Speciation Chapter 24

In hybrid zones where reinforcement is occurring, we should see a decline in _____.

gene flow between distinct gene pools

Which of the following describes the most likely order of events in allopatric speciation?

genetic isolation, genetic drift, divergence

Which of the following is the first step in allopatric speciation?

geographic isolation

Sympatric speciation is _____.

the appearance of a new species in the same area as the parent population

Hybrid zones provide an opportunity to investigate _____.

the evolution of reproductive isolation. A hybrid zone allows researchers to see what happens when closely related species come together. Reproductive barriers may be strengthened or weakened, depending on environmental and genetic factors.

What does the biological species concept use as the primary criterion for determining species boundaries?

gene flow

How long does it take new species to form on Earth?

The time required varies considerably.

Plant species F has a diploid number of 8. Plant species G has a diploid number of 10. What would be the diploid number of an allopolyploid hybrid of species F and species G?

18. The diploid number of chromosomes in an allopolyploid of these two species would be 18 chromosomes. The gamete of species F would have 4 chromosomes, and the gamete of species G would have 5 chromosomes. After the two haploid gametes combine to form a haploid hybrid zygote with 9 chromosomes, if nondisjunction occurred during mitosis, the doubling of the chromosomes would result in a diploid cell with 18 chromosomes.

You want to study divergence of populations, and you need to maximize the rate of divergence to see results within the period of your grant funding. You will form a new population by taking some individuals from a source population and isolating them so the two populations cannot interbreed. What combination of characteristics would maximize your chance of seeing divergence in this study? 1. Choose a random sample of individuals to form the new population. 2. Choose individuals from one extreme to form the new population. 3. Choose a species to study that produces many offspring. 4. Choose a species to study that produces a few, large offspring. 5. Place the new population in the same type of environment as the source population. 6. Place the new population in a novel environment compared to that of the source population.

2, 3, and 6

In the oceans on either side of the Isthmus of Panama are 30 species of snapping shrimp; some are shallow-water species, others are adapted to deep water. There are 15 species on the Pacific side and 15 different species on the Atlantic side. The Isthmus of Panama started rising about 10 million years ago. The oceans were completely separated by the isthmus about 3 million years ago. In the figure, the isthmus separates the Pacific Ocean on the left (side A) from the Atlantic Ocean on the right (side B). The seawater on either side of the isthmus is separated into five depth habitats (1-5), with 1 being the shallowest. Which habitats should harbor snapping shrimp species with the greatest degree of genetic divergence from each other?

A5 and B5

What is the most important factor that holds a gene pool of a species together and prevents speciation?

Gene flow. Gene flow refers to the transfer of alleles among populations. As long as populations are exchanging alleles, speciation is unlikely.

The sequence of events illustrated in this figure results in a fertile hybrid plant called an allopolyploid. Which of the following statements is the most complete description of an allopolyploid?

It contains more than two sets of chromosomes, which are derived from two species.

What role does nondisjunction play in the formation of a fertile allopolyploid hybrid?

It doubles the chromosome number in the hybrid.

Gametes from two plant species combine and produce a haploid zygote, and that zygote develops into a haploid, hybrid plant. Why is the hybrid plant sterile?

Meiosis cannot occur. AND The cells do not contain homologous chromosomes.

Which statement describes unity within a species?

Members have the potential to interbreed in nature and produce viable, fertile offspring.

Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?

The two forms interbreed often in nature, and their offspring have good survival and reproduction.

The peppered moth provides a well-known example of natural selection. The light-colored form of the moth was predominant in England before the Industrial Revolution. In the mid-19th century, a dark-colored form appeared. The difference is produced by a dominant allele of one gene. By about 1900, approximately 90% of the moths around industrial areas were dark colored, whereas light-colored moths were still abundant elsewhere. Apparently, birds could readily find the light moths against the soot-darkened background in industrial areas and, therefore, were eating more light moths. Recently, use of cleaner fuels has greatly reduced soot in the landscape, and the dark-colored moths have been disappearing. Should the two forms of moths be considered separate species?

No; they still can interbreed.

Which of these is an example of temporal isolation?

One species is nocturnal, and the other species is not

Adaptive radiations on archipelagos (island chains) represent some of the best-understood speciation events. Why is an ancestral species more likely to give rise to multiple descendent species on an archipelago than on an equal-sized area of mainland?

Populations on nearby islands are more likely to be genetically isolated than populations that are equally close to one another on the mainland.

The common edible frog of Europe is a hybrid between two species, Rana lessonae and Rana ridibunda. The hybrids were first described in 1758 and have a wide distribution, from France across central Europe to Russia. Both male and female hybrids exist, but when they mate among themselves, they are rarely successful in producing offspring. What can you infer from this information?

Postzygotic isolation exists between the two frog species.

Select the correct statement describing sympatric speciation.

Sympatric speciation can occur in a single generation.

