Genome skimming for improved phylogenetics of Taiwanese phasmids (Insecta: Phasmatodea)

Taiwan, a relatively young continental island, harbors a high proportion of endemic phasmids, reflecting its unique evolutionary history. However, a comprehensive phylogenetic framework to clarify these phasmids is still lacking. In this study, we sequenced ten of eleven valid genera and two undescribed species of Taiwanese phasmids (total 16 species) using the genome-skimming approach. We also integrated these sequences with public databases to create two aligned datasets: one comprising 92 taxa (mitogenomes) and the other 606 taxa (seven nuclear and mitochondrial genes), enabling us to examine their phylogenetic relationships using longer sequences and more samples. Our analyses show that Taiwanese phasmids should be categorized into six families, with a revised number of genera to 13. Furthermore, four species require taxonomic treatments: namely Micadina honei (Günther, 1940) comb. nov., Micadina truncatum (Shiraki, 1935) comb. nov., Otraleus okunii (Shiraki, 1935) comb. nov., and Ramulus granulatus (Shiraki, 1935) syn. nov. now recognized as Ramulus artemis (Westwood, 1859). While some Taiwanese genera exhibit polyphyletic relationships, our findings highlight the importance of taxon sampling, particularly for type species in resolving these systematic issues. The genome-skimming approach has proven to be an excellent method for producing comparable sequence datasets, facilitating the investigation of highly diverse insects, even when samples are old, small, or have highly fragmented DNAs.

Divergence time and environmental similarity predict the strength of morphological convergence in stick and leaf insects

Independent evolution of similar traits in lineages inhabiting similar environments (convergent or repeated evolution) is often taken as evidence for adaptation by natural selection, and used to illustrate the predictability of evolution. Yet convergence is rarely perfect for two reasons. First, environments may not be as similar as they appear. Second, responses to selection are contingent upon available genetic variation and independent lineages may differ in the alleles, genetic backgrounds, and even the developmental mechanisms responsible for the phenotypes in question. Both impediments to convergence are predicted to increase as the length of time separating two lineages increases, making it difficult to discern their relative importance. We quantified environmental similarity and the extent of convergence to show how habitat and divergence time each contribute to observed patterns of morphological evolution in 212 species of stick and leaf insects (order Phasmatodea). Dozens of phasmid lineages independently colonized similar habitats, repeatedly evolving in parallel directions on a 23-trait morphospace, though the magnitude and direction of these shifts varied. Lineages converging toward more similar environments ended up closer on the morphospace, as did closely related lineages, and closely related lineages followed more parallel evolutionary trajectories to arrive there than more distantly related ones. Remarkably, after accounting for habitat similarity, we show that divergence time reduced the extent of convergence at a constant rate across more than 100 My of separation, suggesting even the magnitude of contingency can be predictable, given sufficient spans of time.

Insight into the Phylogenetic Relationships of Phasmatodea and Selection Pressure Analysis of Phraortes liaoningensis Chen & He, 1991 (Phasmatodea: Lonchodidae) Using Mitogenomes

Stick and leaf insects are a group among the Insecta that are famous for their extraordinary mimicry ability. Since the establishment of the Phasmatodea, their internal classification has been constantly revised. Mitochondrial genes as molecular markers have been widely used for species classification, but the phylogenetic relationships within the Phasmatodea remain to be thoroughly discussed. In the present study, five mitogenomes of Phasmatodea ranging from 15,746 bp to 16,747 bp in length were sequenced. Bayesian inference (BI) and maximum likelihood (ML) analyses were carried out based on a 13 PCGs data matrix (nt123) and a combined matrix of 13 PCGs and two rRNA genes (nt123_rRNA). The present study supports the conclusion that Phylliidae was the basal group of Neophasmatodea and confirms the monophyly of Lonchodinae and Necrosciinae, but it shows that Lonchodidae was polyphyletic. A sister group of Bacillidae and Pseudophasmatidae was also recovered. The phylogenetic tree based on the nt_123 dataset showed higher node support values. The construction of a divergent time tree in this study supported the conclusion that extant Phasmatodea originated in the Jurassic (170 Mya) and most lineages diverged after the Cretaceous-Paleogene extinction event. To explore whether the mitochondrial genes of Phraortes liaoningensis collected from high latitudes where low temperatures occur for eight months of the year are under selection pressure, this study used the branch-site model and the branch model to analyze the selection pressure on the 13 mitochondria protein-coding genes (PCGs). We found that both ND2 and ND4L of Ph. liaoningensis exhibited positive selection sites using the branch-site model. This study shows that a low-temperature environment causes mitochondrial genes to be selected to meet the energy requirements for survival.

On the Brazilian Exocnophila stick insects (Insecta: Phasmatodea), with the description of a new species

Several stick insects occurring in Brazil belong to the Diapheromerinae. Before this work, the Brazilian genus Exocnophila contained three species known only from females, Exocnophila exintegra Zompro, 2001, Exocnophila tuberculata (Brunner von Wattenwyl, 1907) and Exocnophila cornuta (Brunner von Wattenwyl, 1907). Based on recently collected material, we found that the males of Exocnophila are assigned to another genus in the Diapheromerinae, the heterogeneous Bacteria. Here we show that the type species Exocnophila exintegra Zompro, 2001 syn. nov. is a junior synonym of Bacteria brevitarsata Brunner von Wattenwyl, 1907, which is transferred and redescribed as Exocnophila brevitarsata comb. nov.. We also transfer and redescribe Bacteria hastata as Exocnophila hastata comb. nov. and propose a new species, Exocnophila ovifuscum sp. nov., from Rio de Janeiro state, Brazil, with descriptions of females, males and eggs. We provide the first biological observations for the genus and a short discussion about its relationships.

Diversity of attachment systems in heelwalkers (Mantophasmatodea) - highly specialized, but uniform

BACKGROUND

Heelwalkers possess a highly modified tarsal attachment system. All extant species lift the distalmost tarsomere permanently off the substrate and primarily use their euplantulae for locomotion. The combination of a smooth adhesive pad (arolium) on the pretarsus and fibrillary attachment pads on the euplantulae offers valuable insights for translational approaches, but its infra-order diversity remains unexplored.

RESULTS

We explored the morphology of the tarsal attachment apparatus of Mantophasmatodea based on a representative taxon sampling spanning a large fraction of species of this group and compared morphological differences in the specialized morphology of this system across species and sexes. Our scanning electron microscope investigation of the tarsi of 11 species (52% of all described extant species) revealed an overall very consistent ground pattern and almost no specific adaptations. There are only minor, but mostly clade-specific differences in the shape of the adhesive setae on the tarsal euplantulae and in the morphology and density of the acanthae on the pretarsal arolium. Both features differ primarily between Austrophasmatidae in comparison to the remaining Mantophasmatodea taxa.

CONCLUSION

We conclude that the strong specialization of the mantophasmatodean tarsal attachment sufficiently copes with the diversity of substrates the insects are exposed to.

An annotated catalogue of the type specimens of Phasmatodea deposited at the Zoological Museum Hamburg (ZMH)

We here present an updated and annotated catalogue of the stick and leaf insect (Phasmatodea) types currently housed in the Zoological Museum Hamburg (ZMH), part of the Leibniz Institute for the Analysis of Biodiversity Change (LIB). We found a total of 305 type specimens, belonging to 130 species. This includes 110 primary types (45 holotypes, 13 lectotypes, 52 syntypes) and 195 paratypes and paralectotypes. Most of the species were described by Redtenbacher, others come from Zompro, Brunner von Wattenwyl, Weidner and others. We provide updated information on the taxonomy of all species. This catalogue will represent an important resource for future taxonomic work on the group.

Scoutknife: A naïve, whole genome informed phylogenetic robusticity metric

Background: The phylogenetic bootstrap, first proposed by Felsenstein in 1985, is a critically important statistical method in assessing the robusticity of phylogenetic datasets. Core to its concept was the use of pseudo sampling - assessing the data by generating new replicates derived from the initial dataset that was used to generate the phylogeny. In this way, phylogenetic support metrics could overcome the lack of perfect, infinite data. With infinite data, however, it is possible to sample smaller replicates directly from the data to obtain both the phylogeny and its statistical robusticity in the same analysis. Due to the growth of whole genome sequencing, the depth and breadth of our datasets have greatly expanded and are set to only expand further. With genome-scale datasets comprising thousands of genes, we can now obtain a proxy for infinite data. Accordingly, we can potentially abandon the notion of pseudo sampling and instead randomly sample small subsets of genes from the thousands of genes in our analyses. Methods: We introduce Scoutknife, a jackknife-style subsampling implementation that generates 100 datasets by randomly sampling a small number of genes from an initial large-gene dataset to jointly establish both a phylogenetic hypothesis and assess its robusticity. We assess its effectiveness by using 18 previously published datasets and 100 simulation studies. Results: We show that Scoutknife is conservative and informative as to conflicts and incongruence across the whole genome, without the need for subsampling based on traditional model selection criteria. Conclusions: Scoutknife reliably achieves comparable results to selecting the best genes on both real and simulation datasets, while being resistant to the potential biases caused by selecting for model fit. As the amount of genome data grows, it becomes an even more exciting option to assess the robusticity of phylogenetic hypotheses.

