Short- and mid-wavelength artificial light influences the flash signals of Aquatica ficta fireflies (Coleoptera: Lampyridae)

The Evolutionary Importance of Intraspecific Variation in Sexual Communication Across Sensory Modalities

The evolution of sexual communication is critically important in the diversity of arthropods, which are declining at a fast pace worldwide. Their environments are rapidly changing, with increasing chemical, acoustic, and light pollution. To predict how arthropod species will respond to changing climates, habitats, and communities, we need to understand how sexual communication systems can evolve. In the past decades, intraspecific variation in sexual signals and responses across different modalities has been identified, but never in a comparative way. In this review, we identify and compare the level and extent of intraspecific variation in sexual signals and responses across three different modalities, chemical, acoustic, and visual, focusing mostly on insects. By comparing causes and possible consequences of intraspecific variation in sexual communication among these modalities, we identify shared and unique patterns, as well as knowledge needed to predict the evolution of sexual communication systems in arthropods in a changing world.

Sperm Competition and Paternity in the Endangered Firefly Pyrocoelia pectoralis (Coleoptera: Lampyridae: Lampyrinae)

The endangered terrestrial firefly Pyrocoelia pectoralis (Olivier) is endemic to China. Populations of P. pectoralis have decreased dramatically due to urbanization and pollution. Breeding and re-introduction to a suitable habitat may save the species from becoming extinct. Because of its polyandrous character, an investigation into the possibility of sperm competition and paternity outcomes from multiple matings was initiated to better understand its reproductive physiology. To achieve these goals, 13 SSR markers were developed. The results of paternity experiments indicate there is a significant difference between P3 and P1 or P2. The female reproductive system has three spermathecae which accept sperm from different matings, and no bursa or spermatophore-digesting organ is developed. Our research established that multiple inseminations with sperm from different males occur, leading to competition between ejaculates. The benefits of such competition include an increasing number of sperm in the ejaculates of competing males and the consequential increase in fertilized eggs (thus, fecundity), and thereby a higher chance of genetic diversity and fitness in the offspring of the firefly P. pectoralis.

An Overview of Aquatica Fu et al., a Phylogeny of Aquatic Fireflies Using Mitochondrial Genomes, a Description of Two New Species, and a New Record of Aquatic Fireflies in China (Coleoptera: Lampyridae: Luciolinae)

There are now seven species in the genus Aquatica Fu & Ballantyne, with all but one known from the characteristics of males, females, and larvae. Molecular information is combined with morphological taxonomy for the delimitation of both genus and species. The monophyly of the genus Aquatica is strongly supported in six trees, and its position as sister to the genus Nipponoluciola Ballantyne Kawashima Jusoh et Suzuki is stable across maximum likelihood and Bayesian inference results. Two new species of Aquatica Fu & Ballantyne, A. qingshen sp. nov. and A. xianning sp. nov., described from the features of males, females, and larvae, are closely related within a single clade within the genus Aquatica. Females have distinctively shaped median oviduct plates. A Chinese population identified as A. lateralis was found to be morphologically similar to the Japanese population, but genetic distances suggest that it is a distinctive species. No larvae are associated with this species. Definitions of the aquatic status of Luciolinae fireflies are expanded.

The color of artificial light affects mate attraction in the common glow-worm

Artificial light at night, often referred to as 'light pollution', is a global environmental problem that threatens many nocturnal organisms. One such species is the European common glow-worm (Lampyris noctiluca), in which reproduction relies on the ability of sedentary bioluminescent females to attract flying males to mate. Previous studies show that broad-spectrum white artificial light interferes with mate attraction in this beetle. However, much less is known about wavelength-specific effects. In this study, we experimentally investigate how the peak wavelength (color) of artificial light affects glow-worm mate attraction success in the field by using dummy females that trap males landing to mate. Each dummy was illuminated from above by either a blue (peak wavelength: 452 nm), white (449 nm), yellow (575 nm), or red (625 nm) LED lighting, or light switched off in the control. We estimated mate attraction success as both the probability of attracting at least one male and the number of males attracted. In both cases, mate attraction success depended on the peak wavelength of the artificial light, with short wavelengths (blue and white) decreasing it more than long wavelengths (yellow and red). Hence, adjusting the spectrum of artificial light can be an effective measure for mitigating the negative effects of light pollution on glow-worm reproduction.

