Analyzing the Biological Species Concept Practice | Biology Practice Problems

Use this material to answer questions #1 through #5

The biological species concept defines a species as a population whose members can interbreed to produce viable, fertile offspring that are reproductively isolated from others. There are several ways species are isolated reproductively, both before zygote formation and after.

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Word count: 49

Musa acuminata and Musa balbisiana herbs hybridize to form Cavendish bananas, which are common table bananas. Cavendish bananas cannot reproduce genetically unique banana plants because Cavendish banana seeds are infertile. However, they can clone themselves. Cavendish bananas reproduce by root sprouts that eventually grow large enough to survive independently. Describe the characteristics of the Cavendish banana that fit the biological species concept (BSC).

Answers:

The Cavendish banana is viable but not fertile, so it is not its own species according to the BSC.
The Cavendish banana can cross-breed with a parent plant to create a new hybrid, so it must be its own species according to the BSC.
The Cavendish banana is viable and can reproduce asexually, so it is its own species.
The Cavendish banana is so popular it has been given species status.

Abalone gastropods use broadcast spawning as a means of reproduction. Eggs and sperm are released in open water. The abalone sperm carries a protein called lysin that dissolves a hole in the envelope of the egg so sperm can pass through, but only if the sperm and egg are of the same species. Predict the impact this has on the Abalone's ability to hybridize with other gastropods.

Answers:

The Abalone genetic material will be able to pass into other species by dissolving the egg's envelope.
The Abalone will only reproduce asexually.
The Abalone are infertile.
The Abalone genetic material will select same-species gametes.

Female Pacific oysters can produce between 50-200 million eggs when spawning. The eggs are released in open water, where fertilization occurs. Explain how the Pacific oyster's genetic information flows into the next generation.

Answers:

Oysters reproduce asexually, so all the offspring will be clones.
The egg and sperm genetic information flows readily into different species.
The egg will develop into a female Pacific oyster and the sperm will develop into a male Pacific oyster.
The egg and sperm are biochemically selective to react to each other to form a Pacific oyster zygote.

Hybrid sterility is a common reproductive barrier, though often only one sex is sterile. This observation lead to Haldane's Rule, which states that the inviable/sterile sex is usually the heterogametic sex. In mammals, that would be the XY sex. There can be varying degrees of viability and fertility among the homogametic, which is the XX sex in mammals. Describe how this serves as a reproductive barrier according to the biological species concept (BSC).

Answers:

Genetic information from the hybrid may flow into a parent species, so the homogametic hybrid is its own species.
The heterogametic sex can reproduce asexually, so the hybrids are a new species.
If the chromosomes are unique enough, the hybrids will be their own species.
To meet the BSC, the population as a whole must be viable and fertile, including both sexes.

Oak trees (Quercus) hybridize easily. A common hybrid is Q. xbinundorum (Q. robar x Q. alba). The "x" refers to the fact it is a hybrid. Q. xbinundorum is called "Two Worlds Oak" because it is hybridized from an old-world oak and new-world oak. Q. xbinundorum often can't reproduce, but when it does, the progeny looks like Q. robar or Q. alba. Describe why Two Worlds Oak does not meet the biological species concept (BSC).

Answers:

Two Worlds Oak can't reproduce new Two Worlds Oaks.
Two Worlds Oak is a tree, which falls outside the BSC.
Two Worlds Oak is viable and fertile, so it should be its own species.
Two Worlds Oak only reproduces clones, so it can't be its own species.

Use this material to answer questions #6 through #10

Ensatina salamanders live in California's Sierra Nevada and along the coastal range. Seven populations are identified on the map, each with strikingly different coloration. The salamander populations form a ring around Central Valley.

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Word count: 43

Salamander population A hybridizes with populations B and C. The hybrid populations are viable and fertile with their own unique markings. Identify the characteristics of the hybrid offspring that determine whether or not salamander populations A and B are the same species according to the biological species concept.