Resource allocation strategies and mechanical constraints drive the diversification of stick and leaf insect eggs

The diversity of insect eggs is astounding but still largely unexplained. Here, we apply phylogenetic analyses to 208 species of stick and leaf insects, coupled with physiological measurements of metabolic rate and water loss on five species, to evaluate classes of factors that may drive egg morphological diversification: life history constraints, material costs, mechanical constraints, and ecological circumstances. We show support for all three classes, but egg size is primarily influenced by female body size and strongly trades off with egg number. Females that lay relatively fewer but larger eggs, which develop more slowly because of disproportionately low metabolic rates, also tend to bury or glue them in specific locations instead of simply dropping them from the foliage (ancestral state). This form of parental care then directly favors relatively elongated eggs, which may facilitate their placement and allow easier passage through the oviducts in slender species. In addition, flightless females display a higher reproductive output and consequently lay relatively more and larger eggs compared with flight-capable females. Surprisingly, local climatic conditions had only weak effects on egg traits. Overall, our results suggest that morphological diversification of stick insect eggs is driven by a complex web of causal relationships among traits, with dominant effects of resource allocation and oviposition strategies, and of mechanical constraints.

Studies on Neotropical Phasmatodea XXVI: Taxonomic review of Cladomorformia tax. n., a lineage of Diapheromerinae stick insects, with the descriptions of seven new genera and 41 new species (Phasmatodea: Occidophasmata: Diapheromerinae)

Stick and leaf insects (Phasmatodea) are a moderately diverse order that comprises almost 3,500 extant species of large to very large often impressively camouflaged nocturnal herbivores. The order also stands out as one of the few insect orders that have until lately lacked a robust higher-level phylogeny and still the relationships between many New World taxa in particular remain unknown. The Diapheromerinae is one of the main lineages of the Occidophasmata and comprises a bulk of the diversity of New World stick insects. The clade is endemic to the Americas and includes the longest insects of that region. During the past 25 years Diapheromerinae has experienced various often inconsistent attempts of a classification, which have resulted in a complicated history that has meanwhile constituted a heterogenous mixture of historical and contemporary views. To counter these challenges workers have made use of rank-free taxa to provisionally group supposedly monophyletic clades. Currently the Diapheromerinae are sub-divided into the two tribes Diapheromerini and Oreophoetini and recent molecular analyses have shown taxa of the Cladomorphinae Günther, 1953 to belong to Diapheromerinae. Certainly, the clade still deserves much work to delimit meaningful sub-groups within Diapheromerinae reflective of their evolutionary history and the results of the latest comprehensive molecular-based phylogenetic studies already imply sub-divisions within the Diapheromerini. The rank-free taxon Cladomorformia tax. n. is established to comprise former Cladomorphini, Cranidiini, Otocrania Redtenbacher, 1908 as well as sections of Diapheromerini sensu Robertson et al., 2018, which are the genera that have previously been placed in the "Phanocles group" sensu Zompro, 2001 as well as two genera of the "Bacteria group" and one genus of the "Clonistria group": Alienobostra, Bostriana, Calynda, Globocalynda, Laciphorus, Phanocles, Phanocloidea and Trychopeplus. The genus Cranidium and all genera of Cladomorphini sensu Hennemann et al., 2016 are here formally transferred to Diapheromerinae, this is Aplopocranidium, Cladomorphus, Jeremia, Jeremiodes, Otocraniella and Xylodus. A holistic review of Cladomorformia at the genus level is conducted herein and new diagnoses, differentiations and keys to all 25 genera that are now contained in that clade are presented. Lists of species are provided for all genera, which include detailed type data, synonymies and distributional records. Moreover, identification keys to all 163 known valid species are provided to render identification of species within the 25 known genera possible. In total, 232 species are covered if the 69 synonymous taxa are included. The subfamily Haplopodinae is introduced to comprise all genera of the tribes Haplopodini, Hesperophasmatini and Pterinoxylini as classified by Hennemann et al. (2016) as well as the recently described Teruelphasmini. Renaming former Cladomorphinae sensu Robertson et al. (2018) into Haplopodinae is necessary, because the type-genus Cladomorphus can no longer be considered a member of that lineage and belongs in Diapheromerinae. Haplopodinae is the only New World clade that belongs into the Old World Oriophasmata. Bostranova Villet, 2023 has been introduced to replace the preoccupied Bostra Stål, 1875. The type-species of Bostranova, Bacteria turgida Westwood, 1859, however is here shown to belong in Phanocloidea Zompro, 2001. Thus, Bostranova is synonymised under Phanocloidea (n. syn.) and all species are transferred to Phanocloidea and other genera. Paraphanocles Zompro, 2001 (Type-species: Mantis keratosqueleton Olivier, 1792) is synonymised with Phanocles Stål, 1875 (syn. n.). Seven new genera are described: Globocrania gen. n. (Type-species: Bacteria emesa Westwood, 1859), Hirtuleiodes gen. n. (Type-species: Phibalosoma gibbosa Chopard, 1911), Lanceobostra gen. n. (Type-species: Bacteria aetolus Westwood, 1859), Ocreatophasma gen. n. (Type-species: Ocreatophasma elegans sp. n.), Parotocrania gen. n. (Type-species: Parotocrania panamae sp. n.), Phanoclocrania gen. n. (Type-species: Bostra dorsuaria Stål, 1875) and Spinocloidea gen. n. (Type-species: Spinocloidea panamaense sp. n.). All seven genera are described from both sexes and the eggs, with the exception of Ocreatophasma gen. n., which is known from the females only. Forty-one new species are described: Globocalynda cornuta sp. n. from Ecuador, Globocalynda marcapatae sp. n. from Peru, Globocalynda ruficollis sp. n. from Bolivia, Hirtuleiodes peruanus sp. n. from Peru, Jeremiodes costaricensis sp. n. from Costa Rica, Jeremiodes ecuadoricus sp. n. from Ecuador, Jeremiodes peruanus sp. n. from Peru, Lanceobostra chapalaense sp. n. from Mexico, Lanceobostra glabra sp. n. from Mexico, Lanceobostra oaxacaee sp. n. from Mexico, Lanceobostra ornata sp. n. from Mexico, Lanceobostra torquata sp. n. from Mexico, Lanceobostra tuckerae sp. n. from Mexico, Ocreatophasma elegans gen. n., sp. n. from Peru, Ocreatophasma fragile gen. n., sp. n. from Peru, Ocreatophasma modestum gen. n., sp. n. from Peru, Parotocrania acutilobata gen. n., sp. n. from Ecuador, Parotocrania curvata gen. n., sp. n. from Peru, Parotocrania panamae gen. n., sp. n. from Panama, Phanocles acutecornutus sp. n. from Ecuador, Phanocles barbadosense sp. n. from Barbados, Phanocles berezini sp. n. from Mexico, Phanocles brevipes sp. n. from Peru, Phanocles chiapasense sp. n. from Mexico, Phanocles cuzcoense sp. n. from Peru, Phanocles ecuadoricus sp. n. from Ecuador, Phanocles falcatus sp. n. from Ecuador, Phanocles maximus sp. n. from Panama, Phanocles mexicanus sp. n. from Mexico, Phanocles pleurospinosus sp. n. from Costa Rica, Phanocles rehni sp. n. from Honduras, Phanocles solidus sp. n. from Ecuador, Phanocles spectabilis sp. n. from Costa Rica, Phanocles superbus sp. n. from Ecuador, Phanocloidea sanguinea sp. n. from Ecuador, Phanocloidea semiptera sp. n. from Venezuela, Phanocloidea venezuelica sp. n. from Venezuela, Spinocloidea panamaense gen. n., sp. n. from Panama, Spinocloidea splendida gen. n., sp. n. from Colombia and Spinocloidea tumescens gen. n., sp. n. from Costa Rica. With a maximum recorded body length of 285.0 mm the new species Phanocles maximus sp. n. from Panama is the longest extant insect of the Americas and the Occidophasmata clade. A total of 132 taxonomic changes are conducted: 64 species are transferred to other genera and 43 new synonyms are established. Lectotypes are designated for 25 taxa to ensure stability of the concerned names or new synonymies here established. Moreover, the previously unknown females of five and males of twelve species are described and illustrated for the first time. Colour illustrations are presented of the eggs of 39 species, of which those of 26 species are formally described and illustrated for the first time.

