Question 1

Among known plant species, which of these have been the two most commonly occurring phenomena that have led to the origin of new species?

Accepted Answer

Allopatric speciation occurs when populations of the same species are geographically separated, while sympatric speciation occurs when populations diverge while living in the same geographic region. Polyploidy is a common mechanism in plants, where an increase in the number of chromosome sets can create a reproductively isolated population, leading to the origin of a new species. Sexual selection, on the other hand, can lead to the evolution of unique traits and behaviors that enhance mating success, but it is not as commonly associated with the origin of new species in plants. Therefore, the best choice is D, where both polyploidy and sympatric speciation are commonly observed in the origin of new plant species.

Question 2

Beetle pollinators of a particular plant are attracted to its flowers' bright orange color. The beetles not only pollinate the flowers but mate while inside of the flowers. A mutant version of the plant with red flowers becomes more common with the passage of time. A particular variant of the beetle prefers the red flowers to the orange flowers. Over time, these two beetle variants diverge from each other to such an extent that interbreeding is no longer possible. What kind of speciation has occurred in this example, and what has driven it?

Accepted Answer

The answer of Beetle pollinators of a particular plant are...

Question 3

Use the following description to answer the question below.
On the volcanic, equatorial West African island of Sao Tomé, two species of fruit fly exist. Drosophila yakuba inhabits the island's lowlands, and is also found on the African mainland, located about 200 miles away. At higher elevations, and only on Sao Tomé, is found the very closely related Drosophila santomea. The two species can hybridize, though male hybrids are sterile. A hybrid zone exists at middle elevations, but hybrids there are greatly outnumbered by D. santomea. Studies of the two species' nuclear genomes reveal that D. yakuba on the island is more closely related to mainland D. yakuba than to D. santomea (2n = 4 in both species). Sao Tomé rose from the Atlantic Ocean about 14 million years ago.
If the low number of hybrid flies in the hybrid zone, relative to the number of D. santomea flies there, is due to the fact that hybrids are poorly adapted to conditions in the hybrid zone, and if fewer hybrid flies are produced with the passage of time, these conditions will most likely lead to ________.

Accepted Answer

Reinforcement occurs when natural selection favors the evolution of prezygotic barriers that prevent hybridization between diverging populations, ultimately leading to their complete reproductive isolation. If hybrid flies are poorly adapted to conditions in the hybrid zone and produce fewer offspring over time, natural selection would favor the evolution of stronger prezygotic barriers that prevent hybridization between D. santomea and D. yakuba, reinforcing their genetic divergence and reducing the frequency of hybrids.

Question 4

The data collected by the researchers indicate that ________.

Accepted Answer

The answer of The data collected by the researchers indicate...

Question 5

Use the following description to answer the question below.
On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusive breeding preferences.
What is the best way to promote fusion between two related populations of mosquitofish, one of which lives in a predator-rich pond and the other of which lives in a predator-poor pond?

Accepted Answer

Building a canal that allows mosquitofish to move freely between the two ponds without transferring predators would encourage natural interaction and potential breeding between the two populations, promoting genetic exchange and fusion without increasing predation risk.

Question 6

Male frogs give calls that attract female frogs to approach and mate. Researchers examined mating calls of closely related but separate species of tree frogs in South America. What outcomes could possibly occur where the ranges of two species overlap?
I. The species will interbreed, eventually fusing over time.
II. A stable hybrid zone will form if hybrids are better adapted to the area of overlap than either parent species is.
III. Species will continue to diverge and be isolated by behavioral or genetic mechanisms.

Accepted Answer

When the ranges of two closely related species overlap, several outcomes are possible: interbreeding could lead to the fusion of the species over time (I), a stable hybrid zone could form if the hybrids are better adapted to the overlap area (II), and the species could continue to diverge and be isolated by behavioral or genetic mechanisms to prevent interbreeding (III).

Question 7

In hybrid zones where reinforcement is occurring, you should see a decline in ________.

Accepted Answer

Reinforcement occurs when natural selection favors individuals who do not mate with individuals from the other gene pool in hybrid zones, resulting in a decrease in gene flow between distinct gene pools. This leads to increased genetic distinctness between the two gene pools.

Question 8

Suppose that a group of male pied flycatchers migrated from a region where there were no collared flycatchers to a region where both species were present. Assuming events like this are very rare, which of the following scenarios is LEAST likely?

Accepted Answer

The introduction of new genes from the collared flycatcher gene pool would increase the likelihood of hybridization between the two species. Therefore, it is least likely that the frequency of hybrid offspring would decrease.