Answers:

The hybrid offspring are viable and fertile, so populations A and B are the same species.
The hybrid offspring have unique markings, so populations A and B are different species.
The hybrid offspring are viable, but can only reproduce clones, so populations A and B are not the same species.
The hybrid offspring may have better camouflage abilities, so they are all different species.

Salamander populations B and D successfully create hybrid offspring, as well as C and E. Both hybrid populations are frail and fail to develop to maturity. Using the biological species concept, predict whether populations B and D are the same species.

Answers:

No, they cannot produce viable and fertile offspring, so they are different species.
No, the hybrid offspring can only reproduce asexually, so they are different species.
Yes, the hybrid offspring are viable, so they are the same species.
Yes, they can produce fertile offspring with shorter lifespans, so they are the same species.

Salamander populations D and E do not hybridize. Mitochondrial DNA samples indicate that populations B, C, D and E are related to population A. Researchers suggest the salamanders in population A originated up north and traveled south, going around the Central Valley on either side. Explain why the salamander populations interbreed to form hybrids north of the valley but not south.

Answers:

Salamander juveniles look differently than adults, so they are really all the same species.
The southern salamanders are all infertile due to pollution south of the Central Valley.
The salamanders became increasingly genetically different from each other as they traveled south around the valley until the two populations were no longer genetically compatible.
Over the generations, the salamander populations inbred to the point the offspring were no longer viable.

The image shows the greenish warbler bird's migration. As the population spread north around the Himalayas, the two groups became increasingly genetically different. Applying the BSC, predict whether the descendants will be able to interbreed when the two populations meet.

Answers:

The two populations have different chromosome counts, so they are different species.
The descendants are all the same species, so they should be able to interbreed.
The two populations may not be able to interbreed.
The descendants are not viable, so they cannot interbreed.

10.

Dog breeders choose dogs with specific qualities for breeding. Though dogs are one species with great variability, there are limits to dog breeding. For example, Saint Bernards are held to be a large breed. Chihuahuas are held to be the smallest. They cannot interbreed. Explain why this individual example cannot be applied to the biological species concept.

Answers:

They are the same species, but the mechanics of mating and birth would make reproduction unlikely.
They are not genetically similar enough to form a zygote.
Chihuahuas are infertile hybrids.
Saint Bernards only reproduce with Saint Bernards because they are the same species.

Use this material to answer questions #11 through #15

Physical isolation of one population can lead to changes that result in reproductive barriers between the populations when their habitats overlap again, as shown in the image. Sometimes these barriers are due to behavioral changes or preference.

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Word count: 47

11.

Towhees (Pililo erythrophthalmus and Pipilo ocai) interbreed to form hybrids in some places where their habitats overlap, but in other places they act like two different species and no hybrid towhees can be found. Propose a hypothesis that explains this phenomenon.

Answers:

The towhees that interbreed are more genetically similar than the towhees that cannot interbreed.
The hybrid towhees are mistaken variations of the two species.
The towhees that don't interbreed were only studied outside of mating season.
The towhees that don't interbreed have better mating options.

12.

Borneon elephants are native to the island of Borneo. They are also called pygmy elephants because of their smaller size. They are most genetically similar to the Asian elephant. Borneo and Asian elephants may be able to interbreed to produce viable, fertile offspring, but due to their endangered status and the fact their habitats do not overlap, it's difficult to prove. Describe the relationship between the Borneo and Asian elephants applying the BSC.

Answers:

The Borneon elephant is smaller than the Asian elephant, so they are different species.
Though they may produce viable and fertile offspring in captivity, it is likely the populations will become increasingly genetically different over time.
The Borneon elephant is just a younger Asian elephant, so they are the same species.
The Borneon elephant is most genetically similar to the Asian elephant, so they are the same species.

13.

A fertile hybrid population that does not grow to maturity cannot pass genetic information on to another generation. Some hybrids may reproduce in captivity, but the offspring are not as viable compared to their parent species. Describe why a frail hybrid population does not meet the biological species concept.

