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

Abstract

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 andex situplayback 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.

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

“…Almost all statistical analyses were performed using linear models unless otherwise noted. Specifics for each model are below and can be found in the code [74]. For all our models where possible, we used the 'check_model' function from the package 'performance' to visually inspect residuals and check model assumptions.…”

“…In all scatterplots, data are jittered for visualization purposes, and all regression lines are only demonstrative unless specifically noted. Model fits can be found in the electronic supplementary material data [74].…”

“…displays) are uncorrelated. Because our data are coded at the level of single displays (each composed of many pulses), and not at the level of flashes within bursts (the analogous situation in terrestrial fireflies, and for which data these tests were devised), we modified the T test to exclude excess correlation in the structure of measured occurrences (see code in electronic supplementary material [74]). Significant p-values calculated from these tests would reject the null hypothesis that the observed distribution was generated from a Poisson process.…”

“…The following R packages were used to handle, analyse, and visualize all data: tidyverse [78], ggplot2 [79], readxl [80], RColorBrewer [81], ggpmisc [82], ggpubr [83], dplyr [84], ggExtra [85], MASS [86], ggpointdensity [87], tidyr [88], patchwork [89], png [90], spatstat [91], broom [92], stringr [93], ggbreak [94], performance [95], sjPlot [96], jtools [97], emmeans [98], multcomp [99], multcompView [100], scales [101], GGally [102]. See electronic supplementary material for details [74].…”

“…Data accessibility. All data and code for this project can be accessed from Dryad: https://doi.org/10.5061/dryad.6m905qg6c [74].…”