Two researchers experimentally formed tetraploid frogs by fertilizing diploid eggs from Rana porosa brevipoda with diploid sperm from Rana nigromaculata. When they mated these tetraploid frogs with each other, most of the offspring that survived to maturity were tetraploid, with chromosome sets of both diploid parent species. Based on these results, if this type of tetraploid formed in the wild, what would be the result? (Reference: Y. Kondo and A. Kashiwagi. 2004. Experimentally induced autotetraploidy and allotetraploidy in two Japanese pond frogs. Journal of Herpetology 38(3):38192.)

The tetraploids would be reproductively isolated from both parent species.

Three populations of crickets look very similar, but the males have courtship songs that sound different. What function would this difference in song likely serve if the populations came in contact?

a behavioral reproductive isolating mechanism

According to the phylogenetic species concept, what is a species?

a set of organisms with a unique genetic history

House finches were found only in western North America until 1939, when a few individuals were released in New York City. These individuals established a breeding population and gradually expanded their range. The western population also expanded its range somewhat eastward, and the two populations have recently come in contact. If the two forms were unable to interbreed when their expanding ranges met, it would be an example of ___

allopatric speciation

A hybrid zone is properly defined as _____.

an area where mating occurs between members of two closely related species, producing viable offspring

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

an increasing number of viable, fertile hybrids is produced over the course of the next 100 generations

According to the biological species concept, for speciation to occur, ________.

at least one gene, affecting one reproductive barrier, must change

Which of the following has been shown to cause speciation most rapidly?

autopolyploidy

Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian Islands have different elaborate courtship rituals. These rituals involve fighting other males and making stylized movements that attract females. What type of reproductive isolation does this represent?

behavioral isolation

Which of the various species concepts distinguishes two species based on the degree of genetic exchange between their gene pools?

biological

Speciation _____.

can involve changes to a single gene

Two animals are considered members of different species if they _____.

cannot mate and produce viable, fertile offspring

Rocky Mountain juniper (Juniperus scopulorum) and one-seeded juniper (J. monosperma) have overlapping ranges. Pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species. These two juniper species are kept separate by _____.

gametic isolation

About 3 million years ago, the Isthmus of Panama (a narrow strip of land connecting North and South America) formed, dividing marine organisms into Pacific and Caribbean populations. Researchers have examined species of snapping shrimp on both sides of the isthmus. Based on the morphological species concept, there appeared to be seven pairs of species, with one species of each pair in the Pacific and the other in the Caribbean. The different species pairs live at somewhat different depths in the ocean. Using mitochondrial DNA sequences, the researchers estimated phylogenies and found that each of these species pairs, separated by the isthmus, were indeed each other's closest relatives. The researchers investigated mating in the lab and found that many species pairs were not very interested in courting with each other, and any that did mate almost never produced fertile offspring. (Reference: Y. Kondo and A. Kashiwagi. 2004. Experimentally induced autotetraploidy and allotetraploidy in two Japanese pond frogs. Journal of Herpetology 38(3):381-92.) If the isthmus formed gradually rather than suddenly, what pattern of genetic divergence would you expect to find in these species pairs?

greater percentage of difference in DNA sequence between species that inhabit deep water than between species that inhabit shallow water

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 two hundred 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, though 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. Using only the information provided in the paragraph, which of the following is the best initial hypothesis for how D. santomea descended from D. yakuba?

habitat differentiation

Two populations of birds with somewhat different coloration live on opposite sides of a peninsula. The habitat between the populations is not suitable for these birds. When birds from the two populations are brought together, they produce young whose appearance is intermediate between the two parents. These offspring will breed with each other or with birds from either parent population, and all offspring of these pairings appear intermediate to various degrees. What keeps the two populations separate?

habitat isolation

Reinforcement is most likely to occur when ________.

hybrids have lower fitness than either parent population

You are confronted with a box of preserved grasshoppers of various species that are new to science and have not been described. Your assignment is to separate them into species. There is no accompanying information as to where or when they were collected. Which species concept will you have to use?

morphological

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 difference most likely evolved first?

polyploidy

According to the _____ model, evolution occurs in spurts; species evolve relatively rapidly then remain unchanged for long periods

punctuated equilibrium

The production of sterile mules by interbreeding between female horses (mares) and male donkeys (jacks) is an example of _____.

reduced hybrid fertility

Two species of frogs belonging to the same genus occasionally mate, but the embryos stop developing after a day and then die. These two frog species separate by _____.

reduced hybrid viability

If biological species are defined in terms of reproductive compatibility, the formation of a new species hinges on ________.

reproductive isolation

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

species.

In a hypothetical situation, a certain species of flea feeds only on pronghorn antelopes. In the western United States, pronghorns and cattle often associate with one another in the same open rangeland. Some of these fleas develop a strong preference for cattle blood and mate only with other fleas that prefer cattle blood. The host mammal can be considered as the fleas' habitat. If this situation persists, and new species evolve, this would be an example of _____.

sympatric speciation and habitat isolation

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

sympatric speciation and polyploidy

Which of the following statements describes mechanical isolation prezygotic barrier?

two snails have shells that spiral in different directions