Phylomitogenomics of two Neotropical species of long-legged crickets Endecous Saussure, 1878 (Orthoptera: Phalangopsidae)

Mitochondrial genomes have provided significant insights into the evolution of several insects. A typical mitogenome contains 37 genes, and variations in gene order can indicate evolutionary relationships between species. In this study, we have assembled the first complete mitogenomes of Endecous chape and E. onthophagus and analyzed the phylogenetic implications for the Gryllidea infraorder. We performed DNA extractions and genome sequencing for both Endecous species. Subsequently, we searched for raw data in the Sequence Read Archive (SRA) in NCBI. Using the SRA data, we assembled the partial mitogenome of Dianemobius nigrofasciatus and annotated the protein-coding genes (PCGs) for nine species. Phylogenomic relationships were reconstructed using Maximum Likelihood (ML) and Bayesian Inference (BI), utilizing the PCGs from 49 Gryllidea species. The mitogenome lengths of E. chape and E. onthophagus are 16,266 bp and 16,023 bp, respectively, while D. nigrofasciatus has a length of 15,359 bp. Our results indicate that species within the infraorder exhibit four types of gene order arrangements that align with their phylogenetic relationships. Both phylogenomic trees displayed strong support, and the ML corroborated with the literature. Gryllidea species have significantly contributed to various fields, and studying their mitogenomes can provide valuable insights into this infraorder evolution.

Phylogeny and biogeography of the wingless orthopteran family Rhaphidophoridae

Cave crickets (Rhaphidophoridae) are insects of an ancient and wingless lineage within Orthoptera that are distributed worldwide except in Antarctica, and each subfamily has a high level of endemicity. Here, we show the comprehensive phylogeny of cave crickets using multi-gene datasets from mitochondrial and nuclear loci, including all extant subfamilies for the first time. We reveal phylogenetic relationships between subfamilies, including the sister relationship between Anoplophilinae and Gammarotettiginae, based on which we suggest new synapomorphies. Through biogeographic analyses based on divergence time estimations and ancestral range reconstruction, we propose novel hypotheses regarding the biogeographic history of cave crickets. We suggest that Gammarotettiginae in California originated from the Asian lineage when Asia and the Americas were connected by the Bering land bridge, and the opening of the western interior seaway affected the division of Ceuthophilinae from Tropidischiinae in North America. We estimate that Rhaphidophoridae originated at 138 Mya throughout Pangea. We further hypothesize that the loss of wings in Rhaphidophoridae could be the result of their adaptation to low temperatures in the Mesozoic era.

New species of the elusive crickets from the genus Pendleburyella Chopard, 1969 (Gryllidae, Pentacentrinae) from Sabah, Borneo

Only one species of Pendleburyella Chopard, 1969 (Gryllidae, Pentacentrinae) was previously known to occur in Borneo: Pendleburyella eirmosa Tan, Muhammad & Wahab, 2023 from Brunei Darussalam. Here, two additional new species of crickets from the genus Pendleburyella are described from the highlands of Sabah, Borneo: Pendleburyella eremita sp. nov. from Bukit Hampuan and Pendleburyella nimba sp. nov. from Mount Trus Madi. In total, six species of Pendleburyella are currently known, three from Borneo and three from Malay Peninsula. It is likely that many more species are awaiting discovery owing to its cryptic morphology and elusive nature.

New genus of Steirodontini Brunner von Wattenwyl, 1878 (Orthoptera: Tettigoniidae: Phaneropterinae) from the Brazilian Amazon Rainforest

The tribe Steirodontini (Phaneropterinae: Tettigoniidae) currently comprises five genera and 56 species, with its distribution restricted to the Neotropical region. In Brazil, four genera and 20 species of this tribe are recorded, all with records restricted to the Brazilian Southeast and South regions. This fact is a strong indication that the Brazilian fauna of this group is underestimated. In this work, the new monotypic genus Coronophyllum gen. nov. and the new species Coronophyllum catarinae sp. nov. from Amazonas, Brazil, are described and illustrated. Additionally, a map and comments on its distribution in an endemic area of the Brazilian Amazon are provided.

Studies on Neotropical crickets: A new Perugryllae cricket (Orthoptera: Gryllidae: Gryllinae: Gryllini: Brachytrupina) from the foothills of the Colombian Andes

A new tiny field cricket species of the genus Laureopsis (Orthoptera: Gryllidae), from the foothills of the Colombian Andes is described. With the description of Laureopsis andinus n. sp., the distribution of the Perugryllae Group expands outside the Amazon rainforest of Colombia and Peru, and is recorded for the first time in areas of Andean influence. A distribution map and a key for the identification of the species of the group are also provided. Finally, the morphology and distribution of the species of the two genera known for the Perugryllae group are discussed.

The ground offers acoustic efficiency gains for crickets and other calling animals

Male crickets attract females by producing calls with their forewings. Louder calls travel further and are more effective at attracting mates. However, crickets are much smaller than the wavelength of their call, and this limits their power output. A small group called tree crickets make acoustic tools called baffles which reduce acoustic short-circuiting, a source of dipole inefficiency. Here, we ask why baffling is uncommon among crickets. We hypothesize that baffling may be rare because like other tools they offer insufficient advantage for most species. To test this, we modelled the calling efficiencies of crickets within the full space of possible natural wing sizes and call frequencies, in multiple acoustic environments. We then generated efficiency landscapes, within which we plotted 112 cricket species across 7 phylogenetic clades. We found that all sampled crickets, in all conditions, could gain efficiency from tool use. Surprisingly, we also found that calling from the ground significantly increased efficiency, with or without a baffle, by as much as an order of magnitude. We found that the ground provides some reduction of acoustic short-circuiting but also halves the air volume within which sound is radiated. It simultaneously reflects sound upwards, allowing recapture of a significant amount of acoustic energy through constructive interference. Thus, using the ground as a reflective baffle is an effective strategy for increasing calling efficiency. Indeed, theory suggests that this increase in efficiency is accessible not just to crickets but to all acoustically communicating animals whether they are dipole or monopole sound sources.

