Ossicular density in golden moles (Chrysochloridae)

The densities of middle ear ossicles of golden moles (family Chrysochloridae, order Afrosoricida) were measured using the buoyancy method. The internal structure of the malleus was examined by high-resolution computed tomography, and solid-state NMR was used to determine relative phosphorus content. The malleus density of the desert golden mole Eremitalpa granti (2.44 g/cm³) was found to be higher than that reported in the literature for any other terrestrial mammal, whereas the ossicles of other golden mole species are not unusually dense. The increased density in Eremitalpa mallei is apparently related both to a relative paucity of internal vascularization and to a high level of mineralization. This high density is expected to augment inertial bone conduction, used for the detection of seismic vibrations, while limiting the skull modifications needed to accommodate the disproportionately large malleus. The mallei of the two subspecies of E. granti, E. g. granti and E. g. namibensis, were found to differ considerably from one another in both size and shape.     

Morphology of the middle ear of golden moles (Chrysochloridae)

The middle ear structures of nine species of golden moles (family Chrysochloridae) were examined under the light microscope. Auditory structures of several of these species are described here for the first time in detail, the emphasis being on the ossicular apparatus. Confirming previous observations, some golden moles (e.g. Amblysomus species) have ossicles of a morphology typical of mammals, whereas others ( Chrysospalax , Chrysochloris , Cryptochloris and Eremitalpa species) have enormously hypertrophied mallei. Golden moles differ in the nature and extent of the interbullar connection, the shape of the tympanic membrane and that of the manubrium. The stapes has an unusual orientation, projecting dorsomedially from the incus. It has been proposed that hypertrophied ossicles in golden moles are adapted towards the detection of seismic vibrations. The functional morphology of the middle ear apparatus is reconsidered in this light, and it is proposed that adaptations towards low-frequency airborne hearing might have predisposed golden moles towards the evolution of seismic sensitivity through inertial bone conduction. The morphology of the middle ear apparatus sheds little light on the disputed ordinal position of the Chrysochloridae.     

Bone conduction and seismic sensitivity in golden moles (Chrysochloridae)

Some genera of golden moles are known to possess enormously hypertrophied auditory ossicles. These structures have been implicated as potentially mediating a form of inertial bone conduction, used by the golden mole to detect seismic vibrations. A simple model of ossicular inertial bone conduction, based on an existing model of the human middle ear from the literature, was used in an attempt to examine vibrational sensitivity in these animals. Those golden moles with hypertrophied ossicles are predicted to possess a sensitive inertial bone conduction response at frequencies below a few hundred hertz, whereas species lacking these middle ear adaptations are predicted to have a far less sensitive response in this ecologically important frequency range. An alternative mode of inertial bone conduction in golden moles, potentially conferring sensitivity to vertically-polarized seismic vibrations such as Rayleigh waves, is proposed. Certain behaviours of golden moles described in the literature are interpreted as augmenting seismic sensitivity.     

Functional and systematic implications of the ear in golden moles (Chrysochloridae)

Golden moles (Chrysochloridae) are fossorial mammals known to have unusual mallei. The aim of this study was to describe and quantify aspects of the auditory morphology of golden moles in order to determine their systematic and functional implications. Observations were made on skeletal material as well as histological sections. The results of this study do not support the separation of the genus Calcochloris from Amblysomus . It was found that the morphology shared by all the studied genera is indicative of specialization for hearing low frequency sound. The tympanic membrane to stapes footplate ratios, ossicular lever arm ratios and incudomallear joint morphology suggest low frequency specializations in genera with small mallear heads and high frequency specializations in genera with large mallear heads. However, the size and degree of trabeculation of the tympanic cavity are not consistent with this result. It is proposed that all golden moles are low frequency hearers with differences in their range of sensitivity according to how much time they spend foraging above ground.     

