Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. II. Wing reduction and the sensory field

Loss of the flight ability and wing reduction has been reported for many taxa of Coleoptera. If elytra are closed, their roots are clenched between the tergum and the pleuron, forces applied to the elytra can not be transmitted to the field of campaniform sensilla situated on the root. That is why it is plausible to assume that the field becomes redundant in non-flying beetles. We examined the relationships between the hind wing reduction and characters of this mechanosensory field in beetles of six families. We measured the size of the elytron, that of the hind wing and counted the number of sensilla in the sensory field. Mesopterous non-flying beetles retain one half to one third of sensilla present in macropterous species of the same body size. Further reduction of the sensory field in brachypterous species is obvious, but sensilla are still present in insects with strongly reduced wings, as long as their elytra are separable and mesothoracic axillaries are present. Complete loss of sensilla coincides with the existence of a permanent sutural lock. However, some beetles with permanently locked elytra and absence of axillaries still retain few campaniform sensilla. A very special case of an extreme wing modification in feather-wing beetles is considered. No sensilla were revealed either on the root of the elytron or on the basal segment of such fringed wings in flying ptiliid species.     

Arboreallty and morphological evolution in ground beetles (Carabidae: Harpalinae): testing the taxon pulse model

Abstract.— One-third to two-thirds of all tropical carabids, or ground beetles, are arboreal, and evolution of arboreality has been proposed to be a dead end in this group. Many arboreal carabids have unusual morphological features that have been proposed to be adaptations for life on vegetation, including large, hemispheric eyes; an elongated prothorax; long elytra; long legs; bilobed fourth tarsomeres; adhesive setae on tarsi; and pectinate claws. However, correlations between these features and arboreality have not been rigorously tested previously. I examined the evolution of arboreality and morphological features often associated with this habitat in a phylogenetic context. The number and rates of origins and losses of arboreality in carabids in the subfamily Harpalinae were inferred with parsimony and maximum-likelihood on a variety of phylogenetic hypotheses. Correlated evolution in arboreality and morphological characters was tested with concentrated changes tests, maximum-likelihood, and independent contrasts on optimal phylogenies. There is strong evidence that both arboreality and the morphological features examined originated multiple times and can be reversed, and in no case could the hypothesis of equal rates of gains and losses be rejected. Several features are associated with arboreality: adhesive setae on the tarsi, bilobed tarsomeres, and possibly pectinate claws and an elongated prothorax. Bulgy eyes, long legs, and long elytra were not correlated with arboreality and are probably not arboreal adaptations. The evolution of arboreal carabids has not been unidirectional. These beetles have experienced multiple gains and losses of arboreality and the morphological characters commonly associated with the arboreal habitat. The evolutionary process of unidirectional character change may not be as widespread as previously thought and reversal from specialized lifestyles or habitats may be common.     

Indirect closing of elytra by the prothorax in beetles (Coleoptera): general observations and exceptions

Voluntary movements of the prothorax and the elytra in tethered flying beetles and manually induced movements of these parts in fresh dead beetles were recorded in 30 species representing 14 families. Participation of prothoracic elevation in the closing of the elytra was demonstrated in three ways. (i) The elevation was always simultaneous with elytral closing, in contrast to depression and elytral opening; a rare exception occurred in Lucanus cervus, whose elytra sometimes started to close before the cessation of wing strokes and the elevation of the prothorax. (ii) The manipulated elevation always induced closing of the spread elytra; the mechanical interaction between the hind edge of the pronotum and the roots of the elytra is a universal mechanism of closing the elytra in beetles. (iii) The prevention of pronoto-elytral contact in live beetles by the excision of the hind edge of the pronotum in front of the root prevented elytral closing after normal flight. Exceptions to this rule included some beetles that were able to close their elytra after such an excision: tiger beetles and diving beetles (seldomly) and rose chafers (always). This ability in Adephaga may be explained by attachments of the muscle actuating the 4th axillary plate, which differ from the attachments in Polyphaga. Cetoniinae open their elytra only by a small amount. It is proposed that their small direct adductors in combination with the elasticity of the sclerites are enough to achieve elytral closing without additional help from the prothorax.     

