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Which of the following is not a geographic barrier to speciation?
Plant polyploidy—the presence of more than one genotype—is not a geographic barrier. Plant polyploidy helps enable speciation.
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Two populations of the same species over time grow distant from one another. At what point will these two populations be considered different species?
Speciation is the event that occurs when two populations of a particular species can no longer interbreed. Speciation is not defined by physical barriers or by the time that two populations are separate from one another. In fact, two populations of the same species can be apart any distance or time, and if they can still interbreed they are considered the same species even if they look completely different.
Note that carrying capacity refers to the maximum number of individuals in a population that the natural resources of the surrounding environment can support. It is, essentially, the maximum healthy population size, and is not a measure of distance as implied in the answer choice.
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A horse and a donkey can successfully mate to produce an offspring known as a mule. Mules are sterile, display a mixture of donkey and horse traits, and have a different number of chromosomes from both parent species. Would mules be classified as their own species?
Classifying species can be a difficult and particularly gray area. The key to this question, however, is that mules are sterile. This is an example of post-zygotic reproductive isolation. Hybrids that are sterile are not considered unique species.
Simply identifying traits or chromosome number is not enough to determine species. The defining factor of speciation is that the organism can no longer reproduce with the parent species, but can reproduce with other individuals of the species. Note that all breeds of dog still fall in the same species, despite the variety of different traits displayed across breeds, because they can produce offspring. Chromosome number also cannot solely determine species. Some genetic disorders result in aneuploidy in humans, in which individuals have too many or too few chromosomes.
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A researcher has discovered two species of frogs that live in the same location. In the lab he is able to generate a viable hybrid by combining gametes from each species, however, no such hybrids exist in the wild. Which of the following methods of reproductive isolation might explain this phenomenon?
Out of the choices, only temporal isolation can explain this phenomenon. Temporal isolation describes a type of reproductive isolation that comes about because the two species mate at different times.
Habitat isolation cannot explain this occurrence because we are told that the two species live in the same area. Hybrid breakdown also cannot be correct because the researcher was able to generate a viable hybrid (so he should reasonably be able to find first generation hybrids in the wild). Gametic isolation is also not correct because a hybrid was successfully generated.
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Which of the following is a NOT potential outcome from a speciation hybrid zone?
A hybrid zone is a geographic region where allopatric populations happen to come back in contact with one another. There are three potential outcomes for the hybrid zone over time. It is possible for the two species to re-integrate due to a weakening of reproductive barriers. In this scenario, the two species become one again. It is also possible that the reproductive barriers will strengthen, resulting in an inability to produce the hybrid offspring and a retention of species identity. The final option is a stable intermediate in which the species remain separate, but are still naturally able to create hybrid offspring.
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Different fish living in the same pond mate at different times during the year. What type of reproductive isolation is this?
This is an example of temporal isolation. Temporal isolation means that different species are kept reproductively isolated because they mate at different times.
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While donkeys and horses have ignored each other historically in the wild, hybrids can be made through artificial insemination. The resulting hybrids are unusual in that they are generally viable, but always sterile. Because of their sterility, a blended lineage of the two animals cannot exist. What evolutionary force is this an example of?
Reproductive barriers can be divided into two major categories: pre-zygotic or post zygotic. The former is an issue that arises before fertilization such as two animals not being compatible anatomically or a behavioral incompatibility (think of bird mating rituals, or imagine a mouse trying to reproduce with a whale). A Post-zygotic barrier is a reproductive barrier that prevents the zygote from forming, or hampers the developmental process. It does not prevent the animals from mating however. Thus, The sterile mule example falls under the post-zygotic category since the animals were not prevented from mating.
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Which of the following is true regarding speciation?
Speciation is a process in which one species diverges into two. Two major types of speciation are allopatric and sympatric speciation, with each type featuring a unique barrier to reproduction that halts genetic exchange between populations.
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What are the two major classifications of barriers to reproduction?
Barriers to reproduction are behaviors and physiological processes that maintain distinct species and prevent hybridization. There are two major classifications of barriers to reproduction: pre-zygotic barriers and post-zygotic barriers. Pre-zygotic barriers prevent hybridization before fertilization and post-zygotic barriers prevent it after fertilization.
