Problem 4 - Campbell Biology Concepts & Connections

Question

A male redwing blackbird will chase predatory birds away from his breeding territory during nesting season. Which hypothesis best explains his behavior? a. He is acting for the good of the species. He may die, but other birds of his species will be saved. b. He knows this will increase his fitness, so he chases away the predator. c. He carries a gene that causes fathers to protect their offspring, which increases inclusive fitness. d. He has imprinted on the offspring in his nest, so he knows that they are his.

Step-by-Step Solution

Answer

Hypothesis c is the best explanation: the bird carries a gene that increases inclusive fitness by protecting its offspring.

Step 1: Understand the Question

Read the question carefully and identify what is being asked. The question is about the best hypothesis explaining a male redwing blackbird's behavior of chasing predatory birds away from his breeding territory during the nesting season.

Step 2: Analyze Each Hypothesis

Examine each provided hypothesis and determine its plausibility based on known biological principles.

Step 2a: Evaluate Hypothesis a

Hypothesis a suggests the bird is acting for the good of the species, even at the risk of his own life. This idea is less accepted in modern evolutionary biology because natural selection typically acts on individuals rather than species.

Step 2b: Evaluate Hypothesis b

Hypothesis b states the bird chases the predator because it increases his fitness. This fits the principle of natural selection, where behaviors that increase individual fitness are favored.

Step 2c: Evaluate Hypothesis c

Hypothesis c proposes that the bird has a gene causing fathers to protect offspring, increasing inclusive fitness. This is plausible as protecting offspring can increase the chances of the parent's genes being passed on.

Step 2d: Evaluate Hypothesis d

Hypothesis d involves imprinting, suggesting the bird knows the offspring are his due to imprinting. Imprinting is not typically the mechanistic explanation for this type of behavior in wild birds.

Step 3: Choose the Best Hypothesis

After evaluating all hypotheses, choose the best explanation that aligns most closely with principles of evolutionary biology and individual fitness.

Key Concepts

Natural Selection

Natural selection is a key mechanism of evolution. It explains why certain traits become more common in a population over time. These traits improve an individual's chances of surviving and reproducing. In our example of the redwing blackbird, natural selection helps to understand why the bird chases away predators.
When the male blackbird defends its nest from predators, it ensures the safety of its offspring. This behavior increases the chances that his genes will be passed on to the next generation. Behaviors that improve an individual's fitness, like protecting offspring, are favored by natural selection. In summary, natural selection is about the survival and reproduction of those best adapted to their environment.

Inclusive Fitness

Inclusive fitness broadens the idea of fitness. It includes an individual's own offspring and also the offspring of relatives. This concept explains why animals sometimes behave in ways that benefit their relatives. If a trait helps relatives survive and reproduce, it can be favored by evolution.
For the redwing blackbird, inclusive fitness can explain why he protects his nestlings. By ensuring the survival of his own offspring, he increases the possibility of his genes being passed down. Protecting close relatives can also increase his genetic contribution to the next generation. Therefore, inclusive fitness incorporates both direct and indirect reproduction into evolutionary benefits.

Evolutionary Biology

Evolutionary biology studies how living organisms evolve over time through changes in traits. It combines aspects of genetics, ecology, and paleontology.
For the redwing blackbird, evolutionary biology offers insights into behaviors like nest defense. Evolutionary principles help us understand why protecting offspring evolved as a common behavior. These behaviors would have been naturally selected because they increased reproductive success. Evolutionary biology helps to predict and explain the adaptations and behaviors observed in current species.

Imprinting

Imprinting is a form of learning occurring at a specific life stage. It usually happens early in life and forms a strong bond between parent and offspring. While imprinting is well-documented in some species, it might not explain all protective behaviors in birds.
For instance, while imprinting might help a bird recognize its offspring, it does not fully explain the protective nature of the male redwing blackbird. Other evolutionary mechanisms, like natural and inclusive fitness, play a more crucial role in this behavior. Overall, imprinting is essential but might not be the sole explanation for parental protective behaviors.