Question 1

Which of the following statements about stable hybrid zones is most accurate?

Accepted Answer

Stable hybrid zones can persist even if hybrids are selected against, as long as the zone is narrow and the parental species frequently come into contact, allowing for continuous hybridization.

Question 2

Which of the following statements most accurately applies to speciation?

Accepted Answer

Speciation can indeed involve changes to a single gene, which can have significant effects on the reproductive capabilities or survival of organisms, leading to the emergence of new species. This process does not always require vast expanses of time, geographic isolation, or only the accumulation of small genetic changes, as other mechanisms can also drive speciation.

Question 3

A female fly, full of fertilized eggs, is swept by high winds to an island far from the mainland. She is the first, and only, fly to arrive on this island. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species and their geographic ranges overlap. Each species eats a different kind of food. None of the species can fly and the balancing organs of males differ among species and are now used in courtship displays. Fly species W produces fertile offspring with species Y, but not with species X or Z. Furthermore, X and Z do not hybridize. Which of the following statements about species W and Y is most likely to be accurate?

Accepted Answer

Species W and Y producing fertile offspring suggests that their genomes are compatible enough for successful meiosis, indicating a closer genetic relationship. Over many generations, if these hybrids continue to be fertile, it could lead to the fusion of species W and Y into a single species.

Question 4

A small number of birds arrive on an island from a neighboring larger island. This small population begins to adapt to the new food plants available on the island, and their beaks begin to change. About twice a year, one or two more birds from the neighboring island arrive. Which of the following effects is most likely to result from the immigration?

Accepted Answer

The continuous arrival of birds from the neighboring island introduces new genetic material into the small population, potentially diluting the adaptations (like changes in beak shape) that the initial population was developing in response to the new environment. This gene flow can slow or decrease the adaptation process to the new food plants.

Question 5

A team of scientists is trying to understand the evolutionary history of three species of grasses. They hypothesize that Species T is a descendent of a hybrid between Species R and Species S. Which of the following experimental approaches would best help elucidate the evolutionary history of these three species?

Accepted Answer

This approach allows for a direct comparison of the hybrid offspring under various environmental conditions to Species T, which can help determine if Species T could have evolved from a hybrid of Species R and S.

Question 6

Which of the following statements about the punctuated and gradual models of speciation is most accurate?

Accepted Answer

The punctuated and gradual models of speciation describe different rates at which species evolve. The fossil record, while useful, often lacks the detail necessary to precisely determine the speed of speciation events, supporting the idea that both rapid (punctuated) and gradual speciation can occur but may not always be distinguishable in the fossil record.

Question 7

Which of the following conditions is most likely to reinforce isolating mechanisms between two species that occasionally hybridize?

Accepted Answer

Hybrids with lower fitness than either parent population are less likely to survive and reproduce, reinforcing the reproductive barriers between the two species and preventing the blending of the species through hybridization. This process is known as reinforcement, where natural selection increases reproductive isolation.

Question 8

Which of the following statements correctly describes a change that must occur for a new species to arise?

Accepted Answer

For a new species to arise, changes that affect reproductive barriers are crucial. These barriers prevent different species from interbreeding. A change in even a single gene affecting a reproductive barrier can lead to speciation, as it may prevent successful reproduction with the original population, leading to the emergence of a new species.

Question 9

Lions and tigers sometimes breed in zoos, but hybrids have not been seen in nature, nor can the hybrids in zoos reproduce well. Which of the following statements is the best conclusion that can be derived from this information?

Accepted Answer

Breeding between lions and tigers in zoos, but not in nature, suggests that the unnatural proximity and lack of other mating options in captivity are likely the reasons for such hybridization, rather than a natural inclination or compatibility between the species.

Question 10

According to the concept of punctuated equilibrium, the "sudden" appearance of a new species in the fossil record means that ________.

Accepted Answer

Punctuated equilibrium is a theory in evolutionary biology which proposes that most sexually reproducing species will experience little evolutionary change for most of their geological history, but when they do evolve, it is in relatively short, rapid events of branching speciation. The "sudden" appearance of a new species in the fossil record, according to this concept, indicates that speciation occurred rapidly in geologic time, not instantaneously but over thousands or millions of years, which is rapid on a geologic scale.

