Describing whisker morphology of the Carnivora.

One of the largest ecological transitions in carnivoran evolution was the shift from terrestrial to aquatic lifestyles, which has driven morphological diversity in skulls and other skeletal structures. In this paper, we investigate the association between those lifestyles and whisker morphology. However, comparing whisker morphology over a range of species is challenging since the number of whiskers and their positions on the mystacial pads vary between species. Also, each whisker will be at a different stage of growth and may have incurred damage due to wear and tear. Identifying a way to easily capture whisker morphology in a small number of whisker samples would be beneficial. Here, we describe individual and species variation in whisker morphology from two-dimensional scans in red fox, European otter and grey seal. A comparison of long, caudal whiskers shows inter-species differences most clearly. We go on to describe global whisker shape in 24 species of carnivorans, using linear approximations of curvature and taper, as well as traditional morphometric methods. We also qualitatively examine surface texture, or the presence of scales, using scanning electron micrographs. We show that gross whisker shape is highly conserved, with whisker curvature and taper obeying simple linear relationships with length. However, measures of whisker base radius, length, and maybe even curvature, can vary between species and substrate preferences. Specifically, the aquatic species in our sample have thicker, shorter whiskers that are smoother, with less scales present than those of terrestrial species. We suggest that these thicker whiskers may be stiffer and able to maintain their shape and position during underwater sensing, but being stiffer may also increase wear.

Morphological peculiarities of a harbour seal (Phoca vitulina) whisker revealed by normal skeletonisation.

Of all mammalian vibrissae, those of certain species of pinnipeds are exceptional. Researchers believe that their curious undulating form evolved for hydrodynamic detection. Our understanding of how these whiskers work depends on a geometrical model that captures the crucial pertinent features of the natural vibrissae including its tapering and curvature. It should also account for the form of the whisker when it flexes under external loading. We introduce and study a normal skeleton of a two-dimensional projection of a harbour seal whisker. The normal skeleton is a complete shape descriptor that involves reduction to the centreline equipped with a thickness function of the orthogonal cross-section. The contours of the whisker shape are extracted from a 2D greyscale scan. Our analysis reveals correspondence between the undulations of the width and oscillations of the centreline curvature as functions of arc length. We discuss two possible explanations for that remarkable feature: one based on consideration of growth and the other of plastic deformation. For the latter we employ a mechanical model to demonstrate appearance of curvature oscillations caused by extensive deflection of the undulating whisker due to external loading.

Investigating cat predation as the cause of bat wing tears using forensic DNA analysis.

Cat predation upon bat species has been reported to have significant effects on bat populations in both rural and urban areas. The majority of research in this area has focussed on observational data from bat rehabilitators documenting injuries, and cat owners, when domestic cats present prey. However, this has the potential to underestimate the number of bats killed or injured by cats. Here, we use forensic DNA analysis techniques to analyze swabs taken from injured bats in the United Kingdom, mainly including Pipistrellus pipistrellus (40 out of 72 specimens). Using quantitative PCR, cat DNA was found in two-thirds of samples submitted by bat rehabilitators. Of these samples, short tandem repeat analysis produced partial DNA profiles for approximately one-third of samples, which could be used to link predation events to individual cats. The use of genetic analysis can complement observational data and potentially provide additional information to give a more accurate estimation of cat predation.

Ecomorphology reveals Euler spiral of mammalian whiskers.

Whiskers are present in many species of mammals. They are specialised vibrotactile sensors that sit within strongly innervated follicles. Whisker size and shape will affect the mechanical signals that reach the follicle, and hence the information that reaches the brain. However, whisker size and shape have not been quantified across mammals before. Using a novel method for describing whisker curvature, this study quantifies whisker size and shape across 19 mammalian species. We find that gross two-dimensional whisker shape is relatively conserved across mammals. Indeed, whiskers are all curved, tapered rods that can be summarised by Euler spiral models of curvature and linear models of taper, which has implications for whisker growth and function. We also observe that aquatic and semi-aquatic mammals have relatively thicker, stiffer, and more highly tapered whiskers than arboreal and terrestrial species. In addition, smaller mammals tend to have relatively long, slender, flexible whiskers compared to larger species. Therefore, we propose that whisker morphology varies between larger aquatic species, and smaller scansorial species. These two whisker morphotypes are likely to induce quite different mechanical signals in the follicle, which has implications for follicle anatomy as well as whisker function.

