Shûhei Yamamoto

Evidence for social parasitism of early insect societies by Cretaceous rove beetles

The evolution of eusociality in ants and termites propelled both insect groups to their modern ecological dominance. Yet, eusociality also fostered the evolution of social parasitism—an adverse symbiosis, in which the superorganismal colonies formed by these insects are infiltrated by a profusion of invertebrate species that target nest resources. Predominant among these are the aleocharine rove beetles (Staphylinidae), a vast and ecologically diverse subfamily with numerous morphologically and behaviourally specialized socially parasitic lineages. Here, we report a fossil aleocharine, Mesosymbion compactus gen. et sp. nov., in Burmese amber (∼99 million years old), displaying specialized anatomy that is a hallmark of social parasites. Mesosymbion coexisted in the Burmese palaeofauna with stem-group ants and termites that provide the earliest indications of eusociality in both insect groups. We infer that the advent of eusociality led automatically and unavoidably to selection for social parasitism. The antiquity and adaptive flexibility of aleocharines made them among the first organisms to engage in this type of symbiosis.

Asymmetric hindwing foldings in rove beetles

Significance Rove beetles are known to fold their wings in the most complicated and sophisticated ways that have right–left asymmetric patterns. This asymmetric folding can confer both high deployment capability and high storage efficiency, and therefore has a great deal of potential for engineering applications. However, the detailed folding mechanisms have been unclear because of the difficulty of observing of the folding processes. This study used a high-speed camera to observe the wing folding movements of rove beetles. The results show that these characteristic asymmetrical patterns emerge as a result of simultaneous folding of overlapped wings. The specific crease patterns of respective wings and detailed folding motions in each folding sequence are also described here. Foldable wings of insects are the ultimate deployable structures and have attracted the interest of aerospace engineering scientists as well as entomologists. Rove beetles are known to fold their wings in the most sophisticated ways that have right–left asymmetric patterns. However, the specific folding process and the reason for this asymmetry remain unclear. This study reveals how these asymmetric patterns emerge as a result of the folding process of rove beetles. A high-speed camera was used to reveal the details of the wing-folding movement. The results show that these characteristic asymmetrical patterns emerge as a result of simultaneous folding of overlapped wings. The revealed folding mechanisms can achieve not only highly compact wing storage but also immediate deployment. In addition, the right and left crease patterns are interchangeable, and thus each wing internalizes two crease patterns and can be folded in two different ways. This two-way folding gives freedom of choice for the folding direction to a rove beetle. The use of asymmetric patterns and the capability of two-way folding are unique features not found in artificial structures. These features have great potential to extend the design possibilities for all deployable structures, from space structures to articles of daily use.

Cretaceous origin of the unique prey-capture apparatus in mega-diverse genus: stem lineage of Steninae rove beetles discovered in Burmese amber

Stenus is the largest genus of rove beetles and the second largest among animals. Its evolutionary success was associated with the adhesive labial prey-capture apparatus, a unique apomorphy of that genus. Definite Stenus with prey-capture apparatus are known from the Cenozoic fossils, while the age and early evolution of Steninae was hardly ever hypothesized. Our study of several Cretaceous Burmese amber inclusions revealed a stem lineage of Steninae that possibly possesses the Stenus-like prey-capture apparatus. Phylogenetic analysis of extinct and extant taxa of Steninae and putatively allied subfamilies of Staphylinidae with parsimony and Bayesian approaches resolved the Burmese amber lineage as a member of Steninae. It justified the description of a new extinct stenine genus Festenus with two new species, F. robustus and F. gracilis. The Late Cretaceous age of Festenus suggests an early origin of prey-capture apparatus in Steninae that, perhaps, drove the evolution towards the crown Stenus. Our analysis confirmed the well-established sister relationships between Steninae and Euaesthetinae and resolved Scydmaeninae as their next closest relative, the latter having no stable position in recent phylogenetic studies of rove beetles. Close affiliation of Megalopsidiinae, a subfamily often considered as a sister group to Euaesthetinae + Steninae clade, is rejected.