Integrated phylogenomic approaches in insect systematics

The increased accessibility of genomic and imaging methods, and the improved access to ecological, spatial, and other natural history-related data is allowing for insect systematics to grow and find answers to central evolutionary and taxonomic questions. Today, integrated studies in insect phylogenomics and systematics are combining natural history, behavior, developmental biology, morphology, fossils, geographic range data, and ecological interactions. This integration is contributing to the clarification of evolutionary relationships, and the recognition of the role played by these factors on the evolution of insects. Future work should continue to build on these advances, seeking to further increase open-access databasing and support for natural history research, as well as expand its analytical palettes.

High disparity in repellent gland anatomy across major lineages of stick and leaf insects (Insecta: Phasmatodea)

BACKGROUND

Phasmatodea are well known for their ability to disguise themselves by mimicking twigs, leaves, or bark, and are therefore commonly referred to as stick and leaf insects. In addition to this and other defensive strategies, many phasmatodean species use paired prothoracic repellent glands to release defensive chemicals when disturbed by predators or parasites. These glands are considered as an autapomorphic trait of the Phasmatodea. However, detailed knowledge of the gland anatomy and chemical compounds is scarce and only a few species were studied until now. We investigated the repellent glands for a global sampling of stick and leaf insects that represents all major phasmatodean lineages morphologically via µCT scans and analyzed the anatomical traits in a phylogenetic context.

RESULTS

All twelve investigated species possess prothoracic repellent glands that we classify into four distinct gland types. 1: lobe-like glands, 2: sac-like glands without ejaculatory duct, 3: sac-like glands with ejaculatory duct and 4: tube-like glands. Lobe-like glands are exclusively present in Timema, sac-like glands without ejaculatory duct are only found in Orthomeria, whereas the other two types are distributed across all other taxa (= Neophasmatodea). The relative size differences of these glands vary significantly between species, with some glands not exceeding in length the anterior quarter of the prothorax, and other glands extending to the end of the metathorax.

CONCLUSIONS

We could not detect any strong correlation between aposematic or cryptic coloration of the examined phasmatodeans and gland type or size. We hypothesize that a comparatively small gland was present in the last common ancestor of Phasmatodea and Euphasmatodea, and that the gland volume increased independently in subordinate lineages of the Occidophasmata and Oriophasmata. Alternatively, the stem species of Neophasmatodea already developed large glands that were reduced in size several times independently. In any case, our results indicate a convergent evolution of the gland types, which was probably closely linked to properties of the chemical components and different predator selection pressures. Our study is the first showing the great anatomical variability of repellent glands in stick and leaf insects.

Unraveling the Sexual Dimorphism of First Instar Nymphs of the Giant Stick Insect, Cladomorphus phyllinus Gray, 1835, from the Atlantic Forest, Brazil

The first instar nymphs, both male and female, of the giant stick insect Cladomorphus phyllinus Gray, 1835 were carefully described and measured, revealing a remarkable sexual dimorphism that is considered rare among insects and is poorly explored in the order Phasmida. The studied F1 nymphs originated in captivity from eggs laid by a coupled female specimen collected in the Atlantic Forest in the vicinity of Petrópolis city, state of Rio de Janeiro, Brazil. The first instar nymphs of C. phyllinus were measured and illustrated in high-resolution photographs to show the general aspects and details of sexually dimorphic traits, making clear the phenotypic differences in the sexes. A total of 100 nymphs were kept alive until morphological sexual dimorphism was confirmed and quantified. All recently hatched first instar nymphs were separated based on the presumed male and female characteristics, i.e., the presence and absence of the suture in the metanotum in the males and females, respectively, had their sexes confirmed in 100% of the specimens as previously assigned. These results confirm this new morphological trait, which here is named "alar suture" as sex-specific in the first instar nymphs, a novelty in this stage of development of sexual differentiation. In addition, the distinct conformations of the last three abdominal sternites of both sexes were recorded.

Phylogeographical evidence for historical long-distance dispersal in the flightless stick insect Ramulus mikado

Exploring how organisms overcome geographical barriers to dispersal is a fundamental question in biology. Passive long-distance dispersal events, although infrequent and unpredictable, have a considerable impact on species range expansions. Despite limited active dispersal capabilities, many stick insect species have vast geographical ranges, indicating that passive long-distance dispersal is vital for their distribution. A potential mode of passive dispersal in stick insects is via the egg stage within avian digestive tracts, as suggested by experimental evidence. However, detecting such events under natural conditions is challenging due to their rarity. Therefore, to indirectly assess the potential of historical avian-mediated dispersal, we examined the population genetic structure of the flightless stick insect Ramulus mikado across Japan, based on a multifaceted molecular approach [cytochrome oxidase subunit I (COI) haplotypes, nuclear simple sequence repeat markers and genome-wide single nucleotide polymorphisms]. Subsequently, we identified unique phylogeographic patterns, including the discovery of identical COI genotypes spanning considerable distances, which substantiates the notion of passive long-distance genotypic dispersal. Overall, all the molecular data revealed the low and mostly non-significant genetic differentiation among populations, with identical or very similar genotypes across distant populations. We propose that long-distance dispersal facilitated by birds is the plausible explanation for the unique phylogeographic pattern observed in this flightless stick insect.

Descriptions of two new stick insect species of Cnipsomorpha Hennemann, Conle, Zhang & Liu (Phasmatodea) from China based on integrative taxonomy

Accurate taxonomical identification is an extremely important basis for stick insect research, including evolutionary biology but also applied biology such as pest control. In addition, genetic methods are a valuable identification auxiliary technology at present. Therefore, this paper used morphological and molecular data to investigate five stick insect specimens from the genus Cnipsomorpha in Yunnan, successfully identifying two new species: Cnipsomorphayunnanensis Xu, Jiang & Yang, sp. nov. and C.yuxiensis Xu, Jiang & Yang, sp. nov. A phylogenetic tree was constructed through their 28S and COI genes in order to infer the phylogenetic position of the two new species. Photographs of the new species and a key to all known Cnipsomorpha species are provided.

On seven undescribed leaf insect species revealed within the recent "Tree of Leaves" (Phasmatodea, Phylliidae)

With the recent advance in molecular phylogenetics focused on the leaf insects (Phasmatodea, Phylliidae), gaps in knowledge are beginning to be filled. Yet, shortcomings are also being highlighted, for instance, the unveiling of numerous undescribed phylliid species. Here, some of these taxa are described, including Phylliumiyadaonsp. nov. from Mindoro Island, Philippines; Phylliumsamarensesp. nov. from Samar Island, Philippines; Phylliumortizisp. nov. from Mindanao Island, Philippines; Pulchriphylliumheraclessp. nov. from Vietnam; Pulchriphylliumdelisleisp. nov. from South Kalimantan, Indonesia; and Pulchriphylliumbhaskaraisp. nov. from Java, Indonesia. Several additional specimens of these species together with a seventh species described herein, Pulchriphylliumanangusp. nov. from southwestern India, were incorporated into a newly constructed phylogenetic tree. Additionally, two taxa that were originally described as species, but in recent decades have been treated as subspecies, are elevated back to species status to reflect their unique morphology and geographic isolation, creating the following new combinations: Pulchriphylliumscythe (Gray, 1843) stat. rev., comb. nov. from Bangladesh and northeastern India, and Pulchriphylliumcrurifolium (Audinet-Serville, 1838) stat. rev., comb. nov. from the Seychelles islands. Lectotype specimens are also designated for Pulchriphylliumscythe (Gray, 1843) stat. rev., comb. nov. and Pulchriphylliumcrurifolium (Audinet-Serville, 1838) stat. rev., comb. nov. from original type material.

Phasmid species that inhabit colder environments are less likely to have the ability to fly

A vast majority of insects can fly, but some cannot. Flight generally increases how far an individual can travel to access mates, enables the exploitation of additional food resources, and aids in predator avoidance. Despite its functional significance, much remains unknown about the factors that influence the evolution of flight. Here, I use phylogenetic comparative methods to investigate whether average annual temperature or wind speed, two components of the flying environment, is correlated with the evolution of flight using data from 107 species of stick and leaf insects (Insecta: Phasmatodea). I find no association between wind speed and flying ability in this clade. However, I find that colder temperatures are associated with the lack of flying ability. This pattern may be explained by the additional metabolic costs required for insects to fly when it is cold. This finding contradicts previous patterns observed in other insect groups and supports the hypothesis that cold temperatures can influence the evolution of flight.

