Kin selection and cooperative courtship in wild turkeys

Abstract

In the few species of birds in which males form display partnerships to attract females, one male secures most or all of the copulations. This leads to the question of why subordinate males help in the absence of observable reproductive benefits. Hamilton's concept of kin selection, whereby individuals can benefit indirectly by helping a relative, was a crucial breakthrough for understanding apparently altruistic systems. However in the only direct test of kin selection in coordinated display partnerships, partners were unrelated, discounting kin selection as an explanation for the evolution of cooperation. Here I show, using genetic measures of relatedness and reproductive success, that kin selection can explain the evolution of cooperative courtship in wild turkeys. Subordinate (helper) males do not themselves reproduce, but their indirect fitness as calculated by Hamilton's rule more than offsets the cost of helping. This result confirms a textbook example of kin selection that until now has been controversial and also extends recent findings of male relatedness on avian leks by quantifying the kin-selected benefits gained by non-reproducing males.

There is no fitness but fitness, and the lineage is its bearer

“…In many cases (like wild turkeys), the assumption underlying the canonical Hamilton's rule almost certainly does not hold, and a different condition for adaptedness is required. We emphasize that highlighting this issue in no way detracts from the novelty or significance of Krakauer's study [12] in particular, which is a good example of the painstaking work required to quantify the fitness consequences of social behaviour in the wild. More generally, this issue is not a reason to stop quantifying inclusive fitness or Hamilton's rule.…”

“…Worryingly, the conclusions from the same data can be very different depending on whether or not these assumptions hold, even if the costs, benefits and relatedness are quantified properly. We illustrate our point by considering a seemingly straightforward case, that of cooperative courtship of wild turkeys [12].…”

“…This idea was not tested quantitatively until Krakauer [12] measured the reproductive success of males in singletons and pairs along with the relatedness of males within a pair. In particular, he measured the average siring success of singleton males and the dominant male in pairs.…”

“…To quantify Hamilton's rule or inclusive fitness using field or experimental data, one needs to carefully specify the structure of the social interaction, which will determine the relevant condition to be met for the trait in question to be adaptive. We illustrate these complexities using the example of cooperative courtship in wild turkeys [12].…”

Queller’s Separation Condition Explained and Defended

“…Empirical studies which use an inclusive fitness approach (e.g. Pfennig et al 1999;Krakauer 2005;Chuang et al 2010;Hatchwell et al 2014) and those which use a multi-level selection approach (e.g. Tsuji 1995;Eldakar et al 2010;Formica et al 2010) all fall under this broad description, although (as we show below) the two approaches represent two different ways of extending the traditional breeder's equation.…”