Two new species of Endecous Saussure, 1878 (Orthoptera: Grylloidea: Phalangopsidae) from caves in central-western Brazil, with the proposition of a new subgenus to accommodate E. vitreus Bolfarini & Campos, 2023

The genus Endecous (Orthoptera, Grylloidea, Phalangopsidae) encompasses over 20 species, grouped into four subgenera: E. (Endecous), E. (Pedroecous), E. (Notendecous), and E. (Ramalhoecous). In this study, we present the description of two novel species belonging to the subgenus Endecous (Endecous) Saussure, 1878 (Phalangopsidae) discovered in caves located within the Serra da Bodoquena region of Mato Grosso do Sul state, Brazil. The descriptions are based on the distinguishing male genitalia characteristics, among other traits. Furthermore, we introduce a new subgenus, namely Endecous (Bodoquenaecous), specifically created to accommodate the recently discovered species E. vitreus, also found in caves within the same area. Initially, E. vitreus was placed under the subgenus Endecous; however, due to its numerous distinct traits, the establishment of a new subgenus became justified. In this study, we also introduce the first pictorial key for the subgenera within the genus Endecous. Additionally, we briefly discuss observed troglomorphic adaptations in species belonging to this genus. Finally, comprehensive ecological observations and conservation status assessments are provided for both newly described species, as well as for E. vitreus.

Taxonomy and bioacoustics of little-known Grylloidea crickets (Orthoptera, Ensifera) from Mindanao, Philippines

Orthopteran surveys were conducted recently on Mindanao Island of the Philippines. Four species new to science are described here: Mistshenkoana lunotan sp. nov., Mistshenkoana higaonon sp. nov. and Ectatoderus dubius sp. nov. from Misamis Oriental; and Phaloria (Phaloria) rotundata sp. nov. from Agusan del Sur. Based on new collected material, Madasumma fuscoirrorata Chopard, 1925, first described based on a single female from Mindanao, is transferred to Varitrella (Cantotrella) fuscoirrorata (Chopard, 1925) comb. nov. We also describe the male of this species for the first time. Madasumma zamboanga Otte, 2007, first described from Zamboanga del Norte (Mindanao), is also transferred to Mnesibulus (Amnesibulus) and redescribed: Mnesibulus (Amnesibulus) zamboanga (Otte, 2007) comb. nov. We also describe previously unknown calling songs of seven species: Falcerminthus parvus (Baroga-Barbecho & Robillard, 2020), Ajorama balatukanis Otte, 1988, Varitrella (Cantotrella) bakeri (Chopard, 1925), Varitrella (Cantotrella) fuscoirrorata (Chopard, 1925) comb. nov., Phaloria (Phaloria) rotundata sp. nov., Ornebius bioculatus Tan et al., 2019 and Ectatoderus dubius sp. nov.

New species of Tyrannoraptor Mendes, Oliveira, Chamorro-Rengifo & Rafael, 2018 (Orthoptera: Tettigoniidae: Meconematinae: Phlugidini) with asymmetrical jaws from the Brazilian Amazon Rainforest

Tyrannoraptor Mendes, Oliveira, Chamorro-Rengifo & Rafael, 2018 (Tettigoniidae: Meconematinae: Phlugidini) is currently a monotypic genus. The type-species Tyrannoraptor arboreus (Nickle, 2003) is recorded to Peru (Loreto) and Brazil (Amazonas). In this work, we describe the second species of the genus, Tyrannoraptor venator sp. nov., recorded to the Brazilian Amazon rainforest. The new species is described based on a male and three female specimens. A key to species of Tyrannoraptor and a distribution map of the genus are provided as well as comments on the natural history of the new species.

Notes on the Eneopterinae (Orthoptera, Grylloidea, Gryllidae) from eastern Sabah

Based on material collected during recent fieldwork in eastern Sabah, the males of Nisitrus danum Robillard & Tan and Cardiodactylus variegatus Gorochov & Robillard are described for the first time, along with their calling songs. New locality records of N. danum, N. vittatus (Haan), Falcerminthus sandakan (Tan et al.), Cardiodactylus borneoe Robillard & Gorochov and C. variegatus are also presented. New material of Nisitrus species-N. danum and N. vittatus-allowed us to compare these syntopic species.

Are the recently described fossil Mole Crickets of Myanmar amber real gryllotalpids? (Orthoptera: Gryllotalpidae & Gryllidae)

We report five new Myanmar amber specimens attributable to "Mole Cricket" †Pherodactylus rectanguli n. comb., hitherto regarded as a Mole Cricket (Orthoptera: Grylloptalpidae). The new material includes two adult males, two adult females, and one nymph. The specimens are redescribed, and additional new characters are provided for their delimitation and corresponding species identification. We carry out a comparison between these new specimens with other taxa of mole crickets from Myanmar amber and extant true crickets. The result indicates that some species merely represent different nymphal development stages or adults of †Pherodactylus rectanguli n. comb., however, they were misidentified as different species. We also treated genera †Tresdigitus n. syn. and †Chunxiania n. syn. as synonyms of genus †Pherodactylus Poinar, Su & Brown, 2020, and treat †Tresdigitus gracilis Jiang, Xu, Jarzembowski & Xiao, 2022 n. syn. and †Chunxiania fania n. syn. as synonyms of †Pherodactylus rectanguli n. comb. †Burmagryllotalpa longa is valid, because its shape of the pronotum curved without lateral carinae. The morphological convergences and specializations of subterranean dwelling species are discussed. The robust fore tibia and long apical spurs of †P. micromorphus, †P. rectanguli n. comb. and †B. longa are insufficient evidence for an assignment to the family Gryllotalpidae. Instead, we suggest place them into the subfamily Gryllinae (Gryllidae), tribe Sclerogryllini, and group them into their own subtribe Pherodactylina n. subtr.. A key to the identification of recent and fossil Sclerogryllini is also provided. Their taxonomy and morphology are discussed.

