Flash Precision at the Start of Synchrony in Photuris frontalis

Synchronous flashing occurs in certain species of SoutheastAsian and North American fireflies. Most Southeast Asian synchronyinvolves stationary congregating fireflies, but North Americansynchrony occurs in flying fireflies that do not congregate.Southeast Asian synchrony is usually continuous, but North Americansynchrony is interrupted. Photuris frontalis, the only memberof the North American genus Photuris to synchronize, shows anintermittent synchrony. This involves synchronization and repeatedre-synchronizations while in flight. The precision that occursat the start of synchrony was studied in Ph. frontalis usingcaged fireflies and photometry. Barrier experiments (using twofireflies) or flash entrainment experiments (using one LED andone firefly) were performed to measure the temporal precisionof the first entrained flash. In both cases, the first entrainedflash was close to unison synchrony (phase = 1.0) and showedlittle variability. The behavioral implications of the abilityto synchronize with the first entrained flash are not known,but it might facilitate male-male interactions during brief,transient encounters such as maintaining distance between closelyflying males in search of females.     

The occurrence of synchrony in the North American fireflyPhotinus carolinus (Coleoptera: Lampyridae)

Synchronous flashing has been described for some Southeast Asian fireflies but has rarely been reported in North American fireflies. Our field observations indicated thatPhotinus carolinus flash synchronously. The flash pattern of individualP. carolinus was characterized by a burst of five to eight flashes over a period of approximately 4 s. These flash bursts were repeated about every 12 s. Groups of fireflies comprised individuals exhibiting this species-specific flash pattern. Remarkably, members of the group flashed synchronously: Flash bursts started and stopped at the same time and the flashes among individuals occurred at the same time as well. We used low-light level videography to examine this behavior in caged groups of (3 or 10) fireflies for synchronic flashing. The occurrence of concurrent rhythmic group flashing satisfies the criteria for synchrony as defined by Buck (1988). The intermittent nature of the bursts of flashes shown byP. carolinus makes this a discontinuous synchrony. The mechanisms underlying discontinuous synchrony are not known.     

Landing distance in a synchronic North American firefly

Abstract.  The flash communication system of Photinus carolinus in Great Smoky Mountain National Park (Tennessee) is characterized by male firefly synchrony. Photinus carolinus males signal a conspecific female with synchronic trains of flashes. A solitary responding female attracts several males, which is not common in North American rover fireflies. The female and the group of males that she attracts are called a cluster. It is hypothesized that the first male attracted to the female would land closer to the female than would additional males because there would be less tendency for visual confusion. This hypothesis is explored under controlled conditions by replacing the responsive female with an appropriately flashing light-emitting diode (LED) located in the center of a flat target area. When infra-red videography is used to measure the first male and the additional males' landing distances from the counterfeit female (LED), most fireflies land within 15 cm of the target LED, and the first male does not land closer than the additional males. It is suggested that cluster formation is a by-product of male synchrony and is facilitated by the tendency of males to land near, but not on, females.     

Variation in flash speed of Japanese firefly,Luciola cruciata (Coleoptera: Lampyridae), identifies distinct southern “quick‐flash” population on Goto Islands,Japan

Luciola cruciata, a bioluminescent firefly endemic to Japan, communicates with species‐specific flashing patterns. Previous studies reported that flying males possess three distinct flashing frequencies: slow (4 s), intermediate (3 s) and fast (2 s). Our study focused on geographical variations in flashing patterns in the northwestern part of the Kyushu region of southern Japan (including its isolated islands) and their relationship to the mitochondrial COII region of firefly DNA. We found that “quick‐flash (1 s)” fireflies occur in the Goto Islands, at the western tip of Kyushu, and that, although they possess a unique haplotype, they do not differ much genetically from “fast‐flash” fireflies inhabiting mainland Kyushu. In contrast, although fireflies inhabiting the Tsushima and Iki Islands also possess a unique haplotype, their flashing patterns were the same (fast‐flash) as fireflies inhabiting mainland Kyushu. We determined that flash patterns of L. cruciata in Japan should be classified according to four flashing patterns: slow, intermediate, fast and quick.     

