Kin Selection - Examples

Examples

Eusociality (true sociality) is used to describe social systems with three characteristics: one is an overlap in generations between parents and their offspring, two is cooperative brood care, and the third characteristic is specialized castes of nonreproductive individuals. Social insects are an excellent example of organisms that display presumed kin selected traits. The workers of some species are sterile, a trait that would not occur if individual selection was the only process at work. The relatedness coefficient r is abnormally high between the worker sisters in a colony of Hymenoptera due to haplodiploidy, and Hamilton's rule is presumed to be satisfied because the benefits in fitness for the workers are believed to exceed the costs in terms of lost reproductive opportunity, though this has never been demonstrated empirically. There are competing hypotheses, as well, which may also explain the evolution of social behavior in such organisms (see Eusociality).

Another example is preference among individuals in sun-tailed monkey communities. Data shows that maternal kin (kin related to by mothers) behaved more preferentially towards each other. However, once kin got beyond half-siblings or further relatives, this bias dropped significantly.

Alarm calls in ground squirrels are another example. While they may alert others of the same species to danger, they draw attention to the caller and expose it to increased risk of predation. Paul Sherman, of Cornell University, studied the alarm calls of ground squirrels. He observed that they occurred most frequently when the caller had relatives nearby. In a similar study, John Hoogland was able to follow individual males through different stages of life. He found that the male prairie dogs modified their rate of calling when closer to kin. These behaviors show that self-sacrifice is directed towards close relatives and that there is an indirect fitness gain.

Alan Krakauer of University of California, Berkeley has studied kin selection in the courtship behavior of wild turkeys. Like a teenager helping her older sister prepare for prom night, a subordinate turkey may help his dominant brother put on an impressive team display that is only of direct benefit to the dominant member.

Recent studies provide evidence that even certain plants can recognize and respond to kinship ties. Using sea rocket for her experiments, Susan Dudley at McMaster University in Canada compared the growth patterns of unrelated plants sharing a pot to plants from the same clone. She found that unrelated plants competed for soil nutrients by aggressive root growth. This did not occur with sibling plants.

In the wood mouse (Apodemus sylvaticus), aggregates of spermatozoa form mobile trains, some of the spermatozoa undergo a premature acrosome reactions that correlate to improved mobility of the mobile trains towards the female egg for fertilization. This association is thought to proceed as a result of a "green beard effect" in which the spermatozoa perform a kin-selective altruistic act after identifying genetic similarity with the surrounding spermatozoa.