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Sexual Selection in Fireflies

    Fredric V. Vencl and Albert D. Carlson

Keywords: Behavior, firefly, sexual selection, mate competition, Photinus

Male competition in courtships of the firefly Photinus pyralis is intense. Male size is variable, possibly exhibiting alternative body plans. We examined the outcomes of courtships to determine the mechanisms of selection that may have led to differences in male size.

Two distinct selective events occur in mate competition: (1) searching and (2) scramble competition. Males approach females through the air, then land and approach over the substrate of leaves or weeds. Although many courtships failed, those without rivals were shorter and successful males spent less time in the "mate-guarding" position than when several males were in competition. Winners flashed more often than losers, but flash dialogs between males and females averaged similar number across rival densities, indicating that females require some minimal amount of information before mating.

Female flash preference was examined in choice tests to evaluate female discrimination ability. Females preferred the earlier and brighter flashes. This suggests that what might appear to be flash "synchronization" could really be attempts by males to become flash leaders, not followers. Large males possess correspondingly large lanterns and therefore greater flash intensity. Not surprisingly females preferred large males in the searching period, while small males were favored in scrambles. Simulated scrambles showed that small males have superior locomotor abilities, allowing them to reach the female more rapidly.

Comparison with a species lacking scrambles, P. macdermotti, with no size differences among males revealed that selection in P. pyralis is disruptive, targeting traits alternately, and may have led to the evolution of greater size difference between males with direct male competition. Both male competition and female choice are important determinants of the outcome of P. pyralis courtships.

Reference: Vencl, F.V. and A.D. Carlson (1997) Proximate mechanisms of sexual selection in the firefly Photinus pyralis (Coleoptera: Lampyridae). J. Insect Behav. 11:191 - 207.

Submitted: 19-Jan-99

The contents of this page are the sole responsibility of the person named below.

Albert D. Carlson |
Dept of Neurobiology & Behavior | phone: 516-632-8661
SUNY at Stony Brook |
Stony Brook, New York  11794 USA |
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