Biology subjects

Gerrish, G. A.

Publications and source records attributed to Gerrish, G. A..

4 recordsLinked to original sources

bioRxiv2026

Aposematic signals are dynamic over time in bioluminescent ostracods

Aposematic signals convey information about prey unpalatability to potential predators. Such signals are defined as advertisements, with prey usually signalling unpalatability before an attack. Overlooked, however, is whether signals presented after an attack can function as aposematic warnings and influence the efficacy of defense. Here, we test if post-attack signals can be aposematic by observing fish predators responding to prey (Ostracoda, Cypridinidae) that produce bioluminescence following an attack. By manipulating potential chemical defenses of prey, and by comparing feeding responses to both bioluminescent and nonluminescent prey, we provide multiple lines of evidence to show bioluminescent prey are unpalatable and use post-attack bioluminescence as an aposematic signal. First, live, bioluminescent prey secrete bioluminescence only after being attacked. Second, predatory fishes rarely consumed bioluminescent prey, especially compared to nonluminescent alternatives. Third, because fishes readily ate bioluminescent prey that had been treated (frozen or boiled), which should remove defenses, bioluminescent species likely possess some unidentified defense over nonluminescent relatives. Finally, over the course of four experimental trials, predators were less likely to consume bioluminescent prey as their cumulative exposure to bioluminescent displays increased, indicative of learning. Post-attack aposematic signals, like bioluminescence, may be as common and effective a defensive strategy as pre-attack signals.

animal behavior and cognition↗

bioRxiv2023

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.

animal behavior and cognition↗

bioRxiv2021

Transcriptome phylogenies support ancient evolutionary transitions in bioluminescence traits of cypridinid ostracods

Although the the diversity, beauty, and intricacy of sexually selected courtship displays command the attention of evolutionists, the longevity of these traits in deep time is poorly understood. Population-based theory suggests sexual selection could either lower or raise extinction risk, resulting in high or low persistence of lineages with sexually selected traits. Furthermore, empirical studies that directly estimate longevity of sexually selected traits are uncommon. Sexually selected signals - including bioluminescent courtship - originated multiple times during evolution, allowing empirical study of their longevity after careful phylogenetic and divergence time analyses. Here, we estimate the first transcriptome-based molecular phylogeny and divergence times of Cypridinidae. We report extreme longevity of bioluminescent courtship, a trait important in mate choice and probably under sexual selection. Our relaxed-clock estimates of divergence times coupled with stochastic character mapping show luminous courtship evolved only once in Cypridinidae in a Sub-Tribe we name Luxorina at least 151 Million Years Ago (Ma) from cypridinid ancestors that used bioluminescence only in anti-predator displays, defining a Tribe we name Luminini. This time-calibrated molecular phylogeny of cypridinids will serve as a foundation for integrative and comparative studies on the biochemistry, molecular evolution, courtship, diversification, and ecology of cypridinid bioluminescence. The persistence of luminous courtship for hundreds of millions of years indicates that rates of speciation within the group exceeded extinction risk, allowing for the persistence of a diverse clade of signalling species and that sexual selection did not cause rapid loss of associated traits.

evolutionary biology↗

bioRxiv2020

Molecular evolution of luciferase diversified bioluminescent signals in sea fireflies (Crustacea:Ostracoda:Cypridinidae)

Understanding the genetic causes of evolutionary diversification is challenging because differences across species are complex, often involving many genes. However, cases where single or few genetic loci affect a feature that varies dramatically across a radiation of species would provide tractable opportunities to understand the genetics of diversification. Here, we show the diversification of bioluminescent signals in cypridinid ostracods ("sea fireflies") to be strongly influenced by a single gene, cypridinid-luciferase. We find different evolutionary processes, including selection, drift, and constraint, each acted on c-luciferase at different times during evolutionary history and impacted different phenotypes, diversifying behavioral signals across species. In particular, some amino acid sites in c-luciferase evolved under episodic diversifying selection, and are associated significantly with phenotypic changes in both enzyme kinetics and color, which impact signals directly. We also find that multiple other amino acid positions in c-luciferase evolved neutrally or under purifying selection and may have impacted the variation of color of bioluminescent signals across genera. This work provides a rare glimpse into the genetic basis of diversification across many species, showing how multiple evolutionary processes may act at different times during a radiation of species to diversify phenotypes. These results indicate not only selection but also drift and constraint may be important evolutionary drivers of species diversification. Significance statementA hallmark of life is its astounding diversity. While we are beginning to understand the drivers of biodiversity, uncovering the genetic basis remains challenging. As such, how different molecular evolutionary processes act to diversify phenotypes is a major question in biology. Here we show a single gene to be important in a riotous diversity of fantastical behaviors - the bioluminescent signals of sea fireflies - allowing us to demonstrate multiple evolutionary forces including selection, drift, and constraint contributed to diversification. Our work highlights that not only selection but also neutral processes and constraint have each worked at different times to shape phenotypic diversity.

evolutionary biology↗