The taxonomy and bioacoustics of the elusive crickets from the genus Pendleburyella Chopard, 1969 (Gryllidae: Pentacentrinae)

The taxonomy of poorly known crickets from the genus Pendleburyella Chopard, 1969 (Gryllidae, Pentacentrinae) is reviewed. The type specimens of described species were re-located and re-examined. Based on more recent collections, we describe two new species: Pendleburyella eirmosa sp. nov. and Pendleburyella pimela sp. nov., from Brunei Darussalam and Singapore respectively. The new material also allowed us to examine the male genitalia and describe the male calling song of the genus for the first time.

Peulerneca ubaira gen. et sp. nov.: A new Lernecina cricket with white and hyaline forewings from the Brazilian Atlantic Forest (Phalangopsidae, Luzarinae, Lernecina)

Here we describe a new genus and species of cricket belonging to Lernecina from the Brazilian Atlantic Forest. It is presently known only from Ubaíra, State of Bahia, Brazil. The new genus is the only known member of this subtribe having males with a mostly white and hyaline dorsal field of the forewing (an additional genus with that condition is in the process of being described).

Studies on Neotropical crickets: Crinklyalis n. gen., a new cricket genus (Orthoptera: Phalangopsidae: Paragryllinae) from the foothills of theColombian Andes

A new genus of small phalangopsids (Orthoptera: Phalangopsidae) from the foothills of the Colombian Andes is described. Crinklyalis n. gen. is distinguished from the other genera of the subtribe Strogulomorphina (Paragryllini) by the modification in the mesal region of the tegmina, apparently an acoustic chamber; reduction of wing venation; male genitalia tubular, elongated and mostly membranous, with only the distal section sclerotized. Additionally, the key for the identification of the genera of the subtribe was updated, and the morphology of the new genus was discussed, as well as distributional gaps that currently exist for the Strogulomorphina taxa.

The Austral Predator Katydid—new species of Megatympanon Piza, 1958 (Orthoptera: Tettigoniidae: Listroscelidinae: Terpandrini) from the Brazilian Atlantic Rainforest

Megatympanon Piza, 1958 (Tettigoniidae: Listroscelidinae: Terpandrini) is presently a monotypic genus and the only Terpandrini occurring in South America. The type-species M. speculatum Piza, 1958 is recorded in the Atlantic Forest biome in southeastern Brazil. In this work, we describe an additional species, Megatympanon austroraptorum sp. nov., the second species of the genus, occurring in the Southern Atlantic Forest biome. The new species is described based only on a single male; the female of the new species is unknown. A distribution map of the genus is provided as well as comments on the natural history of the new species.  

Three new cricket species and a new subgenus of Endecous Saussure, 1878 (Grylloidea: Phalangopsidae) from caves in northeastern Brazil

The genus Endecous (Orthoptera, Grylloidea, Phalangopsidae), commonly found in caves, comprises more than 20 species, grouped into three subgenera: E. (Endecous), E. (Pedroecous) and E. (Notendecous). In this study, from differences observed mainly in the male genitalia, we describe a new subgenus—Endecous (Ramalhoecous) n. sp.—as well as three new species—E. (R.) infernalis n. sp., E. (E.) zin n. sp. and E. (E.) zaum n. sp.—all of them collected in caves in the Serra do Ramalho region, Northeastern, Brazil. We also briefly discuss some troglomorphisms verified in one of the new species: E. (R.) infernalis n. sp.  

Local prothoracic auditory neurons in Ensifera

A new method for individually staining insect neurons with metal ions was described in the late 60s, closely followed by the introduction of the first bright fluorescent dye, Lucifer Yellow, for the same purpose. These milestones enabled an unprecedented level of detail regarding the neuronal basis of sensory processes such as hearing. Due to their conspicuous auditory behavior, orthopterans rapidly established themselves as a popular model for studies on hearing (first identified auditory neuron: 1974; first local auditory interneuron: 1977). Although crickets (Ensifera, Gryllidae) surpassed grasshoppers (Caelifera) as the main model taxon, surprisingly few neuronal elements have been described in crickets. More auditory neurons are described for bush crickets (Ensifera, Tettigoniidae), but due to their great biodiversity, the described auditory neurons in bush crickets are scattered over distantly related groups, hence being confounded by potential differences in the neuronal pathways themselves. Our review will outline all local auditory elements described in ensiferans so far. We will focus on one bush cricket species, Ancistrura nigrovittata (Phaneropterinae), which has the so-far highest diversity of identified auditory interneurons within Ensifera. We will present one novel and three previously described local prothoracic auditory neuron classes, comparing their morphology and aspects of sensory processing. Finally, we will hypothesize about their functions and evolutionary connections between ensiferan insects.