Phylogenomic analysis resolves the relationships among net‐winged beetles (Coleoptera: Lycidae) and reveals the parallel evolution of morphological traits

Net‐winged beetles (Coleoptera: Lycidae) are a diverse group of elateroids known for aposematism and neoteny. Phylogenetic analyses of morphological and molecular data have revealed different results with respect to within‐group relationships. In this study, we recovered a highly supported phylogenomic phylogeny and identified seven subfamilies: Dexorinae stat.n. , Calochrominae stat.n. , Erotinae, Ateliinae, Lycinae, Lyropaeinae stat.n. and Metriorrhynchinae stat.n. Our results suggest that female neoteny evolved multiple times. Therefore, the development of similar morphological modifications in neotenics may be linked and may have produced characteristics such as body miniaturization, structural simplification, i.e. reduction of mouthparts, fewer antennomeres and palpomeres, uniquely shaped terminal palpomeres, shortened elytra, the loss of coadaptation between the elytra and pronotum, and others. Additional traits evolved in parallel due to similarities in biology, function and sexual selection. These characteristics include mimetic similarities, the presence of the rostrum, pronotal carinae and elytral costae, and the structure of male genitalia. By comparing the phylogenomic topology with the evolution of morphological characters, we were able to identify evolutionary trends in lycids and compare them with analogues for other neotenic elateroids. These traits have not been accepted as homoplasies due to the ambiguous phylogenetic signal from Sanger sequencing markers.     

Effect of temperature and diet on hind wing colouration development and elytral hardness of adult Colorado potato beetle (Coleoptera: Chrysomelidae)

The effects of food and temperature on the development of colour pigment in the hind wings of adult Colorado potato beetle, Leptinotarsa decemlineata (Say), were investigated. In a replicated study, adults were held at 18°C, 28°C and 18/28°C on potato foliage (Solanum tuberosum L.), potato tubers, or without food in controlled-environment chambers. Representative subsamples of wings were collected at two-day intervals, mounted on microscope slides, and photographed to document the progression of colour change. Observations were also made on elytral hardening over time. Hind wing colour developed more quickly at 28°C than at 18°C, and after three weeks had attained a deeper red colour at the higher temperature. Colour development was also more rapid when adult beetles were fed on foliage compared with tubers. In foliage-fed beetles, elytra hardened more quickly at 28°C than 18°C, and many tuber-fed beetles never developed hardened elytra, regardless of temperature treatment. Unfed beetles developed no hind wing colour pigment and their elytra remained soft for the duration of the experiment. Colour plates documenting wing colour development over time are presented; variation in colour development under the conditions tested, suggests that the use of hind wing colouration to estimate beetle age in the field may be problematic.     

Lehr's fields of campaniform sensilla in beetles (Coleoptera): Functional morphology. III. Modification of elytral mobility or shape in flying beetles

Some flying beetles have peculiar functional properties of their elytra, if compared with the vast majority of beetles. A “typical” beetle covers its pterothorax and the abdomen from above with closed elytra and links closed elytra together along the sutural edges. In the open state during flight, the sutural edges diverge much more than by 90°. Several beetles of unrelated taxa spread wings through lateral incisions on the elytra and turn the elytron during opening about 10–12° (Cetoniini, Scarabaeus, Gymnopleurus) or elevate their elytra without partition (Sisyphus, Tragocerus). The number of campaniform sensilla in their elytral sensory field is diminished in comparison with beetles of closely related taxa lacking that incision. Elytra are very short in rove beetles and in long-horn beetles Necydalini. The abundance of sensilla in brachyelytrous long-horn beetles Necydalini does not decrease in comparison with macroelytrous Cerambycinae. Strong reduction of the sensory field was found in brachyelytrous Staphylinidae. Lastly, there are beetles lacking the linkage of the elytra down the sutural edge (stenoelytry). Effects of stenoelytry were also not uniform: Oedemera and flying Meloidae have the normal amount of sensilla with respect to their body size, whereas the sensory field in the stenoelytrous Eulosia bombyliformis is 5–6 times less than in chafers of the same size but with normally linking broad elytra.     

