Illuminating patterns of firefly abundance using citizen science data and machine learning models.

As insect populations decline in many regions, conservation biologists are increasingly tasked with identifying factors that threaten insect species and developing effective strategies for their conservation. One insect group of global conservation concern are fireflies (Coleoptera: Lampyridae). Although quantitative data on firefly populations are lacking for most species, anecdotal reports suggest that some firefly populations have declined in recent decades. Researchers have hypothesized that North American firefly populations are most threatened by habitat loss, pesticide use, and light pollution, but the importance of these factors in shaping firefly populations has not been rigorously examined at broad spatial scales. Using data from >24,000 surveys (spanning 2008-16) from the citizen science program Firefly Watch, we trained machine learning models to evaluate the relative importance of a variety of factors on bioluminescent firefly populations: pesticides, artificial lights at night, land cover, soil/topography, short-term weather, and long-term climate. Our analyses revealed that firefly abundance was driven by complex interactions among soil conditions (e.g., percent sand composition), climate/weather (e.g., growing degree days), and land cover characteristics (e.g., percent agriculture and impervious cover). Given the significant impact that climactic and weather conditions have on firefly abundance, there is a strong likelihood that firefly populations will be influenced by climate change, with some regions becoming higher quality and supporting larger firefly populations, and others potentially losing populations altogether. Collectively, our results support hypotheses related to factors threatening firefly populations, especially habitat loss, and suggest that climate change may pose a greater threat than appreciated in previous assessments. Thus, future conservation of North American firefly populations will depend upon 1) consistent and continued monitoring of populations via programs like Firefly Watch, 2) efforts to mitigate the impacts of climate change, and 3) insect-friendly conservation practices.

Identification of a Female-Produced Sex Attractant Pheromone of the Winter Firefly, Photinus corruscus Linnaeus (Coleoptera: Lampyridae).

Firefly flashes are well-known visual signals used by these insects to find, identify, and choose mates. However, many firefly species have lost the ability to produce light as adults. These "unlighted" species generally lack developed adult light organs, are diurnal rather than nocturnal, and are believed to use volatile pheromones acting over a distance to locate mates. While cuticular hydrocarbons, which may function in mate recognition at close range, have been examined for a handful of the over 2000 extant firefly species, no volatile pheromone has ever been identified. In this study, using coupled gas chromatography - electroantennographic detection, we detected a single female-emitted compound that elicited antennal responses from wild-caught male winter fireflies, Photinus corruscus. The compound was identified as (1S)-exo-3-hydroxycamphor (hydroxycamphor). In field trials at two sites across the species' eastern North American range, large numbers of male P. corruscus were attracted to synthesized hydroxycamphor, verifying its function as a volatile sex attractant pheromone. Males spent more time in contact with lures treated with synthesized hydroxycamphor than those treated with solvent only in laboratory two-choice assays. Further, using single sensillum recordings, we characterized a pheromone-sensitive odorant receptor neuron in a specific olfactory sensillum on male P. corruscus antennae and demonstrated its sensitivity to hydroxycamphor. Thus, this study has identified the first volatile pheromone and its corresponding sensory neuron for any firefly species, and provides a tool for monitoring P. corruscus populations for conservation and further inquiry into the chemical and cellular bases for sexual communication among fireflies.

An improved firefly algorithm with dynamic self-adaptive adjustment.

The firefly algorithm (FA) is proposed as a heuristic algorithm, inspired by natural phenomena. The FA has attracted a lot of attention due to its effectiveness in dealing with various global optimization problems. However, it could easily fall into a local optimal value or suffer from low accuracy when solving high-dimensional optimization problems. To improve the performance of the FA, this paper adds the self-adaptive logarithmic inertia weight to the updating formula of the FA, and proposes the introduction of a minimum attractiveness of a firefly, which greatly improves the convergence speed and balances the global exploration and local exploitation capabilities of FA. Additionally, a step-size decreasing factor is introduced to dynamically adjust the random step-size term. When the dimension of a search is high, the random step-size becomes very small. This strategy enables the FA to explore solution more accurately. This improved FA (LWFA) was evaluated with ten benchmark test functions under different dimensions (D = 10, 30, and 100) and with standard IEEE CEC 2010 benchmark functions. Simulation results show that the performance of improved FA is superior comparing to the standard FA and other algorithms, i.e., particle swarm optimization, the cuckoo search algorithm, the flower pollination algorithm, the sine cosine algorithm, and other modified FA. The LWFA also has high performance and optimal efficiency for a number of optimization problems.