A phylogenetic estimate for golden moles (Mammalia,Afrotheria, Chrysochloridae)

Background  

Golden moles (Chrysochloridae) are small, subterranean, afrotherian mammals from South Africa and neighboring regions. Of the 21 species now recognized, some (e.g., Chrysochloris asiatica, Amblysomus hottentotus) are relatively common, whereas others (e.g., species of Chrysospalax, Cryptochloris, Neamblysomus) are rare and endangered. Here, we use a combined analysis of partial sequences of the nuclear GHR gene and morphological characters to derive a phylogeny of species in the family Chrysochloridae.     

Chromosomal evolution and distribution of telomeric repeats in golden moles (Chrysochloridae, Mammalia)

Golden moles (Chrysochloridae) are small, subterranean mammals endemic to sub-Saharan Africa that together with tenrecs constitute one of six orders in Afrotheria. Here we present a comprehensive karyotypic comparison among six species/subspecies of golden moles based on G-banding and chromosome painting. By expanding the species representation to include a further five species recently published in a companion paper, we were able to map the distribution of telomeric repeats in ten species/subspecies that are representative of six of the nine currently recognized genera. We conclude that: (i) the monophyly of Amblysomus is supported by the amplification of heterochromatin in several pericentric regions and one intrachromosomal rearrangement; (ii) A. hottentotus meesteri groups as sister to a clade that contains A. h. hottentotus, A. h. longiceps, A. h. pondoliae and A. robustus, an association that is underpinned by a shared intrachromosomal rearrangement and the detection of telomeric sequences in the centromeres of all chromosomes of the three A. hottentotus subspecies and A. robustus but, importantly, not in those of A. h. meesteri. These findings indicate an absence of gene flow suggesting that A. h. meesteri should be elevated to specific status. We hypothesize that the lack of gene flow may, in part, reflect hybrid dysgenesis resulting from abnormal meiotic segregation as a consequence of differences in the nature of the centromeric specific satellites; (iii) chromosomes 7 and 13 of Chrysochloris asiatica are fused in both Calcochloris obtusirostris and Eremitalpa granti, but that the position of the centromere in the fused chromosome differs in each species. This suggests that rather than being indicative of common ancestry, the fusion is more likely a convergent character which has arisen independently in each lineage. Furthermore our painting data show two centromeric shifts that are probably autapomorphic for C. obtusirostris. Finally, we conclude that (iv) golden moles are characterized by strong karyotypic conservatism but in marked contrast to the constrained rates of change exhibited by most species, A. robustus is unique in that three autapomorphic fissions define its evolutionary history, and hence the more extensive reshuffling of its genome.     

Functional morphology of the middle ear in Chlorotalpa golden moles (Mammalia, Chrysochloridae): predictions from three models

The ossicular apparatus of golden moles in the genus Chlorotalpa has received comparatively little attention in the literature, although the malleus is known to be intermediate in size between the unmodified malleus of Amblysomus and the hypertrophied mallei found in some other golden moles. In the present study, the middle ear structures of three Chlorotalpa species (C. duthieae, C. sclateri, and C. arendsi) are described. Measurements of middle ear structures were applied into three existing models of middle ear function. The predictions from the models suggest that the airborne hearing of Chlorotalpa species is limited to relatively low frequencies, but the impedance transformation by the middle ear apparatus is expected to be reasonably efficient. The sensitivity of the middle ear apparatus to inertial bone conduction is intermediate between that predicted for Amblysomus and that predicted for species with hypertrophied mallei. Hearing in fossorial mammals may be limited by factors other than the middle ear apparatus: the predictions for Chlorotalpa must therefore be treated with caution. However, a consideration of the intermediate middle ear morphology of Chlorotalpa species sheds some light on the origin of ossicular hypertrophy in golden moles. The limited enlargement of the malleus seen in Chlorotalpa is expected to have improved seismic sensitivity by bone conduction significantly at low frequencies, while airborne hearing might not have been adversely affected.     

