The relative cost of using luminescence for sex and defense: light budgets in cypridinid ostracods.

Luminescent signals can be used by animals for a number of purposes, including courtship and defense, sometimes by the same individual. However, the relative costs of producing these different behaviors are largely unknown. In the marine ostracod Photeros annecohenae, males utilize extracellular luminescence for complex courtship displays, and both males and females luminesce as a predation defense. We compared the relative luminescent output of courtship with that of defensive displays and also with respect to their total luminescent stores. Courtship displays are relatively inexpensive compared with defensive displays, with an average defensive display releasing 50 times more luminescence than the average courtship display. Furthermore, in order to completely exhaust its stores, a male would have to produce 450 typical courtship displays or approximately 10 average defensive displays. Both courtship pulses and defensive displays show first-order decay kinetics, yet courtship pulses decay three times faster than defensive displays, suggesting that there is differential release of the luciferin, luciferase and mucus in order to control the reaction kinetics.