Problem 9 - AP Biology Premium Prep 2021

Question

Peacock males have evolved to have huge, beautiful tails with numerous large eye spots. Long, colorful tails are difficult to carry when you are running from a predator. However, peahens (female peacocks) have been shown by researchers to mate preferably with males with more eye spots and longer tails, despite these traits making the males more susceptible to predation. Over time, this preference has resulted in peacocks with huge tails due to (A) sexual selection (B) disrupted selection (C) divergent evolution (D) sympatric speciation

Step-by-Step Solution

Answer

The correct answer is (A) sexual selection, as male peacocks have evolved long, colorful tails with eye spots due to the preference of peahens, making them more likely to secure mates despite increased predation risk.

Step 1: Understand the given concepts

We know that peacocks have developed a particular trait (long, colorful tails with eye spots) that makes them more susceptible to predation but also more likely to mate with peahens. Understand the four options given: (A) Sexual selection - a natural selection process in which individuals with particular traits are more likely to secure a mate. (B) Disrupted selection - an unnatural event where individuals with extreme traits have higher fitness, resulting in a bimodal population distribution. (C) Divergent evolution - the process by which a species splits into two or more distinct species due to the development of different traits. (D) Sympatric speciation - a process where a new species evolves from a single ancestral species while inhabiting the same geographic area.

Step 2: Eliminate unrelated concepts

We can first rule out options (C) and (D) as they involve the formation of new species. The given example is all about preference in mating and does not imply the formation of new species. This leaves us with (A) sexual selection and (B) disrupted selection.

Step 3: Relate the scenario to the concepts

Since we know that the peacocks have developed long, colorful tails with eye spots due to the preference of peahens, and this has made them more likely to secure mates, this trait is a result of sexual selection. Disrupted selection is not applicable because it involves an unnatural occurrence.

Step 4: Choose the correct option

The correct answer is therefore (A) sexual selection, as it best explains the given scenario with peacocks and the evolution of their long, colorful tails with eye spots.

Key Concepts

Peacock Evolution

Peacock evolution is a captivating example of how certain physical traits can arise and persist over generations due to specific mating preferences. Male peacocks, known as peacocks, have developed eye-catching long tails adorned with eye spots. These extravagant tails serve as a visual spectacle intended to attract mates. The evolution of these features can primarily be attributed to sexual selection, where traits that do not necessarily offer survival advantages can still become prevalent if they increase reproductive success.

This process has led male peacocks to evolve tails that, while beautiful, make them more vulnerable to predators. Despite this risk, the presence of long, colorful tails has persisted because peahens consistently prefer mates with these traits. As a result, males with pronounced features are more likely to reproduce, passing on their genetic traits to future generations, reinforcing the peacock's evolutionary pattern.

Natural Selection Processes

Natural selection is a cornerstone in evolutionary biology, describing how certain traits become more common within a population due to better survival and reproduction rates. In the case of peacocks, sexual selection is a type of natural selection focusing on reproductive success rather than survival. While natural selection traditionally might favor traits that aid in avoiding predators, sexual selection can drive the evolution of features that seem contrary to survival, like the peacock's ornate tail.

When a trait enhances a peacock's chance of mating, even at the cost of survival, it becomes prominent through sexual selection. Thus, natural selection covers various pathways, and in the peacock's case, it emphasizes how successful reproduction can prioritize mating advantages over immediate survival traits. Peacocks illustrate how natural and sexual selection processes can intermingle, especially when reproductive success dictates evolutionary tendencies.

Mating Preferences

Mating preferences play a crucial role in shaping the physical traits of many species, including peacocks. These preferences are often tied to visual or behavioral cues that signal health, genetic superiority, or increased fitness. In the case of peahens, their choice in males is heavily influenced by the visual display of eye spots and tail length. Such preferences are not superficial; they are deeply rooted in an evolutionary strategy to select the best genes for offspring.

Peahens tend to favor males with more elaborate tails as these features may represent a peacock's ability to survive despite the handicap. The bright tails signify vigor and genetic quality, leading to healthier, more viable offspring. Through these focused preferences, mating acts as a powerful selection force that drives the evolution of particular traits in a population.

Evolutionary Biology

Evolutionary biology explores the processes driving the changes in traits over generations within populations. It looks into the dynamics of how environmental pressures, genetic variation, and mating systems like sexual selection shape the biodiversity we see today. Regarding peacocks, evolutionary biology provides insight into how and why certain traits develop, such as the peacock's extravagant tail, which is a product of sexual selection pressures.

In evolutionary terms, the peacock tail's evolution exemplifies how natural selection can lead to striking and sometimes puzzling adaptations. By studying evolution through the lens of biology, we understand that mate selection criteria can significantly shape a species' evolutionary trajectory. Here, the interplay of genetic inheritance and environmental interactions highlights how evolutionary biology accounts for the fascinating diversity of life.