Luminescent characteristics and mitochondrial COI barcodes of nine cohabitated Taiwanese fireflies

Background

Over 50 Taiwanese firefly species have been discovered, but scientists lack information regarding most of their genetics, bioluminescent features, and cohabitating phenomena. In this study, we focus on morphological species identification and phylogeny reconstructed by COI barcoding, as well as luminescent characteristics of cohabited Taiwanese firefly species to determine the key factors that influenced how distinct bioluminescent species evolved to coexist and proliferate within the same habitat.

Methods

In this study, 366 specimens from nine species were collected in northern Taiwan from April to August, 2016-2019. First, the species and sex of the specimens were morphologically and genetically identified. Then, their luminescent spectra and intensities were recorded using a spectrometer and a power meter, respectively. The habitat temperature, relative humidity, and environmental light intensity were also measured. The cytochrome oxidase I (COI) gene sequence was used as a DNA barcode to reveal the phylogenetic relationships of cohabitated species.

Results

Nine species-eight adult species (Abscondita chinensis, Abscondita cerata, Aquatica ficta, Luciola curtithorax, Luciola kagiana, Luciola filiformis, Curtos sauteri, and Curtos costipennis) and one larval Pyrocoelia praetexta-were morphologically identified. The nine species could be found in April-August. Six of the eight adult species shared an overlap occurrence period in May. Luminescent spectra analysis revealed that the λ _max of studied species ranged from 552-572 nm (yellow-green to orange-yellow). The average luminescent intensity range of these species was about 1.2-14 lux (182.1-2,048 nW/cm²) for males and 0.8-5.8 lux (122.8-850 nW/cm²) for females, and the maximum luminescent intensity of males was 1.01-7.26-fold higher than that of females. Compared with previous studies, this study demonstrates that different λ _max, species-specific flash patterns, microhabitat choices, nocturnal activity time, and/or an isolated mating season are key factors that may lead to the species-specific courtship of cohabitated fireflies. Moreover, we estimated that the fireflies start flashing or flying when the environmental light intensity decreased to 6.49-28.1 lux. Thus, based on a rough theoretical calculation, the sensing distance between male and female fireflies might be 1.8-2.7 m apart in the dark. In addition, the mitochondrial COI barcode identified species with high resolution and suggested that most of the studied species have been placed correctly with congeners in previous phylogenies. Several cryptic species were revealed by the COI barcode with 3.27%-12.3% variation. This study renews the idea that fireflies' luminescence color originated from the green color of a Lampyridae ancestor, then red-shifted to yellow-green in Luciolinae, and further changed to orange-yellow color in some derived species.

Behavioral responses of bioluminescent fireflies to artificial light at night

Bioluminescent insects have been the subject of scientific interest and popular wonder for millennia. But in the 21st century, the fireflies, click beetles, and cave glow-worms that brighten our nights are threatened by an unprecedented competitor: anthropogenic light pollution. Artificial lights can obscure the light-based signals on which these and other bioluminescent organisms rely to court mates, deter predators, and attract prey. In the following review we summarize a recent influx of research into the behavioral consequences of artificial light at night for firefly beetles (Coleoptera: Lampyridae), which we organize into four distinct courtship signaling systems. We conclude by highlighting several opportunities for further research to advance this emerging field and by offering a set of up-to-date lighting recommendations that can help land managers and other stakeholders balance public safety and ecological sustainability.