Nine Mitochondrial Genomes of Phasmatodea with Two Novel Mitochondrial Gene Rearrangements and Phylogeny

The classification of stick and leaf insects (Order Phasmatodea) is flawed at various taxonomic ranks due to a lack of robust phylogenetic relationships and convergent morphological characteristics. In this study, we sequenced nine new mitogenomes that ranged from 15,011 bp to 17,761 bp in length. In the mitogenome of Carausis sp., we found a translocation of trnR and trnA, which can be explained by the tandem duplication/random loss (TDRL) model. In the Stheneboea repudiosa Brunner von Wattenwyl, 1907, a novel mitochondrial structure of 12S rRNA-CR1-trnI-CR2-trnQ-trnM was found for the first time in Phasmatodea. Due to the low homology of CR1 and CR2, we hypothesized that trnI was inverted through recombination and then translocated into the middle of the control region. Control region repeats were frequently detected in the newly sequenced mitogenomes. To explore phylogenetic relationships in Phasmatodea, mtPCGs from 56 Phasmatodean species (composed of 9 stick insects from this study, 31 GenBank data, and 16 data derived from transcriptome splicing) were used for Bayesian inference (BI), and maximum likelihood (ML) analyses. Both analyses supported the monophyly of Lonchodinae and Necrosciinae, but Lonchodidae was polyphyletic. Phasmatidae was monophyletic, and Clitumninae was paraphyletic. Phyllidae was located at the base of Neophasmatodea and formed a sister group with the remaining Neophasmatodea. Bacillidae and Pseudophasmatidae were recovered as a sister group. Heteroptergidae was monophyletic, and the Heteropteryginae sister to the clade (Obriminae + Dataminae) was supported by BI analysis and ML analysis.

The neuronal innervation pattern of the subgenual organ complex in Peruphasma schultei (Insecta: Phasmatodea)

The proximal tibia of orthopteroid insects contains sensory organs, the subgenual organ complex, detecting mechanical stimuli including substrate vibration. In stick insects, two chordotonal organs occur in close proximity, the subgenual organ and the distal organ, which likely detect substrate vibrations. In most stick insects, both organs are innervated by separate nerve branches. To obtain more data on the neuroanatomy of the subgenual organ complex from the New World phasmids (Occidophasmata), the present study documents the neuronal innervation of sensory organs in the subgenual organ complex of Peruphasma schultei, the first species from Pseudophasmatinae investigated for this sensory complex. The innervation pattern shows a distinct nerve branch for the subgenual organ and for the distal organ in most cases. Some variability in the innervation, which generally occurs for these chordotonal organs, was noted for both organs in P. schultei. The most common innervation for both organs was by a single nerve branch for each organ. The innervation of the subgenual organ resembled the nerve pattern of another New World phasmid, but was simpler than in the Old World phasmids (Oriophasmata) studied so far. Therefore, the peripheral neuronal innervation of sensory organs could reflect phylogenetic relationships and provide phylogenetic information, while the overall neuroanatomy of the subgenual organ complex is similar in stick insects.

Systematics of Lepidocyrtinus boneti Denis, 1948 (Collembola, Seirinae) reveals a new position for the species within Seirinae

Seira boneti Denis, 1948, comb. nov. is examined and redescribed based on syntypes and by a newly discovered Chinese population. Lectotype and paralectotypes were designated, and the type locality of the species has been fixed to Câuda, near Nhatrang, Vietnam. The species was first described in the genus Lepidocyrtinus, but based on morphological and molecular evidence it is here transferred to Seira. For the phylogenetic placement of Seira boneticomb. nov., its mitogenome was included in a dataset comprising 19 species of Seirinae. Maximum Likelihood and Bayesian inferences clustered the species next to Seira sanloemensis Godeiro & Cipola, 2020 from Cambodia, forming a distinct Seira clade from the Old World, confirming the hypothesis of the existence of a different basal lineage of Seirinae in Southern Asia.

Behavioural function and development of body-to-limb proportions and active movement ranges in three stick insect species

Overall body proportions and relative limb length are highly characteristic for most insect taxa. In case of the legs, limb length has mostly been discussed with regard to parameters of locomotor performance and, in particular cases, as an adaptation to environmental factors or to the mating system. Here, we compare three species of stick and leaf insects (Phasmatodea) that differ strongly in the length ratio between antennae and walking legs, with the antennae of Medauroidea extradentata being much shorter than its legs, nearly equal length of antennae and legs in Carausius morosus, and considerably longer antennae than front legs in Aretaon asperrimus. We show that that relative limb length is directly related to the near-range exploration effort, with complementary function of the antennae and front legs irrespective of their length ratio. Assuming that these inter-species differences hold for both sexes and all developmental stages, we further explore how relative limb length differs between sexes and how it changes throughout postembryonic development. We show that the pattern of limb-to-body proportions is species-characteristic despite sexual dimorphism, and find that the change in sexual dimorphism is strongest during the last two moults. Finally, we show that antennal growth rate is consistently higher than that of front legs, but differs categorically between the species investigated. Whereas antennal growth rate is constant in Carausius, the antennae grow exponentially in Medauroidea and with a sudden boost during the last moult in Aretaon.

Comparative Neuroanatomy of the Mechanosensory Subgenual Organ Complex in the Peruvian Stick Insect, Oreophoetes peruana

The subgenual organ complex in the leg of Polyneoptera (Insecta) consists of several chordotonal organs specialized to detect mechanical stimuli from substrate vibrations and airborne sound. In stick insects (Phasmatodea), the subgenual organ complex contains the subgenual organ and the distal organ located distally to the subgenual organ. The subgenual organ is a highly sensitive detector for substrate vibrations. The distal organ has a characteristic linear organization of sensilla and likely also responds to substrate vibrations. Despite its unique combination of sensory organs, the neuroanatomy of the subgenual organ complex of stick insects has been investigated for only very few species so far. Phylogenomic analysis has established for Phasmatodea the early branching of the sister groups Oriophasmata, the Old World phasmids, and Occidophasmata, the New World phasmids. The species studied for the sensory neuroanatomy, including the Indian stick insect Carausius morosus, belong to the Old World stick insects. Here, the neuroanatomy of the subgenual organ complex is presented for a first species of the New World stick insects, the Peruvian stick insect Oreophoetes peruana. To document the sensory organs in the subgenual organ complex and their innervation pattern, and to compare these between females and males of this species and also to the Old World stick insects, axonal tracing is used. This study documents the same sensory organs for O. peruana, subgenual organ and distal organ, as in other stick insects. Between the sexes of this species, there are no notable differences in the neuroanatomy of their sensory organs. The innervation pattern of tibial nerve branches in O. peruana is identical to other stick insect species, although the innervation pattern of the subgenual organ by a single tibial nerve branch is simpler. The shared organization of the organs in the subgenual organ complex in both groups of Neophasmatodea (Old World and New World stick insects) indicates the sensory importance of the subgenual organ but also of the distal organ. Some variation exists in the innervation of the chordotonal organs in O. peruana though a common innervation pattern can be identified. The findings raise the question for the ancestral neuroanatomical organization and innervation in stick insects.

Gene transcriptional profiles in gonads of Bacillus taxa (Phasmida) with different cytological mechanisms of automictic parthenogenesis

The evolution of automixis - i.e., meiotic parthenogenesis - requires several features, including ploidy restoration after meiosis and maintenance of fertility. Characterizing the relative contribution of novel versus pre-existing genes and the similarities in their expression and sequence evolution is fundamental to understand the evolution of reproductive novelties. Here we identify gonads-biased genes in two Bacillus automictic stick-insects and compare their expression profile and sequence evolution with a bisexual congeneric species. The two parthenogens restore ploidy through different cytological mechanisms: in Bacillus atticus, nuclei derived from the first meiotic division fuse to restore a diploid egg nucleus, while in Bacillus rossius, diploidization occurs in some cells of the haploid blastula through anaphase restitution. Parthenogens' gonads transcriptional program is found to be largely assembled from genes that were already present before the establishment of automixis. The three species transcriptional profiles largely reflect their phyletic relationships, yet we identify a shared core of genes with gonad-biased patterns of expression in parthenogens which are either male gonads-biased in the sexual species or are not differentially expressed there. At the sequence level, just a handful of gonads-biased genes were inferred to have undergone instances of positive selection exclusively in the parthenogen species. This work is the first to explore the molecular underpinnings of automixis in a comparative framework: it delineates how reproductive novelties can be sustained by genes whose origin precedes the establishment of the novelty itself and shows that different meiotic mechanisms of reproduction can be associated with a shared molecular ground plan.

