Adaptive Value

Adaptive value of eusociality

There are a number of theories that attempt to explain the phenomenon of eusociality.  One of these is the theory of kin selection, expounded by William Hamilton.  Kin selection is the theory that cooperative care between workers can be beneficial to a non-reproducing individual if the genetic relatedness between the caretaker and the cared for is such that the survival of the cared for will increase representation of selected-for characteristics in the colony.  Hamilton’s rule describes kin selection and how it might account for eusociality.  (19)

r = genetic relatedness of the caretaker to the cared for
B = the benefit gained by the caretaker
C = the reproductive cost to the caretaker in performing the act.

In essence – the genetic relatedness of the actor and the recipient, multiplied by the benefit gained by the actor, must be greater than the reproductive cost incurred.

Along with kin selection is the idea that a eusocial structure allows for increased parental care. Offspring of eusocial species are cared for by a number of attentive adult individuals, thus reducing the cost of rearing by any one individual, and increasing the likelihood of survival for offspring.

In Heterocephalus glaber

Food-aridity hypothesis

The food-aridity hypothesis posits that the eusocial social structure of the naked mole-rat is an adaptive response to the harsh conditions in which the mole-rat lives.  To cope with these conditions, the mole-rat forms large social communities that cooperatively perform necessary tasks.  Large burrow networks that are built and defended by worker mole-rats allow the mole-rats to find and maintain adequate amounts of food.  Fundamentally, this idea is based on the fact that in conditions where food is scarce and distributed over a wide area, it is unlikely for a solitary mole-rat to be able to find enough food to sustain itself.  This risk is greatly decreased when several mole rats search for food. (15)

“In these arid regions, survival therefore depends on having a work force that reduces the risks of not finding food and that shares the cost of burrowing, of repairing the tunnel system, and also of defending it against predators.”(15)

The food-aridity hypothesis is supported by the fact that in the arid parts of Africa where the naked mole-rat is found, there are no species of solitary mole-rats, though there are several in the family Bathyrergidae.