Answers:

If the hybrid can reproduce asexually it cannot be its own species.
Viability is not that important, so hybrids that reproduce are a new species.
A frail population can't compete and thrive independently.
Frail offspring may have other strengths that make them dangerous.

14.

Sheep cannot produce offspring with goats, but the union may result in a zygote that fails to survive birth. Predict why sheep and goats cannot have healthy offspring together.

Answers:

They are genetically similar, but the offspring is a clone. They are different species.
They are not genetically similar. No zygote forms, so they are different species.
They are genetically similar, but not enough to produce viable, fertile offspring. They are different species.
They are genetically similar, but the offspring was diseased. They are the same species.

15.

Many flowers reproduce by cross-pollinating, as well as self-fertilizing. Pollinators, like bees and hummingbirds, are often responsible for these cross-pollinating events, and many prefer the nectar of only one kind of flower. This creates additional barriers to reproduction between species. Describe how pollinator preferences may limit the chances a flower has to hybridize.

Answers:

The flowers that attract many different kinds of pollinators are more likely to hybridize.
The pollinators that only pollinate one type of flower don't want it to change.
The flower will stop producing pollen and become extinct.
The flower will change its scent to attract a new pollinator and become a hybrid.

Use this material to answer questions #16 through #20

Below is a graph showing the population of coywolves in an area over time. Coywolves are a hybrid between coyotes and wolves. Wolves and coyotes don't normally hybridize, however, due to habitat loss, previously separate populations have been forced together in close quarters.

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Word count: 53

16.

Describe the trend shown in the graph.

Answers:

The population of coywolves steadily declines.
The population of coywolves increases exponentially and then continues to grow but at a slower rate.
The population of coywolves decreases exponentially and then continues to decrease but at a slower rate.
The population of coywolves steadily increases.

17.

These coywolf hybrid are fertile and can produce fertile offspring. Explain what this implies in the context of the biological species concept.

Answers:

According to the concept of biological species, this implies that wolves and coyotes are genetically similar enough to produce offspring, but not enough to be the same species.
According to the concept of biological species, this implies that wolves and coyotes are different species.
According to the concept of biological species, this implies that wolves and coyotes are the same species as each other.
This does not imply anything in the context of the concept of biological species.

18.

If wolves and coyotes are continued to live close together and continue to hybridize, predict the most likely result.

Answers:

They will continue to hybridize and produce coywolves and eventually the coywolf population will come to dominate the wolf and coyote populations.
Nothing will happen. The populations will maintain themselves with a small number of coywolves.
It is impossible to predict what may happen in this situation. There is too much left to chance.
They will go extinct because they are in a small space with each other.

19.

If the new population of coywolves is subsequently genetically isolated from other members of the canis genus, predict the most likely result.

Answers:

It is impossible to predict what will happen in this scenario.
Nothing special will happen, they will still be coywolves.
Eventually they will become so genetically distinct as to develop into their own separate species.
They will slowly become infertile due to inbreeding.

20.

Since coyotes and wolves are currently classified as different species, explain what their ability to produce fertile offspring implies about their evolutionary history.

Answers:

Coyotes and wolves are still extremely closely related and only very recently began to split off from each other.
This does not imply anything about their evolutionary history.
It is impossible to say what this implies about their evolutionary history.
Coyotes and wolves are not related at all and have been separated from each other for a very long time.

Use this material to answer questions #21 through #25

Below is a picture of two different breeds of dog. One of these breeds is quite small and the other is quite large.

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Word count: 33

21.

Currently these two animals are both classified as the same species. Describe what impediments, if any, exist to mating between these dog breeds.

Answers:

The color difference may prevent mating unless there is human intervention.
It is impossible to determine if there are any impediments to mating.
The size difference may prevent mating unless there is human intervention.
No impediments to mating exist between these dog breeds.

22.

Say these two animals are mated and they produce fertile offspring. Explain what this implies under the concept of biological species.

Answers:

It is impossible to say what this implies under the concept of biological species.
These two animals belong to the same species.
This implies nothing under the concept of biological species.
These two animals belong to a different species.

23.

