Louse flies holding on mammals' hair: Comparative functional morphology of specialized attachment devices of ectoparasites (Diptera: Hippoboscoidea)

Hippoboscidae and Nycteribiidae of the dipteran superfamily Hippoboscoidea are obligate ectoparasites, which feed on the blood of different mammals. Due to their limited flight capability, the attachment system on all tarsi is of great importance for a secure grasp onto their host and thus for their survival. In this study, the functional morphology of the attachment system of two hippoboscid species and two nycteribiid species was compared in their specificity to the host substrate. Based on data from scanning electron microscopy and confocal laser scanning microscopy, it was shown that the attachment systems of both Hippoboscidae and Nycteribiidae (Hippoboscoidea) differ greatly from that of other calyptrate flies and are uniform within the respective families. All studied species have an attachment system with two monodentate claws and two pulvilli. The claws and pulvilli of the Hippoboscidae are asymmetric, which is an adaptation to the fur of even-toed ungulates (Artiodactyla). The fur of these mammals possesses both, thinner woolen and thicker coat hair; thus, the asymmetry of the attachment system of the hippoboscid species enables a secure attachment to all surfaces of their hosts. The claws and pulvilli of the nyceribiid species do not show an asymmetry, since the fur of their bat (Chiroptera) hosts consists of hairs with the same thickness. The claws are important for the attachment to mammals' fur, because they enable a secure grip by mechanical interlocking of the hairs through the claws. Additionally, well-developed pulvilli are able to attach on thicker hairs of Artiodactyla or on smooth substrates such as the skin

Computational assessment of environmental hazards of nitroaromatic compounds: influence of the type and position of aromatic ring substituents on toxicity

This study summarizes the results of our recent QSAR and QSPR investigations on prediction of numerous aspects of environmental behavior of nitro compounds. In this study, we applied the QSAR/QSPR models previously developed by our group for virtual screening of energetic compounds, their precursors and other compounds containing nitro groups. To make predictions on the environmental impact of nitro compounds, we analyzed the trends in the change of the experimentally obtained and QSAR/QSPR-predicted values of aqueous solubility, lipophilicity, Ames mutagenicity, bioavailability, blood–brain barrier penetration, aquatic toxicity on T. pyriformis and acute oral toxicity on rats as a function of chemical structure of nitro compounds. All the models were developed using simplex descriptors in combination with random forest (RF) modeling techniques. We interpreted the possible environmental impact (different toxicological properties) in terms of dividing considered nitro compounds based on hydrophobic and hydrophilic characteristics and in terms of the influence of their molecular fragments that promote and interfere with toxicity. In particular, we found that, in general, the presence of amide or tertiary amine groups leads to an increase in toxicity. Also, it was predicted that compounds containing a NO2 group in the para-position of a benzene ring are more toxic than meta-isomers, which, in turn, are more toxic than ortho-isomers. In general, we concluded that hydrophobic nitroaromatic compounds, especially the ones with electron-accepting substituents, halogens and amino groups, are the most environmentally hazardous

Dispersion in the large-deviation regime. Part 1: shear flows and periodic flows

The dispersion of a passive scalar in a fluid through the combined action of advection and molecular diffusion is often described as a diffusive process, with an effective diffusivity that is enhanced compared to the molecular value. However, this description fails to capture the tails of the scalar concentration distribution in initial-value problems. To remedy this, we develop a large-deviation theory of scalar dispersion that provides an approximation to the scalar concentration valid at much larger distances away from the centre of mass, specifically distances that are $O(t)$ rather than $O(t^{1/2})$, where $t \gg 1$ is the time from the scalar release. The theory centres on the calculation of a rate function obtained by solving a one-parameter family of eigenvalue problems which we derive using two alternative approaches, one asymptotic, the other probabilistic. We emphasise the connection between large deviations and homogenisation: a perturbative solution of the eigenvalue problems reduces at leading order to the cell problem of homogenisation theory. We consider two classes of flows in some detail: shear flows and cellular flows. In both cases, large deviation generalises classical results on effective diffusivity and captures new phenomena relevant to the tails of the scalar distribution. These include approximately finite dispersion speeds arising at large P\'eclet number $\mathrm{Pe}$ (corresponding to small molecular diffusivity) and, for two-dimensional cellular flows, anisotropic dispersion. Explicit asymptotic results are obtained for shear flows in the limit of large $\mathrm{Pe}$. (A companion paper, Part II, is devoted to the large-$\mathrm{Pe}$ asymptotic treatment of cellular flows.) The predictions of large-deviation theory are compared with Monte Carlo simulations that estimate the tails of concentration accurately using importance sampling.Comment: Accepted for publication in the Journal of Fluid Mechanic

Dispersion in the large-deviation regime. Part 2: Cellular flow at large Peclet number

