Jennifer Colvin

Alan Krakauer[1] (2005) studied coalitions of a single dominant and subordinate male wild turkey who courted females in Monterey, California to determine if the method for courtship display was due to kin selection.

Each of the pairs studied were located on Hastings Natural History Reservation and were observed from 1999 to 2004 in the field. It was determined that three criteria must be met in order to establish kin selection as the explanation for the cooperative signaling: the paired coalition must be related, there must be a benefit to the dominant male because of the help of the subordinate, and that the subordinate’s benefits to helping must outweigh the costs. Each male turkey, some solitary and some in a coaltion, was captured, had a blood sample drawn, was tagged (some were also outfitted with a radio transmitter), and released. Females were also captured for blood samples and tagging then released. Computer software was used to analyze the blood samples. Unlinked gene loci were used to determine the relatedness among individuals, the average in the coalitions being 0.46 (which would indicate half-brothers, and brothers in a coaltion). Mating behaviors were observed by all males, and researchers collected very young turkeys (presumably those from that year’s matings), unhatched eggs from abandon nests, and early nests to determine parentage so that copulations and fitness of males could be determined. On average, it was determined that each dominant male gained more copulations in a coalition than did equally matched solitary males. Also, assuming that the subordinate had the same cost for signaling as a solitary individual, it was found that the subordinate actually benefited from an increase in indirect fitness more than a solitary male would from a direct benefit from mating (+1.7, as determined through use of Hamilton’s rule). They also found that the benefit to the subordinates outweighed the minimum costs incurred. Through these findings, Krakauer showed that male wild turkeys form coalitions with closely related individuals to increase direct (dominant individuals) and indirect fitness (subordinate individuals), thereby demonstrating that kin selection was the reason for formation of these pairs.

This is consistent to the information presented in class regarding signal evolution in animal groups. It was mentioned that honest signaling is very expensive to the sender, and that it would only evolve if the benefits outweighed the costs. Kin selection was proposed as a means for evolution of honest signaling and cooperative signaling between two individuals (as with leks and coalitions). This study clearly demonstrates that kin selection is working on wild turkeys as both individuals incur the same costs; however, only one individual in the coalition actually receives a direct increase in his overall fitness. By demonstrating that subordinate males have no direct increase in their lifetime reproductive success by signaling, but do have an increase in their indirect fitness by helping closely related individuals to mate, the researcher clearly shows that kin selection was the reason for this type of cooperative signaling to evolve.