Question 1

Imagine you are looking down on the top of a mountain. As you hike from the highest elevation to the lowest elevation, you find three different species of related mice. None of them is found at the same elevation, and the vegetation changes at each elevation level.  At the highest elevation some of the individuals of species A mate with individuals in species B that make their way up from the middle elevation. Their offspring are unable to survive or reproduce in either elevation, and never reproduce. This is an example of:

Accepted Answer

The answer of Imagine you are looking down on the...

Question 2

_____ is the process by which divergent populations undergo natural selection in favor of enhanced pre-zygotic isolation.

Accepted Answer

Reinforcement is the evolutionary process by which species that are initially somewhat compatible become more distinct and less able to interbreed. This occurs through natural selection favoring traits that enhance pre-zygotic isolation mechanisms, reducing the likelihood of hybrid offspring between divergent populations.

Question 3

When two populations have undergone divergence in allopatry long enough to have a difference of one fixed allele between the two populations, they are always then sufficiently different to be considered two different species.

Accepted Answer

The presence of just one fixed allele difference does not always indicate that two populations are different enough to be considered two different species. Other factors such as morphological, ecological, and behavioral differences should also be taken into consideration.

Question 4

All else being equal, selection should more strongly favor reinforcement of reproductive isolation among related species in:

Accepted Answer

Sympatric populations are those that share the same geographical area, making it easier for individuals from different species to interact and potentially mate. Therefore, selection should favor reinforcement of reproductive isolation among related species in sympatric populations over allopatric populations, where individuals from different species are separated by geographical barriers and have less opportunity to interact and mate. Peripatric populations are those that are geographically isolated, but with a small founder population entering a new area, and would not necessarily have a stronger selection for reinforcement of reproductive isolation among related species compared to sympatric populations.

Question 5

You are a biologist on a trip to an island in the South Pacific. While on the island, you are allowed to collect DNA samples from a local species of rat that resembles a species seen on a nearby continent. If your DNA analysis also indicates the two species are closely related, you might conclude that the evolution of the two separate species was an example of _____ speciation through _____.

Accepted Answer

Allopatric speciation through dispersal is suggested by the scenario where a species from a nearby continent resembles a local species on an island, implying that the species might have dispersed from the continent to the island and then evolved into a new species due to geographical separation.

Question 6

Which of the following describes reinforcement of reproductive isolation?

Accepted Answer

Reinforcement of reproductive isolation refers to the reinforcement of mechanisms that prevent hybridization between two different populations. Option C, the ability to identify and preferentially mate with only members of the same population, is an example of such a mechanism. Option A describes geographic isolation, option B describes post-zygotic barriers, and option D describes natural selection.

Question 7

Imagine a scenario in which a common population of animals is separated into two groups by a natural event. Over time, you might expect the two populations to become _____ genetically similar. This process is known as _____ speciation.

Accepted Answer

When a population is separated by a natural event, it is an example of allopatric speciation, as opposed to sympatric speciation where a population diverges while occupying the same geographic area. Over time, the two populations would become less genetically similar because they are no longer interbreeding and sharing genes.

Question 8

A neutral mutation is a mutation that _____ increase the reproductive fitness of an organism.

Accepted Answer

A neutral mutation does not provide any advantage or disadvantage to an organism in terms of survival or reproduction. Therefore, it does not increase the reproductive fitness of an organism.

Question 9

Imagine that European explorers sailing across the Pacific left several male and female pairs of pigs on a remote island with the intention of visiting again in future years to harvest fresh meat. This would MOST closely resemble a case of artificially induced allopatric speciation through:

Accepted Answer

This is an example of dispersal, as the pigs were intentionally transported from their original habitat (Europe) to a new, isolated habitat (the remote island in the Pacific). Artificial selection may eventually lead to divergence in the pig populations on the island, leading to allopatric speciation. However, the initial event that led to their separation was dispersal. Vicariance, on the other hand, would involve a physical barrier separating a population, such as the formation of a new island or a geological event that splits a landmass in two.

Question 10

Natural selection is always the driving force of speciation.

Accepted Answer

While natural selection can play a role in speciation by favoring certain traits that increase the chances of survival and reproduction, it is not the only factor. Other factors that can contribute to speciation include genetic drift and geographic isolation.

