Sven Bradler

Loss and recovery of wings in stick insects

The evolution of wings was the central adaptation allowing insects to escape predators, exploit scattered resources, and disperse into new niches, resulting in radiations into vast numbers of species. Despite the presumed evolutionary advantages associated with full-sized wings (macroptery), nearly all pterygote (winged) orders have many partially winged (brachypterous) or wingless (apterous) lineages, and some entire orders are secondarily wingless (for example, fleas, lice, grylloblattids and mantophasmatids), with about 5% of extant pterygote species being flightless. Thousands of independent transitions from a winged form to winglessness have occurred during the course of insect evolution; however, an evolutionary reversal from a flightless to a volant form has never been demonstrated clearly for any pterygote lineage. Such a reversal is considered highly unlikely because complex interactions between nerves, muscles, sclerites and wing foils are required to accommodate flight. Here we show that stick insects (order Phasmatodea) diversified as wingless insects and that wings were derived secondarily, perhaps on many occasions. These results suggest that wing developmental pathways are conserved in wingless phasmids, and that ‘re-evolution’ of wings has had an unrecognized role in insect diversification.

Extreme convergence in stick insect evolution: phylogenetic placement of the Lord Howe Island tree lobster

The ‘tree lobsters’ are an enigmatic group of robust, ground-dwelling stick insects (order Phasmatodea) from the subfamily Eurycanthinae, distributed in New Guinea, New Caledonia and associated islands. Its most famous member is the Lord Howe Island stick insect Dryococelus australis (Montrouzier), which was believed to have become extinct but was rediscovered in 2001 and is considered to be one of the rarest insects in the world. To resolve the evolutionary position of Dryococelus, we constructed a phylogeny from approximately 2.4 kb of mitochondrial and nuclear sequence data from representatives of all major phasmatodean lineages. Our data placed Dryococelus and the New Caledonian tree lobsters outside the New Guinean Eurycanthinae as members of an unrelated Australasian stick insect clade, the Lanceocercata. These results suggest a convergent origin of the ‘tree lobster’ body form. Our reanalysis of tree lobster characters provides additional support for our hypothesis of convergent evolution. We conclude that the phenotypic traits leading to the traditional classification are convergent adaptations to ground-living behaviour. Our molecular dating analyses indicate an ancient divergence (more than 22 Myr ago) between Dryococelus and its Australian relatives. Hence, Dryococelus represents a long-standing separate evolutionary lineage within the stick insects and must be regarded as a key taxon to protect with respect to phasmatodean diversity.

The first fossil leaf insect: 47 million years of specialized cryptic morphology and behavior

Stick and leaf insects (insect order Phasmatodea) are represented primarily by twig-imitating slender forms. Only a small percentage (≈1%) of extant phasmids belong to the leaf insects (Phylliinae), which exhibit an extreme form of morphological and behavioral leaf mimicry. Fossils of phasmid insects are extremely rare worldwide. Here we report the first fossil leaf insect, Eophyllium messelensis gen. et sp. nov., from 47-million-year-old deposits at Messel in Germany. The new specimen, a male, is exquisitely preserved and displays the same foliaceous appearance as extant male leaf insects. Clearly, an advanced form of extant angiosperm leaf mimicry had already evolved early in the Eocene. We infer that this trait was combined with a special behavior, catalepsy or “adaptive stillness,” enabling Eophyllium to deceive visually oriented predators. Potential predators reported from the Eocene are birds, early primates, and bats. The combination of primitive and derived characters revealed by Eophyllium allows the determination of its exact phylogenetic position and illuminates the evolution of leaf mimicry for this insect group. It provides direct evidence that Phylliinae originated at least 47 Mya. Eophyllium enlarges the known geographical range of Phylliinae, currently restricted to southeast Asia, which is apparently a relict distribution. This fossil leaf insect bears considerable resemblance to extant individuals in size and cryptic morphology, indicating minimal change in 47 million years. This absence of evolutionary change is an outstanding example of morphological and, probably, behavioral stasis.

The phylogenetic placement and biogeographical origins of the New Zealand stick insects (Phasmatodea)

