Evolution (C736)

Explanation:

Allopatric speciation occurs when populations of the same species become geographically separated by a physical barrier, such as a mountain range, river, or canyon. This separation prevents gene flow between the populations, allowing them to evolve independently through natural selection, mutation, and genetic drift. Over time, the accumulated genetic differences can result in the formation of new species. This concept is central to understanding how geographic isolation drives evolutionary divergence.

Correct Answer:

Allopatric speciation

Why Other Options Are Wrong:

Sympatric speciation

Sympatric speciation occurs without physical separation; populations diverge while living in the same geographic area, often due to ecological niches, behavioral isolation, or genetic differences. This does not match the condition of populations being separated by physical barriers, making it an incorrect choice for this scenario.

Parapatric speciation

Parapatric speciation happens when populations are adjacent to each other but experience limited gene flow, often along environmental gradients. Unlike allopatric speciation, it does not require complete geographic isolation, so it does not fully explain speciation due to a physical barrier.

Peripatric speciation

Peripatric speciation is a specific form of allopatric speciation that occurs when a small population becomes isolated at the edge of a larger population’s range. While related, the term is more specific and not the general type of speciation caused by physical barriers as asked in the question.

Explanation:

Allopatric speciation occurs when populations are geographically separated, preventing gene flow. Over time, genetic differences accumulate due to natural selection, mutation, and genetic drift, leading to reproductive isolation and the formation of new species. The presence of a geographical barrier is the defining feature of allopatric speciation.

Correct Answer:

Evolution of reproductive isolation within a population in the presence of a geographical barrier.

Why Other Options Are Wrong:

Evolution of reproductive isolation within a population in the absence of a geographical barrier

This describes sympatric speciation, not allopatric speciation, because there is no physical separation.

Evolution of reproductive isolation by forming sterile hybrid progeny

This describes postzygotic isolation, which can occur after speciation but is not the defining mechanism of allopatric speciation.

Evolution of reproductive isolation by having different mating seasons

This is temporal isolation, a type of prezygotic barrier, and does not necessarily involve geographic separation.

Evolution of reproductive isolation by developing incompatible gametes

This describes gametic isolation, another prezygotic barrier, and does not define allopatric speciation.

Explanation:

Behavioral adaptations in response to predators, such as increased vigilance or avoidance strategies, can increase an organism’s survival rates. By altering its behavior to detect and evade the goshawk, the woodpigeon is more likely to avoid predation, survive longer, and reproduce. Such behavioral changes are examples of traits that can be favored by natural selection because they enhance fitness.

Correct Answer:

Increased survival rates

Why Other Options Are Wrong:

Reduced awareness of surroundings

This would be disadvantageous rather than beneficial. Reduced awareness would increase the likelihood of predation, decreasing survival and fitness, making it the opposite of an evolutionary advantage.

Increased energy expenditure

While behavioral changes may require more energy, this is a cost rather than an advantage. The net evolutionary advantage comes from enhanced survival, not energy expenditure.

Decreased reproductive success

A decrease in reproductive success is a negative outcome. Altering behavior to avoid predators is expected to increase survival and, indirectly, reproductive opportunities, so this option is incorrect.

Explanation:

The evolution of silent male crickets on Kauai is an example of directional selection. A novel predator (the parasitoid fly) targets males producing chirps, creating selective pressure for individuals that do not produce sound. Over generations, natural selection favors silent males, shifting the population phenotype from chirping to quiet individuals. This demonstrates how directional selection drives evolutionary change in a specific direction based on environmental pressures.

Correct Answer:

Directional selection, because natural selection drove the population away from sound production and towards being quiet

Why Other Options Are Wrong:

Disruptive selection, because the presence of a new predator disrupted the lifestyle of the crickets

Disruptive selection favors extreme phenotypes at both ends of a trait distribution. In this case, the population shifted entirely towards silence rather than maintaining two extremes, so disruptive selection does not explain the change.

Sexual selection, because females prefer quiet males

There is no evidence that female preference drove the evolution of silence. The change is due to predation pressure, not mate choice, making sexual selection an incorrect explanation.

Convergent evolution, because the crickets of Kauai are better off if they converge on the behavior of the crickets on Oahu

Convergent evolution occurs when unrelated species independently evolve similar traits. This situation involves a single population evolving in response to a predator, not convergence between different species, so this option is incorrect.

Explanation:

Sympatric speciation occurs when new species evolve from a single ancestral species while inhabiting the same geographic region. In the case of Rhagoletis pomonella, populations diverged based on host plant preference (e.g., apple versus hawthorn), despite living in overlapping habitats. The differentiation in host preference leads to reproductive isolation, allowing speciation to occur without physical barriers, which is characteristic of sympatric speciation.

