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

A winged relative of ice-crawlers in amber bridges the cryptic extant Xenonomia and a rich fossil record

Until the advent of phylogenomics, the atypical morphology of extant representatives of the insect orders Grylloblattodea (ice-crawlers) and Mantophasmatodea (gladiators) had confounding effects on efforts to resolve their placement within Polyneoptera. This recent research has unequivocally shown that these species-poor groups are closely related and form the clade Xenonomia. Nonetheless, divergence dates of these groups remain poorly constrained, and their evolutionary history debated, as the few well-identified fossils, characterized by a suite of morphological features similar to that of extant forms, are comparatively young. Notably, the extant forms of both groups are wingless, whereas most of the pre-Cretaceous insect fossil record is composed of winged insects, which represents a major shortcoming of the taxonomy. Here, we present new specimens embedded in mid-Cretaceous amber from Myanmar and belonging to the recently described species Aristovia daniili. The abundant material and pristine preservation allowed a detailed documentation of the morphology of the species, including critical head features. Combined with a morphological data set encompassing all Polyneoptera, these new data unequivocally demonstrate that A. daniili is a winged stem Grylloblattodea. This discovery demonstrates that winglessness was acquired independently in Grylloblattodea and Mantophasmatodea. Concurrently, wing apomorphic traits shared by the new fossil and earlier fossils demonstrate that a large subset of the former "Protorthoptera" assemblage, representing a third of all known insect species in some Permian localities, are genuine representatives of Xenonomia. Data from the fossil record depict a distinctive evolutionary trajectory, with the group being both highly diverse and abundant during the Permian but experiencing a severe decline from the Triassic onwards.

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.

Independent wing reductions and losses among stick and leaf insects (Phasmatodea), supported by new Cretaceous fossils in amber

BACKGROUND

Phasmatodea (stick and leaf insects) play a central role on the debate regarding wing reduction and loss, and its wings are putative reacquisition from secondarily wingless ancestors based solely on extant species. A pivotal taxon in this respect is the species-poor Timematodea, consisting of approximately 21 wingless extant species, which form the sister group of all remaining winged or wingless stick and leaf insects, the Euphasmatodea.

RESULTS

Herein, the new fossils of Timematodea from mid-Cretaceous Kachin amber are reported, with winged and wingless species co-occurring. The palaeogeographic distributions of all fossils of Holophasmatodea are summarized, showing their wide paleo-distributions. The phylogenetic analysis based on morphological characters confirms the earliest-diverging lineage of winged Breviala cretacea gen. et sp. nov. in Timematodea, and the possible relationships among all families of Holophasmatodea. These are critical for the reconstruction of patterns of wing evolution in early Phasmatodea.

CONCLUSIONS

The new fossils suggest that Timematodea once had wings, at least during the mid-Cretaceous. The palaeogeographic occurrences imply that Timematodea probably have been widely distributed since at least the Jurassic. The phylogenetic analysis with the ancestral-state reconstruction of wings indicates that the common ancestors of Holophasmatodea were winged, the reductions and losses of wings among Timematodea and Euphasmatodea have occurred independently since at least the Cretaceous, and the reduction or loss of the forewing earlier than the hind wings.

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.

Taxonomic Revision, Morphology and Natural History of the Stick Insect Genus Xerosoma Serville, 1831 (Insecta: Phasmatodea)

Stick insects (Phasmatodea) are quite diverse in the Neotropical region. Among them, Xerosoma Serville belongs to Pseudophasmatidae and comprises winged, roughly brownish phasmids that resemble bark or dry branches and inhabit the Atlantic Forest in Brazil. In this study, we present a redescription and revision of the genus that include three valid species, Xerosoma canaliculatum, Xerosoma michaelis, and Xerosoma nannospinus sp. nov. Xerosoma senticosum syn. nov. was found to be a junior synonym of X. canaliculatum. We also provide an identification key and geographic records for these three species. Additionally, we present a detailed study on the morphology and natural history of X. canaliculatum with the description of its nymphal stages, egg, male genitalia, ontogeny, oviposition method, life habits, defense mechanisms, mating behavior, and other aspects regarding its biology. The study also highlights the shortcomings related to the classification of Xerosomatinae, since its tribes find themselves without proper characterization and contain heterogeneous genera. We expect to provide a basis for a proper diagnosis of Xerosomatinae and encourage future studies on this group, as there is still much to be discovered about this lineage of Neotropical stick insects.

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.