Cladomorphus petropolisensis, a New Species of Stick Insect from the Atlantic Forest, Rio de Janeiro, Brazil

Simple Summary

The order Phasmatodea includes the longest Brazilian insects, known by their remarkable morphological and behavioural adaptations for camouflage such as sticks, moss, and leaves; they are predominantly nocturnal and phytophagous insects. Cladomorphus phyllinus Gray, 1835 is one of the most common and best-known stick insect species in Brazil. It feeds mainly on guava leaves, angico, and powder-puff, and reproduces sexually and asexually. Cladomorphus phyllinus presents marked sexual dimorphism in the adult: winged males are significantly smaller in size than females and can reach up to 13 cm, while females can reach 23 cm in length and are apterous. A female specimen collected in the Atlantic Forest in Petrópolis, Rio de Janeiro, Brazil, was compared with a C. phyllinus specimen, identified according to published literature. The differences between the two specimens related to the general size and several morphological characters were observed. In order to add evidence that the recently collected specimen belonged to a species distinct from C. phyllinus, part of the cytochrome oxidase I (COI) gene was sequenced and analysed. The comparative analysis of the COI sequences from the two specimens revealed significant differences that, together with the morphological characters and recorded sympatry of the two specimens, support the existence of a new species, which is described here as Cladomorphus petropolisensis.

Abstract

Cladomorphus petropolisensis sp. nov., a new species of stick insect from Petrópolis, Rio de Janeiro, Brazil, is herein described and compared to the other sympatric species, C. phyllinus Gray, 1835 (Phasmatidae, Cladomorphinae). The description of the new species is supported by morphological and molecular evidence. Kimura-2-parameter (K2P) intraspecific COI divergences among the holotype of C. petropolisensis sp. nov. and C. phyllinus individuals ranged from 2.9% to 4.4%, which are suggestive of distinct species, especially when considering that all Cladomorphus individuals studied were collected in the Petrópolis municipality. The new species can be distinguished from C. phyllinus Gray, 1835 by several characteristics: smaller size, the presence of two spines on the hind femora, the relative longer length of the ovipositor, and spiny tegument, especially in the mesonotum, sculpturing of the operculum of the egg.

Cytochrome P450 Genes Expressed in Phasmatodea Midguts

Cytochrome P450s (CYPs) are xenobiotic detoxification genes found in most eukaryotes, and linked in insects to the tolerance of plant secondary chemicals and insecticide resistance. The number and diversity of CYP clans, families, and subfamilies that an organism produces could correlate with its dietary breadth or specialization. This study examined the CYP diversity expressed in the midguts of six species of folivorous stick insects (Phasmatodea), to identify their CYP complement and see if any CYPs correlate with diet toxicity or specialization, and see what factors influenced their evolution in this insect order. CYP genes were mined from six published Phasmatodea transcriptomes and analyzed phylogenetically. The Phasmatodea CYP complement resembles that of other insects, though with relatively low numbers, and with significant expansions in the CYP clades 6J1, 6A13/14, 4C1, and 15A1. The CYP6 group is known to be the dominant CYP family in insects, but most insects have no more than one CYP15 gene, so the function of the multiple CYP15A1 genes in Phasmatodea is unknown, with neofunctionalization following gene duplication hypothesized. No correlation was found between CYPs and diet specialization or toxicity, with some CYP clades expanding within the Phasmatodea and others likely inherited from a common ancestor.

Integrative taxonomy of the stick insect genus

Austrocarausius Brock, 2000 is a stick insect (Phasmatodea: Lonchodidae) genus containing two species restricted to the tropical rainforests of northern Queensland. Recent specimen collections between the two species’ type localities, Lizard Island and Rockhampton, have suggested that Austrocarausius might represent more than the two nominal species. Here, we apply morphological and molecular analyses to revise the taxonomy of this genus. Using both field-collected and historic museum samples, we developed morphological species hypotheses and descriptions. Genetic sequencing of mitochondrial COI and 16S were undertaken for species delimitation and phylogenetic analysis, including an estimate of the evolutionary timescale of the genus. Based on these results, we propose nine new Austrocarausius species, increasing the number of species in the genus to eleven: A. nigropunctatus (Kirby, 1896), A. mercurius (Stål, 1877), A. coronatus sp. nov., A. decorus sp. nov., A. eirmosus sp. nov., A. gasterbulla sp. nov., A. tuberosus sp. nov., A. macropunctatus sp. nov., A. truncatus sp. nov. A. waiben sp. nov. and A. walkeri sp. nov. Our results suggest Austrocarausius species diversified over the last c. 25–70 Ma, resulting in the now endemic distributions in the tropical rainforests of the central and northern Queensland coasts. This is the first integrative systematic study of an Australian phasmid genus, combining morphological, molecular and biogeographical methods. Additional species of Austrocarausius likely remain undescribed as can be inferred from methodical sampling of rainforest patches along the Queensland coast.

X chromosomes show relaxed selection and complete somatic dosage compensation across Timema stick insect species

Sex chromosomes have evolved repeatedly across the tree of life. As they are present in different copy numbers in males and females, they are expected to experience different selection pressures than the autosomes, with consequences including a faster rate of evolution, increased accumulation of sexually antagonistic alleles and the evolution of dosage compensation. Whether these consequences are general or linked to idiosyncrasies of specific taxa is not clear as relatively few taxa have been studied thus far. Here, we use whole-genome sequencing to identify and characterize the evolution of the X chromosome in five species of Timema stick insects with XX:X0 sex determination. The X chromosome had a similar size (approximately 12% of the genome) and gene content across all five species, suggesting that the X chromosome originated prior to the diversification of the genus. Genes on the X showed evidence of relaxed selection (elevated dN/dS) and a slower evolutionary rate (dN + dS) than genes on the autosomes, likely due to sex-biased mutation rates. Genes on the X also showed almost complete dosage compensation in somatic tissues (heads and legs), but dosage compensation was absent in the reproductive tracts. Contrary to prediction, sex-biased genes showed little enrichment on the X, suggesting that the advantage X-linkage provides to the accumulation of sexually antagonistic alleles is weak. Overall, we found the consequences of X-linkage on gene sequences and expression to be similar across Timema species, showing the characteristics of the X chromosome are surprisingly consistent over 30 million years of evolution.

Macroevolutionary Analyses Provide New Evidence of Phasmid Wings Evolution as a Reversible Process

The concept that complex ancestral traits can never be recovered after their loss is still widely accepted, despite phylogenetic and molecular approaches suggest instances where phenotypes may have been lost throughout the evolutionary history of a clade and subsequently reverted back in derived lineages. One of the first and most notable examples of such a process is wing evolution in phasmids; this polyneopteran order of insects, which comprises stick and leaf insects, has played a central role in initiating a long-standing debate on the topic. In this study, a novel and comprehensive time tree including over 300 Phasmatodea species is used as a framework for investigating wing evolutionary patterns in the clade. Despite accounting for several possible biases and sources of uncertainty, macroevolutionary analyses consistently revealed multiple reversals to winged states taking place after their loss, and reversibility is coupled with higher species diversification rates. Our findings support a loss of or reduction in wings that occurred in the lineage leading to the extant phasmid most recent common ancestor, and brachyptery is inferred to be an unstable state unless co-opted for nonaerodynamic adaptations. We also explored how different assumptions of wing reversals probability could impact their inference: we found that until reversals are assumed to be over 30 times more unlikely than losses, they are consistently inferred despite uncertainty in tree and model parameters. Our findings demonstrate that wing evolution is a reversible and dynamic process in phasmids and contribute to our understanding of complex trait evolution.

A second view on the evolution of flight in stick and leaf insects (Phasmatodea)

BACKGROUND

The re-evolution of complex characters is generally considered impossible, yet, studies of recent years have provided several examples of phenotypic reversals shown to violate Dollo's law. Along these lines, the regain of wings in stick and leaf insects (Phasmatodea) was hypothesised to have occurred several times independently after an ancestral loss, a scenario controversially discussed among evolutionary biologists due to overestimation of the potential for trait reacquisition as well as to the lack of taxonomic data.

RESULTS

We revisited the recovery of wings by reconstructing a phylogeny based on a comprehensive taxon sample of over 500 representative phasmatodean species to infer the evolutionary history of wings. We additionally explored the presence of ocelli, the photoreceptive organs used for flight stabilisation in winged insects, which might provide further information for interpreting flight evolution. Our findings support an ancestral loss of wings and that the ancestors of most major lineages were wingless. While the evolution of ocelli was estimated to be dependent on the presence of (fully-developed) wings, ocelli are nevertheless absent in the majority of all examined winged species and only appear in the members of few subordinate clades, albeit winged and volant taxa are found in every euphasmatodean lineage.

