variation in space and use it to infer how changes occurred over time.

Concept 17.1 Species Are Reproductively Isolated Lineages on the Tree of Life

One example of a ring species is the Greenish warbler (Phylloscopus trochiloides), a bird native to parts of Asia and eastern Europe.

These songbirds breed in the forests of central and northern Asia and eastern Europe. In the center of Asia, the large region of desert, including the Tibetan Plateau and the Taklamakan and Gobi Deserts, are inhospitable habitats for these birds. As a result, their distribution follows a ring of mountains that surrounds the desert, including the forests of Siberia to the north.

Greenish warblers have remarkable geographic variation in plumage patterns, songs, and genetics. Male warbler song is crucial to their successful reproduction. In birds, males usually react aggressively to other males singing the same type of song, since these are potential competitors for female mates.

Concept 17.1 Species Are Reproductively Isolated Lineages on the Tree of Life

The geographical variation in songs of greenish warblers provides a rare illustration of gradual change in a trait.

To the right are examples of song spectrograms (a pictorial representation of their song pattern) from 12 populations of greenish warblers. Spectrograms are arranged in geographic order according to the ring species configuration, starting in western Siberia and moving south, then east, then north around the ring.

Note the gradual change in song length and syntax (wave shape) around the ring.

Concept 17.2 Speciation Is a Natural Consequence of Population Subdivision

Referring to the figure, if female warblers from populations JL do not recognize the songs of males in population XN, they are unable to pair with them.

This is an example of the evolution of reproductive isolation.

a. True

b. False

c. I don’t understand this question.

Concept 17.2 Speciation Is a Natural Consequence of Population Subdivision

When the female warblers from population JL do not recognize the songs of males in population XN, and therefore do not mate with them, what processes could have occurred?

Discuss.

Concept 17.2 Speciation Is a Natural Consequence of Population Subdivision

When the female warblers from population JL do not recognize the songs of males in population XN, and therefore do not mate with them, what processes could have occurred?

a. Speciation

b. Reproductive isolation

c. Evolution

d. All of the above

e. None of the above

Concept 17.1 Species Are Reproductively Isolated Lineages on the Tree of Life, and 17.2 Speciation Is a Natural Consequence of

Population Subdivision

Figure 17.3 The Dobzhansky–Muller Model

Figure 17.3 The Dobzhansky–Muller Model

Figure 17.4 Speciation by Centric Fusion

Figure 17.4 Speciation by Centric Fusion

Figure 17.4 Speciation by Centric Fusion (Part 1)

Figure 17.4 Speciation by Centric Fusion (Part 2)

Figure 17.5 Reproductive Isolation Increases with Genetic Divergence

Figure 17.5 Reproductive Isolation Increases with Genetic Divergence

Figure 17.6 Allopatric Speciation

Figure 17.6 Allopatric Speciation

Figure 17.6 Allopatric Speciation (Part 1)

Figure 17.6 Allopatric Speciation (Part 2)

Concept 17.1 Species Are Reproductively Isolated Lineages on the Tree of Life, and Speciation Is a Natural Consequence of Population

Subdivision

Concept 17.3 Speciation May Occur through Geographic Isolation or in Sympatry

Refer to the case study just discussed about Greenish warblers.

Does this example of ring speciation represent allopatric or sympatric speciation?

Concept 17.3 Speciation May Occur through Geographic Isolation or in Sympatry

The ring speciation of Greenish warblers is a variation of allopatric speciation (requiring geographic isolation).

a. True

b. False

c. I don’t know.

Apply the concept page 338• Speciation may occur through geographic isolation

• The different species of Darwin’s finches shown in the phylogeny in figure 17.7 have all evolved on islands of the Galapagos archipelago within the past 3 million years. Molecular clock analysis has been used to determine the dates of the various speciation events in that phylogeny. Geological techniques for dating rock sample have been used to determine the ages of the various Galapagos islands. The table show the number of species of Darwin’s finches and the number of islands that have existed in the archipelago at several times during the past 4 million years.