The Euler spiral of rat whiskers.

This paper reports on an analytical study of the intrinsic shapes of 523 whiskers from 15 rats. We show that the variety of whiskers on a rat's cheek, each of which has different lengths and shapes, can be described by a simple mathematical equation such that each whisker is represented as an interval on the Euler spiral. When all the representative curves of mystacial vibrissae for a single rat are assembled together, they span an interval extending from one coiled domain of the Euler spiral to the other. We additionally find that each whisker makes nearly the same angle of 47∘ with the normal to the spherical virtual surface formed by the tips of whiskers, which constitutes the rat's tactile sensory shroud or "search space." The implications of the linear curvature model for gaining insight into relationships between growth, form, and function are discussed.

Paw Morphology in the Domestic Guinea Pig (Cavia porcellus) and Brown Rat (Rattus norvegicus).

Mammals have adapted to different habitats, food types, and modes of locomotion, which are reflected in a diverse range of paw morphologies. While the behavior of rats and guinea pigs is well defined, especially in terms of their locomotor and foraging behaviors, the anatomy of their foot pads has not yet been explored and compared. This study investigated adaptations in paw morphology in the domestic guinea pig (Cavia porcellus) and the brown rat (Rattus norvegicus). We predicted that rat paws would display adaptations associated with paw dexterity for handling prey items and climbing, whereas guinea pig paws would support mechanical pressure absorption for a herbivorous, sedentary, and terrestrial lifestyle. Using histology techniques and scanning electron microscope, we show that rat paws have many small, deformable pads that are relatively spaced out to enable movement. The pads are clustered toward the anterior of the foot, which coincides with where the most force occurs during locomotion, as rats walk on their toes and toward the front of their paw. Guinea pigs had fewer and larger pads and the posterior pad of the forepaw was textured and contained cartilage, which may act to reduce friction and compression during standing and locomotion. We suggest that differences in paw morphology in rat and guinea pig are associated with loading during locomotion as well as paw mobility. Examining paw morphology and movement abilities in more species will give further insights in to the evolution of locomotor adaptations and paw dexterity in rodents. Anat Rec, 302:2300-2310, 2019. © 2019 American Association for Anatomy.

Characterizing wing tears in common pipistrelles (Pipistrellus pipistrellus): investigating tear distribution, wing strength, and possible causes.

Bats have large, thin wings that are particularly susceptible to tearing. Anatomical specializations, such as fiber reinforcement, strengthen the wing and increase its resistance to puncture, and an extensive vasculature system across the wing also promotes healing. We investigated whether tear positioning is associated with anatomy in common pipistrelles (Pipistrellus pipistrellus). Wing anatomy was described using histological techniques, imaging, and material testing. Tear information, including type, position, time in rehabilitation, and possible causes, was collected from rehabilitators of injured bats across the United Kingdom. Results suggest that the position of the plagiopatagium (the most proximal wing section to the body), rather than its anatomy, influenced the number, location, and orientation of wing tears. While material testing did not identify the plagiopatagium as being significantly weaker than the chiropatagium (the more distal sections of the wing), the plagiopatagium tended to have the most tears. The position of the tears, close to the body and toward the trailing edge, suggests that they are caused by predator attacks, such as from a cat (Felis catus), rather than collisions. Consistent with this, 38% of P. pipistrellus individuals had confirmed wing tears caused by cats, with an additional 38% identified by rehabilitators as due to suspected cat attacks. The plagiopatagium had the lowest number of blood vessels and highest amounts of elastin fibers, suggesting that healing may take longer in this section. Further investigations into the causes of tears, and their effect on flight capabilities, will help to improve bat rehabilitation.