August 2013 Featured Paper

"Lek Assembly and Flash Synchrony in the Arizona Photinus knulli Green" by Joseph M. Cicero. The Coleopterists Bulletin, Vol. 37, No. 4 (December 1983), pp. 318-342.
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This paper describes the unusual mating behavior of Photinus knulli, a firefly found in canyon bottoms in Arizona. Unlike most Photinus males that seek out females individually, male P. knulli congregate in special breeding arenas called leks. These leks comprise an area of about five square meters and may contain hundreds of fireflies.

As evening approaches, males emerge from their daytime hiding places under rocks. A few males will surface simultaneously in close proximity to each other. These males will remain on the ground and exchange flashes. Most of the males, however, emerge singly and take to the air to patrol a flyway stretching approximately one half mile, with the lek at one end. They patrol back and forth for about an hour, at which time they fly over the lek and land to join the grounded males.

On the ground, the males are scattered among the rocks and vegetation, each male in sight of only a couple other males. One male, termed the initiator, fires off a series of three quick flashes. His flash triplet stimulates an adjacent male to flash a triplet. A third male responds to the second with his triplet, and so on until a group of up to sixty males have flashed in sequence. Since each male can only see one or two other males, this flash sequence almost always takes the form of a single line or train of flashes winding its way throughout the lek.

The initiator repeats his triplet every six seconds up to 5 times. Each male in the train responds, but with a shorter delay between his triplet and the preceding male. By the third set of triplets, all of the males in the train are flashing simultaneously. During the fourth and fifth sequences, the train begins to break up, with some males wandering off to find females. After the fifth sequence, all flashing stops. A period of darkness lasting up to ten minutes will occur before another flash train begins.

There are three possible benefits to males flashing in a train:

  1. The group of males that remain on the ground upon emergence from their daytime shelters may act as a beacon to the patrolling males, guiding them back to the lek.
  2. The train may serve to indicate the density of rival males in any one area of the lek. While the time delay between triplets is a constant six seconds for the initiator, all other males in the train must shorten their delay if they are to line up their flashes with the initiator by the third set of triplets. The time delay becomes progressively shorter for each successive male in the train. Therefore, a male may judge the number of males in the train by the length of time between the triplets of the male preceding him.
  3. The train may help the males locate females. When a male leaves the train in search of a female, he may direct his wandering away from the males on either side of him, assuming that there are no females in their general vicinity.

Females are evenly distributed throughout the lek. When a female is approached by a number of males, she will emit a prolonged flare. Upon seeing this flare the males will approach her, producing a dimmed flash—either single or triplet. When they reach the female, they will try to mate with her. She will reject them at first, and only after an hour of complex interactions among the males will she allow a male to mate with her. How she chooses the male to be her mate is not known.

If there are no males in her immediate vicinity, the female will broadcast an "advertising phrase." The male that spots this signal will fly high above and spiral down to her, and mate within minutes.

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