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.