A biomechanical analysis of prognathous and orthognathous insect head capsules: evidence for a many-to-one mapping of form to function.

Insect head shapes are remarkably variable, but the influences of these changes on biomechanical performance are unclear. Among 'basal' winged insects, such as dragonflies, mayflies, earwigs and stoneflies, some of the most prominent anatomical changes are the general mouthpart orientation, eye size and the connection of the endoskeleton to the head. Here, we assess these variations as well as differing ridge and sclerite configurations using modern engineering methods including multibody dynamics modelling and finite element analysis in order to quantify and compare the influence of anatomical changes on strain in particular head regions and the whole head. We show that a range of peculiar structures such as the genal/subgenal, epistomal and circumocular areas are consistently highly loaded in all species, despite drastically differing morphologies in species with forward-projecting (prognathous) and downward-projecting (orthognathous) mouthparts. Sensitivity analyses show that the presence of eyes has a negligible influence on head capsule strain if a circumocular ridge is present. In contrast, the connection of the dorsal endoskeletal arms to the head capsule especially affects overall head loading in species with downward-projecting mouthparts. Analysis of the relative strains between species for each head region reveals that concerted changes in head substructures such as the subgenal area, the endoskeleton and the epistomal area lead to a consistent relative loading for the whole head capsule and vulnerable structures such as the eyes. It appears that biting-chewing loads are managed by a system of strengthening ridges on the head capsule irrespective of the general mouthpart and head orientation. Concerted changes in ridge and endoskeleton configuration might allow for more radical anatomical changes such as the general mouthpart orientation, which could be an explanation for the variability of this trait among insects. In an evolutionary context, many-to-one mapping of strain patterns onto a relatively similar overall head loading indeed could have fostered the dynamic diversification processes seen in insects.

INSECT PHYLOGENOMICS. Response to Comment on "Phylogenomics resolves the timing and pattern of insect evolution".

Tong et al. comment on the accuracy of the dating analysis presented in our work on the phylogeny of insects and provide a reanalysis of our data. They replace log-normal priors with uniform priors and add a "roachoid" fossil as a calibration point. Although the reanalysis provides an interesting alternative viewpoint, we maintain that our choices were appropriate.

Histological study of the external, middle and inner ear of horses.

Clinical, anatomical and histological aspects of the equine acoustic organ have been poorly investigated and illustrated in literature so far. It is understood that an intact acoustic organ and hearing function are of vital importance for the well-being of flight animals like horses. The knowledge of the acoustic organ is usually transferred analogously from other mammals to horses. The purpose of this study was to provide a detailed and complete histological description of the healthy equine auditory organ, and to determine its congruity to other mammalians. Anatomical dissections and histological preparations were carried out on ten cadaver heads. Specimens of various parts of the equine acoustic organ were taken and evaluated histologically. The histological composition of external, middle and inner ear structures are predominantly congruent to those of other mammals, especially to human beings. Unique inwardly directed rete pegs within the osseous ear canal and the prominent tensor tympani muscle are described for the first time. Results obtained in this study can be employed as references for further research on the equine acoustic organ and improve the understanding of the clinical development of hearing loss, otitis externa/media/interna or tympanosclerosis.

X-ray mosaic nanotomography of large microorganisms.

Full-field X-ray microscopy is a valuable tool for 3D observation of biological systems. In the soft X-ray domain organelles can be visualized in individual cells while hard X-ray microscopes excel in imaging of larger complex biological tissue. The field of view of these instruments is typically 10(3) times the spatial resolution. We exploit the assets of the hard X-ray sub-micrometer imaging and extend the standard approach by widening the effective field of view to match the size of the sample. We show that global tomography of biological systems exceeding several times the field of view is feasible also at the nanoscale with moderate radiation dose. We address the performance issues and limitations of the TOMCAT full-field microscope and more generally for Zernike phase contrast imaging. Two biologically relevant systems were investigated. The first being the largest known bacteria (Thiomargarita namibiensis), the second is a small myriapod species (Pauropoda sp.). Both examples illustrate the capacity of the unique, structured condenser based broad-band full-field microscope to access the 3D structural details of biological systems at the nanoscale while avoiding complicated sample preparation, or even keeping the sample environment close to the natural state.