The fifth family of the true crickets (Insecta: Orthoptera: Ensifera: Grylloidea), Oecanthidae defin. nov.: phylogenetic relationships and divergence times

Crickets are frequently used as a model in several areas of science, including acoustic communication, behaviour and neurobiology. However, only a few of these studies are placed in an evolutionary framework due to the limited number of phylogenetic hypotheses for true crickets. We present a phylogenetic hypothesis for a newly defined family of crickets, Oecanthidae defin. nov., sister-group of Gryllidae defin. nov. The phylogenetic analyses are based on molecular and morphological data under likelihood and parsimony criteria and molecular data for divergence-times estimation (Bayesian inference). We used 107 terminals from all biogeographic regions and six fossils for the time calibration of the tree. All analyses resulted in Oecanthidae with four subfamilies: Euscyrtinae, Oecanthinae defin. nov., Podoscirtinae defin. nov. and Tafaliscinae defin. nov. Based on our results, we revise the definition and internal classifications of the subfamilies, supertribes and tribes. A new tribe, Phyllogryllini trib. nov. is described. We also update their diagnoses, list the genera of the tribes and list their apomorphies. We provide an identification key for all suprageneric taxa of Oecanthidae, plus all genera of Tafaliscinae. Finally, we discuss the phylogenetic relationships of Oecanthidae, their divergence times, habitat diversity and the importance of ovipositor variation in this clade.

The Little Fog Dragon—a new genus of Mountain Lichen Katydid (Orthoptera: Tettigoniidae: Phaneropterinae: Dysoniini) from the Serra do Sol, Roraima, Brazil

The Dysoniini tribe (Phaneropterinae: Tettigoniidae) currently comprises 15 genera and 85 species with a Neotropical distribution. The group is notable for its representatives possessing morphological adaptations to camouflage with lichens and fungi. In this work, the new genus Nebulodraculus gen. nov. is described with two species included: Nebulodraculus marioi sp. nov. (type species) and Nebulodraculus holgeri (Cadena-Castañeda, 2013) comb. nov. (transferred from Lichenodraculus Braun, 2011), known from mountainous environments in northern Brazil and Venezuela. Pictorial keys to the species of the genus, maps and natural history observations are provided.  

Reviving the sound of a 150-year-old insect: The bioacoustics of Prophalangopsis obscura (Ensifera: Hagloidea)

Determining the acoustic ecology of extinct or rare species is challenging due to the inability to record their acoustic signals or hearing thresholds. Katydids and their relatives (Orthoptera: Ensifera) offer a model for inferring acoustic ecology of extinct and rare species, due to allometric parameters of their sound production organs. Here, the bioacoustics of the orthopteran Prophalangopsis obscura are investigated. This species is one of only eight remaining members of an ancient family with over 90 extinct species that dominated the acoustic landscape of the Jurassic. The species is known from only a single confirmed specimen–the 150-year-old holotype material housed at the London Natural History Museum. Using Laser-Doppler Vibrometry, 3D surface scanning microscopy, and known scaling relationships, it is shown that P. obscura produces a pure-tone song at a frequency of ~4.7 kHz. This frequency range is distinct but comparable to the calls of Jurassic relatives, suggesting a limitation of early acoustic signals in insects to sonic frequencies (<20 kHz). The acoustic ecology and importance of this species in understanding ensiferan evolution, is discussed.

Differentiation between left and right wing stridulatory files in the field cricket Gryllus bimaculatus (Orthoptera: Gryllidae)

Male crickets produce acoustic signals by wing stridulation, attracting females for mating. A plectrum on the left forewing's (or tegmen) anal margin rapidly strikes along a serrated vein (stridulatory file, SF) on the opposite tegmen as they close, producing vibrations, ending in a tonal sound. The tooth strike rate of the plectrum across file teeth is equal to the sound frequency produced by the cricket (i.e., ∼5k teeth/s for ∼5 kHz in field crickets) and is specific to the forewing's resonant frequency. Sound is subsequently amplified using specialised wing cells. Anatomically, the forewings appear to mirror each other: both tegmina bear a SF and plectrum; however, most cricket species stridulate using right-over-left wing overlap making the stridulatory mechanism asymmetrical by default, rendering the left tegmen's SF unused. Therefore, we hypothesised structural differences between functional and unfunctional SFs. Three-dimensional mapping was used to accurately measure SF structures in Gryllus bimaculatus wings. We found that the left SF shows significantly greater variation in inter-tooth distance than the right, but less variation within the first sixty teeth (the functional part) than the right file. The left SF's slow evolutionary change over millions of years is discussed considering modern molecular phylogenies and fossil records.

Two new and rare genera of angle-winged katydids (Orthoptera: Tettigoniidae: Phaneropterinae: Microcentrini) from the Brazilian Amazon Rainforest

Angle-winged katydids belong to the Microcentrini Brunner von Wattenwyl, 1878 (Phaneropterinae: Tettigoniidae). This tribe currently comprises 17 genera and 102 species with a Neotropical distribution. In this paper we described two new genera with two new species each: Capanema gen. nov. including Capanema pocanga sp. nov. (type species) and Capanema capara sp. nov.; Tukunha gen. nov., including Tukunha pinimauna sp. nov. (type species) and Tukunha minor sp. nov., comprising a total of four new species. Keys to the species of the described genera, maps and observations of natural history are provided.

Lesions of abdominal connectives reveal a conserved organization of the calling song central pattern generator (CPG) network in different cricket species

Although crickets move their front wings for sound production, the abdominal ganglia house the network of the singing central pattern generator. We compared the effects of specific lesions to the connectives of the abdominal ganglion chain on calling song activity in four different species of crickets, generating very different pulse patterns in their calling songs. In all species, singing activity was abolished after the connectives between the metathoracic ganglion complex and the first abdominal ganglion A3 were severed. The song structure was lost and males generated only single sound pulses when connectives between A3 and A4 were cut. Severing connectives between A4 and A5 had no effect in the trilling species, it led to an extension of chirps in a chirping species and to a loss of the phrase structure in two Teleogryllus species. Cutting the connectives between A5 and A6 caused no or minor changes in singing activity. In spite of the species-specific pulse patterns of calling songs, our data indicate a conserved organisation of the calling song motor pattern generating network. The generation of pulses is controlled by ganglia A3 and A4 while A4 and A5 provide the timing information for the chirp and/or phrase structure of the song.