1. Plot the number of species of Darwin’s finches and the number of islands in the Galapagos archipelago (dependent variables) as a function of time (independent variable).

2. Are the data consistent with the hypothesis that isolation of populations on newly formed islands is related to speciation in this group of birds? Why or why not?

3. If no more islands form in the Galapagos archipelago, do you think that speciation by geographic isolation will continue to occur among Darwin’s finches? Why or why not? What additional data could you collect to test your hypothesis (without waiting to see if speciation occurs)?

Apply the Concept, Ch. 17, p. 338

Figure 17.7 Allopatric Speciation among Darwin’s Finches

Figure 17.7 Allopatric Speciation among Darwin’s Finches

Figure 17.8 Mechanical Isolation through Mimicry

Figure 17.9 Temporal Isolation of Breeding Seasons

Figure 17.9 Temporal Isolation of Breeding Seasons (Part 1)

Figure 17.9 Temporal Isolation of Breeding Seasons (Part 2)

Figure 17.10 Behavioral Isolation in Mating Calls

Figure 17.10 Behavioral Isolation in Mating Calls

Figure 17.11 Floral Morphology Is Associated with Pollinator Morphology

Figure 17.11 Floral Morphology Is Associated with Pollinator Morphology (Part 1)

Figure 17.11 Floral Morphology Is Associated with Pollinator Morphology (Part 2)

Figure 17.11 Floral Morphology Is Associated with Pollinator Morphology (Part 3)

Figure 17.11 Floral Morphology Is Associated with Pollinator Morphology (Part 4)

Figure 17.12 Flower Color and Reproductive Isolation

Figure 17.12 Flower Color and Reproductive Isolation (Part 1)

Figure 17.12 Flower Color and Reproductive Isolation (Part 2)

Apply the concept page 344• Reproductive isolation is reinforced when diverging species come

into contact

• As shown in Fig. 17.9, the leopard frogs Rana berlandieri and R. sphenocephala usually have non-overlapping breeding seasons in areas of sympatry, but where the species are allopatric, both species breed in both spring and fall. But when new ponds are created where the ranges of the two species come together, frogs from previously allopatric populations may colonize the new ponds and hybridize during their overlapping breeding seasons. Imagine you have collected data on hybridization between these two frog species. You have sampled various life stages of frogs and their tadpoles for two years after an initial spring breeding season at a newly established pond.

1. Create four pie charts (one for each life stage) showing the percentage of each species and the percentage of hybrids at each stage.

2. What are some possible reasons for the differences in the percentage of hybrids found at each life stage? Suggest some postzygotic isolating mechanisms that are consistent with your data.

3. Over time, what changes might you expect in the breeding seasons of the two species at this particular pond, and why? How would future pie charts change if your predictions about breeding seasons are correct?

Apply the Concept, Ch. 17, p. 344

Figure 17.13 A Hybrid Zone

Concept 17.4 Reproductive Isolation Is Reinforced When Diverging Species Come into Contact

If lack of recognition of male song by the female Greenish warblers is the main mode by which reproductive isolation occurs, is this an example of a prezygotic or postzygotic isolating mechanism?

Concept 17.4 Reproductive Isolation Is Reinforced When Diverging Species Come into Contact

If lack of recognition of male song by the female Greenish warblers is the main mode by which reproductive isolation occurs, this is an example of a postzygotic isolating mechanism.

a. True

b. False

c. I don’t know.

Concept 17.4 Reproductive Isolation Is Reinforced When Diverging Species Come into Contact

If lack of recognition of male song by the female Greenish warblers is the main mode by which reproductive isolation occurs, this is an example of what type of prezygotic isolating mechanism?

a. Mechanical

b. Temporal

c. Behavioral

d. Habitat isolation

e. Gametic isolation

Figure 17.14 Evolution in the Laboratory