Costs and benefits of "insect friendly" artificial lights are taxon specific

The expansion of human activity into natural habitats often results in the introduction of artificial light at night, which can disrupt local ecosystems. Recent advances in LED technology have enabled spectral tuning of artificial light sources, which could in theory limit their impact on vulnerable taxa. To date, however, experimental comparisons of ecologically friendly candidate colors have often considered only one type of behavioral impact, sometimes on only single species. Resulting recommendations cannot be broadly implemented if their consequences for other local taxa are unknown. Working at a popular firefly ecotourism site, we exposed the insect community to artificial illumination of three colors (blue, broad-spectrum amber, red) and measured flight-to-light behavior as well as the courtship flash behavior of male Photinus carolinus fireflies. Firefly courtship activity was greatest under blue and red lights, while the most flying insects were attracted to blue and broad-spectrum amber lights. Thus, while impacts of spectrally tuned artificial light varied across taxa, our results suggest that red light, rather than amber light, is least disruptive to insects overall, and therefore more generally insect friendly.

Urban forest invertebrates: how they shape and respond to the urban environment

Invertebrates comprise the most diversified animal group on Earth. Due to their long evolutionary history and small size, invertebrates occupy a remarkable range of ecological niches, and play an important role as “ecosystem engineers” by structuring networks of mutualistic and antagonistic ecological interactions in almost all terrestrial ecosystems. Urban forests provide critical ecosystem services to humans, and, as in other systems, invertebrates are central to structuring and maintaining the functioning of urban forests. Identifying the role of invertebrates in urban forests can help elucidate their importance to practitioners and the public, not only to preserve biodiversity in urban environments, but also to make the public aware of their functional importance in maintaining healthy greenspaces. In this review, we examine the multiple functional roles that invertebrates play in urban forests that contribute to ecosystem service provisioning, including pollination, predation, herbivory, seed and microorganism dispersal and organic matter decomposition, but also those that lead to disservices, primarily from a public health perspective, e.g., transmission of invertebrate-borne diseases. We then identify a number of ecological filters that structure urban forest invertebrate communities, such as changes in habitat structure, increased landscape imperviousness, microclimatic changes and pollution. We also discuss the complexity of ways that forest invertebrates respond to urbanisation, including acclimation, local extinction and evolution. Finally, we present management recommendations to support and conserve viable and diverse urban forest invertebrate populations into the future.

Species-Specific Flash Patterns Track the Nocturnal Behavior of Sympatric Taiwanese Fireflies

It is highly challenging to evaluate the species' content and behavior changes in wild fireflies, especially for a sympatric population. Here, the flash interval (FI) and flash duration (FD) of flying males from three sympatric species (Abscondita cerata, Luciola kagiana, and Luciola curtithorax) were investigated for their potentials in assessing species composition and nocturnal behaviors during the A. cerata mating season. Both FI and FD were quantified from the continuous flashes of adult fireflies (lasting 5-30 s) via spatiotemporal analyses of video recorded along the Genliao hiking trail in Taipei, Taiwan. Compared to FD patterns and flash colors, FI patterns exhibited the highest species specificity, making them a suitable reference for differentiating firefly species. Through the case study of a massive occurrence of A. cerata (21 April 2018), the species contents (~85% of the flying population) and active periods of a sympatric population comprising A. cerata and L. kagiana were successfully evaluated by FI pattern matching, as well as field specimen collections. Our study suggests that FI patterns may be a reliable species-specific luminous marker for monitoring the behavioral changes in a sympatric firefly population in the field, and has implication values for firefly conservation.