Correct Answer:

Sympatric speciation

Why Other Options Are Wrong:

Peripatric speciation

Peripatric speciation involves a small population becoming isolated at the edge of a larger population, often leading to rapid divergence. Rhagoletis pomonella populations are not geographically isolated, so this does not apply.

Allopatric speciation

Allopatric speciation occurs when populations are physically separated by geographic barriers. In this case, the populations remain in the same geographic area, so allopatric speciation is incorrect.

Parapatric speciation

Parapatric speciation occurs when populations are adjacent but experience limited interbreeding across a gradient. Rhagoletis pomonella diverged based on host preference within the same area rather than along a gradient, so this option is incorrect.

Explanation:

Prezygotic isolating mechanisms prevent fertilization from occurring. Differences in mate-attracting signals (behavioral isolation), differences in genitalia shape (mechanical isolation), and differences in timing of spawning (temporal isolation) all prevent mating or fertilization. Hybrid sterility, however, is a postzygotic barrier because it occurs after fertilization; the hybrid zygote forms but the offspring are sterile, preventing gene flow between species.

Correct Answer:

hybrid sterility

Why Other Options Are Wrong:

differences in mate attracting signals

This is a prezygotic behavioral barrier, preventing mating before fertilization occurs, so it is not the correct answer.

differences in genitalia shape preventing mating

This is a mechanical isolation mechanism, which acts before fertilization, making it a prezygotic barrier and therefore incorrect for this question.

differences in the timing of spawning

Temporal isolation prevents fertilization because the species reproduce at different times. It is a classic prezygotic mechanism, so this option is incorrect.

Explanation:

Artificial selection is the process by which humans intentionally breed organisms to enhance or favor specific traits. In the case of broccoli, cauliflower, and kale, selective breeding over generations produced different varieties with desirable characteristics. Unlike natural selection, which is driven by environmental pressures, artificial selection is directed by human choice, allowing certain traits to become more common in the population due to deliberate reproductive selection.

Correct Answer:

Artificial selection

Why Other Options Are Wrong:

Negative-frequency dependent selection

Negative-frequency dependent selection occurs when the fitness of a trait decreases as it becomes more common in a population. This concept involves natural population dynamics and does not describe deliberate human-driven breeding, making it incorrect.

Natural selection

Natural selection is driven by environmental pressures that favor certain traits over others for survival and reproduction. While similar in effect, it differs from artificial selection, which is guided intentionally by humans, so this option is incorrect.

Founder effect

The founder effect occurs when a small population becomes isolated and certain alleles are overrepresented by chance. This mechanism does not involve selective breeding for specific traits, so it is not the correct answer.

Stabilizing selection

Stabilizing selection favors intermediate phenotypes and reduces variation around a mean trait. It occurs naturally and is not a result of intentional breeding, so it does not describe the process in the question.

Explanation:

Inductive reasoning involves collecting observations or specific data and using them to form generalizations or principles. Scientists often use inductive reasoning to develop hypotheses or theories based on patterns observed in experiments or natural phenomena. This approach moves from specific instances to broader generalizations.

Correct Answer:

Inductive reasoning

Why Other Options Are Wrong:

Descriptive reasoning

Descriptive reasoning focuses on observing and describing phenomena without forming general predictions. It does not involve the inferential step central to inductive reasoning, so it is incorrect.

Logical reasoning

Logical reasoning refers broadly to reasoning processes that follow formal rules, including both inductive and deductive reasoning. It is too general to describe the specific process of forming general principles from observations.

Deductive reasoning

Deductive reasoning starts with general principles or theories and makes specific predictions. Since the question asks about reasoning from observations to general principles, deductive reasoning is the opposite process and is incorrect.

Explanation:

Artificial selection is the process by which humans selectively breed plants or animals to emphasize desired traits. In the case of broccoli, cauliflower, kale, and cabbage, humans chose individuals with specific characteristics from the wild mustard plant and bred them over generations to enhance those traits. This human-directed breeding differs from natural selection because the selection pressures come from human preferences rather than environmental pressures.

Correct Answer:

artificial selection.

Why Other Options Are Wrong:

commensalism

Commensalism is a type of ecological interaction where one species benefits while the other is unaffected. It does not involve breeding or selection of traits, so it is not relevant to the domestication of mustard plants.

sexual selection

Sexual selection involves mate choice based on traits that increase reproductive success. While related to evolution, it is not directed by humans in horticulture, making this option incorrect.

natural selection

Natural selection is the process by which traits that increase survival and reproduction in the wild become more common. In this case, human intervention, not environmental pressures, drove the trait selection, so natural selection is not correct.

genetic drift

Genetic drift is the random change in allele frequencies due to chance events, which is not a controlled process like breeding. It does not explain the intentional development of these cultivated plants.