The Lanceocercata are a clade of stick insects (Phasmatodea) that have undergone an impressive evolutionary radiation in Australia, New Caledonia, the Mascarene Islands and areas of the Pacific. Previous research showed that this clade also contained at least two of the nine New Zealand stick insect genera. We have constructed a phylogeny of the Lanceocercata using 2277 bp of mitochondrial and nuclear DNA sequence data to determine whether all nine New Zealand genera are indeed Lanceocercata and whether the New Zealand fauna is monophyletic. DNA sequence data were obtained from mitochondrial cytochrome oxidase subunits I and II and the nuclear large subunit ribosomal RNA and histone subunit 3. These data were subjected to Bayesian phylogenetic inference under a partitioned model and maximum parsimony. The resulting trees show that all the New Zealand genera are nested within a large New Caledonian radiation. The New Zealand genera do not form a monophyletic group, with the genus Spinotectarchus Salmon forming an independent lineage from the remaining eight genera. We analysed Lanceocercata apomorphies to confirm the molecular placement of the New Zealand genera and to identify characters that confirm the polyphyly of the fauna. Molecular dating analyses under a relaxed clock coupled with a Bayesian extension to dispersal‐vicariance analysis was used to reconstruct the biogeographical history for the Lanceocercata. These analyses show that Lanceocercata and their sister group, the Stephanacridini, probably diverged from their South American relatives, the Cladomorphinae, as a result of the separation of Australia, Antarctica and South America. The radiation of the New Caledonian and New Zealand clade began 41.06 million years ago (mya, 29.05–55.40 mya), which corresponds to a period of uplift in New Caledonia. The main New Zealand lineage and Spinotectarchus split from their New Caledonian sister groups 33.72 (23.9–45.62 mya) and 29.9 mya (19.79–41.16 mya) and began to radiate during the late Oligocene and early Miocene, probably in response to a reduction in land area and subsequent uplift in the late Oligocene and early Miocene. We discuss briefly shared host plant patterns between New Zealand and New Caledonia. Because Acrophylla sensu Brock & Hasenpusch is polyphyletic, we have removed Vetilia Stål from synonymy with Acrophylla Gray.

A molecular phylogeny of Phasmatodea with emphasis on Necrosciinae, the most species‐rich subfamily of stick insects

The phasmatodeans or stick and leaf insects are considered to be a mesodiverse insect order with more than 3000 species reported mainly from the tropics. The stick insect subfamily Necrosciinae comprises approximately 700 described species in more than 60 genera from the Oriental and Australian region, forming the most species‐rich subfamily traditionally recognized within Phasmatodea. However, the monophyly of this taxon has never been thoroughly tested and the evolutionary relationships among its members are unknown. We analyse three nuclear (18S and 28S rDNA, histone 3) and three mitochondrial (CO II, 12S and 16S rDNA) genes to infer the phylogeny of 60 species of stick insects that represent all recognized families and major subfamilies sensu Günther and the remarkable diversity within Necrosciinae. Maximum parsimony, maximum likelihood and Bayesian techniques largely recover the same substantial clades, albeit with highly discordant relationships between them. Most members of the subfamily Necrosciinae form a clade. However, the genus Neohirasea – currently classified within Lonchodinae – is strongly supported as subordinate to Necrosciinae, whereas Baculofractum, currently classified within Necrosciinae, is strongly supported within Lonchodinae. Accordingly, we formally transfer Neohirasea and allied taxa (namely Neohiraseini) to Necrosciinae sensu nova (s.n.) and Baculofractum to Lonchodinae s.n. We also provide further evidence that Leprocaulinus, until recently recognized as Necrosciinae, belongs to Lonchodinae, and forms the sister taxon of Baculofractum. Furthermore, Lonchodinae is paraphyletic under exclusion of Eurycantha and Neopromachus. We reinstate the traditional view that Neopromachus and related taxa (Neopromachini sensu Günther) are a subgroup of Lonchodinae and transfer those taxa + the New Guinean Eurycanthinae accordingly. Morphological evidence largely corroborates our molecular‐based findings and also reveals that Menexenus fruhstorferi is a member of the genus Neohirasea and is thus transferred from Menexenus (Lonchodinae) to Neohirasea, as Neohirasea fruhstorferi comb.n. (Necrosciinae s.n.). Other phylogenetic results include Areolatae and Anareolatae each supported as polyphyletic, Heteropteryginae and Lanceocercata (Bayesian analysis) are monophyletic, albeit with low support, and Necrosciinae s.n. and Lonchodinae s.n. are recovered as sister taxa (Bayesian analysis).

Stick insect on unsafe ground: does a fossil from the early Eocene of France really link Mesozoic taxa with the extant crown group of Phasmatodea?

The recently described Gallophasma longipalpis from Earliest Eocene French amber is considered to be a key fossil taxon that phylogenetically links ‘Mesozoic Phasmatodea’ with extant stick and leaf insects. However, our re‐evaluation of the evidence provided for this placement reveals that Gallophasma does not possess any unambiguous synapomorphies with extant forms, e.g. neither with Euphasmatodea nor with the more inclusive Phasmatodea. The fusion of abdominal segment 1 with the metathoracic segment, a derived character state present in both Gallophasma and Euphasmatodea, shows fundamental structural differences, and cannot be homologized between both taxa. We argue that the presence of a well‐developed, externally visible ovipositor and four‐segmented cerci in Gallophasma can be interpreted only as plesiomorphic with regards to all extant Phasmatodea, or even to Phasmatodea plus its putative sister groups Embioptera or Orthoptera. Gallophasma does not belong to the stem lineage of recent Phasmatodea, and is referred to best as ‘lower Neoptera’ or Polyneoptera incertae sedis. Therefore, this fossil may be central to reconstructing the ground pattern of the aforementioned orthopteroid lineages, and to determining wing character polarity within Polyneoptera.