Investigation of hindwing folding in ladybird beetles by artificial elytron transplantation and microcomputed tomography

Significance Hindwings in ladybird beetles successfully achieve compatibility between the deformability (instability) required for wing folding and strength property (stability) required for flying. This study demonstrates how ladybird beetles address these two conflicting requirements by an unprecedented technique using artificial wings. Our results, which clarify the detailed wing-folding process and reveal the supporting structures, provide indispensable initial knowledge for revealing this naturally evolved optimization system. Investigating the characteristics in the venations and crease patterns revealed in this study could provide an innovative designing method, enabling the integration of structural stability and deformability, and thus could have a considerable impact on engineering science. Ladybird beetles are high-mobility insects and explore broad areas by switching between walking and flying. Their excellent wing transformation systems enabling this lifestyle are expected to provide large potential for engineering applications. However, the mechanism behind the folding of their hindwings remains unclear. The reason is that ladybird beetles close the elytra ahead of wing folding, preventing the observation of detailed processes occurring under the elytra. In the present study, artificial transparent elytra were transplanted on living ladybird beetles, thereby enabling us to observe the detailed wing-folding processes. The result revealed that in addition to the abdominal movements mentioned in previous studies, the edge and ventral surface of the elytra, as well as characteristic shaped veins, play important roles in wing folding. The structures of the wing frames enabling this folding process and detailed 3D shape of the hindwing were investigated using microcomputed tomography. The results showed that the tape spring-like elastic frame plays an important role in the wing transformation mechanism. Compared with other beetles, hindwings in ladybird beetles are characterized by two seemingly incompatible properties: (i) the wing rigidity with relatively thick veins and (ii) the compactness in stored shapes with complex crease patterns. The detailed wing-folding process revealed in this study is expected to facilitate understanding of the naturally optimized system in this excellent deployable structure.

A new genus and species of the rove beetle tribe Mesoporini from Baltic amber (Coleoptera: Staphylinidae: Aleocharinae)

Abstract A new extinct rove beetle, Palaeomesoporus electiricus gen. et sp.n., is described from a single specimen of Eocene Baltic amber. This fossil beetle is placed in the tribe Mesoporini, a ‘basal’ group of the mega-diverse subfamily Aleocharinae. Palaeomesoporus is easily discriminated from other mesoporine genera due to its less-developed antennal club, longer and slender elytron lacking a sinuate posterior margin, and prominently shorter mesotarsus. This finding sheds light on the paleodiversity and evolutionary history of the tribe and ‘basal’ Aleocharinae.

Coproporus electron sp. nov., the first tachyporine rove beetle in Dominican amber (Coleoptera, Staphylinidae)

A new fossil rove beetle, Coproporus electron Yamamoto, sp. nov., is described from Dominican amber (early Middle Miocene). This is the first fossil of the genus and also represents the first formal record of the subfamily from Dominican amber. Coproporus electron even stands for the first fossil tachyporine described from the Neotropical region. Our finding is congruent with the hypothesis that the ancient forests that produced Dominican amber were long-vanished tropical forests, as modern members of Coproporus are restricted primarily to wet tropical regions.KurzfassungEin neuer fossiler Kurzflügler, Coproporus electron Yamamoto, sp. nov., wird aus dem Dominikanischen Bernstein (frühes Mittel-Miozän) beschrieben. Dieser erste fossile Vertreter der Gattung stellt gleichzeitig auch die erste offizielle Entdeckung der Unterfamilie Tachyporinae aus Dominikanischem Bernstein dar. Coproporus electron sp. nov. steht desweiteren für die ersten fossilen Tachyporinae überhaupt, die aus der Neotropis beschrieben werden. Unsere Entdeckung deckt sich mit der Hypothese, dass die ehemaligen Wälder, die Dominikanischen Bernstein produzierten, vor langer Zeit verschwundene tropische Wälder waren, da moderne Vertreter von Coproporus vor allem auf feucht-tropische Regionen beschränkt sind.