How urbanization affects sexual communication

Urbanization is rapidly altering landscapes worldwide, changing environmental conditions, and creating novel selection pressures for many organisms. Local environmental conditions affect the expression and evolution of sexual signals and mating behaviors; changes in such traits have important evolutionary consequences because of their effect on reproduction. In this review, we synthesize research investigating how sexual communication is affected by the environmental changes associated with urbanization-including pollution from noise, light, and heavy metals, habitat fragmentation, impervious surfaces, urban heat islands, and changes in resources and predation. Urbanization often has negative effects on sexual communication through signal masking, altering condition-dependent signal expression, and weakening female preferences. Though there are documented instances of seemingly adaptive shifts in trait expression, the ultimate impact on fitness is rarely tested. The field of urban evolution is still relatively young, and most work has tested whether differences occur in response to various aspects of urbanization. There is limited information available about whether these responses represent phenotypic plasticity or genetic changes, and the extent to which observed shifts in sexual communication affect reproductive fitness. Our understanding of how sexual selection operates in novel, urbanized environments would be bolstered by more studies that perform common garden studies and reciprocal transplants, and that simultaneously evaluate multiple environmental factors to tease out causal drivers of observed phenotypic shifts. Urbanization provides a unique testing ground for evolutionary biologists to study the interplay between ecology and sexual selection, and we suggest that more researchers take advantage of these natural experiments. Furthermore, understanding how sexual communication and mating systems differ between cities and rural areas can offer insights on how to mitigate negative, and accentuate positive, consequences of urban expansion on the biota, and provide new opportunities to underscore the relevance of evolutionary biology in the Anthropocene.

The duration of artificial light defines sexual signalling in the common glow-worm

Abstract

Artificial light at night is increasing globally, interfering with both sensory ecology and temporal rhythms of organisms, from zooplankton to mammals. This interference can change the behaviour of the affected organisms, and hence compromise the viability of their populations. Limiting the use of artificial light may mitigate these negative effects. Accordingly, we investigated whether the duration of artificial light affects sexual signalling in female glow-worms, Lampyris noctiluca, which are flightless and attract flying males to mate by emitting glow that is interfered by light pollution. The study included three treatments: no artificial light (control), 15 min of artificial light, and 45 min of artificial light. The results show that females were more likely to cease glowing when the exposure to light was longer. Furthermore, small females were more likely to cease their glow, and responded faster to the light, than larger females. These findings suggest that glow-worms can react rapidly to anthropogenic changes in nocturnal light levels, and that prolonged periods of artificial light trigger females to stop sexual signalling. Thus, limiting the duration of artificial light can mitigate the adverse effects of light pollution on sexual signalling, highlighting the importance of such mitigation measures.

Significance statement

Interest in the effects of artificial light at night on animal behaviour has increased in recent years. With evidence for its negative impact accumulating, potential remedies, such as limiting the duration of light exposure, have emerged. To date, however, knowledge on the effectiveness of these methods has remained very limited. We show that female European common glow-worms, which are wingless beetles that glow to attract flying males to mate, responded to prolonged artificial light exposure by discontinuing their glow. Such non-glowing females are not expected to find a mate, making it difficult for them to reproduce. Hence, our study indicates that the duration of artificial light should be limited to protect this night-active beetle and its opportunities for effective sexual signalling. Because many other nocturnal species also need darkness, this study provides valuable information for the development and use of less disruptive night-time lights.

Artificial light at night disrupts species interactions and changes insect communities

Artificial light at night (ALAN) is globally increasing, posing a threat to biodiversity. The impact of nocturnal illumination on individual insects has been relatively well documented. Recent studies show that ALAN also impacts species interactions, including intra-specific communication, trophic interactions and plant-pollinator interactions, with cascading effects in the ecosystem and impacts on ecosystem functioning that extend beyond nocturnal communities and illuminated areas. Reduced population sizes and changes in community composition because of exposure to ALAN have been reported but the understanding of the impacts of ALAN on insect communities is currently limited to few groups and ecosystems. The theoretical framework on how ALAN impacts insect communities and populations is poorly developed, limiting our understanding and the formulation of relevant hypotheses.

Blinded by the Light: Artificial Light Lowers Mate Attraction Success in Female Glow-Worms (Lampyris noctiluca L.)

Nocturnal light pollution from anthropogenic origin is increasing worldwide and is recognised as a major threat for nocturnal biodiversity. We studied the impact of artificial light on the mate attraction success of female common glow-worms (Lampyris noctiluca L.) by daily monitoring their glowing status in the field, acting as a proxy for mating status throughout the mating season. We found that females in dark surroundings typically stopped glowing after one night, indicating that they had mated, while females in illuminated areas glowed for significantly more nights, in some cases up to 15 nights. Our study confirms previous findings and hypotheses that females exposed to artificial light suffer from a reduced mate attraction success with a negative impact on populations.