Passive aerodynamic stabilization by beetle elytra (wing covers)

Summary. Most beetles extend their elytra laterally during flight, where they can act as fixed airfoils; typically, such elytra are held at a pronounced dihedral angle. We fixed extended elytra of June beetles (Scarabaeidae: Melolonthinae) and tiger beetles (Cicindelidae) over a range of dihedral angles (-10° to 45°) and towed them in a water tunnel. We also towed them with flexed elytra (i.e. in the resting position). (Reynolds number was used to maintain dynamic similarity with air.) We measured the maximum rolling angle and the lateral oscillation rate as two indices of stability. There was no relationship between oscillation rate and dihedral angle, or between maximum roll angle and dihedral angle. At all dihedral angles tested, however, beetles were much more stable than when they were towed with the elytra flexed. We also included a third beetle type, flower beetle (Scarabaeidae: Cetoniine), which normally flies with flexed elytra. We measured stability indices for these beetles with elytra only in the flexed position. When all beetles were tested with flexed elytra, flower beetles showed no difference in maximum roll angle, but more stability in oscillation rate than the other two beetle types.     

How Could Beetle＇s Elytra Support Their Own Weight during Forward Flight？

The aerodynamic role of the elytra during a beetle＇s flapping motion is not well-elucidated, although it is well-recognized that the evolution of elytra has been a key in the success of coleopteran insects due to their protective function. An experimental study on wing kinematics reveals that for almost concurrent flapping with the hind wings, the flapping angle of the elytra is 5 times smaller than that of the hind wings. Then, we explore the aerodynamic forces on elytra in free forward flight with and without an effect of elytron-hind wing interaction by three-dimensional numerical simulation. The numerical results show that vertical force generated by the elytra without interaction is not sufficient to support even its own weight. However, the elytron-hind wing interaction improves the vertical force on the elytra up to 80%; thus, the total vertical force could fully support its own weight. The interaction slightly increases the vertical force on the hind wind by 6% as well.     

When a key innovation becomes redundant: Patterns,drivers and consequences of elytral reduction in Coleoptera

The transformation of the fore wings into strongly sclerotized protective covers (elytra) is considered a fundamental evolutionary innovation of the megadiverse order Coleoptera. Surprisingly, these multifunctional structures have been reduced in many distantly related groups of beetles. Patterns, drivers and the evolutionary implications of this modification have never been comprehensively discussed. In the present study, we surveyed the entire order Coleoptera to analyse the patterns of elytral shortening and loss, with a special focus on prevalence, forms, degree of reduction and the functional background of this significant deviation from the coleopteran ground plan. Our analysis revealed that about 20% of all extant species (roughly 88,000 out of 442,275 spp.), distributed across all four suborders, have shortened or even absent elytra. The elytral loss was more frequent within the polyphagan series Elateriformia and Staphyliniformia. Moreover, we found that elytral reduction has independently occurred multiple times in the evolutionary history of Coleoptera and that it has been driven by a wide array of selective drivers. One of the main drivers is the improved flexibility of the uncovered abdomen and the correlated increased manoeuvrability in narrow spaces, as well as the option of using the flexible abdomen as a steering organ or to facilitate mating. Another common driver is mimicry, where exposed metathoracic wings potentially improve the overall similarity to hymenopteran models. Exposure of the abdomen can facilitate the targeted release of defensive abdominal gland secretions and was most likely a crucial step towards establishing relations with social insects enhanced by chemical communication. In the Elateriformia, and rarely in other lineages, elytral loss is a consequence of paedomorphosis, related to a specific resource-allocation strategy. In many groups of beetles with reduced elytra, alternative defensive strategies can be found. This includes, for instance, aposematic coloration, chemical defence, mimicry or bioluminescence. Direct drivers of elytral loss in many groups remain unclear, and more studies are needed to understand the evolutionary background and implications of this significant morphological modification in Coleoptera.     

Animal or Plant: Which Is the Better Fog Water Collector?

Occasional fog is a critical water source utilised by plants and animals in the Namib Desert. Fog basking beetles (Onymacris unguicularis, Tenebrionidae) and Namib dune bushman grass (Stipagrostris sabulicola, Poaceae) collect water directly from the fog. While the beetles position themselves optimally for fog water collection on dune ridges, the grass occurs predominantly at the dune base where less fog water is available. Differences in the fog-water collecting abilities in animals and plants have never been addressed. Here we place beetles and grass side-by-side in a fog chamber and measure the amount of water they collect over time. Based on the accumulated amount of water over a two hour period, grass is the better fog collector. However, in contrast to the episodic cascading water run-off from the grass, the beetles obtain water in a steady flow from their elytra. This steady trickle from the beetles' elytra to their mouth could ensure that even short periods of fog basking--while exposed to predators--will yield water. Up to now there is no indication of specialised surface properties on the grass leafs, but the steady run-off from the beetles could point to specific property adaptations of their elytra surface.     

