Adaptive tail-length evolution in deer mice is associated with differential Hoxd13 expression in early development

Variation in the size and number of axial segments underlies much of the diversity in animal body plans. Here, we investigate the evolutionary, genetic, and developmental mechanisms driving tail-length differences between forest and prairie ecotypes of deer mice (Peromyscus maniculatus). We first show that long-tailed forest mice perform better in an arboreal locomotion assay, consistent with tails being important for balance during climbing. The long tails of these forest mice consist of both longer and more caudal vertebrae than prairie mice. Using quantitative genetics, we identify six genomic regions that contribute to differences in total tail length, three of which associate with vertebra length and the other three with vertebra number. For all six loci, the forest allele increases tail length, consistent with the cumulative effect of natural selection. Two of the genomic regions associated with variation in vertebra number contain Hox gene clusters. Of those, we find an allele-specific decrease in Hoxd13 expression in the embryonic tail bud of long-tailed forest mice, consistent with its role in axial elongation. Additionally, we find that forest embryos have more presomitic mesoderm than prairie embryos, and that this correlates with an increase in the number of neuromesodermal progenitors (NMPs), which are modulated by Hox13 paralogs. Together, these results suggest a role for Hoxd13 in the development of natural variation in adaptive morphology on a microevolutionary timescale.

A new Lepanthes (Pleurothallidinae) from South-western Colombia

A new species of Lepanthes from southwestern Colombia is presented here. Lepanthes farallonensis belongs to the informal group “manabina”, which comprises species with concave and commonly pubescent leaves, flowers resting at the adaxial side of the leaves, and the synsepal with short to long tails. Lepanthes farallonensis is similar to L. smaragdina in the broadly ovate dorsal sepal but differs in the conspicuously twisted upper lobes of the petals, outwardly bent and a depression at the center of the laminae of the lip.

Analysis of Automatically Extracted Hallux Valgus Angles Using Markerless 3D Foot Scans From North America, Europe and Asia

Background The forefoot is the foot most affected part by ill-fitting shoes. Footwear fitting standards have the measurements of length, width and arch length. Toe shape has not yet been used in footwear measurement. This study aims at investigating the variation in toe shape, as measured by the hallux valgus angle. Methods An automatic and reproducible hallux valgus angle measuring method using 3D foot scans with no palpation markers is proposed and applied to about half a million samples collected across North America, Europe and Asia. The measuring method is robust, it can detect the medial contour along the proximal phalanx even in extreme cases. Results The hallux valgus angle has a normal distribution with long tails on both sides in the general population. In the three regions (North America, Europe, Asia), the mean and standard deviation of this angle are 9° ± 6°, 8 ° ± 6°, 12° ± 6° for males and 11 ° ± 7°, 12 ° ± 7°, 16° ± 7° for females. Conclusions The hallux valgus angle has a broad distribution in the general population. Females have larger hallux valgus angle than males, and people from Asia have larger hallux valgus angle than people from North America and Europe.

Ptychography Reduces Spectral Distortions Intrinsic to Conventional Zone-Plate-Based X-Ray Spectromicroscopy

Scanning transmission X-ray microscopy is a powerful method for mapping chemical phases in nano-materials. The point spread function (PSF) of a conventional zone-plate-based microscope limits the achievable spatial resolution and also results in spatially resolved spectra that do not accurately reflect the spatial heterogeneity of the samples when the scale of the detail approaches the probe size. X-ray ptychography, a coherent-scattering-based imaging scheme that effectively removes the probe from the image data, returns accurate spectra from regions smaller than the probe size. We show through simulation how the long tails on the PSF of an x-ray optic can cause spectral distortion near a boundary between two spectrally distinct regions. The resulting apparent point spectra can appear mixed, with the species on one side of the boundary seeming to be present on the other even at a distance from the boundary equal to several times the spatial resolution. We further demonstrate the effect experimentally and show that ptychographic microscopy can return the expected spectra from a model system, whereas conventional microscopy does not.

Synchrotron mechanism of X-ray and gamma-ray emissions in lightning and spark discharges

X-ray and γ-ray emissions observed in lightning and long sparks are usually connected with the bremsstrahlung of high-energy runaway electrons. Here, an alternative physical mechanism for producing X-ray and gamma-ray emissions caused by the polarization current and associated electromagnetic field moving with relativistic velocity along a curved discharge channel has been proposed. The existence of fast electromagnetic surface waves propagating along the lightning discharge channel at a speed close to the speed of light in vacuum is shown. The possibility of the production of microwave, X-ray and gamma-ray emissions by a polarization current pulse moving along a curved path via synchrotron radiation mechanism is pointed out. The existence of long tails in the power spectrum is shown, which explains observations of photon energies in the range of 10–100 MeV in the terrestrial gamma-ray flashes, as well as measured power spectrum of laboratory spark discharge.