HERMES: An improved method to test mitochondrial genome molecular synapomorphies among clades

Mitochondrial chromosomes have diversified among eukaryotes and many different architectures and features are now acknowledged for this genome. Here we present the improved HERMES index, which can measure and quantify the amount of molecular change experienced by mitochondrial genomes. We test the improved approach with ten molecular phylogenetic studies based on complete mitochondrial genomes, representing six bilaterian Phyla. In most cases, HERMES analysis spotted out clades or single species with peculiar molecular synapomorphies, allowing to identify phylogenetic and ecological patterns. The software presented herein handles linear, circular, and multi-chromosome genomes, thus widening the HERMES scope to the complete eukaryotic domain.

Colonization of different biomes drove the diversification of the Neotropical Eidmanacris crickets (Insecta: Orthoptera: Grylloidea: Phalangopsidae)

The phylogeny of the cricket genus Eidmanacris is used to analyse its historical distribution and diversification in three South American biomes: Atlantic Forest, Cerrado, and Chiquitano Dry Forest. A morphological phylogeny with all the 29 species of Eidmanacris and the Geographically explicit Event Model (GEM) is used to explain their colonization and diversification through three different biomes and their ancestral habitats and distributional areas. We analysed ecologically-significant characters, such as body size and metanotal characters, to test whether if morphology, habitat, or behaviour are connected. The relations of these features with the colonisation of wetter or drier biomes based on the distributional area, phylogeny and diversity of the genus were also tested. The results show that the ancestral distribution of the genus was the Atlantic Forest, and that biome occupancy, habitat, size, and mating behaviour evolved congruently through the phylogeny, drawing a coherent pattern of changes through Eidmanacris evolution toward the colonisation of drier biomes. Our results indicate that gallery forests could play a key role in the distribution and diversification of Eidmanacris species.

Phylogenomic analysis sheds light on the evolutionary pathways towards acoustic communication in Orthoptera

Acoustic communication is enabled by the evolution of specialised hearing and sound producing organs. In this study, we performed a large-scale macroevolutionary study to understand how both hearing and sound production evolved and affected diversification in the insect order Orthoptera, which includes many familiar singing insects, such as crickets, katydids, and grasshoppers. Using phylogenomic data, we firmly establish phylogenetic relationships among the major lineages and divergence time estimates within Orthoptera, as well as the lineage-specific and dynamic patterns of evolution for hearing and sound producing organs. In the suborder Ensifera, we infer that forewing-based stridulation and tibial tympanal ears co-evolved, but in the suborder Caelifera, abdominal tympanal ears first evolved in a non-sexual context, and later co-opted for sexual signalling when sound producing organs evolved. However, we find little evidence that the evolution of hearing and sound producing organs increased diversification rates in those lineages with known acoustic communication.

A guild classification system proposed for anuran advertisement calls

Zoologists have widely acknowledged the utility of classification systems for characterising variation in anuran egg and clutch types, tadpole morphotypes, embryonic and tadpole development, amplexus types and reproductive modes. These classification systems have facilitated unambiguous communication between researchers, often working in completely different fields (e.g. taxonomy, ecology, behaviour), as well as comparisons among studies. A syntactic system, classifying anuran call guilds, is so far lacking. Based on examination of the calls of 1253 anuran species we present a simple, easy to use dichotomous key and guild system for classifying anuran advertisement calls – the call type most frequently emitted by anurans and studied by researchers. The use of only three call elements, namely clearly-defined calls, notes, and pulses, plus presence or absence of frequency modulation, allows assigning all currently known anuran advertisement calls to one of eight distinct call guilds defined here. This novel toolkit will facilitate comparative studies across the many thousand anuran species, and may help to unravel drivers of anuran call evolution, and to identify ecological patterns at the level of acoustic communities.

Decision making in the face of a deadly predator: high-amplitude behavioural thresholds can be adaptive for rainforest crickets under high background noise levels

Many insect families have evolved ears that are adapted to detect ultrasonic calls of bats. The acoustic sensory cues indicating the presence of a bat are then used to initiate bat avoidance behaviours. Background noise, in particular at ultrasonic frequencies, complicates these decisions, since a response to the background may result in costly false alarms. Here, we quantify bat avoidance responses of small rainforest crickets (Gryllidae, Trigoniinae), which live under conditions of high levels of ultrasonic background noise. Their bat avoidance behaviour exhibits markedly higher thresholds than most other studied eared insects. Their responses do not qualitatively differ at suprathreshold amplitudes up to sound pressure levels of 105 dB. Moreover, they also exhibit evasive responses to single, high-frequency events and do not require the repetitive sequence of ultrasonic calls typical for the search phase of bat echolocation calls. Analysis of bat and katydid sound amplitudes and peak frequencies in the crickets' rainforest habitat revealed that the cricket's behavioural threshold would successfully reject the katydid background noise. Using measurements of the crickets' echo target strength for bat predators, we calculated the detection distances for both predators and prey. Despite their high behavioural threshold, the cricket prey still has a significant detection advantage at frequencies between 20 and 40 kHz. The low-amplitude bat calls they ignore are no predation threat because even much louder calls would be detected before the bat would hear the cricket echo. This leaves ample time for evasive actions. Thus, a simple decision criterion based on a high-amplitude behavioural threshold can be adaptive under the high background noise levels in nocturnal rainforests, in avoiding false alarms and only missing detection for bat calls too far away to pose a risk. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

MtOrt: an empirical mitochondrial amino acid substitution model for evolutionary studies of Orthoptera insects

BACKGROUND

Amino acid substitution models play an important role in inferring phylogenies from proteins. Although different amino acid substitution models have been proposed, only a few were estimated from mitochondrial protein sequences for specific taxa such as the mtArt model for Arthropoda. The increasing of mitochondrial genome data from broad Orthoptera taxa provides an opportunity to estimate the Orthoptera-specific mitochondrial amino acid empirical model.