Two new combinations of Medaurini (Phasmatodea: Phasmatidae: Clitumninae) from Yunnan Province, China

Two new combinations are proposed for Chinese species previously described in the endemic Australian genus Pachymorpha Gray, 1835: Interphasma belocerca (Chen & He, 2008) comb. nov., of which the male and egg are described are illustrated for the first time and Neomedaura arguta (Chen & He, 2008) comb. nov., the first report of the genus Neomedaura Ho, 2020, in China.

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.

Leaves that walk and eggs that stick: comparative functional morphology and evolution of the adhesive system of leaf insect eggs (Phasmatodea: Phylliidae)

Phylliidae are herbivorous insects exhibiting impressive cryptic masquerade and are colloquially called "walking leaves". They imitate angiosperm leaves and their eggs often resemble plant seeds structurally and in some cases functionally. Despite overall morphological similarity of adult Phylliidae, their eggs reveal a significant diversity in overall shape and exochorionic surface features. Previous studies have shown that the eggs of most Phylliidae possess a specialised attachment mechanism with hierarchical exochorionic fan-like structures (pinnae), which are mantled by a film of an adhesive secretion (glue). The folded pinnae and glue respond to water contact, with the fibrous pinnae expanding and the glue being capable of reversible liquefaction. In general, the eggs of phylliids appear to exhibit varying structures that were suggested to represent specific adaptations to the different environments the eggs are deposited in. Here, we investigated the diversity of phylliid eggs and the functional morphology of their exochorionic structure. Based on the examination of all phylliid taxa for which the eggs are known, we were able to characterise eleven different morphological types. We explored the adhesiveness of these different egg morphotypes and experimentally compared the attachment performance on a broad range of substrates with different surface roughness, surface chemistry and tested whether the adhesion is replicable after detachment in multiple cycles. Furthermore, we used molecular phylogenetic methods to reconstruct the evolutionary history of different egg types and their adhesive systems within this lineage, based on 53 phylliid taxa. Our results suggest that the egg morphology is congruent with the phylogenetic relationships within Phylliidae. The morphological differences are likely caused by adaptations to the specific environmental requirements for the particular clades, as the egg morphology has an influence on the performance regarding the surface roughness. Furthermore, we show that different pinnae and the adhesive glue evolved convergently in different species. While the evolution of the Phylliidae in general appears to be non-adaptive judging on the strong similarity of the adults and nymphs of most species, the eggs represent a stage with complex and rather diverse functional adaptations including mechanisms for both fixation and dispersal of the eggs.

Goldilocks mushrooms: How ballistospory has shaped basidiomycete evolution

Ballistospory has been a governing factor in mushroom diversification. Modifications to fruit body morphology are subject to a series of fundamental constraints imposed by this uniquely fungal mechanism. Gill spacing in lamellate mushrooms, tube width in poroid species, and other configurations of the hymenium must comply with the distance that spores shoot themselves from their basidia. This reciprocal relationship between the development of fruit bodies and spores may have been maintained by a form of evolutionary seesaw proposed in this article. The necessity of the accurate gravitropic orientation of gills and tubes is another constraint on mushroom development and physiology, along with the importance of evaporative cooling of the hymenium for successful spore discharge and the aerodynamic shaping of the fruit body to aid dispersal. Ballistospory has been lost in secotioid and gasteroid basidiomycetes whose spores are dispersed by animal vectors and has been replaced by alterative mechanisms of active spore discharge in some species. Partnered with the conclusions drawn from molecular phylogenetic research, the biomechanical themes discussed in this review afford new ways to think about the evolution of basidiomycetes.

Rapid adaptation in a fast-changing world: Emerging insights from insect genomics

Many researchers have questioned the ability of biota to adapt to rapid anthropogenic environmental shifts. Here, we synthesize emerging genomic evidence for rapid insect evolution in response to human pressure. These new data reveal diverse genomic mechanisms (single locus, polygenic, structural shifts; introgression) underpinning rapid adaptive responses to a variety of anthropogenic selective pressures. While the effects of some human impacts (e.g. pollution; pesticides) have been previously documented, here we highlight startling new evidence for rapid evolutionary responses to additional anthropogenic processes such as deforestation. These recent findings indicate that diverse insect assemblages can indeed respond dynamically to major anthropogenic evolutionary challenges. Our synthesis also emphasizes the critical roles of genomic architecture, standing variation and gene flow in maintaining future adaptive potential. Broadly, it is clear that genomic approaches are essential for predicting, monitoring and responding to ongoing anthropogenic biodiversity shifts in a fast-changing world.