Tepakiphasma ngatikuri, a new genus and species of stick insect (Phasmatodea) from the Far North of New Zealand

We describe a new genus and species of stick insect from Northland, New Zealand, Tepakiphasma ngatikuri, gen. nov., sp. nov. We have classifi ed this genus as a member of Phasmatidae, Phasmatinae, Acanthoxylini, and due to the presence of certain key synapomorphies it is phylogenetically placed within the Australasian clade Lanceocercata. A number of character states differentiate Tepakiphasma from other New Zealand Acanthoxylini genera including the number and arrangement of teeth on the claspers and a perforate egg capitulum or capitular cone. Like many New Zealand phasmatodeans the known host plants of T. ngatikuri include species of Myrtaceae. This genus appears to have an extremely limited geographic distribution and is known from only two specimens collected in the Te Paki / North Cape area at the northernmost tip of mainland New Zealand. This discovery further emphasises the importance of the Te Paki / North Cape area in New Zealand biodiversity. The phasmatodean fauna of New Zealand now contains 10 genera and 23 described species.

Under cover at pre-angiosperm times: a cloaked phasmatodean insect from the Early Cretaceous Jehol biota.

Background Fossil species that can be conclusively identified as stem-relatives of stick- and leaf-insects (Phasmatodea) are extremely rare, especially for the Mesozoic era. This dearth in the paleontological record makes assessments on the origin and age of the group problematic and impedes investigations of evolutionary key aspects, such as wing development, sexual size dimorphism and plant mimicry. Methodology/Principal Findings A new fossil insect species, Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov., is described on the basis of one female and two male specimens recovered from the Yixian Formation (Early Cretaceous, ca. 126±4 mya; Inner Mongolia, NE China; known as ‘Jehol biota’). The occurrence of a female abdominal operculum and of a characteristic ‘shoulder pad’ in the forewing allows for the interpretation of a true stem-Phasmatodea. In contrast to the situation in extant forms, sexual size dimorphism is only weakly female-biased in this species. The peculiar wing coloration, viz. dark longitudinal veins, suggests that the leaf-shaped plant organ from the contemporaneous ‘gymnosperm’ Membranifolia admirabilis was used as model for crypsis. Conclusions/Significance As early as in the Early Cretaceous, some stem-Phasmatodea achieved effective leaf mimicry, although additional refinements characteristic of recent forms, such as curved fore femora, were still lacking. The diversification of small-sized arboreal insectivore birds and mammals might have triggered the acquisition of such primary defenses.

Horizontal Gene Transfer of Pectinases from Bacteria Preceded the Diversification of Stick and Leaf Insects

Genes acquired by horizontal transfer are increasingly being found in animal genomes. Understanding their origin and evolution requires knowledge about the phylogenetic relationships from both source and recipient organisms. We used RNASeq data and respective assembled transcript libraries to trace the evolutionary history of polygalacturonase (pectinase) genes in stick insects (Phasmatodea). By mapping the distribution of pectinase genes on a Polyneoptera phylogeny, we identified the transfer of pectinase genes from known phasmatodean gut microbes into the genome of an early euphasmatodean ancestor that took place between 60 and 100 million years ago. This transfer preceded the rapid diversification of the suborder, enabling symbiont-free pectinase production that would increase the insects’ digestive efficiency and reduce dependence on microbes. Bacteria-to-insect gene transfer was thought to be uncommon, however the increasing availability of large-scale genomic data may change this prevailing notion.

TrOn: An Anatomical Ontology for the Beetle Tribolium castaneum

In a morphological ontology the expert’s knowledge is represented in terms, which describe morphological structures and how these structures relate to each other. With the assistance of ontologies this expert knowledge is made processable by machines, through a formal and standardized representation of terms and their relations to each other. The red flour beetle Tribolium castaneum, a representative of the most species rich animal taxon on earth (the Coleoptera), is an emerging model organism for development, evolution, physiology, and pest control. In order to foster Tribolium research, we have initiated the Tribolium Ontology (TrOn), which describes the morphology of the red flour beetle. The content of this ontology comprises so far most external morphological structures as well as some internal ones. All modeled structures are consistently annotated for the developmental stages larva, pupa and adult. In TrOn all terms are grouped into three categories: Generic terms represent morphological structures, which are independent of a developmental stage. In contrast, downstream of such terms are concrete terms which stand for a dissectible structure of a beetle at a specific life stage. Finally, there are mixed terms describing structures that are only found at one developmental stage. These terms combine the characteristics of generic and concrete terms with features of both. These annotation principles take into account the changing morphology of the beetle during development and provide generic terms to be used in applications or for cross linking with other ontologies and data resources. We use the ontology for implementing an intuitive search function at the electronic iBeetle-Base, which stores morphological defects found in a genome wide RNA interference (RNAi) screen. The ontology is available for download at http://ibeetle-base.uni-goettingen.de.