RESULTS

We sequenced complete mitochondrial genomes of 54 Orthoptera species, and estimated an amino acid substitution model (named mtOrt) by maximum likelihood method based on the 283 complete mitochondrial genomes available currently. The results indicated that there are obvious differences between mtOrt and the existing models, and the new model can better fit the Orthoptera mitochondrial protein datasets. Moreover, topologies of trees constructed using mtOrt and existing models are frequently different. MtOrt does indeed have an impact on likelihood improvement as well as tree topologies. The comparisons between the topologies of trees constructed using mtOrt and existing models show that the new model outperforms the existing models in inferring phylogenies from Orthoptera mitochondrial protein data.

CONCLUSIONS

The new mitochondrial amino acid substitution model of Orthoptera shows obvious differences from the existing models, and outperforms the existing models in inferring phylogenies from Orthoptera mitochondrial protein sequences.

Testing the role of trait reversal in evolutionary diversification using song loss in wild crickets

The mechanisms underlying rapid macroevolution are controversial. One largely untested hypothesis that could inform this debate is that evolutionary reversals might release variation in vestigial traits, which then facilitates subsequent diversification. We evaluated this idea by testing key predictions about vestigial traits arising from sexual trait reversal in wild field crickets. In Hawaiian Teleogryllus oceanicus, the recent genetic loss of sound-producing and -amplifying structures on male wings eliminates their acoustic signals. Silence protects these "flatwing" males from an acoustically orienting parasitoid and appears to have evolved independently more than once. Here, we report that flatwing males show enhanced variation in vestigial resonator morphology under varied genetic backgrounds. Using laser Doppler vibrometry, we found that these vestigial sound-producing wing features resonate at highly variable acoustic frequencies well outside the normal range for this species. These results satisfy two important criteria for a mechanism driving rapid evolutionary diversification: Sexual signal loss was accompanied by a release of vestigial morphological variants, and these could facilitate the rapid evolution of novel signal values. Widespread secondary trait losses have been inferred from fossil and phylogenetic evidence across numerous taxa, and our results suggest that such reversals could play a role in shaping historical patterns of diversification.

Phylogeny and acoustic signal evolution of a pure tone song katydid Pseudophyllus titan (Orthoptera: Tettigoniidae) based on the complete mitogenome

Ensifera is an extremely diverse group in the order Orthoptera, and it has been the subject of considerable research, especially in terms of phylogeny and bioacoustics. Katydids are known for using high-frequency broadband signals whereas most cricket songs are pure tones with a frequency range of 2-8 kHz. Pseudophyllus titan is a special katydid emits low-frequency pure tone songs similar to that of crickets. Acoustic communication of Ensifera were widely studied, but song evolution could deserve new examination taking into account the newly available phylogenies. To examine the song evolution of P. titan in the Ensifera, the mitogenomes of P. titan and three other ensiferan species (Sphagniana ussuriana, Oecanthus sinensis, Truljalia hibinonis) were obtained by high-throughput sequencing. In addition, the phylogeny of Ensifera was reconstructed including 63 in-group taxa, and the divergence time was further estimated for major ensiferan lineages. Lastly, the evolutions of song frequency were evaluated based on an ancestral character state reconstruction (ACSR). Moreover, we have studied the calling songs of 78 katydids and performed ACSR based on five genes. All phylogeny analyses confirmed that the superfamily Schizodactyloidea was placed basally to the non-grylloid clade. P. titan was in the Pseudophyllinae clade, and this clade had a distant relationship form other lineages in Phaneropteridae. The ACSR showed that P. titan evolved low-frequency pure tone songs independently after ancestors of katydids evolved high-frequency broadband noise. Referring to the geologic time scale, we suggest that the song frequency evolution in the Ensifera to some extent caused by adaptations to the changing habitat under conditions of climate change and plant evolution.

Comparative analysis of mitochondrial genomes of the superfamily Grylloidea (Insecta, Orthoptera) reveals phylogenetic distribution of gene rearrangements

To further characterize mitochondrial genome (mitogenome) features of the superfamily Grylloidea (Insecta, Orthoptera), mitogenomes of Cacoplistes rogenhoferi and Meloimorpha japonica representing the family Mogoplistidae and three Ornebius species of Phalangopsidae were sequenced. A repeat-containing control region (CR) and 37 genes were present in these mitogenomes. Unusual start codons (TCG, CCG, and CTG) of cox1 and, in Ornebius, a partial stop codon (T) of nad1 followed by a 15-17-bp intergenic spacer were proposed based on transcript information and sequence alignments. The mitogenome-based phylogenetic trees suggest strongly the familial relationships as (((Phalangopsidae + Gryllidae) + Trigonidiidae) + Mogoplistidae). The exclusive occurrence of the trnE-trnS1-trnN rearrangement in Phalangopsidae, Gryllidae, and Trigonidiidae is suggestive of its appearance in the common ancestor of these families after the separation of Mogoplistidae. The trnV transposition in O. bimaculatus and formerly sequenced Trigonidium sjostedti (Trigonidiidae) indicates a potential consequence of parallel evolution. This study offers novel insights into mitogenome evolution, especially gene rearrangements, of Grylloidea.