Effects of artificial light at night (ALAN) on gene expression of Aquatica ficta firefly larvae

Artificial light at night (ALAN) is a major driver of firefly population declines, but its physiological effects are not well understood. To investigate the impact of ALAN on firefly development, we exposed larval Aquatica ficta fireflies to ALAN for two weeks. High larval mortality was observed in the periods of 1-68 days and 106-134 days post-treatment, which may represent the short- and long-term impacts of ALAN. We then profiled the transcriptome of larval Aquatica ficta fireflies following two weeks of ALAN exposure. A total of 1262 (1.67% out of 75777 unigenes) were differentially expressed in the treatment group: 1157 were down-regulated, and 105 were up-regulated. Up-regulated unigenes were related to regulation of hormone levels, ecdysteroid metabolic process, and response to stimulus; down-regulated unigenes were related to negative regulation of insulin receptor signaling, germ cell development, oogenesis, spermatid development, and regulation of neuron differentiation. Transcriptome results suggest that the endocrine, reproductive, and neural development of firefly larvae could be impaired by even relatively brief period of ALAN exposure. This report contributes a much-needed molecular perspective to the growing body of research documenting the fitness impacts of ALAN on bioluminescent fireflies.

Anticipated effects of abiotic environmental change on intraspecific social interactions

Social interactions are ubiquitous across the animal kingdom. A variety of ecological and evolutionary processes are dependent on social interactions, such as movement, disease spread, information transmission, and density-dependent reproduction and survival. Social interactions, like any behaviour, are context dependent, varying with environmental conditions. Currently, environments are changing rapidly across multiple dimensions, becoming warmer and more variable, while habitats are increasingly fragmented and contaminated with pollutants. Social interactions are expected to change in response to these stressors and to continue to change into the future. However, a comprehensive understanding of the form and magnitude of the effects of these environmental changes on social interactions is currently lacking. Focusing on four major forms of rapid environmental change currently occurring, we review how these changing environmental gradients are expected to have immediate effects on social interactions such as communication, agonistic behaviours, and group formation, which will thereby induce changes in social organisation including mating systems, dominance hierarchies, and collective behaviour. Our review covers intraspecific variation in social interactions across environments, including studies in both the wild and in laboratory settings, and across a range of taxa. The expected responses of social behaviour to environmental change are diverse, but we identify several general themes. First, very dry, variable, fragmented, or polluted environments are likely to destabilise existing social systems. This occurs as these conditions limit the energy available for complex social interactions and affect dissimilar phenotypes differently. Second, a given environmental change can lead to opposite responses in social behaviour, and the direction of the response often hinges on the natural history of the organism in question. Third, our review highlights the fact that changes in environmental factors are not occurring in isolation: multiple factors are changing simultaneously, which may have antagonistic or synergistic effects, and more work should be done to understand these combined effects. We close by identifying methodological and analytical techniques that might help to study the response of social interactions to changing environments, highlight consistent patterns among taxa, and predict subsequent evolutionary change. We expect that the changes in social interactions that we document here will have consequences for individuals, groups, and for the ecology and evolution of populations, and therefore warrant a central place in the study of animal populations, particularly in an era of rapid environmental change.

Selection and Validation of Suitable Reference Genes for RT-qPCR Analysis in the Rare Aquatic Firefly Aquatica leii (Coleoptera: Lampyridae)

Simple Summary

The purpose of this paper was to determine which genes in Aquatica leii, an endemic Chinese firefly, are suitable for use as reference genes in future RT-qPCR studies. This is the first example of an effective knockdown in fireflies and an important methodological advance for continuing research in A. leii. The results of this study will help improve accuracy and reliability to normalize RT-qPCR data in A. leii for further molecular analysis. Since luciferase is very abundant in the adult light organ of fireflies generally, this is an encouraging result and of interest not just for A. leii researchers but other researchers who plan to perform RNAi or RT-qPCR in fireflies, or other nonmodel insects, as well.