Validating species distribution models to illuminate coastal fireflies in the South Pacific (Coleoptera: Lampyridae).

The coastal areas of Vanuatu are under a multitude of threats stemming from commercialization, human development, and climate change. Atyphella Olliff is a genus of firefly that includes species endemic to these coastal areas and will need protection. The research that has already been conducted was affected by accessibility due to the remote nature of the islands which left numerous knowledge gaps caused by a lack of distributional data (e.g., Wallacean shortfall). Species distribution models (SDM) are a powerful tool that allow for the modeling of the broader distribution of a taxon, even with limited distributional data available. SDMs assist in filling the knowledge gap by predicting potential areas that could contain the species of interest, making targeted collecting and conservation efforts more feasible when time, resources, and accessibility are major limiting factors. Here a MaxEnt prediction was used to direct field collecting and we now provide an updated predictive distribution for this endemic firefly genus. The original model was validated with additional fieldwork, ultimately expanding the known range with additional locations first identified using MaxEnt. A bias analysis was also conducted, providing insight into the effect that developments such as roads and settlements have on collecting and therefore the SDM, ultimately allowing for a more critical assessment of the overall model. After demonstrating the accuracy of the original model, this new updated SDM can be used to identify specific areas that will need to be the target of future conservation efforts by local government officials.

Light from a firefly at temperatures considerably higher and lower than normal.

Bioluminescence emissions from a few species of fireflies have been studied at different temperatures. Variations in the flash-duration have been observed and interesting conclusions drawn in those studies. Here we investigate steady-state and pulsed emissions from male specimens of the Indian species Sclerotia substriata at temperatures considerably higher and lower than the ones at which they normally flash. When the temperature is raised to 34 °C, the peak wavelength gets red-shifted and the emitted pulses become the narrowest which broaden considerably thereafter for small increases in temperature; this probably indicates denaturation of the enzyme luciferase catalyzing the light-producing reaction. When the temperature is decreased to the region of 10.5-9 °C, the peak gets blue-shifted and the flash-duration increased abnormally with large fluctuation; this possibly implies cold denaturation of the luciferase. We conclude that the first or hot effect is very likely to be the reason of the species being dark-active on hot days, and the second or cold one is the probable reason for its disappearance at the onset of the winter. Our study makes the inference that these two happenings determine the temperature-tolerance, which plays a major role in the selection of the habitat for the firefly.

Three new species of emLamprigera/em Motschulsky (Coleoptera, Lampyridae) from China, with notes on known species.

Lamprigera is found only in those countries from the Himalaya-Karakoran -Tibet region to SE Asia where 17 species have been previously recorded. These 17 include four species from China. In this work, combined molecular data (COI) and morphological traits identified eight species in our collections. Among these, we found three Chinese species (Lamprigera alticola Dong Li, sp. nov., Lamprigera luquanensis Dong Li, sp. nov. and Lamprigera magnapronotum Dong Li, sp. nov.) that are new to science, bringing the total number of species of Lamprigera to 20 (17+3), and four other known species that are herein newly recorded for the first time in China. These four new records, the three new species, and the four previously known records bring the total number of Chinese species to 11. The morphological traits, especially the male genitalia and pronotum, are described for all eight species. We conclude that male genitalia and pronotum are the most important diagnostic traits for separating species of Lamprigera, and this is confirmed by COI data.

Effects of artificial light on growth, development, and dispersal of two North American fireflies (Coleoptera: Lampyridae).

Holometabolous insects exhibit complex life cycles in which both morphology and ecological niche change dramatically during development. In the larval stage, many insects have soft, slow-moving bodies and poor vision, limiting their ability to respond to environmental threats. Artificial light at night (ALAN) is an environmental perturbation known to severely impact the fitness of adult insects by disrupting both temporal and spatial orientation. The impact of ALAN on earlier life stages, however, is largely unknown. We conducted a series of laboratory experiments to investigate how two distinct forms of ALAN affect the development and movement of immature Photuris sp. and Photinus obscurellus fireflies. Although long-term exposure to dim light at night (dLAN), akin to urban skyglow, did not impact overall survivorship or duration of egg, larval, and pupal stages in either species, it did accelerate weight gain in early-instar Photuris larvae. Late-instar Photuris exposed to point sources of ALAN at the start of their nightly foraging period were also significantly more likely to burrow beneath the soil surface, rather than disperse across it. ALAN may therefore impede dispersal of firefly larvae away from illuminated areas, which could have downstream consequences for the reproductive fitness of adults.