CONCLUSION

In this study, we explored the evolutionary history of wings in Phasmatodea and demonstrate that the disjunct distribution of ocelli substantiates the hypothesis on their regain and thus on trait reacquisition in general. Evidence from the fossil record as well as future studies focussing on the underlying genetic mechanisms are needed to validate our findings and to further assess the evolutionary process of phenotypic reversals.

The phylogenic position of aschiphasmatidae in euphasmatodea based on mitochondrial genomic evidence

The mitochondrial genome (mitogenome) has been regarded as significant source of data to better understand the phylogenetic relationships within the Euphasmatodea, but no mitogenome in Aschiphasmatoidea has been sequenced to date. In this study, two mitogenomes of Orthomeria smaragdinum and Nanhuaphasma hamicercum of Aschiphasmatidae were sequenced and annotated for the first time. The same mitochondrial gene rearrangement structure was present in the two mitogenomes sequenced, showing as the translocation of tRNA-Arg and tRNA-Asn, which conformed to the tandem duplication-random loss and could be used as a possible synapomorphy for Aschiphasmatidae. The phylogenetic results based on the maximum likelihood (ML) and bayesian inference (BI) methods both showed that Aschiphasmatidae and Neophasmatodea in Euphasmatodea are sister taxa. Although the monophyly of Oriophasmata, Occidophasmata, Diapheromeridae, Phasmatidae, Lonchodidae and Bacilloidea has not been solved, the monophyly of Neophasmatodea and Phyllioidea was well supported.

Three Complete Mitochondrial Genomes of Orestes guangxiensis, Peruphasma schultei, and Phryganistria guangxiensis (Insecta: Phasmatodea) and Their Phylogeny

Insects of the order Phasmatodea are mainly distributed in the tropics and subtropics and are best known for their remarkable camouflage as plants. In this study, we sequenced three complete mitochondrial genomes from three different families: Orestes guangxiensis, Peruphasma schultei, and Phryganistria guangxiensis. The lengths of the three mitochondrial genomes were 15,896 bp, 16,869 bp, and 17,005 bp, respectively, and the gene composition and structure of the three stick insects were identical to those of the most recent common ancestor of insects. The phylogenetic relationships among stick insects have been chaotic for a long time. In order to discuss the intra- and inter-ordinal relationship of Phasmatodea, we used the 13 protein-coding genes (PCGs) of 85 species for maximum likelihood (ML) and Bayesian inference (BI) analyses. Results showed that the internal topological structure of Phasmatodea had a few differences in both ML and BI trees and long-branch attraction (LBA) appeared between Embioptera and Zoraptera, which led to a non-monophyletic Phasmatodea. Consequently, after removal of the Embioptera and Zoraptera species, we re-performed ML and BI analyses with the remaining 81 species, which showed identical topology except for the position of Tectarchus ovobessus (Phasmatodea). We recovered the monophyly of Phasmatodea and the sister-group relationship between Phasmatodea and Mantophasmatodea. Our analyses also recovered the monophyly of Heteropterygidae and the paraphyly of Diapheromeridae, Phasmatidae, Lonchodidae, Lonchodinae, and Clitumninae. In this study, Peruphasma schultei (Pseudophasmatidae), Phraortes sp. YW-2014 (Lonchodidae), and species of Diapheromeridae clustered into the clade of Phasmatidae. Within Heteropterygidae, O. guangxiensis was the sister clade to O. mouhotii belonging to Dataminae, and the relationship of (Heteropteryginae + (Dataminae + Obriminae)) was recovered.

Phylogenomic Subsampling and the Search for Phylogenetically Reliable Loci

Phylogenomic subsampling is a procedure by which small sets of loci are selected from large genome-scale data sets and used for phylogenetic inference. This step is often motivated by either computational limitations associated with the use of complex inference methods or as a means of testing the robustness of phylogenetic results by discarding loci that are deemed potentially misleading. Although many alternative methods of phylogenomic subsampling have been proposed, little effort has gone into comparing their behavior across different data sets. Here, I calculate multiple gene properties for a range of phylogenomic data sets spanning animal, fungal, and plant clades, uncovering a remarkable predictability in their patterns of covariance. I also show how these patterns provide a means for ordering loci by both their rate of evolution and their relative phylogenetic usefulness. This method of retrieving phylogenetically useful loci is found to be among the top performing when compared with alternative subsampling protocols. Relatively common approaches such as minimizing potential sources of systematic bias or increasing the clock-likeness of the data are found to fare worse than selecting loci at random. Likewise, the general utility of rate-based subsampling is found to be limited: loci evolving at both low and high rates are among the least effective, and even those evolving at optimal rates can still widely differ in usefulness. This study shows that many common subsampling approaches introduce unintended effects in off-target gene properties and proposes an alternative multivariate method that simultaneously optimizes phylogenetic signal while controlling for known sources of bias.

Phylogenomic Subsampling and the Search for Phylogenetically Reliable Loci

Phylogenomic subsampling is a procedure by which small sets of loci are selected from large genome-scale data sets and used for phylogenetic inference. This step is often motivated by either computational limitations associated with the use of complex inference methods or as a means of testing the robustness of phylogenetic results by discarding loci that are deemed potentially misleading. Although many alternative methods of phylogenomic subsampling have been proposed, little effort has gone into comparing their behavior across different data sets. Here, I calculate multiple gene properties for a range of phylogenomic data sets spanning animal, fungal, and plant clades, uncovering a remarkable predictability in their patterns of covariance. I also show how these patterns provide a means for ordering loci by both their rate of evolution and their relative phylogenetic usefulness. This method of retrieving phylogenetically useful loci is found to be among the top performing when compared with alternative subsampling protocols. Relatively common approaches such as minimizing potential sources of systematic bias or increasing the clock-likeness of the data are found to fare worse than selecting loci at random. Likewise, the general utility of rate-based subsampling is found to be limited: loci evolving at both low and high rates are among the least effective, and even those evolving at optimal rates can still widely differ in usefulness. This study shows that many common subsampling approaches introduce unintended effects in off-target gene properties and proposes an alternative multivariate method that simultaneously optimizes phylogenetic signal while controlling for known sources of bias.

Resolving a century-old case of generic mistaken identity: polyphyly of Chitoniscus sensu lato resolved with the description of the endemic New Caledonia Trolicaphyllium gen. nov. (Phasmatodea, Phylliidae)

With every molecular review involving Chitoniscus Stål, 1875 sensu lato samples from Fiji and New Caledonia revealing polyphyly, the morphology from these two distinct clades was extensively reviewed. Morphological results agree with all previously published molecular studies and therefore Trolicaphylliumgen. nov. is erected to accommodate the former Chitoniscus sensu lato species restricted to New Caledonia, leaving the type species Chitoniscuslobiventris (Blanchard, 1853) and all other Fijian species within Chitoniscus sensu stricto. Erection of this new genus for the New Caledonian species warrants the following new combinations: Trolicaphylliumbrachysoma (Sharp, 1898), comb. nov., Trolicaphylliumerosus (Redtenbachher, 1906), comb. nov., and Trolicaphylliumsarrameaense (Größer, 2008a), comb. nov. Morphological details of the female, male, freshly hatched nymph, and egg are illustrated and discussed alongside the Chitoniscus sensu stricto in order to differentiate these two clades which have been mistaken as one for decades.

A tree of leaves: Phylogeny and historical biogeography of the leaf insects (Phasmatodea: Phylliidae)

The insect order Phasmatodea is known for large slender insects masquerading as twigs or bark. In contrast to these so-called stick insects, the subordinated clade of leaf insects (Phylliidae) are dorso-ventrally flattened and therefore resemble leaves in a unique way. Here we show that the origin of extant leaf insects lies in the Australasian/Pacific region with subsequent dispersal westwards to mainland Asia and colonisation of most Southeast Asian landmasses. We further hypothesise that the clade originated in the Early Eocene after the emergence of angiosperm-dominated rainforests. The genus Phyllium to which most of the ~100 described species pertain is recovered as paraphyletic and its three non-nominate subgenera are recovered as distinct, monophyletic groups and are consequently elevated to genus rank. This first phylogeny covering all major phylliid groups provides the basis for future studies on their taxonomy and a framework to unveil more of their cryptic and underestimated diversity.

