April 2016 Featured Paper

“Male Courtship Signals and Female Signal Assessment in Photinus greeni Fireflies,” Constantinos I. Michaelidis, Kristian C. Demary, and Sara M. Lewis
Behavioral Ecology, (May/June 2006) Volume 17, Issue 3, pp. 329-335
first published online January 18, 2006
Read the original paper.

In most Photinus fireflies, males flash while in flight to locate a stationary female. If interested, the female responds with a flash. The male flies down to her and they mate.

The male flash is composed of several elements. These include the duration of the flash, the time between flashes, and for those fireflies whose flash consists of more than one pulse of light, the interval between the pulses, or the Inter-Pulse Interval (IPI). Each species of firefly has a combination of these characteristics that are particular to that species. This study examines the double-pulse firefly Photinus greeni to learn what aspects of the male flash signal attracts female response.

P. greeni is one of three fireflies in the consanguineus group that look identical and have similar flash patterns but have slight differences in their IPI (the time between the two pulses in their paired-pulse flash): P. consanguineus has a 0.5 second IPI, followed by P. greeni with a 1.0–1.5 second IPI, and P. macdermotti with a 2.0 second IPI.

Experimental testing sought to discover:

  • If the male flash IPI has any bearing on the female’s ability to recognize her own species when determining her choice of mate.
  • Fireflies are cold-blooded animals. Their metabolism slows down as the temperature cools and, as the timing of their flash is not fixed, it also slows with a drop in temperature. If temperature changes affect the IPI in the male flash signal, does the female adjust to take those changes into account in responding to her own species?
  • If IPI correlates to the size of the male’s nuptial gift (mass of protein the male passes to the female, along with his sperm, to nourish her eggs), so that IPI could be used by females to choose the most desirable mates. Since adult fireflies typically do not eat, females need this protein mass to nourish their eggs.

Results of comprehensive testing in the lab and in the field indicated that:

  • P. greeni females do recognize males of their species by the timing of their IPI. This was true of all three fireflies in the consanguineus group, as females of all three species did not respond to flash signals other than to males of their own species.
  • As in the single-pulse Photinus fireflies, P. greeni females were able to adjust for the timing change in the male IPI that occurs with temperature difference.
  • Measuring the IPI of male P. greeni against the size of his nuptial gift found no correlation between the two. This suggests that the IPI plays no part in the female’s choice of mate. At present, what factors do influence her choice of mate are not known.

Further studies of the relationship between male courtship signals and male desirability as a mate choice are needed to understand the evolution of the complex firefly signaling systems.

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