Complete mitochondrial genome of bamboo grasshopper, Ceracris fasciata, and the phylogenetic analyses and divergence time estimation of Caelifera (Orthoptera)

The bamboo grasshopper Ceracris fasciata is regarded as a major pest species because of the damage it causes to bamboo, and its classification within the families and subfamilies of the suborder Caelifera remains unclear. Thus, we attempted to resolve these questions using molecular biology methods and analyses. Our results are as follows: (1) the complete mitochondrial genome of C. fasciata is 15,569 bp in length. The mitochondrial genome contains a standard set of 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes and an A + T-rich region in the same order as those of the other analysed Caeliferan species. The putative start codon for the COX1 gene in C. fasciata is ACC, although it is not defined in other genes. The presence of tandem repeats of different sizes in the A + T-rich region may lead to size differences in other mitochondrial genomes. The mitochondrial genome of C. fasciata harbours the typical 37 genes and an A + T-rich region, and it shows similar characteristics to those of other grasshopper species. Characterization of the mitochondrial genome has enriched our knowledge of the mitochondrial genomes of Orthoptera around the world. Therefore, the phylogenetic relationships in Orthoptera can be re-examined. (2) In phylogenetic analyses, the monophyly of Orthoptera and its two suborders (Caelifera and Ensifera) has been consistently recovered based on most of the datasets selected, regardless of the optimal criteria. Our results do not support the monophyly of the subfamily Oedipodinae of Caelifera. We found that Phlaeoba albonema of the Acridinae is sorted into a clade with Ceracris in all our phylogenetic trees, and field experiments show that Phlaeoba always lives with Ceracris in the same ecotopes. Therefore, we suggest that Phlaeoba should be classified as a member of the Oedipodinae. We found that C. fasciata always clustered with Ceracris kiangsu, and both were sisters to Ceracris versicolor. Therefore, the genetic relationship between C. fasciata and C. kiangsu is closer than that between C. fasciata and C. versicolor. (3) The oldest estimated time of divergence of Ensifera in this context was determined to be 146.16 million years ago (Mya), or around the late Jurassic or early Cretaceous. We estimated that katydids (Grylloidea) likely diverged from other groups in the early Cretaceous. According to our divergence time analyses, we concluded that the ancestral Acrididae probably originated in the early Paleogene, and it is likely that the major diversification events happened at the middle Paleogene, well into the next geologic time. We estimated that crickets (Tettigoniidae) likely diverged from other groups in the early Cretaceous. Acrididae and Romaleinae group, Pyrgacrididae and Ommexechidae group, the youngest two clades we observed, were estimated to have diverged 58.79 Mya, between the middle and early Paleogene. C. versicolor is a sister to the group containing C. kiangsu and C. fasciata. First, C. versicolor diverged from the sister group (C. kiangsu + C. fasciata) around 44.81 Mya, and then the C. kiangsu and C. fasciata group separated at 43.04 Mya.

Auditory DUM neurons in a bush-cricket: A filter bank for carrier frequency

In bush-crickets the first stage of central auditory processing occurs in the prothoracic ganglion. About 15 to 50 different auditory dorsal unpaired median neurons (DUM neurons) exist but they have not been studied in any detail. These DUM neurons may be classified into seven different morphological types, although, there is only limited correlation between morphology and physiological responses. Ninety seven percent of the stained neurons were local, 3% were intersegmental. About 90% project nearly exclusively into the auditory neuropile, and 45% into restricted areas therein. Lateral extensions overlap with the axons of primary auditory sensory neurons close to their branching point. DUM neurons are typically tuned to frequencies covering the range between 2 and 50 kHz and thereby may establish a filter bank for carrier frequency. Less than 10% of DUM neurons have their branches in adjacent and more posterior regions of the auditory neuropile and are mostly tuned to low frequencies, less sensitive than the other types and respond to vibration. Thirty five percent of DUM show indications of inhibition, either through reduced responses at higher intensities, or by hyperpolarizing responses to sound. Most DUM neurons produce phasic spike responses preferably at higher intensities. Spikes may be elicited by intracellular current injection. Preliminary data suggest that auditory DUM neurons have GABA as transmitter and therefore may inhibit other auditory interneurons. From all known local auditory neurons, only DUM neurons have frequency specific responses which appear suited for local processing relevant for acoustic communication in bush crickets.

Hearing with exceptionally thin tympana: Ear morphology and tympanal membrane vibrations in eneopterine crickets

The receiver sensory system plays a crucial role in the evolution of new communication signals in insects. Among acoustic communicating crickets, the tribe Lebinthini (Eneopterinae) has evolved a unique communication system in that males produce exceptionally high-frequency calls and females respond with vibratory signals to guide males towards them. In this study, we describe nine species of Eneopterinae in which the sound receiving structures have undergone considerable morphological changes. We revealed that the anterior tympanal membrane (ATM) of the ear was extremely thin, as little as 0.35 µm thick, and to the best of our knowledge, this is the thinnest tympanal membrane found in crickets thus far. Measurements of tympanum vibrations obtained from Lebinthus bitaeniatus demonstrated a strong sensitivity towards higher frequencies. The finding also coincides with the neuronal tuning of ascending neurons and the behavioural response of the Lebinthini. The morphologically specialized ATM and its mechanical sensitivity for high frequencies, therefore, may have driven the sensory exploitation of an anti-predator behaviour that led to the evolution of a new communication system known for this group of crickets. The hypothetical phylogenetic origin of the investigated tympanal ears is discussed.

3-D imaging reveals four extraordinary cases of convergent evolution of acoustic communication in crickets and allies (Insecta)

When the same complex trait is exhibited by closely related species, a single evolutionary origin is frequently invoked. The complex stridulatory apparatus present in the forewings of extant crickets, mole crickets, katydids, and prophalangopsids, is currently interpreted as sharing a single common origin due to their similarity and unique function. An alternative hypothesis of convergent evolution in these ensiferan groups has challenged this common view, but remained controversial because of competing interpretations of wing venation. Here we propose another hypothesis for the widely and long debated homology of ensiferan stridulatory apparatus, performing the first 3D reconstruction of hidden structures at the wing bases. This approach allowed defining the homology of each vein from its very origin rather than after its more distal characteristics, which may be subjected to environmental pressure of selection. The stridulatory apparatus involves different veins in these four singing clades. In light of the most recent phylogenetic evidence, this apparatus developed four times in Ensifera, illustrating extraordinary convergent evolutions between closely related clades, by far exceeding the number of evolutionary steps ever proposed for calling ability in this group.

