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Chapter 18: Problem 22

Which situation means reinforcement is more likely to occur in the hybrid zone? a. The hybrid offspring are more fit than the parent species. b. Reproductive barriers weaken. c. The hybrid offspring are about as fit as the parent species. d. Reproductive barriers strengthen.

Short Answer

Expert verified
d. Reproductive barriers strengthen.

Step by step solution

01

- Define Reinforcement

Reinforcement in evolutionary biology refers to the process where natural selection increases reproductive isolation between two populations of species. This generally happens to prevent the formation of hybrids that are less fit than the parent species.
02

- Analyze Each Situation

a. If hybrid offspring are more fit than the parent species, hybridization would increase, reducing reinforcement. b. If reproductive barriers weaken, it would lead to more hybridization, reducing reinforcement. c. If hybrid offspring are as fit as the parent species, hybrid formation would occur with no strong reinforcement. d. If reproductive barriers strengthen, it prevents hybrid formation, thus increasing reinforcement.
03

- Determine Correct Answer

Reinforcement is more likely to occur when reproductive barriers strengthen, as it prevents the formation of hybrids which are typically less fit.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Reproductive Isolation
Reproductive isolation refers to a collection of mechanisms, behaviors, and physiological processes that prevent members of different species from interbreeding. These mechanisms can be prezygotic, which occur before fertilization, or postzygotic, which occur after fertilization. Prezygotic mechanisms include temporal isolation (breeding at different times), behavioral isolation (different mating rituals), and mechanical isolation (differences in reproductive structures). Postzygotic mechanisms include hybrid inviability (hybrids fail to develop properly) and hybrid sterility (hybrids are sterile and cannot reproduce). Understanding reproductive isolation is crucial for grasping why reinforcement is essential, as it ensures that species remain distinct, thereby promoting biodiversity.
Natural Selection
Natural selection is the process by which traits that enhance survival and reproduction become more common in successive generations. This concept is fundamental to the theory of evolution. In the context of hybrid zones, natural selection plays a pivotal role in either promoting or hindering reinforcement. When hybrids are less fit than their parent species, natural selection favors traits that prevent hybridization, thereby increasing reproductive isolation through reinforcement. Conversely, if hybrids are equally or more fit, natural selection may decrease reinforcement by encouraging hybridization. Therefore, the fitness of hybrids relative to parent species critically affects whether reinforcement will occur.
Hybrid Zones
Hybrid zones are geographic areas where closely related species meet, mate, and produce hybrid offspring. These zones serve as natural laboratories for studying evolutionary processes. Within hybrid zones, different scenarios can unfold based on the relative fitness of hybrids compared to their parent species. If hybrids are less fit, natural selection will favor mechanisms that increase reproductive isolation, leading to reinforcement. On the other hand, if hybrids are as fit or more fit than the parent species, reproductive barriers may weaken, resulting in more gene flow between the species and reduced reinforcement. Thus, the dynamics within hybrid zones are critical for understanding how new species form and maintain distinct identities.

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Most popular questions from this chapter

Directed evolution is an inquiry strategy that is usually used to investigate gene expression or the function of proteins that are expressed. The investigator imposes a selection pressure and observes the evolution of a population. In one investigation, unicellular yeast were allowed to sediment in a column of a nutrient-containing solution. Individuals that traveled furthest towards the bottom of the column were removed and placed in a new column. After 60 generations of repeated selection, yeast became multicellular. In this experiment, selection was acting on the collection of cells and not on the individual. To test the claim that selection was acting on the multicellular system and not just individual cells, the investigators compared the effects on a population of yeast that had acquired multicellularity by strong selection (allowing only 5 minutes to settle) and weak selection (allowing 25 minutes to settle). A strong selection increased cluster size, and a weak selection decreased cluster size. A. Evaluate the claim that the use of both a strong and weak selection demonstrates that evolution is an ongoing process that, under artificially imposed conditions, led to the emergence of multicellularity in a single- celled organism. B. In this directed evolution study, the selection pressure imposed by the investigators led to a new phenotype. Consider a situation in which there is a vertical variation in the density of nutritional resources. Analyze the advantages and disadvantages of cooperative behavior, including changes in the likelihood of replication of the individual and population genomes.

Each of the following observations comes from a different scientific discipline. Which is the best support for Darwin鈥檚 concept of descent with modification? a. Geologists provide evidence that earthquakes reshape life by causing mass extinctions. b. Botanists provide evidence that South American temperate plants have more in common with South American tropical plants than temperate plants from Europe. c. Zoologists provide evidence that fewer animal species live on islands than on nearby mainlands. d. Ecologists provide evidence that species diversity increases closer to the equator

Genes important in the embryonic development of animals have been relatively well conserved during evolution. This means they are more similar among different species than many other genes. What explains this genetic conservation across animal species? a. Changes in the genes that are important to embryonic development have been relatively minor because there are no selective pressures on an individual before it is born b. Changes in the genes that are important to embryonic development have been relatively minor because not much time has elapsed since the divergence of the various animal taxa. c. Changes in the genes that are important to embryonic development have been relatively minor because early embryos are very fragile and even small mutations can result in death d. Changes in the genes that are important to embryonic development have been relatively minor because mutational tweaking in the embryo has magnified consequences in the adult.

If a population stopped reproducing sexually, but still reproduced asexually, how would its genetic variation be affected over time? Could speciation occur in this situation? Explain your ideas. a. Genetic variation would increase and speciation would be possible b. Genetic variation would increase and speciation would not be possible. c. Genetic variation would decrease and speciation would be possible. d. Genetic variation would decrease and speciation would not be possible.

How does the scientific meaning of 鈥渢heory鈥� differ from the common vernacular meaning? a. A scientific theory is a hypothesis that needs to be tested, whereas people often use theory to mean a simple guess. b. A scientific theory is a statement that has been proven correct, while people often use it to mean a statement that has not yet been verified. c. A scientific theory is a thoroughly tested set of explanations for a body of observations of nature, while people often use it to mean a guess or speculation. d. A scientific theory is a random guess, while people often use it to mean a statement that is somewhat based in fact.
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