Comparative Transcriptomics Reveals Gene Families Associated with Predatory Behavior in Photuris femme fatale Fireflies.

Identifying the basis of phenotypic variation is a key objective of genetics. This work has been mostly limited to model systems with a plethora of genetic manipulation and functional characterization tools. With the development of high-throughput sequencing and new computational tools, it is possible to identify candidate genes related to phenotypic variation in non-model organisms. Fireflies are excellent for studying phenotypic variation because of their diverse and well-characterized behaviors. Most adult fireflies emit a single mating flash pattern and do not eat. In contrast, adult females of many species in the genus Photuris employ multiple flash patterns and prey upon mate-seeking males of other firefly species. To investigate the genetic basis for this variation, we used comparative transcriptomics to identify positively selected genes between a predatory firefly, Photuris sp., and a non-predatory relative, Photuris frontalis, controlling for genes generally under selection in fireflies by comparing to a Photinus firefly. Nine gene families were identified under positive selection in the predatory versus non-predatory Photuris comparison, including genes involved in digestion, detoxification, vision, reproduction, and neural processes. These results generate intriguing hypotheses about the genetic basis for insect behavior and highlight the utility of comparative transcriptomic tools to investigate complex behaviors in non-model systems.

Bioluminescence emissions from the Indian winter species of firefly Diaphanes sp.

Numerous studies have been carried out on different aspects of the light from summer-active fireflies. Characteristics of this light have led to very interesting conclusions on the chemiluminescence reaction as well as on the nature of the light from live fireflies. Here we present a first report on bioluminescence emissions from a newly found winter-active Indian species of firefly Diaphanes sp. The steady-state emission spectrum from this species comes out to be apparently similar to those from the other two Indian summer species, Luciola praeusta and Asymmetricata circumdata: asymmetric in nature with a little bit of change in the position of the peak wavelength and in the width of the full width at half maximum. An increase in temperature to approximately 28°C causes a red-shift in the peak wavelength, which probably indicates denaturation of the enzyme luciferase in the live, flashing condition. Emissions in the time domain reveal that the light is never completely off - it decreases in intensity to a low value, sometimes very close to zero, and then increases - a characteristic unheard-of till date. Flash durations are considerably longer than those from the two Indian summer species; those become shorter at about 28°C and increase to noticeably larger values at higher temperatures.

A swarm design paradigm unifying swarm behaviors using minimalistic communication.

Numerous nature inspired algorithms have been suggested to enable robotic swarms, mobile sensor networks and other multi-agent systems to exhibit various self-organized behaviors. Swarm intelligence and swarm robotics research have been underway for a few decades and have produced many such algorithms based on natural self-organizing systems. While a large body of research exists for variations and modifications in swarm intelligence algorithms, there have been few attempts to unify the underlying agent level design of these widely varying behaviors. In this work, a design paradigm for a swarm of agents is presented which can exhibit a wide range of collective behaviors at swarm level while using minimalistic single-bit communication at the agent level. The communication in the proposed paradigm is based on waves of 'ping'-signals inspired by strategies for communication and self organization of slime mold (Dictyostelium discoideum) and fireflies (lampyridae). The unification of common collective behaviors through this Wave Oriented Swarm Paradigm (WOSP) enables the control of swarms with minimalistic communication and yet allowing the emergence of diverse complex behaviors. It is demonstrated both in simulation and using real robotic experiments that even a single-bit communication channel between agents suffices for the design of a substantial set of behaviors. Ultimately, the reader will be enabled to combine different behaviours based on the paradigm to develop a control scheme for individual swarms.

Manifestation of Peaks in a Live Firefly Flash.