The thoracic morphology of the wingless dune cricket Comicus calcaris (Orthoptera: Schizodactylidae): Novel apomorphic characters for the group and adaptations to sand desert environments

Schizodactylidae, splay-footed or dune crickets, represents a distinct lineage among the highly diverse orthopteran subgroup Ensifera (crickets, katydids and allies). Only two extant genera belong to the Schizodactylidae: the winged Eurasian genus Schizodactylus, whose ecology and morphology is well documented, and the wingless South African Comicus, for which hardly any studies providing morphological descriptions have been conducted since its taxonomic description in 1888. Based on the first in-depth study of the skeletomuscular system of the thorax of Comicus calcaris Irish 1986, we provide information on some unique characteristics of this character complex in Schizodactylidae. They include a rigid connection of prospinasternite and mesosternum, a T-shaped mesospina, and a fused meso- and metasternum. Although Schizodactylidae is mainly characterized by group-specific anatomical traits of the thorax, its bifurcated profuca supports a closer relationship to the tettigonioid ensiferans, like katydids, wetas, and hump-winged crickets. Some specific features of the thoracic musculature of Comicus seem to be correlated to the skeletal morphology, e.g., due to the rigid connection of the tergites and pleurites in the pterothorax not a single direct flight muscle is developed. We show that many of the thoracic adaptations in these insects are directly related to their psammophilous way of life. These include a characteristic setation of thoracic sclerites that prevent sand grains from intrusion into vulnerable membranous areas, the striking decrease in size of the thoracic spiracles that reduces the respirational water loss, and a general trend towards a fusion of sclerites in the thorax.

Towards a higher-level Ensifera phylogeny inferred from mitogenome sequences

Although mitogenomes are useful tools for inferring evolutionary history, only a few representative ones can be used for most Ensifera lineages. Thirty-two ensiferan mitogenomes were determined using ABI Sanger sequencing and standard primer walking of 2-3 overlapping Long-PCR fragments, or Illumina® HiSeq2000 for "shotgun" sequenced long-PCR-amplified mitochondrial or total genomic DNA. Six patterns of gene arrangements, including the novel trnR-trnS^AGN-trnA-trnN-trnG-nad3 in Lipotactes tripyrga (Lipotactinae), were identified from 59 ensiferan mitogenomes. The results suggest that trnM-trnI-trnQ and trnA-trnR-trnE-trnS^AGN-trnN-trnF rearrangements might be a shared derived character in Pseudophyllinae and Gryllidae, respectively. We found base composition biases in our dataset, which potentially complicate the inference of higher-level ensiferan phylogeny. Site-heterogeneous Bayesian inference (BI) and site-homogeneous maximum likelihood (ML) analyses recovered all ensiferan superfamilies as monophyletic. The site-homogeneous BI analysis failed to recover the monophyly of Stenopelmatoidea. As Schizodactyloidea was only represented by Comicus campestris, its monophyly could not be tested. In the Triassic/Jurassic boundary, Ensifera diverged into grylloid and non-grylloid clades. All analyses confirmed Grylloidea and Gryllotalpoidea as sister groups. Site-heterogeneous BI analysis found Schizodactyloidea as the most basal lineage and sister to the clade formed by Grylloidea and Gryllotalpoidea, but the site-homogeneous analyses placed it basally to the non-grylloid clade and recovered a sister relationship between Tettigonioidea and (Hagloidea, Rhaphidophoroidea, Stenopelmatoidea), although this clade had a low support. The site-heterogeneous BI analysis found Tettigonioidea and Hagloidea were sister groups (posterior probability (PP)=0.99), Stenopelmatoidea was sister to (Tettigonioidea, Hagloidea) (PP>0.91), and Rhaphidophoroidea was basal to the non-grylloid clade. At a lower level, all analyses divided Tettigonioidea into Phaneropteridae and Tettigoniidae.

Functional morphology of tegmina-based stridulation in the relict species Cyphoderris monstrosa (Orthoptera: Ensifera: Prophalangopsidae)

Male grigs, bush crickets and crickets produce mating calls by tegminal stridulation: the scraping together of modified forewings functioning as sound generators. Bush crickets (Tettigoniidae) and crickets (Gryllinae) diverged some 240 million years ago, with each lineage developing unique characteristics in wing morphology and the associated mechanics of stridulation. The grigs (Prophalangopsidae), a relict lineage more closely related to bush crickets than to crickets, are believed to retain plesiomorphic features of wing morphology. The wing cells widely involved in sound production, such as the harp and mirror, are comparatively small, poorly delimited and/or partially filled with cross-veins. Such morphology is similarly observed in the earliest stridulating ensiferans, for which stridulatory mechanics remains poorly understood. The grigs, therefore, are of major importance to investigate the early evolutionary stages of tegminal stridulation, a critical innovation in the evolution of the Orthoptera. The aim of this study is to appreciate the degree of specialization on grig forewings, through identification of sound radiating areas and their properties. For well-grounded comparisons, homologies in wing venation (and associated areas) of grigs and bush crickets are re-evaluated. Then, using direct evidence, this study confirms the mirror cell, in association with two other areas (termed 'neck' and 'pre-mirror'), as the acoustic resonator in the grig Cyphoderris monstrosa Despite the use of largely symmetrical resonators, as found in field crickets, analogous features of stridulatory mechanics are observed between C. monstrosa and bush crickets. Both morphology and function in grigs represents transitional stages between unspecialized forewings and derived conditions observed in modern species.