Abstract

Aquatica leii Fu and Ballantyne is a species of rare aquatic firefly and endemic in China. It is considered good material to study the molecular mechanism of sexual flash communication systems. To improve conservation and behavioral research strategies, large-scale genetic studies involving gene-expression analysis are required and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) is the most commonly used method. However, there have been very few reports on appropriate reference genes in any species of firefly. Here, we evaluated eight widely utilized reference genes including 18S, Actin, Reep5, Odc1, Tub, Gapdh, Ef1a and S27Ae for their expression stabilities in A. leii under three different conditions, i.e., life stage, tissue and dsRNA injection. Based on the gene stability ranking calculated by RefFinder, which integrates four algorithms (geNorm, delta Ct method, NormFinder, and BestKeeper), we recommend S27Ae and Reep5 as the most appropriate reference genes for molecular studies in different life stages; Ef1a and Odc1 for different tissues; Tub and Odc1 for RNAi studies. The most appropriate reference genes in all treatments are S27Ae and Tub. The results of this study will help improve accuracy and reliability to normalize RT-qPCR data in A. leii for further molecular analysis.

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.

Environmental DNA Metabarcoding as a Means of Estimating Species Diversity in an Urban Aquatic Ecosystem

Adaptation to environments that are changing as a result of human activities is critical to species' survival. A large number of species are adapting to, and even thriving in, urban green spaces, but this diversity remains largely undocumented. In the current study, we explored the potential of environmental DNA (eDNA) to document species diversity in one of the largest green spaces in Johannesburg, South Africa. Using a novel metabarcoding approach that assembles short DNA fragments suitable for massively parallel sequencing platforms to the approximate standard ~710 bp COI barcoding fragment, we document the presence of 26 phyla, 52 classes, 134 orders, 289 families, 380 genera and 522 known species from the study site. Our results highlight the critical role that urban areas play in protecting the world's declining biodiversity.

Reproduction under light pollution: maladaptive response to spatial variation in artificial light in a glow-worm

The amount of artificial light at night is growing worldwide, impacting the behaviour of nocturnal organisms. Yet, we know little about the consequences of these behavioural responses for individual fitness and population viability. We investigated if females of the common glow-worm Lampyris noctiluca—which glow in the night to attract males—mitigate negative effects of artificial light on mate attraction by adjusting the timing and location of glowing to spatial variation in light conditions. We found females do not move away from light when exposed to a gradient of artificial light, but delay or even refrain from glowing. Further, we demonstrate that this response is maladaptive, as our field study showed that staying still when exposed to artificial light from a simulated streetlight decreases mate attraction success, while moving only a short distance from the light source can markedly improve mate attraction. These results indicate that glow-worms are unable to respond to spatial variation in artificial light, which may be a factor in their global decline. Consequently, our results support the hypothesis that animals often lack adaptive behavioural responses to anthropogenic environmental changes and underlines the importance of considering behavioural responses when investigating the effects of human activities on wildlife.

The impact of artificial light at night on nocturnal insects: A review and synthesis

In recent decades, advances in lighting technology have precipitated exponential increases in night sky brightness worldwide, raising concerns in the scientific community about the impact of artificial light at night (ALAN) on crepuscular and nocturnal biodiversity. Long-term records show that insect abundance has declined significantly over this time, with worrying implications for terrestrial ecosystems. The majority of investigations into the vulnerability of nocturnal insects to artificial light have focused on the flight-to-light behavior exhibited by select insect families. However, ALAN can affect insects in other ways as well. This review proposes five categories of ALAN impact on nocturnal insects, highlighting past research and identifying key knowledge gaps. We conclude with a summary of relevant literature on bioluminescent fireflies, which emphasizes the unique vulnerability of terrestrial light-based communication systems to artificial illumination. Comprehensive understanding of the ecological impacts of ALAN on diverse nocturnal insect taxa will enable researchers to seek out methods whereby fireflies, moths, and other essential members of the nocturnal ecosystem can coexist with humans on an increasingly urbanized planet.