Physical constraints lead to parallel evolution of micro- and nanostructures of animal adhesive pads: a review

Adhesive pads are functional systems with specific micro- and nanostructures which evolved as a response to specific environmental conditions and therefore exhibit convergent traits. The functional constraints that shape systems for the attachment to a surface are general requirements. Different strategies to solve similar problems often follow similar physical principles, hence, the morphology of attachment devices is affected by physical constraints. This resulted in two main types of attachment devices in animals: hairy and smooth. They differ in morphology and ultrastructure but achieve mechanical adaptation to substrates with different roughness and maximise the actual contact area with them. Species-specific environmental surface conditions resulted in different solutions for the specific ecological surroundings of different animals. As the conditions are similar in discrete environments unrelated to the group of animals, the micro- and nanostructural adaptations of the attachment systems of different animal groups reveal similar mechanisms. Consequently, similar attachment organs evolved in a convergent manner and different attachment solutions can occur within closely related lineages. In this review, we present a summary of the literature on structural and functional principles of attachment pads with a special focus on insects, describe micro- and nanostructures, surface patterns, origin of different pads and their evolution, discuss the material properties (elasticity, viscoelasticity, adhesion, friction) and basic physical forces contributing to adhesion, show the influence of different factors, such as substrate roughness and pad stiffness, on contact forces, and review the chemical composition of pad fluids, which is an important component of an adhesive function. Attachment systems are omnipresent in animals. We show parallel evolution of attachment structures on micro- and nanoscales at different phylogenetic levels, focus on insects as the largest animal group on earth, and subsequently zoom into the attachment pads of the stick and leaf insects (Phasmatodea) to explore convergent evolution of attachment pads at even smaller scales. Since convergent events might be potentially interesting for engineers as a kind of optimal solution by nature, the biomimetic implications of the discussed results are briefly presented.

A review of the hexapod tracheal system with a focus on the apterygote groups

Respiratory systems are key innovations for the radiation of terrestrial arthropods. It is therefore surprising that there is still a considerable lack of knowledge. In this review of the available information on tracheal systems of hexapods (with a focus on the apterygote lineages Protura, Collembola, Diplura, Archaeognatha and Zygentoma), we summarize available data on the spiracles (number, position and morphology), the shape and variability of tracheal branching patterns including anastomoses, the tracheal fine structure and the respiratory proteins. The available data are strongly fragmented, and information for most subgroups is missing. In various cases, individual observations for one species account for the knowledge of the entire order. The available data show that there are strong differences between but also within apterygote orders. We conclude that the available data are insufficient to derive detailed conclusions on the hexapod ground plan and outline the possible evolutionary scenarios for the tracheal system in this group.

The tracheal system in the stick insect prothorax and prothoracic legs: Homologies to Orthoptera and relations to mechanosensory functions

Arthropod respiration depends on the tracheal system running from spiracles at the body surface through the body and appendages. Here, three species of stick insects (Carausius morosus, Ramulus artemis, Sipyloidea sipylus) are investigated for the tracheae in the prothorax and foreleg. The origin of the tracheae from the mesothoracic spiracle that enter the foreleg is identified: five tracheae originate from the mesothoracic spiracle, of which two enter the foreleg (supraventral trachea, trachea pedalis anterior). These two tracheae run separately through the leg to the femur-tibia joint where they fuse, but in the proximal tibia split again into two tracheae. The leg tracheae in stick insects are homologous to those in Tettigoniidae (bushcrickets). Stick insects have two chordotonal organs in the proximal tibia (subgenual organ and distal organ) which locate dorsally of the leg trachea. The tracheal system shows no adaptation specific to the propagation of airborne sound, like enlarged spiracles or tracheal volumes. Tracheal vesicles form in the tibia proximally to the mechanosensory organs, but no tracheal sacks or expansions occur at the level of the sensory organs that could mediate the detection of airborne sound or amplify substrate vibrations transmitted in the hemolymph fluid. Rather, the morphological characteristics indicate a respiratory function.

Evolutionary morphology of the antennal heart in stick and leaf insects (Phasmatodea) and webspinners (Embioptera) (Insecta: Eukinolabia)

The morphology of the antennal hearts in the head of Phasmatodea and Embioptera was investigated with particular reference to phylogenetically relevant key taxa. The antennal circulatory organs of all examined species have the same basic construction: they consist of antennal vessels that are connected to ampullae located in the head near the antenna base. The ampullae are pulsatile due to associated muscles, but the points of attachment differ between the species studied. All examined Phasmatodea species have a Musculus (M.) interampullaris which extends between the two ampullae plus a M. ampulloaorticus that runs from the ampullae to the anterior end of the aorta; upon contraction, all these muscles dilate the lumina of both ampullae at the same time. In Embioptera, only the australembiid Metoligotoma has an M. interampullaris. All other studied webspinners instead have a M. ampullofrontalis which extends between the ampullae and the frontal region of the head capsule; these species do not have M. ampulloaorticus. Outgroup comparison indicates that an antennal heart with a M. interampullaris is the plesiomorphic character state among Embioptera and the likely ground pattern of the taxon Eukinolabia. Antennal hearts with a M. ampullofrontalis represent a derived condition that occurs among insects only in some embiopterans. These findings help to further clarify the controversially discussed internal phylogeny of webspinners by supporting the view that Australembiidae are the sister group of the remaining Embioptera.

Divergent Gene Expression Following Duplication of Meiotic Genes in the Stick Insect Clitarchus hookeri

Some animal groups, such as stick insects (Phasmatodea), have repeatedly evolved alternative reproductive strategies, including parthenogenesis. Genomic studies have found modification of the genes underlying meiosis exists in some of these animals. Here we examine the evolution of copy number, evolutionary rate, and gene expression in candidate meiotic genes of the New Zealand geographic parthenogenetic stick insect Clitarchus hookeri. We characterized 101 genes from a de novo transcriptome assembly from female and male gonads that have homology with meiotic genes from other arthropods. For each gene we determined copy number, the pattern of gene duplication relative to other arthropod orthologs, and the potential for meiosis-specific expression. There are five genes duplicated in C. hookeri, including one also duplicated in the stick insect Timema cristinae, that are not or are uncommonly duplicated in other arthropods. These included two sister chromatid cohesion associated genes (SA2 and SCC2), a recombination gene (HOP1), an RNA-silencing gene (AGO2) and a cell-cycle regulation gene (WEE1). Interestingly, WEE1 and SA2 are also duplicated in the cyclical parthenogenetic aphid Acyrthosiphon pisum and Daphnia duplex, respectively, indicating possible roles in the evolution of reproductive mode. Three of these genes (SA2, SCC2, and WEE1) have one copy displaying gonad-specific expression. All genes, with the exception of WEE1, have significantly different nonsynonymous/synonymous ratios between the gene duplicates, indicative of a shift in evolutionary constraints following duplication. These results suggest that stick insects may have evolved genes with novel functions in gamete production by gene duplication.

Morphology and Bayesian tip-dating recover deep Cretaceous-age divergences among major chrysidid lineages (Hymenoptera: Chrysididae)

We integrated phylogenetic, biogeographic and palaeontological data to reconstruct the evolutionary history of the cuckoo wasps. We propose a phylogenetic hypothesis based on a comprehensive morphological study resulting in 300 characters coded for both living and extinct species. Phylogenetic relationships and divergence time estimation were simultaneously inferred in a Bayesian tip-dating framework, applying a relaxed morphological clock. Results unequivocally indicate Chrysididae to be monophyletic, as well as all traditionally recognized subfamilies and tribes. Within the Chrysidinae, Elampini was placed as the sister-group of the other three chrysidine tribes, with Parnopini as sister to the clade including Allocoeliini and Chrysidini. Dating analysis indicates that the major lineages started to differentiate around 130 Mya during the Early Cretaceous. The clades recognized as subfamilies started differentiating during the Palaeogene and the Neogene. Our results reveal an intricate process on the geographic evolution of chrysidid wasps and dispute previous ideas that Cretaceous-old splits in their early history could be associated with vicariant events related to the breakup between Africa and South America. The present-day southern disjunctions of some groups are interpreted as the outcome of more recent dispersals and extinctions of representatives from Nearctic and Palaearctic faunas during the Neogene, when northern continents became significantly colder.

Cladistic analysis of Paraphasma (Phasmatodea: Pseudophasmatidae) highlights the importance of the phallic organ for phasmid systematics

The internal male genitalia have been poorly investigated in Phasmatodea, remaining virtually unexplored in phylogenetic studies. Here we describe and illustrate the main phallic elements in several Neotropical stick insects, with emphasis on Paraphasma (Pseudophasmatidae), and present a phylogenetic analysis of this genus. The analysis included ten terminals in the ingroup and 18 in the outgroup, and was based on 32 characters of the phallic organ and 48 of external morphology. In order to compare these datasets in terms of phylogenetic signal and level of homoplasy, the consistency and retention indices of the cladogram were calculated separately for each of them, and partial analyses were also conducted using each dataset alone. The phylogenetic reconstruction revealed Paraphasma as polyphyletic and led us to propose a new, monotypic genus, Ecuadoriphasma gen. nov., three new combinations (Ecuadoriphasma cognatum, Paraphasma trianguliferum and Tithonophasma cancellatum) and place Oestrophora as a synonym of Paraphasma. Additionally, Olcyphides hopii and Paraphasma dentatum are synonymized with Paraphasma laterale. Both external and phallic characters were determinant for the topology obtained, and the latter were less homoplastic in the phylogenetic tree. Our results highlight the usefulness of phallic morphology for inferring phylogenetic relationships in Phasmatodea, especially among closely related genera and species.

