Question

In a flock of birds, parents can raise small clutches on their own but can increase their clutch size if they have a helper. You want to see if altruistic behavior is likely to spread. To do this you observed a male bird that stayed at his birth nest for a year to help raise the offspring of his father and his stepmother (the original mother died) and then built his own nest the following year. You calculated direct fitness (cost) for the male bird by counting the number of offspring he produced in one year and multiplied it by ½ due to the relatedness between parents and offspring. To calculate his indirect fitness (benefit), you took the total number of offspring produced in his birth nest by his father and stepmother when he assisted them and multiplied it by ½. To determine if this altruistic behavior would spread you subtracted the cost from the benefit to determine whether it was greater than 1. What did you do wrong

Answer 1

The student made an error in calculating the indirect fitness (benefit) of the male bird's behavior. The coefficient of relatedness between the male bird and his siblings should be used, not 1/2. Additionally, comparing the net benefits of the behavior to a threshold value of 1 is necessary to assess whether altruistic behavior is likely to spread.

Step-by-step explanation:

It seems that you have made an error in calculating the indirect fitness (benefit) of the male bird's behavior. While you correctly multiplied the total number of offspring produced in his birth nest by his father and stepmother, you should not have multiplied it by 1/2. Instead, you should have multiplied it by the coefficient of relatedness between the male bird and his siblings, which is 1/2 in this case. Additionally, it's important to note that determining whether altruistic behavior is likely to spread involves comparing the net benefits (benefits minus costs) of the behavior to a threshold value of 1, not just the benefit alone.

Answer 2

The mistakes made

• Altruistic behavior is measured as ; b - c > 0 and not b - c > 1
• relatedness for half siblings = 0.25 and not 1/2

Step-by-step explanation:

The relatedness between ; Mother, father, daughter and son = 0.5 ( 1/2 ) which is included in the direct fitness category ( For the MALE bird )

The relatedness for the Half brother and Half sister of the male bird = 0.25 ( 1/4 ) ( indirect fitness )

hence applying Hamilton's rule

Relatedness = rb - c > 0

where b = benefit , c = cost

∴Total fitness = ∑ direct fitness + ∑ indirect fitness

= 0.5x + 0.25y

hence the mistakes made

• Altruistic behavior is measured as ; b - c > 0 and not b - c > 1
• relatedness for half siblings = 0.25 and not 1/2