Morphology-based phylogeny of the coastal rove-beetle subgenera Emplenota Casey and Triochara Bernhauer of the genus Aleochara Gravenhorst (Coleoptera Staphylinidae: Aleocharinae)

A morphology-based cladistic analysis was conducted of the coastal rove-beetle subgenera EmplenotaCasey and TriocharaBernhauer of the genus AleocharaGravenhorst. We used 36 adult characters from the all ten Emplenotaand three Triocharaspecies, and two outgroups, resulting in a single tree. The topology within the Emplenotaclade shows a clear pattern of species diversification that correlates well with the biogeographical distribution of this taxon. The Emplenotaclade was phylogenetically divided into three, consisting of a Nearctic clade forming a sister group relationship with the Eastern Palearctic clade, and a basal Western Palearctic evolutionary grade. In contrast, the geographical origin of Triochararemains unclear due to a paucity of information and difficulties in interpreting the distributional data.

Species diversity and community structure of rove beetles (Coleoptera: Staphylinidae) attracted to dung of sika deer in coniferous forests of southwest Japan

Insect communities of mammal dung have been known as excellent model ecosystems for scientific study. Ecological surveys of diversity and seasonal patterns of coprophilous rove beetles in relation to wild mammals have rarely been conducted, although the high potential species diversity and abundance of the rove beetles are known. In order to investigate biodiversity of these beetles, we analyzed species composition, abundance, feeding guild and seasonality of rove beetles that were attracted to sika deer Cervus nippon dung by using dung‐baited pitfall traps for a 1.5‐year study in two plantations (cypress, cedar) and one secondary natural forest (pine) in Fukuoka Prefecture, southwest Japan. Consequently, saprophagous Anotylus sp. (Oxytelinae) was dominant in all forests. Analyses of feeding guild structure showed the number of individuals were dominated by saprophagous beetles, but the number of species were dominated by predatory beetles. Seasonal effects suggested that the species richness and abundance of rove beetles are possibly regulated by scarabaeoid dung beetles. These findings feature one example of a coprophilous rove beetle community.

A peculiar new species of the genus Tetrasticta Kraatz (Coleoptera, Staphylinidae, Aleocharinae) from Peninsular Malaysia

Abstract Tetrasticta gnatha sp. n., collected under the bark of a rotten fallen tree in Peninsular Malaysia, is described. A habitus photograph, line drawings of diagnostic characters, and a diagnosis are provided. The new species is readily distinguished from all known congeners by having long mandibles, and long, curved maxillary palpi.

Phylogeny of the rove beetle tribe Gymnusini sensu n. (Coleoptera: Staphylinidae: Aleocharinae): implications for the early branching events of the subfamily

The rove beetle subfamily Aleocharinae is the largest subfamily of animals known in terms of species richness. Two small aleocharine tribes, Gymnusini and Deinopsini, are believed to be a monophyletic clade, sister to the rest of the Aleocharinae. Although the phylogenetic relationships of the extant lineages have been well investigated, the monophyly of Gymnusini has been questioned due to a series of previous studies and the recent discovery of the aleocharine †Cretodeinopsis Cai & Huang (Deinopsini) from mid‐Cretaceous Burmese amber. Using an additional specimen of †Cretodeinopsis and well‐preserved specimens of †Electrogymnusa Wolf‐Schwenninger from Eocene Baltic amber, we present here two types of morphology‐based phylogenetic analyses, employing all extant/extinct genera of Gymnusini and Deinopsini for the first time. The maximum parsimony and Bayesian analyses recovered a monophyletic clade of the two tribes combined, but each analysis suggested nonmonophyly of Gymnusini. In agreement with the results of the present study, we synonymize Deinopsini syn.n. under Gymnusini sensu n., by priority.