Collective synchrony of mating signals modulated by ecological cues and social signals in bioluminescent sea fireflies

Individuals often employ simple rules that can emergently synchronise behaviour. Some collective behaviours are intuitively beneficial, but others like mate signalling in leks occur across taxa despite theoretical individual costs. Whether disparate instances of synchronous signalling are similarly organised is unknown, largely due to challenges observing many individuals simultaneously. Recording field collectives and ex situ playback experiments, we describe principles of synchronous bioluminescent signals produced by marine ostracods (Crustacea; Luxorina) that seem behaviorally convergent with terrestrial fireflies, and with whom they last shared a common ancestor over 500 mya. Like synchronous fireflies, groups of signalling males use visual cues (intensity and duration of light) to decide when to signal. Individual ostracods also modulate their signal based on the distance to nearest neighbours. During peak darkness, luminescent "waves" of synchronous displays emerge and ripple across the sea floor every ~60 seconds, but such periodicity decays within and between nights after the full moon. Our data reveal these bioluminescent aggregations are sensitive to both ecological and social light sources. Because the function of collective signals is difficult to dissect, evolutionary convergence, like in the synchronous visual displays of diverse arthropods, provides natural replicates to understand the generalities that produce emergent group behaviour.

Methods
Data are a mixture of types from different methods and experiments. They are most clearly outliend and used in conjunciton with the provided R code for context. Briefly, the majority of data are from observations of collective bioluminescent behaviors of wild, naturally kept, or experimentally manipulated ostracods (marine crustaceans). We used either cameras or human observations to record data. Camera data was either post-processed using computer vision or annotated by eye to record the number of bright pixels or number of behaviors, respectively. One data set was collected with a spectroradiometer, as described in the methods of the paper. Images in the dataset are demonstrative of the methods.