Not all male ants are “sperm missiles”

Image from the phenomenal  Alex Wild.

In a new review Juergen Heinze discusses the adaptive nature of male lifespans in ants. Far from being mere short-lived “sperm missiles”, in EO Wilson’s words, many ants, particularly in the tropics, live an independent existence, sipping nectar and looking for mating opportunities.

Juergen highlights the contributions of  AntLab alum Jon Shik, particularly his  Life History Continuum Hypothesis.  When most folks think of mating ants–and you are likely thinking about them right now–they picture swarms of males and females in some weird, lascivious mating scrum. Kind of a cross between “Dirty Dancing” and “Mad Max Beyond the Thunderdome”. Such scrums leave the wreckage of spent males littering the landscape, typically to be picked up by other ants and carried off for food. Ahh, the cycle of life.

Jon builds the case that “female calling”, the ancestral mating system in ants, favors males that can endure life longer outside the nest. In female calling, new queens emerge from their natal colony and release a pheromone to lure in male suiters. If no male comes along, they may return to the nest and try again the next night. In this slowed down breeding system,Jon argues, it is in the male’s best interest to be persistent in the search for his elusive one-on-one rendezvous with a female. Species with colonies that subscribe to female calling, he shows, provision their males for the potentially long series of nights ahead.

Considering how important the relatively short-lived sexual window is in the long-term existence of a typical colony, we know surprisingly little about male biology, or even the phenology–the timing–of ant flights. Early in my career, I gained access to hundreds of vials from Light Traps and Malaise Traps on Barro Colorado  Island, and spent many delightful hours sorting the winged queens and male to species. My ultimate goal was to test the hypothesis that the some 400 species of ants on the island may partition the calendar, each flying in their own designated window.

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The number of ant queens and males, two species from four genera, flying across the lunar months on Barro Colorado Island, Panama. Even Gnamptogenys hartmani, which prefers to fly in May, will dribble out alates over most of the year. Many of these species exhibit the mating syndrome “Female Calling”, where queens lure individual males using pheromones.

I was shocked, shocked (!) to find my hypothesis pretty much destroyed by something even cooler–that a large fraction of tropical ant species fly year-round. Jon’s work nailed the connection to their mating system.

This still leaves a lot of potential for good work. To me, one of the big questions, relevant to any group with lotsa species in one place, is how do they divy up all that reproductive bandwidth?  Assume, for example, that queens of 200 or so species in the forest of BCI may be releasing their pheromones on a given night, and all those different molecules swirl through the still humid night air. That’s a lot of perfume to sort out. No wonder males are long-lived. They have to be patient.



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