BIOLUMINESCENT ACTIVITY IN THE MATING AND ANTIPREDATORY BEHAVIOR OF A MARINE OSTRACOD (CRUSTACEA, MYODOCOPIDA)

Abstract

About an hour after the sun sets a complex and ritualized light show of precise, vertically placed luminescent pulses erupts over the shallow grassbeds of the western Caribbean throughout the year. These are the most complex displays known in marine systems. Displays consist of repeated trains of secreted bioluminescent pulses in a specific pattern ejected into the water column for courtship by male Vargula annecohenae, small (<2mm) myodocopid ostracod crustaceans. Quantification via the use of image intensification and infrared videography shows that each 40-cm long luminescent display train consists of a stationary phase of 3 (usually) brighter, longer pulses placed close together, followed by a helical phase of about a dozen evenly placed dimmer, shorter pulses secreted by an individual male rapidly spiraling upward. The operational sex ratio in the display grounds above the grassbeds is highly skewed toward males (>175:1). Each participating male is capable of 1) initiating a luminescent display train, 2) entraining on another displaying male in loose luminescent synchrony, and 3) ?sneaking? silently on a luminescing male, and can switch among these three tactics during a single train. Which alternative mating tactic is chosen is predicted by the orientation and distance of the responding male from the initial courtship display at the start of that tactic. Unlike fireflies, females do not respond with luminescent signals of their own. Instead, by using a light-emitting-diode array to mimic a male display, I show that females respond to and intercept the intermittent luminescent displays by compensating their trajectories between each light pulse. Besides courtship, all individuals of V. annecohenae (males, females, and juveniles) respond to predation attempts by their nocturnal predators by releasing enormous quantities of luminescence. Since individuals are distasteful to their predators, the signals probably function as aposematic signals, but also as lures for predators of an attacker (burglar alarm). Based on photomultiplier tube recordings of 1) courtship displays, 2) antipredation displays, and 3) total luminescent available, a male could produce nearly 500 courtship trains or 4 major antipredation displays from its existing stores.