A standard model for the study of scalar dispersion through advection and molecular diffusion is a two-dimensional periodic flow with closed streamlines inside periodic cells. Over long time scales, the dispersion of a scalar in this flow can be characterised by an effective diffusivity that is a factor $\mathrm{Pe}^{1/2}$ larger than molecular diffusivity when the P\'eclet number $\mathrm{Pe}$ is large. Here we provide a more complete description of dispersion in this regime by applying the large-deviation theory developed in Part I of this paper. We derive approximations to the rate function governing the scalar concentration at large time $t$ by carrying out an asymptotic analysis of the relevant family of eigenvalue problems. We identify two asymptotic regimes and make predictions for the rate function and spatial structure of the scalar. Regime I applies to distances from the release point that satisfy $|\boldsymbol{x}| = O(\mathrm{Pe}^{1/4} t)$ . The concentration in this regime is isotropic at large scales, is uniform along streamlines within each cell, and varies rapidly in boundary layers surrounding the separatrices between adjacent cells. The results of homogenisation theory are recovered from our analysis. Regime II applies when $|\boldsymbol{x}|=O(\mathrm{Pe} \, t/\log \mathrm{Pe})$ and is characterised by an anisotropic concentration distribution that is localised around the separatrices. A novel feature of this regime is the crucial role played by the dynamics near the hyperbolic stagnation points. A consequence is that in part of the regime the dispersion can be interpreted as resulting from a random walk on the lattice of stagnation points. The two regimes overlap so that our asymptotic results describe the scalar concentration over a large range of distances. They are verified against numerical solutions of the family of eigenvalue problems yielding the rate function.Comment: Accepted for publication in the Journal of Fluid Mechanic

Localization and density of phoretic deutonymphs of the mite Uropoda orbicularis (Parasitiformes : Mesostigmata) on Aphodius beetles (Aphodiidae) affect pedicel length

The phoretic stage of Uropodina mites is a deutonymph with developed morphological adaptations for dispersal by insects. Phoretic deutonymphs are able to produce a pedicel, a stalk-like temporary attachment structure that connects the mite with the carrier. The aim of our study was to determine whether localization and density of phoretic deutonymphs on the carrier affect pedicel length. The study was conducted on a common phoretic mite-Uropoda orbicularis (Uropodina) and two aphodiid beetles-Aphodius prodromus and Aphodius distinctus. Our results show that pedicel length is influenced by the localization of deutonymphs on the body of the carrier. The longest pedicels are produced by deutonymphs attached to the upper part of elytra, whereas deutonymphs attached to femora and trochanters of the third pair of legs and the apex of elytra construct the shortest pedicels. In general, deutonymphs attached to more exposed parts of the carrier produce longer pedicels, whereas shorter pedicels are produced when deutonymphs are fixed to non-exposed parts of the carrier. A second factor influencing pedicel length is the density of attached deutonymphs. Mean pedicel length and deutonymph densities were highly correlated: higher deutonymph density leads to the formation of longer pedicels. The cause for this correlation is discussed, and we conclude that pedicel length variability can increase successful dispersal

Contrasting Micro/Nano Architecture on Termite Wings: Two Divergent Strategies for Optimising Success of Colonisation Flights

Many termite species typically fly during or shortly after rain periods. Local precipitation will ensure water will be present when establishing a new colony after the initial flight. Here we show how different species of termite utilise two distinct and contrasting strategies for optimising the success of the colonisation flight. Nasutitermes sp. and Microcerotermes sp. fly during rain periods and adopt hydrophobic structuring/‘technologies’ on their wings to contend with a moving canvas of droplets in daylight hours. Schedorhinotermes sp. fly after rain periods (typically at night) and thus do not come into contact with mobile droplets. These termites, in contrast, display hydrophilic structuring on their wings with a small scale roughness which is not dimensionally sufficient to introduce an increase in hydrophobicity. The lack of hydrophobicity allows the termite to be hydrophilicly captured at locations where water may be present in large quantities; sufficient for the initial colonization period. The high wettability of the termite cuticle (Schedorhinotermes sp.) indicates that the membrane has a high surface energy and thus will also have strong attractions with solid particles. To investigate this the termite wings were also interacted with both artificial and natural contaminants in the form of hydrophilic silicon beads of various sizes, 4 µm C18 beads and three differently structured pollens. These were compared to the superhydrophobic surface of the planthopper (Desudaba psittacus) and a native Si wafer surface. The termite cuticle demonstrated higher adhesive interactions with all particles in comparison to those measured on the plant hopper

Elastic modulus of tree frog adhesive toe pads

Previous work using an atomic force microscope in nanoindenter mode indicated that the outer, 10- to 15-μm thick, keratinised layer of tree frog toe pads has a modulus of elasticity equivalent to silicone rubber (5–15 MPa) (Scholz et al. 2009), but gave no information on the physical properties of deeper structures. In this study, micro-indentation is used to measure the stiffness of whole toe pads of the tree frog, Litoria caerulea. We show here that tree frog toe pads are amongst the softest of biological structures (effective elastic modulus 4–25 kPa), and that they exhibit a gradient of stiffness, being stiffest on the outside. This stiffness gradient results from the presence of a dense network of capillaries lying beneath the pad epidermis, which probably has a shock absorbing function. Additionally, we compare the physical properties (elastic modulus, work of adhesion, pull-off force) of the toe pads of immature and adult frogs