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What is true regarding temporal isolation?
Temporal isolation is a pre-zygotic barrier to reproduction. In instances of temporal isolation, fertile individuals do not meet one another, thereby isolating them reproductively. This includes distinct habitats, physical barriers, and different timing of sexual maturity.
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Which is not an example of behavioral isolation?
Behavioral isolation is a type of pre-zygotic barrier to reproduction that isolates species through different mating rituals. “Species of fish living in different areas of a pond due to differential salt concentrations” is not an example of behavioral isolation because there is not difference in mating behaviors that reproductively isolates the two species of fish. The rest of these examples demonstrate barriers to reproduction that originate with mating behavior.
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In cases of mechanical isolation, what is the barrier to reproduction between two species?
Mechanical isolation is a type of pre-zygotic barrier that maintains distinct species through genital incompatibility. In this type of reproductive isolation, the genitals of a male and female of the same species allow for copulation and reproduction, while the genitals of individuals of different species mechanically will not allow for reproduction.
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In which of the following habitats is gametic isolation common?
Gametic isolation is a type of pre-zygotic reproductive isolation in which gametes of different species are unable to hybridize due to genetic incompatibility. In coral reef ecosystems, large numbers of gametes are released by many species of marine reefs, making gametic isolation important in preventing hybridization.
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Which of the following is not true regarding zygote mortality?
Zygote mortality is an example of post-zygotic reproductive isolation. In this type of reproductive isolation, gametes from two species may fuse, however the zygote is inviable shortly after fertilization due to improper development.
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In hybrid sterility, at what stage does reproductive isolation occur?
Hybrid sterility is an example of post-zygotic reproductive isolation. In the case of hybrid sterility, hybridization can occur between two species, however the resulting hybrids are unable to produce; the hybrids are sterile.
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Which of the following is not an example of a reproductive barrier?
A reproductive barrier is something that prevents two populations from interbreeding, eventually leading to speciation. The cicada populations are an example of temporal isolation--the two species do not interbreed because they do not breed at the same time. The horse and donkey example shows hybrid sterility--the two species can produce offspring, but the offspring cannot have offspring of their own. The bird species are an example of behavioral isolation--the two species have different courtship rituals (dance vs. plumage) which leads to minimal interbreeding.
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Which of the following is an example of a post-zygotic reproductive barrier?
A post-zygotic reproductive barrier occurs after fertilization has occurred. That is, the two individuals have already mated but either the offspring has died or it is sterile. A pre-zygotic barrier occurs before fertilization occurs. Pre-zygotic barriers are those that prevent individuals of different species from mating in the first place.
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There was once a population on planet M311, called the Freg, who lived on a planet not unlike Earth. At the height of the Fregs technology and evolution, a collection of asteroids bombarded the planet and the devastation was so great that the planet was split in two, as was the Freg population. Much of the Freg population died, but many still survived on both pieces of M311.
Thousands of years ago, the environment on M311 was almost entirely dry and the Freg had evolved to suit that environment. Over time, the environment became more water-based and the Freg developed webbed feet and gills. However, as a result of the asteroid catastrophe, the climate returned to a more hot, dry, desert-like climate. As a result, the Freg began to to lose their webbed feet and gills. What is this process called?
The correct answer to this question is devolution. Devolution refers to when a species reverts to an earlier, more primitive physical form as a result of environmental demands.
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The wing structures of bats and birds are examples of which of the following?
Bird wings and bat wings arose independently of one another, as they do not share a common ancestor with wings, therefore this is convergent evolution.
Divergent evolution implies a common ancestor from which different traits arise, so that is incorrect. It is not homology, as homology describes structures that are similar due to a common ancestry. Allopatric speciation is the emergence of new species due to a geographic barrier. Genetic drift is random variation in population genetic structure of a single species, which is unrelated to the topic at hand.
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A physical barrier separates a single species, causing two separate populations to form. Over time these two populations adapt to their environments. Eventually, these two populations are no longer able to successfully reproduce with each other. This is known as __________.
Allopatric speciation refers to the process by which a physical barrier separates a single population, causing two (or more) populations to arise and evolve due to environmental differences to become different species. Examples of factors that can lead to allopatric speciation include island formation, canyon and valley formation, and river paths.
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