The Subgenual Organ Complex in Stick Insects: Functional Morphology and Mechanical Coupling of a Complex Mechanosensory Organ

Leg chordotonal organs in insects show different adaptations to detect body movements, substrate vibrations, or airborne sound. In the proximal tibia of stick insects occur two chordotonal organs: the subgenual organ, a highly sensitive vibration receptor organ, and the distal organ, of which the function is yet unknown. The distal organ consists of a linear set of scolopidial sensilla extending in the tibia in distal direction toward the tarsus. Similar organs occur in the elaborate hearing organs in crickets and bushcrickets, where the auditory sensilla are closely associated with thin tympanal membranes and auditory trachea in the leg. Here, we document the position and attachment points for the distal organ in three species of stick insects without auditory adaptations (Ramulus artemis,Sipyloidea sipylus, andCarausius morosus). The distal organ is located in the dorsal hemolymph channel and attaches at the proximal end to the dorsal and posterior leg cuticle by tissue strands. The central part of the distal organ is placed closer to the dorsal cuticle and is suspended by fine tissue strands. The anterior part is clearly separated from the tracheae, while the distal part of the organ is placed over the anterior trachea. The distal organ is not connected to a tendon or muscle, which would indicate a proprioceptive function. The sensilla in the distal organ have dendrites oriented in distal direction in the leg. This morphology does not reveal obvious auditory adaptations as in tympanal organs, while the position in the hemolymph channel and the direction of dendrites indicate responses to forces in longitudinal direction of the leg, likely vibrational stimuli transmitted in the leg’s hemolymph. The evolutionary convergence of complex chordotonal organs with linear sensilla sets between tympanal hearing organs and atympanate organs in stick insects is emphasized by the different functional morphologies and sensory specializations.

Cryptophyllium, the hidden leaf insects - descriptions of a new leaf insect genus and thirteen species from the former celebicum species group (Phasmatodea, Phylliidae)

While the leaf insects (Phylliidae) are a well-supported group within Phasmatodea, the genus Phyllium Illiger, 1798 has repeatedly been recovered as paraphyletic. Here, the Phyllium (Phyllium) celebicum species group is reviewed and its distinctiveness from the remaining Phylliini genera and subgenera in a phylogenetic context based on morphological review and a phylogenetic analysis of three genes (nuclear gene 28S and mitochondrial genes COI and 16S) from most known and multiple undescribed species is shown. A new genus, Cryptophylliumgen. nov., is erected to partially accommodate the former members of the celebicum species group. Two species, PhylliumericoriaiHennemann et al., 2009 and Phylliumbonifacioi Lit & Eusebio, 2014 morphologically and molecularly do not fall within this clade and are therefore left within Phyllium (Phyllium). The transfer of the remaining celebicum group members from Phyllium Illiger, 1798 to this new genus creates the following new combinations; Cryptophylliumathanysus (Westwood, 1859), comb. nov.; Cryptophylliumcelebicum (de Haan, 1842), comb. nov.; Cryptophylliumchrisangi (Seow-Choen, 2017), comb. nov.; Cryptophylliumdrunganum (Yang, 1995), comb. nov.; Cryptophylliumoyae (Cumming & Le Tirant, 2020), comb. nov.; Cryptophylliumparum (Liu, 1993), comb. nov.; Cryptophylliumrarum (Liu, 1993), comb. nov.; Cryptophylliumtibetense (Liu, 1993), comb. nov.; Cryptophylliumwestwoodii (Wood-Mason, 1875), comb. nov.; Cryptophylliumyapicum (Cumming & Teemsma, 2018), comb. nov.; and Cryptophylliumyunnanense (Liu, 1993), comb. nov.

The review of specimens belonging to this clade also revealed 13 undescribed species, which are described within as: Cryptophylliumanimatumgen. et sp. nov. from Vietnam: Quang Nam Province; Cryptophylliumbankoigen. et sp. nov. from Vietnam: Quang Ngai, Thua Thien Hue, Da Nang, Gia Lai, Quang Nam, and Dak Nong Provinces; Cryptophylliumbollensigen. et sp. nov. from Vietnam: Ninh Thuan Province; Cryptophylliumdaparogen. et sp. nov. from China: Yunnan Province; Cryptophylliumechidnagen. et sp. nov. from Indonesia: Wangi-wangi Island; Cryptophylliumfaulknerigen. et sp. nov. from Vietnam: Quang Ngai and Lam Dong Provinces; Cryptophylliumicarusgen. et sp. nov. from Vietnam: Lam Dong and Dak Lak Provinces; Cryptophylliumkhmergen. et sp. nov. from Cambodia: Koh Kong and Siem Reap Provinces; Cryptophylliumlimogesigen. et sp. nov. from Vietnam: Lam Dong, Dak Lak, and Dak Nong Provinces; Cryptophylliumliyananaegen. et sp. nov. from China: Guangxi Province; Cryptophylliumnuichuaensegen. et sp. nov. from Vietnam: Ninh Thuan Province; Cryptophylliumphamigen. et sp. nov. from Vietnam: Dong Nai and Ninh Thuan Provinces; and Cryptophylliumwennaegen. et sp. nov. from China: Yunnan Province. All newly described species are morphologically described, illustrated, and molecularly compared to congenerics.

With the molecular results revealing cryptic taxa, it was found necessary for Cryptophylliumwestwoodii (Wood-Mason, 1875), comb. nov. to have a neotype specimen designated to allow accurate differentiation from congenerics. To conclude, male and female dichotomous keys to species for the Cryptophylliumgen. nov. are presented.

Historical biogeography of a neglected family of armoured harvestmen (Opiliones : Laniatores : Icaleptidae) with the first record and a new genus for tropical Mesoamerica

Among Opiliones (Arachnida), there are many taxa either with no familial assignment or erroneously located in their current family. This is the case of Ethobunus pilosus, formerly in Phalangodidae and before this work in Zalmoxidae. To assess the phylogenetic position of this taxon, we started with a revision of the male genitalia; followed by the inclusion of three molecular markers: nuclear 28S and 18S, and mitochondrial protein-encoding cytochrome c oxidase subunit I (COI) from E. pilosus in the previously published phylogenies of the Samooidea + Zalmoxoidea clade. The results revealed that E. pilosus is a derived lineage within the family Icaleptidae, thus it is transferred from Zalmoxidae, and the new name Trypophobica gen. nov. is proposed to accommodate it, with the new combination Trypophobica pilosa comb. nov. With its inclusion in Icaleptidae, and the description of Trypophobica llama sp. nov., the current diagnosis of the family needs updating, and further morphological characters should be considered as putative synapomorphies. In addition, the reconstruction of the ancestral ranges of Icaleptidae suggests a mid-Cretaceous origin c. 104 Ma in South America, with a subsequent colonisation to north Mesoamerica c. 80 Ma.

Integrated phylogenomic and fossil evidence of stick and leaf insects (Phasmatodea) reveal a Permian-Triassic co-origination with insectivores

Stick and leaf insects (Phasmatodea) are a distinctive insect order whose members are characterized by mimicking various plant tissues such as twigs, foliage and bark. Unfortunately, the phylogenetic relationships among phasmatodean subfamilies and the timescale of their evolution remain uncertain. Recent molecular clock analyses have suggested a Cretaceous-Palaeogene origin of crown Phasmatodea and a subsequent Cenozoic radiation, contrasting with fossil evidence. Here, we analysed transcriptomic data from a broad diversity of phasmatodeans and, combined with the assembly of a new suite of fossil calibrations, we elucidate the evolutionary history of stick and leaf insects. Our results differ from recent studies in the position of the leaf insects (Phylliinae), which are recovered as sister to a clade comprising Clitumninae, Lancerocercata, Lonchodinae, Necrosciinae and Xenophasmina. We recover a Permian to Triassic origin of crown Phasmatodea coinciding with the radiation of early insectivorous parareptiles, amphibians and synapsids. Aschiphasmatinae and Neophasmatodea diverged in the Jurassic-Early Cretaceous. A second spur in origination occurred in the Late Cretaceous, coinciding with the Cretaceous Terrestrial Revolution, and was probably driven by visual predators such as stem birds (Enantiornithes) and the radiation of angiosperms.