The Origin of Species

Cynotilapia afra, introduced at West Thumbi Island in Lake Malawi in the 1960s, has split into two genetically distinct populations, located at the north and south ends of the island. How can scientists determine whether these populations are now different species, according to the biological species concept? See whether the two populations are morphologically different from each other: coloring, bone structure, and so on. Determine whether captured individuals from the two different populations will mate and produce offspring in a laboratory fish tank. Determine whether individuals from one population will interbreed with individuals from the other population when introduced into each other’s native habitats. Answer: C

Cynotilapia afra, introduced at West Thumbi Island in Lake Malawi in the 1960s, has split into two genetically distinct populations, located at the north and south ends of the island. How can scientists determine whether these populations are now different species, according to the biological species concept? See whether the two populations are morphologically different from each other: coloring, bone structure, and so on. Determine whether captured individuals from the two different populations will mate and produce offspring in a laboratory fish tank. Determine whether individuals from one population will interbreed with individuals from the other population when introduced into each other’s native habitats. Answer: C

Cichlids in Lake Victoria are thought to have diversified from a relatively few species to 600 species in about 12,000 years (the last time the lake dried up). What is the best way to test this hypothesis? Examine the fossil record in lake sediments. Look for morphological characteristics shared among Lake Victoria species that are distinct from the species present in other lakes. Look for genetic characteristics shared among Lake Victoria species that are distinct from species present in other lakes. This is not a testable hypothesis. Answer: C A phylogenetic analysis should provide the most conclusive answer: The Lake Victoria species should form one or a few clades distinct from the clades in other African great lakes. 4

Cichlids in Lake Victoria are thought to have diversified from a relatively few species to 600 species in about 12,000 years (the last time the lake dried up). What is the best way to test this hypothesis? Examine the fossil record in lake sediments. Look for morphological characteristics shared among Lake Victoria species that are distinct from the species present in other lakes. Look for genetic characteristics shared among Lake Victoria species that are distinct from species present in other lakes. This is not a testable hypothesis. 5

In what type of environment is a scientist most likely to find examples of ongoing speciation? areas that have a large range of altitudes, such as mountains and deep valleys areas such as large plains that facilitate migration of animals extreme physical environments that are marginal for supporting life areas that are already species-rich areas that have undergone recent environmental disturbance or change Answer: E 6

In what type of environment is a scientist most likely to find examples of ongoing speciation? areas that have a large range of altitudes, such as mountains and deep valleys areas such as large plains that facilitate migration of animals extreme physical environments that are marginal for supporting life areas that are already species-rich areas that have undergone recent environmental disturbance or change 7

Sea urchins are broadcast spawners: They release their gametes into the water without courtship. Which of these reproductive isolation mechanisms is most likely affecting sea urchins? behavioral isolation or mechanical isolation gametic isolation or temporal isolation habitat isolation Answer: B 8

Sea urchins are broadcast spawners: They release their gametes into the water without courtship. Which of these reproductive isolation mechanisms is most likely affecting sea urchins? behavioral isolation or mechanical isolation gametic isolation or temporal isolation habitat isolation 9

You spot a sea snake while you are in a boat on the ocean and remark about how similar it looks to a snake that lives in central Illinois. However, you know that they are most likely separate species due to which of the following reproductive barriers? behavioral isolation gametic isolation ecological/habitat isolation temporal isolation Answer: C Snakes living in the ocean are most likely never going to come into contact with snakes living in the center of a continent. 10

You spot a sea snake while you are in a boat on the ocean and remark about how similar it looks to a snake that lives in central Illinois. However, you know that they are most likely separate species due to which of the following reproductive barriers? behavioral isolation gametic isolation ecological/habitat isolation temporal isolation 11

The century cactus flowers every 100 years The century cactus flowers every 100 years. A similar cactus flowers every 50 years. If the 50-year cactus pollen has the correct characteristics to fertilize the century cactus, which reproductive barrier will most likely be working against that possibility? behavioral isolation gametic isolation ecological/habitat isolation temporal isolation Answer: D They produce flowers on different schedules. 12

The century cactus flowers every 100 years The century cactus flowers every 100 years. A similar cactus flowers every 50 years. If the 50-year cactus pollen has the correct characteristics to fertilize the century cactus, which reproductive barrier will most likely be working against that possibility? behavioral isolation gametic isolation ecological/habitat isolation temporal isolation 13