Several studies have been carried out on flashing of fireflies till now. From patterns of its flashes in different ambient conditions, different conclusions have been drawn and hypotheses put forward. Here we observe flashes emitted by two Indian species of firefly Luciola praeusta and Asymmetricata circumdata. For the species L. praeusta, as the temperature is lowered below about 21 °C, simple pulses become compound or combination ones. Males begin to emit bi-modal flashes while females emit both bi- and tri-modal flashes, along with the simple ones, in a regular manner. For the species A. circumdata, this feature is evident even at their normal flashing temperatures. Though rare, three-peaked flashes do appear from male specimens of both these species, and decay times of all the three peaks in a male- or a female-flash come out to be a few tens of, or a hundred-odd, milliseconds - in contrast to the nanosecond lifetimes determined by different workers for different analogs of the light emitter molecule oxyluciferin. We propose that the tri-modal feature in a flash represents three luminescent forms of the excited state of oxyluciferin, which in the normal flashing state in the living firefly decays via a pathway followed by molecules exhibiting phosphorescence.

Fireflies thwart bat attack with multisensory warnings.

Many defended animals prevent attacks by displaying warning signals that are highly conspicuous to their predators. We hypothesized that bioluminescing fireflies, widely known for their vibrant courtship signals, also advertise their noxiousness to echolocating bats. To test this postulate, we pit naïve big brown bats (Eptesicus fuscus) against chemically defended fireflies (Photinus pyralis) to examine whether and how these beetles transmit salient warnings to bats. We demonstrate that these nocturnal predators learn to avoid noxious fireflies using either vision or echolocation and that bats learn faster when integrating information from both sensory streams-providing fundamental evidence that multisensory integration increases the efficacy of warning signals in a natural predator-prey system. Our findings add support for a warning signal origin of firefly bioluminescence and suggest that bat predation may have driven evolution of firefly bioluminescence.

The evolution of sexual signal modes and associated sensor morphology in fireflies (Lampyridae, Coleoptera).

Animals employ different sexual signal modes (e.g. visual, acoustic, chemical) in different environments and behavioural contexts. If sensory structures are costly, then evolutionary shifts in primary signal mode should be associated with changes in sensor morphology. Further, sex differences are expected if male and female signalling behaviours differ. Fireflies are known for their light displays, but many species communicate exclusively with pheromones, including species that recently lost their light signals. We performed phylogenetically controlled analyses of male eye and antenna size in 46 North American taxa, and found that light signals are associated with larger eyes and shorter antennae. In addition, following a transition from nocturnal light displays to diurnal pheromones, eye size reductions occur more rapidly than antenna size increases. In agreement with the North American taxa, across 101 worldwide firefly taxa in 32 genera, we found light displays are associated with larger eye and smaller antenna sizes in both males and females. For those taxa with both male and female data, we found sex differences in eye size and, for diurnal species, in antenna size.

Firefly Mating Algorithm for Continuous Optimization Problems.

This paper proposes a swarm intelligence algorithm, called firefly mating algorithm (FMA), for solving continuous optimization problems. FMA uses genetic algorithm as the core of the algorithm. The main feature of the algorithm is a novel mating pair selection method which is inspired by the following 2 mating behaviors of fireflies in nature: (i) the mutual attraction between males and females causes them to mate and (ii) fireflies of both sexes are of the multiple-mating type, mating with multiple opposite sex partners. A female continues mating until her spermatheca becomes full, and, in the same vein, a male can provide sperms for several females until his sperm reservoir is depleted. This new feature enhances the global convergence capability of the algorithm. The performance of FMA was tested with 20 benchmark functions (sixteen 30-dimensional functions and four 2-dimensional ones) against FA, ALC-PSO, COA, MCPSO, LWGSODE, MPSODDS, DFOA, SHPSOS, LSA, MPDPGA, DE, and GABC algorithms. The experimental results showed that the success rates of our proposed algorithm with these functions were higher than those of other algorithms and the proposed algorithm also required fewer numbers of iterations to reach the global optima.

Frequency and phase synchronization in large groups: Low dimensional description of synchronized clapping, firefly flashing, and cricket chirping.

A common observation is that large groups of oscillatory biological units often have the ability to synchronize. A paradigmatic model of such behavior is provided by the Kuramoto model, which achieves synchronization through coupling of the phase dynamics of individual oscillators, while each oscillator maintains a different constant inherent natural frequency. Here we consider the biologically likely possibility that the oscillatory units may be capable of enhancing their synchronization ability by adaptive frequency dynamics. We propose a simple augmentation of the Kuramoto model which does this. We also show that, by the use of a previously developed technique [Ott and Antonsen, Chaos 18, 037113 (2008)], it is possible to reduce the resulting dynamics to a lower dimensional system for the macroscopic evolution of the oscillator ensemble. By employing this reduction, we investigate the dynamics of our system, finding a characteristic hysteretic behavior and enhancement of the quality of the achieved synchronization.

