Thanksgiving: Wild Turkey Families

This week take a moment to ponder the beast in your feast. The wild turkey (Meleagris gallopavo) has a sophisticated social system that rivals that of lions or primates.

Let’s start with the wild turkey’s breeding system. Their system defies most traditional organization schemes biologists have proposed, falling somewhere between harem defense in which each male guards…well…a harem and a lek mating system in which the ladies choose among several gents. Groups of female turkeys may be attended by a team of two or more males who act together to try to woo the hens and keep other suitors away, but that doesn’t stop other admirers from orbiting the female flock as it wanders around.

Two tom turkeys court a hen. Photo: Alan Krakauer

But don’t be fooled, lady turkeys are far from passive players. Turkey hens can, and do, mate with more than one male. (To find out what females find sexy, check out the work of Dr. Richard Buchholz, including a recent summary airing on Science Friday Spoiler Alert: it’s all in the snood.) Wild Turkey hens are also prone sneak their eggs into the nest of another unsuspecting female turkey and let her do all the work of raising the poult (chick). This only happens in about a quarter of turkey nests, and about a half have just one mom and one dad. Most poults in a nest are usually close relatives.

UCD-Hen-Turkey 1508 — Female turkey, UC Davis campus. Photo: Alan Krakauer

That fact that becomes important for the next part of the story– remember those teams of males? Why do they help each other out? Shouldn’t males try as hard as they can to pass on their own genes? In the 1960’s, PhD student Charles Watts proposed a solution involving a newly emergent concept called kin selection [2]. If the turkey teams were composed of brothers, these males would share many of the same copies of their genes because they are from the same parents. So even if one of the brothers fails to mate, he can still pass on portions of his genome by helping his bro reproduce. Unfortunately for Watts’, his evidence for kin selection was circumstantial, attempts to replicate the study failed, and eventually one of Watts’ own mentors published a critique of the idea [3].

Confirmation of the kin selection hypothesis for cooperation in male turkeys had to wait almost 40 years. With the advent of DNA analyses, we could test which males have the most offspring and whether a turkey and his wingman are brothers. It turns out that usually only one teammate is able to score, but these males tend to father several times as many offspring as guys who tried to mate solo. Not only that, but most teammates were either half brother or full brothers[4]. Based on evolutionary theory (Hamilton’s Rule), Watts was right. For the male turkeys, the subordinate, non-breeding teammates actually pass on more gene copies by helping their buddy reproduce than if they went off to try their luck at solitary display. Turkey mating is a powerful example of how even counter-intuitive behaviors like self-sacrifice can evolve.