Evolutionary constraints in hind wing shape in Chinese dung beetles (Coleoptera: Scarabaeinae)

This study examines the evolution hindwing shape in Chinese dung beetle species using morphometric and phylogenetic analyses. Previous studies have analyzed the evolution of wing shape within a single or very few species, or by comparing only a few wing traits. No study has analyzed wing shape evolution of a large number of species, or quantitatively compared morphological variation of wings with proposed phylogenetic relationships. This study examines the morphological variation of hindwings based on 19 landmarks, 119 morphological characters, and 81 beetle species. Only one most parsimonious tree (MPT) was found based on 119 wing and body characters. To better understand the possible role of the hindwing in the evolution of Scarabaeinae, additional phylogenetic analyses were proposed based on the only body features (106 characters, wing characters excluded). Two MPT were found based on 106 body characters, and five nodes were collapsed in a strict consensus. There was a strong correlation between the morphometric tree and all phylogenetic trees (r>0.5). Reconstructions of the ancestral wing forms suggest that Scarabaeinae hindwing morphology has not changed substantially over time, but the morphological changes that do occur are focused at the base of the wing. These results suggest that flight has been important since the origin of Scarabaeinae, and that variation in hindwing morphology has been limited by functional constraints. Comparison of metric disparity values and relative evolutionary sequences among Scarabaeinae tribes suggest that the primitive dung beetles had relatively diverse hindwing morphologies, while advanced dung beetles have relatively similar wing morphologies. The strong correlation between the morphometric tree and phylogenetic trees suggest that hindwing features reflect the evolution of whole body morphology and that wing characters are suitable for the phylogenetic analyses. By integrating morphometric and cladistic approaches, this paper sheds new light on the evolution of dung beetle hind wings.     

Surface Chemicals Inform about Sex and Breeding Status in the Biparental Burying Beetle Nicrophorus vespilloides

The multicomponent nature of chemical cues and signals are not very well understood. One reason for the often found complexity of chemical blends might be that they provide multiple messages. Burying beetles which use vertebrate carcasses as food for their larvae and defend these carcasses against inter- and intraspecific competitors are able to recognise the sex and breeding status of conspecifics. Studies have shown that the chemical composition of cuticular lipids is correlated with sex and breeding status, but there is no definitive evidence that these chemicals function in recognition. In the present study, we performed behavioural bioassays to directly asses the role of chemical cues in the recognition system of the burying beetle Nicrophorus vespilloides . After finding a carcass, females were more tolerant of dead males than of females. The behaviour was reversed when a solvent extract from the opposite sex was applied. An earlier experiment had shown that females breeding on a carcass treat non-breeding males more aggressively than breeding ones. In the present study, we could trigger the same dichotomous behaviours by presenting a single elytron from a breeding and a non-breeding beetle. In an additional experiment, females tolerated the elytra of non-breeding beetles if we had first applied an extract from a breeding beetle to these elytra. Our study is the first behavioural proof that female burying beetles obtain multiple information from chemical cues.     

Coupling between elytra of some beetles: Mechanism, forces and effect of surface texture

Lightweight materials, structures and coupling mechanisms are very important for realizing advanced flight vehicles. Here, we obtained the geometric structures and morphologies of the elytra of beetles and ascertained its coupling zone by using the histological section technique and SEM. We set up a three-dimensional motion observing system to monitor the opening and closing behaviour of elytra in beetles and to determine the motion mechanism. We constructed a force measuring system to measure the coupling forces between elytra. The results show that elytra open and close by rotating about a single axle, where the coupling forces may be as high as 160 times its own bodyweight, the elytra coupling with the tenon and mortise mechanism, surface texture and opening angle between elytra heavily influence the coupling forces. These results may provide insights into the design mechanism and structure for future vehicles of flight.     

First report of wing dimorphism in the genus Orthomus (Coleoptera: Carabidae)

Wing polymorphism has been reported for several carabid beetles. Traditionally, a great number of ecological and evolutionary studies have focused on this peculiarity, which has implications on dispersal power. Research based on Orthomus berytensis specimens from two sampling areas of Tenerife (Canary Islands, Spain) has shown that this species exhibits a wing dimorphism, instead of being brachypterous. This makes O. berytensis the first Orthomus wing dimorphic species to date. Statistical differences in macropterous percentage between both sexes and localities were found. Also, a sexual dimorphism in elytra length and width was found, both being higher in females.     