A spiking neuron model for synchronous flashing of fireflies

Certain species of fireflies show a group behavior of synchronous flashing. Their synchronized and rhythmic flashing has received much attention among many researchers, and there has been a study of biological models for their entrainment of flashing. The synchronous behavior of fireflies resembles the firing synchrony of integrate-and-fire neurons with excitatory or inhibitory connections. This paper shows an analysis of spiking neurons specialized for a firefly flashing model, and provides simulation results of multiple neurons with various transmission delays and coupling strengths. It also explains flashing patterns of some firefly species and examines the synchrony conditions depending on transmission delays and coupling strengths.     

Mechanisms of synchrony in the North American fireflyPhotinus carolinus (Coleoptera: Lampyridae)

Photometric recordings combined with computer stimulation, acquisition and analysis were used to study synchrony in the North American fireflyPhotinus carolinus. A computer-generated burst of simulatedP. carolinus flashes was used to trigger a firefly flash burst. We found that the first triggered firefly flashes occurred after the second or third flashes in the stimulus burst, that there were fewer flashes in a triggered burst than a spontaneous burst, and that extending the stimulus flashes into the firefly's interburst interval inhibited firefly flashing. When the stimulus flash interval (389–560 ms) was changed, no change was seen in the interflash interval. When the stimulus flash interval was changed, the average time between stimulus flash and firefly flash (flash delay) changed as if the firefly interflash interval was constant. Thus, interflash interval inP. carolinus does not change its length, making it similar to the Southeast Asian synchronizerPteroptyx cribellata and different fromPteroptyx malaccae, which can change its interval. We suspect that the time between bursts is functionally analogous to the time between flashes in Southeast Asian synchronizers.     

Spontaneous flash communication of females in an Asian firefly

Fireflies are well known for the use of bioluminescence for sexual communication. In species using flash signals for pair formation, species and sexual identity are conferred by flash timing parameters such as flash duration, flash interval, flash number, and response delay. In dialog fireflies in North America, the male is the advertiser and the female is the responder. In these species, the male flash signal parameter varies depending on species, but the female flash signal parameter is limited only to response delay. However, in fireflies other than dialog fireflies, sexual flash communication is not well studied. Although many female-advertisement-like fireflies are reported, we have no confirmed case of sexual communication in a female-advertisement species. Here, we report the sexual flash communication of an Asian firefly, Luciola (Hotaria) parvula, in which the female flashes spontaneously. By using an electronic firefly, we confirm experimentally that males are specifically attracted to flashes with a female-specific flash duration. This is the first experimental report of sexual communication of a female advertiser in firefly communication. In this species, females call males usually with spontaneous flashes unlike dialog fireflies.     

Flash signal evolution in Photinus fireflies: Character displacement and signal exploitation in a visual communication system

Animal communication is an intriguing topic in evolutionary biology. In this comprehensive study of visual signal evolution, we used a phylogenetic approach to study the evolution of the flash communication system of North American fireflies. The North American firefly genus Photinus contains 35 described species with simple ON–OFF visual signals, and information on habitat types, sympatric congeners, and predators. This makes them an ideal study system to test hypotheses on the evolution of male and female visual signal traits. Our analysis of 34 Photinus species suggests two temporal pattern generators: one for flash duration and one for flash intervals. Reproductive character displacement was a main factor for signal divergence in male flash duration among sympatric Photinus species. Male flash pattern intervals (i.e., the duration of the dark periods between signals) were positively correlated with the number of sympatric Photuris fireflies, which include predators of Photinus. Females of different Photinus species differ in their response preferences to male traits. As in other communication systems, firefly male sexual signals seem to be a compromise between optimizing mating success (sexual selection) and minimizing predation risk (natural selection). An integrative model for Photinus signal evolution is proposed.     