If these two dog breeds were to be separated for a very long period of time, predict the most likely outcome.

Answers:

They may genetically converge and be no longer able to produce fertile offspring, thus creating two new species.
They may genetically diverge and be able to produce fertile offspring, thus creating two new species.
They may genetically diverge and be no longer able to produce fertile offspring, thus creating two new species.
Nothing will happen. They will remain unchanged throughout that time.

24.

Let's say that groups of these dogs are placed in a habitat together. Despite being able to produce fertile offspring via artificial insemination, it is observed that when left to their own devices these two dog breeds do not successfully mate or produce offspring. Justify the claim then that these two dog breeds are different species.

Answers:

This claim cannot be justified based on the information above because appearance is not what determines what a biological species is.
Because these dog breeds cannot organically mate and are likely experiencing some form of prezygotic barrier like mechanical isolation from each other, this would indicate that they belong to separate species.
Because these dog breeds can organically mate and are likely experiencing some form of prezygotic barrier like mechanical isolation from each other, this would indicate that they belong to separate species.
Because these dog breeds cannot organically mate and are likely experiencing some form of prezygotic barrier like mechanical isolation from each other, this would indicate that they belong to the same species.

25.

Explain why it is important to the concept of biological species that these two animals must be able to organically produce fertile offspring to be considered the same species.

Answers:

It is important because species in this context is defined as the ability to breed and produce fertile offspring. If that can't happen for any reason when groups of organisms are left to their own devices, this would imply they are not the same species.
There is no reason why this would be important because we have technology that can overcome mechanical, temporal, or geographical barriers and prove if animals are genetically compatible with each other despite these things.
It is important because species in this context is defined as the ability to breed and produce fertile offspring. If that can't happen for any reason when groups of organisms are left to their own devices, this would imply they are the same species.
It is important because species in this context is defined as the ability to breed and produce fertile offspring. If that can happen for any reason when groups of organisms are left to their own devices, this would imply they are not the same species.

Use this material to answer questions #26 through #30

Below is a picture of what is known as a "zorse" or a hybrid between a male zebra and female horse. This hybrid is infertile.

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Word count: 36

26.

Explain what being able to produce a living, infertile hybrid implies about the evolutionary history of the horse and the zebra.

Answers:

This implies nothing about the evolutionary history of the horse and the zebra since they live on different continents.
It is impossible to determine what this implies about the evolutionary history of the horse and zebra since there are too many variables.
They are closely related enough to be able to produce a viable hybrid, but not closely related enough to be considered the same species.
They are closely related enough to be able to produce a viable hybrid, but not closely related enough to be considered a different species.

27.

Identify the most likely reason why the zorse is sterile.

Answers:

It is unhealthy as all hybrids are.
Morphological incompatibilities.
Chromosomal incompatibilities.
It inherited a genetic mutation.

28.

Identify the most likely reason why the horse and zebra developed into different biological species.

Answers:

Temporal and habitat isolation.
Gametic isolation.
Mechanical isolation.
Behavioral isolation.

29.

Say that horses and zebras continue to be separated for many thousands of years and do not continue to hybridize. Estimate the likelihood that after this isolation they will still be able to produce a living hybrid.

Answers:

The longer they are separated and do not hybridize, the more likely it becomes that they will genetically drift too far apart to create a living hybrid.
They will always be able to produce a hybrid since they can produce a hybrid right now.
The longer they are separated and do not hybridize, the less likely it becomes that they will genetically drift too far apart to create a living hybrid.
It is impossible to say whether or not they will be able to hybridize after being separated for a long period of time.

30.

Describe the relationship between hybridization and species in this case.

Answers:

In this case, despite the fact that the horse and zebra are able to hybridize, they are the same species because the hybrid is sterile.
In this case, despite the fact that the horse and zebra are able to hybridize, they are different species because the hybrid is fertile.
In this case, despite the fact that the horse and zebra are able to hybridize, they are different species because the hybrid is sterile.
In this case, despite the fact that the horse and zebra are able to hybridize, they are the same species because the hybrid is fertile.