Question

List and describe the three primary social interactions where the social recipient gains a positive effect on reproduction / fitness. Give one brief example for each of these interactions that clearly supports your definition. Define obligate and facultative altruism. Provide one example each for obligate and facultative altruism that clearly describes how these two forms of altruism work. Name and define the key factor that leads to altruism becoming a common behavior. What is “Hamilton’s Rule?”

Answer 1

The three primary social interactions where the social recipient gains a positive effect on reproduction / fitness are:

1. Mutualism

2. Reciprocity

3. Altruism

Mutualism: Mutualisms are defined as interactions between two organisms of different species, in which each organism benefits from the interaction in some way.

An example of obligate mutualistic symbiosis is the interaction between the fig wasp and fig trees; the life cycles of both depend on the other. The queen fig wasp enters the inside is a cluster of flowers and seeds via ostiole, losing her wings and antennae in the process. Once inside the fig, the wasp lays her eggs and simultaneously deposits the pollen, which she carried from another fig; in doing so, she fertilizes the fig’s ovaries.

Once she has laid her eggs, the queen dies and her body is digested, providing nourishment for the fig. Once the eggs hatch, the males and females mate with each other. The females begin to collect pollen, while the males start to dig through the flesh of the fig to the exterior, creating an exit route for the females. The females leave the fig, and travel to another tree, carrying with them the pollen, which begins the reproduction cycle for both fig and fig wasp again.

Reciprocity: It is an altruistic behavior between two organisms of different species say “A” & “B”, in which one organism (A) behaves in such a manner that it temporarily reduces its own fitness for the better fitness of another organism (B), with an expectation that the other organism(B) will do the same or behave in the same at later time when required by organism (A).

Example: Cleaner fish, the host fish does not eat the cleaner fish and allows it to clean it self. If it doesn’t allow or kills the fish the host fish is seen to get injuries by ecto parasites or disease.

Altruism: it is the selfless act or behavior of an organism, In which say organism A increases the fitness of organism B; While decreasing its own (organism- A) fitness.

Obligate Altruism: Permanent loss of direct fitness (with potential for indirect fitness gain). Example- Honey bee workers foraging for colony

Facultative Altruism: Temporary loss of direct fitness (with potential for indirect fitness gain, followed by personal reproduction). Example- Florida scrub jay helping at the nest, then gaining parental territory.

Hamilton’s Rule:

It specifies the conditions under which reproductive altruism evolves:

r × B > C

where,

B= is the benefit gained by the recipient of the altruism (i.e. gain or benefits is calculated in terms of number of offspring)

C = is the cost suffered by the donor while undertaking the altruistic behavior (i.e. Cost is calculated by number of direct offspring not produced as a result of performing the altruistic act)

r = is the genetic relatedness of the altruist to the beneficiary.