Bioluminescence emissions of female fireflies of the species Luciola praeusta.

Numerous investigations have been carried out on bioluminescence emissions from male fireflies. However, very few observations have been made on the emitted light from female specimens. Even in those, apart from observing responses from females to courtship flashes from conspecific males, detailed studies have not been performed. Here we present a first report on the light of female fireflies of the Indian species Luciola praeusta Kiesenwetter 1874 (Coleoptera:Lampyridae:Luciolinae). In the steady-state emission spectrum over the temperature range of 20-40°C, the peak wavelength is the same as, while the full width at half maximum is larger than, that of a male specimen of this species. Increase in temperature up to 45°C brings out a change in both the peak and FWHM values, shifting towards red. In the time-resolved measurement, duration of a flash, which is noticeably larger than that of a male, is found to decrease exponentially with temperature at 20-40°C. Further increase in the temperature produces a minimum flash duration at 41.5°C, and beyond this causes a considerable increase in duration for small increase in temperature. Additionally, lowering the temperature below 20°C makes a single flash appear as a combination of two or three flashes.

Tibetan Firefly Luciferase with Low Temperature Adaptation.

Fireflies are widespread all over the world and a numerous numbers of luciferases have been isolated and characterized. In this study, we identified and characterized the luciferase and luciferase-like genes from a Tibetan firefly collected in Shangri-La, China. The altitude of this area is more than 3300 m. We saw this Tibetan firefly flying with strong luminescence after sunset at ~10°C. We analyzed the transcriptome of Tibetan firefly using head, thorax, abdomen (without light organ), and light organ tissue by RNA sequencing. We identified one luciferase gene, which was almost identical to luciferase from fireflies Pyrocoelia species, and expressed specifically in the light organ. Interestingly, the optimal temperature of the Tibetan firefly recombinant luciferase was 10°C. The Km for D-luciferin and ATP of the recombinant luciferase was 23 and 154 µm, respectively. The optimal pH was around 7.0-7.5. The emission peak was 556 nm at pH 8.0, while it shifted to 606 nm at pH 6.0. We also found a luciferase-like gene with 43% identical amino acids to the Tibetan firefly luciferase, which was scarcely expressed in any portion of the adult body. No luciferase activity was detected for this luciferase-like protein.

The evolution of adult light emission color in North American fireflies.

Firefly species (Lampyridae) vary in the color of their adult bioluminescence. It has been hypothesized that color is selected to enhance detection by conspecifics. One mechanism to improve visibility of the signal is to increase contrast against ambient light. High contrast implies that fireflies active early in the evening will emit yellower luminescence to contrast against ambient light reflected from green vegetation, especially in habitats with high vegetation cover. Another mechanism to improve visibility is to use reflection off the background to enhance the light signal. Reflectance predicts that sedentary females will produce greener light to maximize reflection off the green vegetation on which they signal. To test these predictions, we recorded over 7500 light emission spectra and determined peak emission wavelength for 675 males, representing 24 species, at 57 field sites across the Eastern United States. We found support for both hypotheses: males active early in more vegetated habitats produced yellower flashes in comparison to later-active males with greener flashes. Further, in two of the eight species with female data, female light emissions were significantly greener as compared to males.

Bioinspired photonic structures by the reflector layer of firefly lantern for highly efficient chemiluminescence.

Fireflies have drawn considerable attention for thousands of years due to their highly efficient bioluminescence, which is important for fundamental research and photonic applications. However, there are few reports on the reflector layer (RL) of firefly lantern, which contributes to the bright luminescence. Here we presented the detailed microstructure of the RL consisting of random hollow granules, which had high reflectance in the range from 450 nm to 800 nm. Inspired by the firefly lantern, artificial films with high reflectance in the visible region were fabricated using hollow silica microparticles mimicking the structure of the RL. Additionally, the bioinspired structures provided an efficient RL for the chemiluminescence system and could substantially enhance the initial chemiluminescence intensity. The work not only provides new insight into the bright bioluminescence of fireflies, but also is importance for the design of photonic materials for theranostics, detection, and imaging.