Question 11

In general, allopatric species will evolve pre-zygotic isolating mechanisms more rapidly than sympatric species.

Accepted Answer

Allopatric species are geographically isolated and thus do not require pre-zygotic isolating mechanisms as urgently as sympatric species, which live in the same area and therefore evolve pre-zygotic isolating mechanisms more rapidly to avoid interbreeding.

Question 12

You begin an experiment with two populations of E. coli that are each composed of 100 cells. The cells are all genetically identical (i.e., they are clones). You grow them up in flasks on a lab bench under identical conditions with unlimited resources. After 10,000 generations, you analyze the genome of each population. Do you expect the genomes of each population to be identical after 10,000 generations?

Accepted Answer

Mutations are a source of genetic variation, which allows natural selection to act upon. Over 10,000 generations, mutations will accumulate independently in each population, leading to genetic drift (random changes in gene frequency) and possibly the fixation of different alleles in each population. Natural selection will also act upon the genetic variation present in each population, which could lead to the fixation of different alleles or traits between the two populations. Therefore, the genomes of each population are unlikely to be identical after 10,000 generations.

Question 13

You begin an experiment with two populations of E. coli that are each composed of 100 cells. The cells are all genetically identical (i.e., they are clones). You grow these populations in flasks on a lab bench under identical conditions with unlimited resources. What process will introduce genetic variation into these populations? Will identical genetic changes occur in each flask?

Accepted Answer

The answer of You begin an experiment with two populations...

Question 14

You are studying a species of frog in which individuals from two successive generations can no longer interbreed, suggesting that the offspring are a different species from the parents. If speciation occurred because of changes in chromosome counts between the parents and the offspring, would this be an example of speciation by natural selection?

Accepted Answer

Changes in chromosome counts are a mechanism for speciation, but they do not necessarily involve natural selection. Speciation can also occur through other mechanisms such as geographic isolation or hybridization.

Question 15

The wide variety of finches Darwin observed in the Galápagos was thought provoking because they appeared to have descended from _____ population. Today, we regard this as an example of _____.

Accepted Answer

The finches Darwin observed in the Galápagos Islands are considered to have descended from the same ancestral population, and their diversification into a variety of species with different beak shapes and sizes is a classic example of adaptive radiation. This process involves the rapid evolution of an ancestral species into new species that exploit different ecological niches.

Question 16

Some cases of hybridization that lead to instantaneous speciation result in alteration of chromosomal number.

Accepted Answer

Hybridization can lead to the combination of different sets of chromosomes, resulting in altered chromosome number and possible speciation. This is known as chromosomal speciation.

Question 17

Reinforcement refers to the development of _____-zygotic factors and is typically more rapid in species living in _____.

Accepted Answer

Reinforcement refers to the development of pre-zygotic factors to prevent hybridization and is typically more rapid in species living in sympatry, where different species are in close proximity and the risk of hybridization is higher.

Question 18

You are a parasitologist interested in roundworms affecting frogs. You note that when two populations of frogs were separated long enough ago for them to speciate, their roundworms have also speciated. What is this process called?

Accepted Answer

This process is called co-speciation, where two closely associated species undergo speciation in parallel with one another due to their close association. In this case, the speciation of roundworms in the separated frog populations is a result of co-speciation.

Question 19

When two populations have undergone divergence in allopatry long enough to be unable to produce fertile offspring, then they are different enough to be considered two different species.

Accepted Answer

This is the biological species concept, which defines a species as a group of organisms that can interbreed and produce fertile offspring. When two populations have diverged to the point that they cannot interbreed and produce fertile offspring, they are considered different species according to this concept.

Question 20

A population of rare frogs is reduced by 90% in number when a large dam is constructed that obliterates most of their prior habitat. Which of the following is probably TRUE?

Accepted Answer

The drastic reduction in population size is likely to result in a reduction of genetic diversity, as some alleles are lost from the gene pool through genetic drift. The small remaining population may not reflect the diversity of the original population, and the effects of natural selection on the surviving population's genetic variation may be significant. While genetic drift alone can cause speciation, it is less likely to occur in a small population that has lost genetic diversity due to a bottleneck such as this.

Quiz 22: Species and Speciation