Several species of amphibians are able to read each other’s mating rituals and understand them, tend to be fertile at the same time, and are usually similar in size. However, when they attempt to mate, they never produce offspring. Which of the following barriers is most likely the cause of this? behavioral isolation gametic isolation reduced hybrid fertility hybrid breakdown Answer: B If they fail to create any offspring, gametic isolation would be the most likely cause. Options C and D are not correct because they refer to offspring that two separate species create. Option A is not correct because it was stated in the question that the mating rituals were working. 14

Several species of amphibians are able to read each other’s mating rituals and understand them, tend to be fertile at the same time, and are usually similar in size. However, when they attempt to mate, they never produce offspring. Which of the following barriers is most likely the cause of this? behavioral isolation gametic isolation reduced hybrid fertility hybrid breakdown 15

The fossil record shows that species remain constant for long periods of time, but then speciation episodes occur rapidly. This is indicative of gradualism. punctuated equilibrium. allopatric speciation. sympatric speciation. Answer: B Punctuated equilibrium suggests that once the process of speciation begins, it can be completed relatively rapidly. 16

The fossil record shows that species remain constant for long periods of time, but then speciation episodes occur rapidly. This is indicative of gradualism. punctuated equilibrium. allopatric speciation. sympatric speciation. 17

When differentiating between two species of fish, you notice that one species stay near the surface and feed on floating algae, while the other species are bottom feeders. This is using the morphological species concept. ecological species concept. phylogenetic species concept. Answer: B This is viewing species based on their ecological niche. 18

When differentiating between two species of fish, you notice that one species stay near the surface and feed on floating algae, while the other species are bottom feeders. This is using the morphological species concept. ecological species concept. phylogenetic species concept. 19

Which of the following is believed to be the primary reproductive isolation mechanism for causing sympatric speciation in North American apple maggot flies (Rhagoletis pomonella)? polyploidy sexual selection phylogenetic species concept habitat differentiation Answer: D 20

Which of the following is believed to be the primary reproductive isolation mechanism for causing sympatric speciation in North American apple maggot flies (Rhagoletis pomonella)? polyploidy sexual selection phylogenetic species concept habitat differentiation Answer: D 21

Scientific Skills Exercises Researchers studied populations of the dusky salamander (Desmognathus ochrophaeus) living on different mountain ranges in the southern Appalachian Mountains. The researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. Four mating combinations were tested for each pair of populations (A and B)—two within the same population (female A with male A and female B with male B) and two between populations (female A with male B and female B with male A).

The proportion of successful matings for each mating combination was measured. For example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. Then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). The reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (AA + BB) minus the sum of the proportion of successful matings of each type between populations (AB + BA).

What hypothesis did the researchers test in this study? Dusky salamanders are undergoing sympatric speciation. Dusky salamanders are in the process of speciation. Reproductive isolation increases with geographic distance between dusky salamander populations. Answer: C

What hypothesis did the researchers test in this study? Dusky salamanders are undergoing sympatric speciation. Dusky salamanders are in the process of speciation. Reproductive isolation increases with geographic distance between dusky salamander populations.

Identify the independent variable in this study. the reproductive isolation values for pairs of dusky salamander populations the geographic distance between dusky salamander populations the mountain ranges that dusky salamander populations live in the presence of sperm in cloacas of female dusky salamanders Answer: B

Identify the independent variable in this study. the reproductive isolation values for pairs of dusky salamander populations the geographic distance between dusky salamander populations the mountain ranges that dusky salamander populations live in the presence of sperm in cloacas of female dusky salamanders

Identify the dependent variable in this study. the courtship behaviors of dusky salamander populations the geographic distance between dusky salamander populations the presence of sperm in cloacas of female dusky salamanders the reproductive isolation values for pairs of dusky salamander populations Answer: D

Identify the dependent variable in this study. the courtship behaviors of dusky salamander populations the geographic distance between dusky salamander populations the presence of sperm in cloacas of female dusky salamanders the reproductive isolation values for pairs of dusky salamander populations

