Final answer:
The male meerkat's altruistic behavior has resulted in 2 units of indirect fitness, as he saved two full siblings and three offspring of another sibling, which is genetically equivalent to saving 2.75 of his own offspring.
Step-by-step explanation:
The benefit of the male meerkat's altruism in terms of indirect fitness can be understood through the concept of inclusive fitness and kin selection. By saving the lives of two sisters, with each sister sharing approximately 50% of his genes, and three offspring of another sibling, likely sharing 25% of his genes, the male meerkat has contributed to the propagation of his genetic information despite not reproducing himself.
When it comes to measuring indirect fitness, we must consider the degree of genetic relatedness and the number of individuals helped. The male meerkat's altruistic act saved two full siblings, equivalent to one of his own offspring for each (since full siblings share 50% of their genes), and the three offspring of another sibling, equivalent to 0.75 of his own offspring (since nieces and nephews share about 25% of their genes).
Therefore, in total, the male meerkat has indirectly supported 2 (from sisters) + 0.75 (from nieces/nephews) = 2.75 units of his genes. Even though he lost the opportunity to have three direct offspring, the indirect fitness benefit totals closer to 2.75 units, rounding down to 2 units of indirect fitness. This is slightly less than if he had his own offspring but still significant. Thus, the correct answer is b. 2 units of indirect fitness.