Natural Selection animation (stabilizing, disruptive and directional selection)

Summary

The script explores Batesian mimicry in butterflies, where edible species mimic the appearance of unpalatable ones to avoid predation. It discusses how different environmental conditions lead to stabilizing, directional, or disruptive selection. Stabilizing selection favors mimics with intermediate markings, directional selection occurs when less marked species disappear, and disruptive selection arises when intermediately marked models decline, leading to a population dominated by extreme phenotypes.

Takeaways

• 🌿 The environment exerts selective pressure on species, affecting their evolution.
• 🦋 Butterflies in the test species are batesian mimics, mimicking the appearance of unpalatable butterfly species to gain protection from predators.
• 🐦 Predators like birds avoid eating unpalatable butterfly species after tasting them, and this behavior extends to edible mimics that resemble them.
• 📊 The abundance of model species (unpalatable butterflies) influences the type of natural selection that mimics undergo.
• 🔄 Stabilizing selection occurs when the model species with intermediate markings is most abundant, leading to a reduction in variation among mimics.
• 📈 Directional selection happens when a specific phenotype becomes more advantageous, such as when predators learn to eat mimics with few markings.
• 🌶 Disruptive selection takes place when the population of mimics is dominated by more extreme phenotypes, resulting in two peaks in the frequency graph.
• 📉 If a distasteful species disappears, predators may learn to eat mimics that previously resembled that species, leading to changes in the mimic population.
• 🔄 Changes in the environment, such as the decrease in abundance of a model species, can lead to shifts in the selection pressures on mimics.
• 🧬 Natural selection is dynamic and can result in different outcomes based on environmental pressures and the availability of model species.

Q & A

What is the role of the environment in the selective pressure on a species?

The environment exerts selective pressure on a species by influencing which traits are advantageous for survival and reproduction. In the script, predators like birds affect the survival of butterflies, favoring those that can avoid predation.

What are the characteristics of the test species of butterflies mentioned in the script?

The test species of butterflies are batesian mimics, meaning they are edible but mimic the appearance of unpalatable species to gain protection from predation.

How do predators like birds respond to the presence of unpalatable butterfly species?

Birds learn to avoid eating unpalatable butterfly species after capturing and tasting them, thus learning to recognize and avoid similar-looking butterflies.

What is stabilizing selection as described in the script?

Stabilizing selection occurs when the most abundant model species has intermediate markings, leading to the test species with similar intermediate markings having an advantage. Over generations, this reduces variation by increasing the frequency of intermediate phenotypes.

How does the disappearance of a distasteful species with few markings affect the test species?

When the distasteful species with few markings disappears, predators learn that butterflies with few markings are edible. This means the edible test species with few markings are no longer protected and thus have a lower survival rate.

What is directional selection in the context of the script?

Directional selection happens when the phenotype of the edible test species with few markings is no longer protected, leading to a shift in the population graph to the right, favoring those with more markings.

Can you explain disruptive selection as mentioned in the script?

Disruptive selection occurs when the intermediately marked model species decreases in abundance, causing predators to avoid only those butterflies that are barely marked or highly marked. This results in the population of mimics being dominated by more extreme phenotypes over many generations.

How does the abundance of model species influence the type of natural selection the mimics undergo?

The abundance of model species determines whether the mimics will undergo stabilizing, directional, or disruptive selection. The specific phenotypes that are advantageous change depending on which model species are most common.

What happens to the population graph of the test species over generations under stabilizing selection?

Under stabilizing selection, the population graph of the test species will have a higher, narrower peak, indicating a reduction in variation as the intermediate phenotype becomes more prevalent.

How does the population graph of the test species change under disruptive selection?

Under disruptive selection, the population graph of the test species will have two peaks, representing the dominance of more extreme phenotypes, with one peak for barely marked and another for highly marked individuals.

What is the significance of batesian mimicry in the survival of the test species?

Bateesian mimicry is significant for the survival of the test species because it allows edible individuals to gain protection from predation by resembling unpalatable species, thus increasing their chances of survival and reproduction.