Examining the Role of Cuticular Hydrocarbons in Firefly Species Recognition

During animal courtship, multiple signals transmitted in different sensory modalities may be used to recognize potential mates. In fireflies (Coleoptera: Lampyridae), nocturnally active species rely on long-range bioluminescent signals for species, sex, and mate recognition, while several diurnally active species rely on pheromonal signals. Although in many insects non-volatile cuticular hydrocarbons (CHC) also function in species and sex discrimination, little is known about the potential role of CHC in fireflies. Here, we used gas chromatography to characterize species and sex differences in the CHC profiles of several North American fireflies, including three nocturnal and two diurnal species. Additionally, we conducted behavioral bioassays to determine whether firefly males (the searching sex) were differentially attracted to extracts from conspecific vs. heterospecific females. Gas chromatography revealed that nocturnal Photinus fireflies had low or undetectable CHC levels in both sexes, while diurnal fireflies showed higher CHC levels. No major sex differences in CHC profiles were observed for any firefly species. Behavioral bioassays demonstrated that males of the diurnal firefly Ellychnia corrusca were preferentially attracted to chemical extracts from conspecific vs. heterospecific females, while males of the remaining species showed no discrimination. These results suggest that while CHC may function as species recognition signals for some diurnal fireflies, these compounds are unlikely to be important contact signals in nocturnal Photinus fireflies.     

The effect of flash duration and flash shape on entrainment in Pteroptyx malaccae,a synchronic Southeast Asian firefly

Southeast Asian synchronic fireflies respond to stimulus flashes by phase-shifting their endogenous oscillator. This is called 'flash entrainment'. The releasers for entrainment were studied by changing stimulus flash shape and duration in Pteroptyx malaccae. Stimulus flash shapes and durations were synthesized digitally and delivered by a field-portable computer system. The computer also recorded male firefly flashes that were detected with a photometer. We found that the type of entrainment and its magnitude was influenced by the duration of the entrainment flash and by its shape.     

Adult firefly abundance is linked to weather during the larval stage in the previous year

1. Much is known about the brief adult phase of fireflies. However, fireflies spend a relatively long developmental period under the soil surface. Climatic and soil conditions may directly affect the eggs, larvae, and pupae, and also affect them indirectly through predators, competitors, and prey items. Climatic conditions during the early life stages of this iconic species are therefore relevant to their hypothesised decline within the context of global warming. 2. Data on the abundance of fireflies were extracted from the publicly available citizen dataset across North America over a period of 9 years. The effects of weather in the 24 months before the observations of firefly abundance were documented based on 6761 observations. 3. Climatic conditions during both the larval and adult phases have a non‐linear effect on adult firefly abundance. Maximum winter and spring temperatures and mean precipitation in the 20‐month period before the observations had the greatest impact on the abundance of firefly adults. Low maximum soil moisture during the 5–19 months preceding the observations affected the adult abundance negatively, and high maximum soil moisture affected it positively. 4. After correcting the firefly abundance for these weather effects, it is estimated that the abundance of fireflies increased over the time period of this study. 5. This study suggests that early life climatic conditions have a small but significant impact on adult firefly abundance with a total R² of 0.017.     

Nocturnal capture of fireflies by lycosid spiders: visual versus vibratory stimuli

The untested idea that wolf spiders such as Lycosa rabida rely on visual cues when preying on fireflies at night was examined. Under controlled conditions, individuals of L. rabida and L. punctulata were exposed to both actual and simulated firefly flashing. These stimuli elicited orientation or approach in only 24% of the spiders. In other experiments, constant light yielded more responses than did flash patterns, and a stationary light elicited more responses than did a moving light. Both of these findings suggest that phototaxis underlies the responses. To determine the importance of vibratory cues, crawling fireflies were offered to blinded spiders on a paper substratum and on living plants; response levels were 85% and 100%, respectively. These data suggest that much, if not most, nocturnal predation by lycosid spiders on fireflies involves vibratory rather than visual stimuli.     