Evolutionary patterns of hind wing morphology in dung beetles (Coleoptera: Scarabaeinae)

The shape of wings can be a good predictor of adaptations to different selective pressures and the value of wing features in taxonomy and phylogeny has long been recognized. In our investigation of the hind wing evolution of dung beetles (Scarabaeinae) we use geometric morphometrics combined with a cladistic approach. The variations of entire hind wings and of three specific regions of 80 dung beetle species were investigated using 19 landmarks and outline data. Extensive evidence indicates that the wing as a whole and the three separate regions were under different selective pressures. The detailed evolutionary patterns of the three regions and the reconstruction of the ancestral forms were computed by mapping the geometric morphometrics data onto a tree based on a cladistic character analysis.     

Molecular phylogeny of Omaliinae (Coleoptera: Staphylinidae) and its implications for evolution of atypically long elytra in rove beetles

Staphylinidae, or rove beetles, are a megadiverse family known for their typically very short elytra exposing most of the abdomen, but the putatively early-derived subfamily Omaliinae and its relatives have been known to include multiple taxa with unusually long elytra. The ancestral elytral length of the family and of this subfamily have long been debated. We present a phylogenetic analysis of Omaliinae based on partial mitochondrial COI (1488 bp), COII (366 bp), 12S rDNA (353 bp), nuclear 18S rDNA (1814 bp), 28S rDNA (876 bp) and CAD (869 bp) data. In all, 51 species in 31 genera and four outgroup species were included. The concatenated sequences were analysed by both parsimony- and model-based (Bayesian and maximum likelihood) methods. The subfamily Omaliinae was not supported as a monophyletic group. The model-based analyses (Bayesian and maximum likelihood trees) showed Empelinae nested within Omaliinae (excluding Corneolabiini), whereas parsimony analysis found all three putative ingroup subfamilies, Empelinae, Glypholomatinae and Microsilphinae, grouped within Omaliinae. Within the Omaliinae, the tribes Coryphiini and Eusphalerini were each supported as monophyletic, whereas Anthophagini and Omaliini were each nonmonophyletic. We hypothesize that there have been at least four independent origins of long elytra from short elytra in the omaliine lineage.     

Tribolium beetles as a model system in evolution and ecology

Flour beetles of the genus Tribolium have been utilised as informative study systems for over a century and contributed to major advances across many fields. This review serves to highlight the significant historical contribution that Tribolium study systems have made to the fields of ecology and evolution, and to promote their use as contemporary research models. We review the broad range of studies employing Tribolium to make significant advances in ecology and evolution. We show that research using Tribolium beetles has contributed a substantial amount to evolutionary and ecological understanding, especially in the fields of population dynamics, reproduction and sexual selection, population and quantitative genetics, and behaviour, physiology and life history. We propose a number of future research opportunities using Tribolium, with particular focus on how their amenability to forward and reverse genetic manipulation may provide a valuable complement to other insect models.Subject terms: Model invertebrates, Evolution, Ecology     

Sexual Dimorphism,Fighting Success and Mating Tactics of Male Onymacris plana Péringuey (Coleoptera: Tenebrionidae) in the Namib Desert

Sexually dimorphic characters of Onymacris plana, a dune-living, solitary tenebrionid beetle of the Namib Desert, were tested for their roles in male-male fighting over females. Males were smaller than females but had extraordinarily wide elytra, with great variance in this characteristic. In males, but not in females, elytra width increased with body length at an allometric scale. Male beetles were often aggressive towards each other, especially when mating or guarding females after mating or waiting for females at shady spots. Interactions were less intense when contesting over females on the open surface, where these fast-running beetles often overran each other in their attempts to retain their positions behind females until the females retreated into the sand, where mating took place. Winners of intrasexual fights and the successful mates of females tended to have longer bodies and wider elytra than the losers. Sexual selection appears to be the best explanation of the allometric scaling of the lateral extensions of male elytra. Sexual selection may furthermore contribute to other characteristics, such as large body length and long legs, that have ecological and ecophysiological significance.