Female ostracods respond to and intercept artificial conspecific male luminescent courtship displays

Some male cypridinid ostracods (ca. 2 mm) utilize luminescent secretions in the most unique and complex light displays yet described in marine environments. While swimming rapidly males secrete pulses of luminescence to attract females, but females do not reciprocate with light production. Females have been hypothesized to be attracted to and exhibit choice between these signals but this remained untested. Their small size and nighttime mating activity necessitated laboratory experiments that used light mimics of the males patterns in order to observe individual female behavior. In this study, we asked 2 simple questions: are females attracted to the light patterns that mimic conspecific male display patterns, and, if so, what do females actually do on detecting and responding to this signal pattern? Using a blue light-emitting diode array, we mimicked the male display of Photeros annecohenae in the lab and, in conjunction with infrared lighting and infrared cameras, we recorded individual behaviors of virgin females. Here, we provide direct evidence that females respond to the pulsed light mimic and approach the intermittent signal in such a way that they would cross closely above the path of an upwardly signaling male. In order to maximize her proximity to each pulse in the display, a responding female swims at a compensatory angle above the display to adjust her vector to intercept the male above each preceding pulse. These data support the hypothesis that luminescence is the initial signal used by males to attract receptive females in courting ostracods.