Synchrotron mechanism of X-ray and gamma-ray emissions in lightning and spark discharges

X-ray and γ-ray emissions observed in lightning and long sparks are usually connected with the bremsstrahlung of high-energy runaway electrons. Here, an alternative physical mechanism for producing X-ray and gamma-ray emissions caused by the polarization current and associated electromagnetic field moving with relativistic velocity along a curved discharge channel has been proposed. The existence of fast electromagnetic surface waves propagating along the lightning discharge channel at a speed close to the speed of light in vacuum is shown. The possibility of the production of microwave, X-ray and gamma-ray emissions by a polarization current pulse moving along a curved path via synchrotron radiation mechanism is pointed out. The existence of long tails in the power spectrum is shown, which explains observations of photon energies in the range of 10-100 MeV in the TGF, as well as measured power spectrum of laboratory spark discharge.

Inertial Tail Effects during Righting of Squirrels in unexpected Falls: From Behavior to Robotics

Arboreal mammals navigate a highly three dimensional and discontinuous habitat. Among arboreal mammals, squirrels demonstrate impressive agility. In a recent ‘viral’ YouTube video, unsuspecting squirrels were mechanically catapulted off of a track, inducing an initially uncontrolled rotation of the body. Interestingly, they skillfully stabilized themselves using tail motion, which ultimately allowed the squirrels to land successfully. Here we analyze the mechanism by which the squirrels recover from large body angular rates. We analyzed from the video that squirrels first use their tail to help stabilizing their head to visually fix a landing site. Then the tail starts to rotate to help stabilizing the body, preparing themselves for landing. To analyze further the mechanism of this tail use during mid-air, we built a multibody squirrel model and showed the righting strategy based on body inertia moment changes and active angular momentum transfer between axes. To validate the hypothesized strategy, we made a squirrel-like robot and demonstrated a fall-stabilizing experiment. Our results demonstrate squirrel’s long tail, despite comprising just 3% of body mass, can inertially stabilize a rapidly rotating body. This research contributes to better understanding the importance of long tails for righting mechanisms in animals living in complex environments such as trees.

Tail length evolution in deer mice: linking morphology, behavior and function

Determining how variation in morphology affects animal performance (and ultimately fitness) is key to understanding the complete process of evolutionary adaptation. Long tails have evolved many times in arboreal and semi-arboreal rodents; in deer mice, long tails have evolved repeatedly in populations occupying forested habit even within a single species (Peromyscus maniculatus). Here we use a combination of functional modeling, laboratory studies, and museum records to test hypotheses about the function of tail-length variation in deer mice. First, we use computational models, informed by museum records documenting natural variation in tail length, to test whether differences in tail morphology between forest and prairie subspecies can influence performance in behavioral contexts relevant for tail use. We find that the deer mouse tail plays little role in statically adjusting center of mass or in correcting body pitch and yaw, but rather it can affect body roll during arboreal locomotion. In this context, we find that even intraspecific tail-length variation could result in substantial differences in how much body rotation results from equivalent tail motions (i.e., tail effectiveness), but the relationship between commonly-used metrics of tail-length variation and effectiveness is non-linear. We further test whether caudal vertebra length, number, and shape are associated with differences in how much the tail can bend to curve around narrow substrates (i.e., tail curvature) and find that, as predicted, the shape of the caudal vertebrae is associated with intervertebral bending angle across taxa. However, although forest and prairie mice typically differ in both the length and number of caudal vertebrae, we do not find evidence that this pattern is the result of a functional trade-off related to tail curvature. Together, these results highlight how even simple models can both generate and exclude hypotheses about the functional consequences of trait variation for organismal-level performance.

Remarkable Spiral Galaxies in Dark Energy Survey Data Release 2

A visual study of spiral galaxies from a subset of spiral galaxies in the Dark Energy Survey Data Release 2 finds that a significant number show long tails of baryonic matter, often much longer than the apparent diameter of the galaxy. Examples from less than 10% of the candidates are shown here and their possible origin is discussed. The tails were only seen connected to spiral galaxies; no examples of tails connected to elliptical galaxies or to artifacts were found. In many examples the tail is associated with what appears to be a colliding galaxy, but in many others there is no sign of one. An intriguing possibility is that in the latter cases the tails are produced by an encounter with an unseen object, either a massive black hole or a compact galaxy with mostly dark matter.