Convergent Evolution of Adhesive Properties in Leaf Insect Eggs and Plant Seeds: Cross-Kingdom Bioinspiration

Plants and animals are often used as a source for inspiration in biomimetic engineering. However, stronger engagement of biologists is often required in the field of biomimetics. The actual strength of using biological systems as a source of inspiration for human problem solving does not lie in a perfect copy of a single system but in the extraction of core principles from similarly functioning systems that have convergently solved the same problem in their evolution. Adhesive systems are an example of such convergent traits that independently evolved in different organisms. We herein compare two analogous adhesive systems, one from plants seeds and one from insect eggs, to test their properties and functional principles for differences and similarities in order to evaluate the input that can be potentially used for biomimetics. Although strikingly similar, the eggs of the leaf insect Phyllium philippinicum and the seeds of the ivy gourd Coccinia grandis make use of different surface structures for the generation of adhesion. Both employ a water-soluble glue that is spread on the surface via reinforcing fibrous surface structures, but the morphology of these structures is different. In addition to microscopic analysis of the two adhesive systems, we mechanically measured the actual adhesion generated by both systems to quantitatively compare their functional differences on various standardized substrates. We found that seeds can generate much stronger adhesion in some cases but overall provided less reliable adherence in comparison to eggs. Furthermore, eggs performed better regarding repetitive attachment. The similarities of these systems, and their differences resulting from their different purposes and different structural/chemical features, can be informative for engineers working on technical adhesive systems.

Taxonomic revision of the Australian stick insect genus Candovia (Phasmida: Necrosciinae): insight from molecular systematics and species-delimitation approaches

The Phasmida genus Candovia comprises nine traditionally recognized species, all endemic to Australia. In this study, Candovia diversity is explored through molecular species-delimitation analyses using the COIFol gene fragment and phylogenetic inferences leveraging seven additional mitochondrial and nuclear loci. Molecular results were integrated with morphological observations, leading us to confirm the already described species and to the delineation of several new taxa and of the new genus Paracandovia. New Candovia species from various parts of Queensland and New South Wales are described and illustrated (C. alata sp. nov., C. byfieldensis sp. nov., C. dalgleishae sp. nov., C. eungellensis sp. nov., C. karasi sp. nov., C. koensi sp. nov. andC. wollumbinensis sp. nov.). New combinations are proposed and species removed from synonymy with the erection of the new genus Paracandovia (P. cercata stat. rev., comb. nov., P. longipes stat. rev., comb. nov., P. pallida comb. nov., P. peridromes comb. nov., P. tenera stat. rev., comb. nov.). Phylogenetic analyses suggest that the egg capitulum may have independently evolved multiple times throughout the evolutionary history of these insects. Furthermore, two newly described species represent the first taxa with fully developed wings in this previously considered apterous clade.

Three new genera and one new species of leaf insect from Melanesia (Phasmatodea, Phylliidae)

With the first large-scale Phylliidae molecular phylogeny recently published adding a great deal of clarity to phylliid diversity, several of the rarer species which could not be included were methodically and morphologically reviewed. This review resulted in identification of numerous substantial morphological features that suggest there are Melanesian clades that create polyphyletic groups within the phylliids which should instead be taxonomically recognized as unique. These rarer Melanesia species have historically been considered to be southern representatives of the Pulchriphyllium Griffini, 1898 sensu lato. However, there are notable morphological differences between the Pulchriphyllium sensu stricto and the "schultzei" group. Therefore, two new genera are erected, Vaabonbonphyllium gen. nov. from the Solomon Islands and Papua New Guinea and Rakaphyllium gen. nov. from New Guinea and the Aru Islands. Erection of these two new genera warrants the following new combinations: Rakaphylliumschultzei (Giglio-Tos, 1912), comb. nov., Rakaphylliumexsectum (Zompro, 2001b), comb. nov., and Vaabonbonphylliumgroesseri (Zompro, 1998), comb. nov. Additionally, while reviewing material an undescribed Vaabonbonphyllium gen. nov. specimen was located and is herein described as Vaabonbonphylliumrafidahae gen. et sp. nov. from Mt. Hagen, Papua New Guinea. Additionally, a morphologically unique clade of several species recovered as sister to the Nanophyllium sensu stricto was recognized and their numerous unique morphological features and monophyly leads the authors to erect the new genus Acentetaphyllium gen. nov. which warrants the following new combinations: Acentetaphylliumbrevipenne (Größer, 1992), comb. nov., Acentetaphylliumlarssoni (Cumming, 2017), comb. nov., Acentetaphylliummiyashitai (Cumming et al. 2020), comb. nov., and Acentetaphylliumstellae (Cumming, 2016), comb. nov. With the addition of several new genera, a key to phylliid genera is included for adult males and females.

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.