Why did the researchers set up four possible matings for each pair of populations: female A + male A; female B + male B; female A + male B; female B + male A? to assess whether males or females determine mating success to compare the proportion of successful matings within populations to the proportion of successful matings between populations to assess whether populations A and B are separate species to identify the behavioral or morphological features that contribute to reproductive isolation Answer: B

Why did the researchers set up four possible matings for each pair of populations: female A + male A; female B + male B; female A + male B; female B + male A? to assess whether males or females determine mating success to compare the proportion of successful matings within populations to the proportion of successful matings between populations to assess whether populations A and B are separate species to identify the behavioral or morphological features that contribute to reproductive isolation

The researchers set up 30 trials for each type of mating between every pair of populations: 30 trials of female A with male A, 30 trials of female B with male B, 30 trials of female A with male B, and 30 trials of female B with male A. Why did the researchers set up 30 trials for each type of mating? to control variables to provide replication to avoid experimenter bias to provide a control group Answer: B

The researchers set up 30 trials for each type of mating between every pair of populations: 30 trials of female A with male A, 30 trials of female B with male B, 30 trials of female A with male B, and 30 trials of female B with male A. Why did the researchers set up 30 trials for each type of mating? to control variables to provide replication to avoid experimenter bias to provide a control group Answer: B

Calculate the value of the reproductive isolation index if all of the matings within a population were successful but none of the matings between populations were successful. 1.0 1.5 2.0 Answer: D

Calculate the value of the reproductive isolation index if all of the matings within a population were successful but none of the matings between populations were successful. 1.0 1.5 2.0

Calculate the value of the reproductive isolation index if salamanders were equally successful in mating with members of their own population and members of another population. 1.0 1.5 2.0 Answer: A

Calculate the value of the reproductive isolation index if salamanders were equally successful in mating with members of their own population and members of another population. 1.0 1.5 2.0

Review the scatter plot of reproductive isolation value versus geographic distance for 27 pairs of dusky salamander populations. How do reproductive isolation values change with geographic distance among pairs of dusky salamander populations? Reproductive isolation values decrease with geographic distance. Reproductive isolation values increase with geographic distance. Reproductive isolation values do not change with geographic distance. Answer: B Looking at this scatterplot, remember that “Geographic distance” is the independent variable of this study and the dependent variable is “Degree of reproductive isolation.” By convention, the independent variable is the x-axis while the dependent variable is the y-axis. 

Review the scatter plot of reproductive isolation value versus geographic distance for 27 pairs of dusky salamander populations. How do reproductive isolation values change with geographic distance among pairs of dusky salamander populations? Reproductive isolation values decrease with geographic distance. Reproductive isolation values increase with geographic distance. Reproductive isolation values do not change with geographic distance. Answer: B Looking at this scatterplot, remember that “Geographic distance” is the independent variable of this study and the dependent variable is “Degree of reproductive isolation.” By convention, the independent variable is the x-axis while the dependent variable is the y-axis. 

What does the scatter plot suggest about the process of allopatric speciation? Geographically isolated populations represent separate species. Reproductive isolation is more likely to occur as populations become separated by greater distances. Reproductive isolation of populations leads to geographic isolation. Geographically isolated populations are also reproductively isolated. Answer: B

What does the scatter plot suggest about the process of allopatric speciation? Geographically isolated populations represent separate species. Reproductive isolation is more likely to occur as populations become separated by greater distances. Reproductive isolation of populations leads to geographic isolation. Geographically isolated populations are also reproductively isolated.

Which hypothesis suggests a possible cause of the relationship shown in the scatter plot? Geographically separated populations of dusky salamanders gradually diverge, and the divergence increases with geographic distance. Small populations of dusky salamanders gradually diverge due to genetic drift. Sympatric populations of dusky salamanders gradually diverge because they exploit different food sources. The founder effect results in divergence between geographically separated populations of dusky salamanders. Answer: A

Which hypothesis suggests a possible cause of the relationship shown in the scatter plot? Geographically separated populations of dusky salamanders gradually diverge, and the divergence increases with geographic distance. Small populations of dusky salamanders gradually diverge due to genetic drift. Sympatric populations of dusky salamanders gradually diverge because they exploit different food sources. The founder effect results in divergence between geographically separated populations of dusky salamanders.