Question 11

One possible outcome of hybridization is fusion of two species. Which of the following conditions is most likely to increase the probability of fusion of the two species as a result of hybridization?

Accepted Answer

An increasing number of viable, fertile hybrids produced over time suggests successful reproduction and genetic mixing between the two species, which can lead to their fusion.

Question 12

Which of the following processes would contribute to divergence between lineages once divergence has already begun?

Accepted Answer

Sexual selection and habitat differences both contribute to divergence between lineages by promoting reproductive isolation and adaptation to different environments, respectively.

Question 13

Some geographic areas contain two closely related species of birds (sympatry), while other areas contain only one of the species (allopatry). Males from allopatric populations look very similar to each other, but males in the sympatric populations look different from each other and from both allopatric types of males. Which of the following outcomes is most likely if a female in a sympatric area is courted by a male that migrated into the area from an allopatric area?

Accepted Answer

In sympatric areas, where two closely related species of birds coexist, sexual selection often favors males that exhibit distinct traits, helping females to choose mates from their own species to avoid hybridization. An immigrant male from an allopatric area, where such distinct traits are not as pronounced due to the lack of need to differentiate from a closely related species, is likely to be less attractive to females in sympatric areas. This is because he may not exhibit the specific traits that females in sympatric populations use to choose mates from their own species.

Question 14

Which of the following statements is the best definition of a hybrid zone?

Accepted Answer

A hybrid zone is best defined as an area where mating occurs between members of two closely related species, producing viable offspring. This emphasizes the interaction and genetic exchange between species, which is a key aspect of hybrid zones.

Question 15

The largest unit within which gene flow can readily occur is a ________.

Accepted Answer

The largest unit within which gene flow can readily occur is a species, as gene flow refers to the transfer of genetic material within a population or between populations of the same species.

Question 16

Plant species X has a diploid number of 12. Plant species Y has a diploid number of 16. A new species, Z, arises as an allopolyploid from X and Y. The diploid number for species Z would probably be ________.

Accepted Answer

Allopolyploidy involves the combination of chromosomes from two different species. In this case, species Z would have the sum of the diploid numbers of species X and Y, which is 12 + 16 = 28.

Question 17

Which of the following outcomes is most likely in hybrid zones where reinforcement of isolating mechanisms is occurring?

Accepted Answer

Reinforcement of isolating mechanisms in hybrid zones typically leads to speciation, as it enhances reproductive barriers between distinct populations, reducing gene flow and thereby increasing the genetic distinctness of the gene pools involved.

Question 18

Which of the following possible isolating mechanisms prevents individuals from wasting time and energy hybridizing with an individual of another species?

Accepted Answer

Behavioral isolation prevents individuals from different species from mating because they have different mating rituals, calls, or other behaviors. This mechanism helps individuals recognize and mate with members of their own species, thus avoiding the wasted effort on hybridization with other species.

Question 19

The number of cichlid species in Lake Victoria is declining, in part because of predation by Nile perch. Which of the following factors is also likely to contribute to the decline in the number of cichlid species in Lake Victoria?

Accepted Answer

Fusion of species contributes to the decline in the number of cichlid species by reducing genetic diversity and leading to the merging of distinct species into fewer, less distinct ones. This can be exacerbated by environmental pressures and changes, such as those introduced by the Nile perch, leading to a decrease in the overall number of distinct cichlid species in Lake Victoria.

Question 20

A narrow hybrid zone separates the toad species Bombina bombina and B. variegata. A genetic study identified a locus where one allele (R) occurred in all B. variegata, occurred in a few B. bombina at the edge of the hybrid zone, and was replaced totally by another allele (r) in B. bombina that lived far from the hybrid zone. Which of the following statements is most likely to be accurate with regard to the frequency of V1 in the hybrid zone?

Accepted Answer

The frequency of the R allele declines in hybrids closer to B. bombina because it is replaced by the r allele in B. bombina populations far from the hybrid zone, indicating a gradient of allele frequency across the hybrid zone.

Quiz 24: Species and Speciation