Limits to Nuptial Gift Production by Male Fireflies, Photinus ignitus

Males of diverse insect species provide females with nuptial gifts, and limits on males' ability to produce these gifts may influence courtship behavior and mating systems. In the firefly Photinus ignitus, males transfer a complex spermatophore to females during mating. We provided firefly males unlimited access to responsive females to examine whether spermatophore production limits male mating success. Male spermatophore mass decreased significantly across sequential matings, and the percentage of successful matings declined during the second half of each male's life span. Male body mass explained a significant proportion of variation in size of the first spermatophore produced by P. ignitus males, but this relationship disappeared with second spermatophores. This study indicates that males' ability to produce spermatophores declines over their lifetime and that limits on nuptial giftproduction can constrain male mating success in Photinus fireflies.     

Cloning and sequence analysis of cDNA for luciferase of a Japanese firefly, Luciola cruciata

Luciferases of Japanese and North American fireflies act on a common substrate (luciferin) but the resulting lights emitted are of different colors. As a step toward an understanding of the molecular mechanism of the luciferase reaction, a cDNA clone (pGLf1) was isolated from a cDNA library of lantern poly(A)+RNA of the Japanese firefly, Luciola cruciata ('Genji-botaru' in Japanese), using a cDNA of North American firefly luciferase. The isolated 2-kb cDNA sequence was able to direct the synthesis of active luciferase in Escherichia coli under the control of the lac promoter. The primary structure of Genji firefly luciferase deduced from the nucleotide sequence was shown to consist of 548 amino acids (aa) with an Mr of 60,024. Homology between the amino acid sequences of the Genji and North American firefly luciferases was 67%, but a number of amino acid changes were found in the first 200 aa from the N terminus.     

Synchronous rhythmic flashing of fireflies. II

Synchronized flashing by males of some firefly species involves a capacity for visually coordinated, rhythmically coincident, inter-individual behavior that is apparently unique in the animal kingdom except for a few other arthropods and for man. This paper reviews (1) diverse communicative interactions that have evolved from elementary photic signals, (2) physiological mechanisms of synchronism, and (3) theories about its biological meaning. Work of the past 20 years shows that flash synchrony is widespread geographically and taxonomically, appears in an astonishing range of spectacular display types, utilizes several neural flash-control mechanisms and is pervasively but enigmatically involved in courtship. No proposed function for synchrony has been fully established but theory and physiology concur in indicating that synchrony aids male orientation toward the female, female recognition of male flashing, or both. Increased mate choice for the female is one likely ultimate benefit.     

Firefly distribution and abundance on mangrove vegetation assemblages in Sepetang estuary,Peninsular Malaysia

Pteroptyx fireflies are commonly reported to congregate in large numbers in mangroves. Not much is known about the relationships between firefly distribution and abundance with specific mangrove vegetation assemblages. We conducted a study to investigate the vegetation assemblages that structure the distribution and abundance of Pteroptyx tener in Peninsular Malaysia. The distribution and abundance of fireflies were assessed along an 8 km stretch of mangroves in Sepetang estuary using visual assessment. Statistical analysis was carried out to test the correlation between length of display section and percentage cover of P. tener colonies and the relationship between percentage cover of fireflies with different vegetation assemblages. Five distinct vegetation assemblages were identified comprising different combination of four mangrove species. It was found that shorter display sections had higher percentage cover of P. tener colonies. In addition, vegetation assemblage which consisting of mainly Sonneratia caseolaris and Nypa fruticans was the most preferred type. The results of this study point to the necessity to consider not only a single mangrove species but the entire vegetation assemblage for firefly conservation.     

Pyrazine emission by a tropical firefly: An example of chemical aposematism?