Question 9

Two species of tree frogs that live sympatrically in the northeastern United States differ in ploidy: Hyla chrysoscelis is diploid, and Hyla versicolor is tetraploid. The frogs are identical in appearance, but their mating calls, which females use to find mates, differ. Which likely evolved first?

Accepted Answer

Polyploidy likely evolved first, as it leads to a change in the number of chromosome sets in a species, creating reproductive isolation between individuals with different ploidy levels. This can lead to rapid speciation. Reproductive and behavioral isolation may then evolve over time, as a result of the polyploidy-induced genetic changes.

Question 10

A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species, each of which eats only a certain type of food. None of the species can fly and their balancing organs (halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap.
Fly species W, found in a certain part of the island, produces fertile offspring with species Y. Species W does not produce fertile offspring with species X or Z. If no other species can hybridize, then which of the following statements about species W and Y is/are TRUE?
I. Species W and Y have genomes that are still similar enough for successful meiosis to occur in hybrid flies.
II. Species W and Y have more genetic similarity with each other than either did with the other two species.
III. Species W and Y may fuse into a single species if their hybrids remain fertile over the course of many generations.

Accepted Answer

I. For species W and Y to produce fertile offspring, their genomes must be compatible enough to allow for successful meiosis in the hybrids. This process requires a significant degree of genetic similarity to ensure that chromosomes can pair and segregate properly.II. The ability of species W and Y to produce fertile offspring suggests a closer genetic relationship between them than with species X or Z, with whom they cannot produce fertile offspring. This implies that W and Y have retained more genetic similarities with each other.III. If hybrids between species W and Y remain fertile over many generations, gene flow between the two species could increase, potentially leading to the merging of the two species into one. This process would depend on various factors, including ecological conditions and the fitness of the hybrids.

Question 11

The origin of a new plant species by hybridizing two existing species, coupled with accidents during cell division, is an example of ________.

Accepted Answer

Sympatric speciation occurs when a new species evolves from a single ancestral species while inhabiting the same geographic region. Allopolyploidy refers to polyploidy (having more than two paired sets of chromosomes) resulting from the hybridization of two different species. This combination of sympatric speciation and allopolyploidy accurately describes the scenario of a new plant species originating from the hybridization of two existing species, along with chromosomal duplication errors.

Question 12

The phenomenon of fusion is likely to occur when, after a period of geographic isolation, two populations meet again and ________.

Accepted Answer

The phenomenon of fusion occurs when two populations meet again after a period of geographic isolation and an increasing number of viable, fertile hybrids is produced over time. This results in the gene pools of the two populations mixing to the extent that they become one population with shared characteristics. Choice A is incorrect because the presence or absence of homologous chromosomes does not necessarily determine the occurrence of fusion. Choice B is incorrect because an increasing number of infertile hybrids would not result in fusion, as they cannot contribute to the gene pool of either population. Choice C is incorrect because if no reproduction occurs in the hybrid zone, there would be no hybrid offspring contributing to the gene pool. Choice E is incorrect because a decreasing number of viable, fertile hybrids would not result in fusion as the populations would eventually separate again.

Question 13

Reinforcement is most likely to occur when ________.

Accepted Answer

Reinforcement typically occurs when hybrids have lower fitness than either parent population, leading to reduced gene flow between the populations and stronger reproductive isolation.

Question 14

A hybrid zone is properly defined as ________.

Accepted Answer

A hybrid zone is an area where members of two closely related species mate and produce viable offspring, which usually have some combination of the characteristics of the two parental species. This differs from situations where the ranges of two species overlap but there is no interbreeding (A), or where postzygotic barriers prevent the hybrids from being viable or fertile (C) or where prezygotic barriers prevent gene flow (D).

Question 15

Male frogs give calls that attract female frogs to approach and mate. Researchers examined mating calls of closely related tree frogs in South America. If reinforcement is occurring, what would you expect if you compare the calls of the two species in zones of sympatry versus zones of allopatry?

Accepted Answer

If reinforcement is occurring, we would expect mating calls to become more different in areas of sympatry because if the calls were too similar, there would be the risk of hybridization and reduced fitness of hybrid offspring. Therefore, selection would favor individuals with more distinct calls in areas of sympatry where the two species overlap, leading eventually to complete reproductive isolation.

Question 16

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

Accepted Answer

Allopolyploid species arise from the hybridization of two different species followed by a doubling of the chromosome number, resulting in a new species with a higher chromosome number than either parent. 
The diploid number for species C would be the sum of the diploid numbers in A and B, which is (12 + 16) = 28. Therefore, the answer is D, 28.

Quiz 24: Speciation