Although famous for photic courtship displays, fireflies (Coleoptera: Lampyridae) are also notable for emitting strong odors when molested. The identity of volatile emissions and their possible role, along with photic signals, as aposematic warnings of unpalatability have been little explored, especially in tropical species. Pursuant to the observation that the widespread Neotropical fireflies, Photuris trivittata and Bicellonycha amoena, emit pungent odors, glows, and flashes when handled, we investigated their cuticular and headspace chemistry. Gas chromatography–mass spectrometry analyses revealed that both fireflies have species‐specific cuticular hydrocarbon profiles. Photuris trivittata headspace was dominated by 2‐methoxy‐3‐(1‐methylpropyl) pyrazine (hereafter, pyrazine), on the order of 1.59 ng/individual and a suite of sesquiterpenes, while B. amoena emitted 3‐methoxy‐2‐butenoic acid methyl ester and a few ketones. This is the first report of such compounds in fireflies. We investigated the role of pyrazine in P. trivittata's interactions with potential predators: sympatric ants, toads, and bats. Solvent‐washed P. trivittata painted with pyrazine incurred lower ant predation than did their solvent‐washed counterparts. Pyrazine significantly repelled ants at baits in concentrations as low as 9.8 × 10^?4 ng/μl. The toad, Rhinella marina, readily accepted intact fireflies, pyrazine‐coated and uncoated mealworms. Both Myotis nigricans and Molossus molossus bats rejected fireflies, but accepted both pyrazine‐coated and uncoated mealworms. While pyrazine repels ants, its role as an aposematic signal warning other potential predators of firefly distastefulness requires further investigation. Our results underscore the idea that multiple enemies exert conflicting selection on firefly defenses.     

Firefly Femmes Fatales: A Case Study in the Semiotics of Deception

Mimicry and deception are two important issues in studies about animal communication. The reliability of animal signs and the problem of the benefits of deceiving in sign exchanges are interesting topics in the evolution of communication. In this paper, we intend to contribute to an understanding of deception by studying the case of aggressive signal mimicry in fireflies, investigated by James Lloyd. Firefly femmes fatales are specialized in mimicking the mating signals of other species of fireflies with the purpose of attracting responding males to become their prey. These aggressive mimics are a major factor in the survival and reproduction of both prey and predator. It is a case of deception through active falsification of information that leads to efficient predation by femmes fatales fireflies and triggered evolutionary processes in their preys’ communicative behaviors. There are even nested coevolutionary interactions between these fireflies, leading to a remarkable system of deceptive and counterdeceptive signaling behaviors. We develop here a semiotic model of firefly deception and also consider ideas advanced by Lloyd about the evolution of communication, acknowledging that deception can be part of the explanation of why communication evolves towards increasing complexity. Increasingly complex sign exchanges between fireflies evolve in an extremely slow pace. Even if deceptive maneuvers are played out time and time again between particular firefly individuals, the evolution of the next level of complexity—and thus the next utterance in the dialogue between species—is likely to take an immense amount of generations.     

Flight Studies on Photic Communication by the Firefly Photinus pyralis

Flash communication by the firefly Photinus pyralis was studiedin a stationary, simulated flight apparatus in which an individualof either sex could be "flown" and its flashing behavior andflight orientation recorded in response to photic stimulation.Males made long "flights" showing many of the characteristicsof their natural, female-seeking patrol flights. Males orientedtheir flight vectors towards light emitting diode (LED) flashesthat mimicked the responses of females to their patrol flashes.Females flew and responded to male-emulating LED flashes, makinga previously unknown early response followed by the typical2 sec delayed response characteristic of the dialoging perchedfemale, including abdominal aiming of the flash. Pairs consistingof males, in tethered flight, and females, perched, were runin an integrating sphere photometer, permitting the first determinationsof flash intensities of both sexes during courtship dialog.The implications of this work on thought about evolution ofphotic behavior in fireflies are considered.     

Fireflies with or without prespermatophores: Evolutionary origins and life-history consequences

During mating, some male North American fireflies produce spermatophores from prespermatophores in their paired reproductive accessory glands. Other species of fireflies have neither prespermatophores nor spermatophores. To establish a pattern of spermatophore occurrence across firefly species, we examined the male internal reproductive system in 20 Japanese species belonging to 10 genera for the presence or absence of prespermatophores. Twelve species from seven genera produced prespermatophores, while eight species from three genera did not. Superimposed on a molecular phylogeny of Japanese fireflies based on mitochondrial 16S ribosomal DNA sequences, the basal group was prespermatophore producers. Prespermatophores appear to have been lost in two different lineages. Species without prespermatophores are characterized by degeneration of both the forewings and hindwings, and by body gigantism in females.