Proximate bases of silver color in anhinga (Anhinga anhinga) feathers

Colors of living organisms are produced by selective light absorption from pigments and/or by light scattering from highly ordered nanostructures (i.e., structural color). While the physical bases of metallic colors of arthropods and fish are fairly well‐known, those of birds are not. Here we examine structurally based silver color and its production in feathers of the waterbird species Anhinga. This achromatic color is distinguished from grey by high specular reflectance, from white by low diffuse reflectance, and from both by high gloss. Light and electron microscopy revealed three modifications of feathers likely leading to silver color. First, proximal barbules were highly elongated and contained glossy black color at their base and white color at their pennulum. Second, this glossy black portion contained a single outer layer of keratin weakly bounded by melanosomes. Finally, the white portion contained a disordered amorphous matrix of keratin and air. Optical analyzes suggest that these structures produce, respectively, glossy black color through thin‐film interference and white color through incoherent light scattering. Silver color likely results from the combined reflectance of these adjacent structures. This represents a distinct mechanism for attaining silver colors that may have been partially derived through selection for display, thermoregulation or decreased hydrophobicity. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

How hollow melanosomes affect iridescent colour production in birds

Developmental constraints and trade-offs can limit diversity, but organisms have repeatedly evolved morphological innovations that overcome these limits by expanding the range and functionality of traits. Iridescent colours in birds are commonly produced by melanin-containing organelles (melanosomes) organized into nanostructured arrays within feather barbules. Variation in array type (e.g. multilayers and photonic crystals, PCs) is known to have remarkable effects on plumage colour, but the optical consequences of variation in melanosome shape remain poorly understood. Here, we used a combination of spectrophotometric, experimental and theoretical methods to test how melanosome hollowness—a morphological innovation largely restricted to birds—affects feather colour. Optical analyses of hexagonal close-packed arrays of hollow melanosomes in two species, wild turkeys (Meleagris gallopavo) and violet-backed starlings (Cinnyricinclus leucogaster), indicated that they function as two-dimensional PCs. Incorporation of a larger dataset and optical modelling showed that, compared with solid melanosomes, hollow melanosomes allow birds to produce distinct colours with the same energetically favourable, close-packed configurations. These data suggest that a morphological novelty has, at least in part, allowed birds to achieve their vast morphological and colour diversity.     

Locomotory activity in the Namib Desert golden mole Eremitalpa granti namibensis (Chrysochloridae)

Eremitalpa granti namibensis is a small, blind, subterranean insectivore endemic to the Namib Desert sand dunes. Unlike other subterranean mammals which seldom leave their burrow systems, the Namib mole forages extensively on the dune surface for its insectivorous prey. Activity phasing in this atypical mole was examined in the field and in the laboratory. Free-living moles were almost exclusively nocturnal, while moles kept in the laboratory were active day and night. These findings are discussed in relation to prey availability, predator pressure and avoidance of diurnal extremes. Light and temperature appeared to be important cues for daily onset and cessation of activity.     

Water metabolism in the Namib Desert golden mole, Eremitalpa granti namibensis (Chrysochloridae)

1. Laboratory and field studies of energy and water metabolism employing isotopic dilution methods examined the ability of Namib Desert moles to survive on an insect diet without drinking water. 2. Water independence is achieved through efficient renal function while low rates of energy usage and torpor are further effective in reducing overall water requirements.     

Shell colour polymorphism associated with substrate colour in the intertidal snail Littorina saxatilis Olivi (Prosobranchia: Littorinidae)

Littorina saxatilis Olivi (1792), the rough winkle, is highly polymorphic in shell colour. Shell colour frequencies were studied at six locations in south-western Wales, U.K., each at a geological contact between red sandstone and grey limestone or volcanic rock. At each site shell colour frequencies were determined in samples from the contact zone and on red or grey rock on either side. Highly significant associations were found between shell colour frequencies and substrate colour. Grey shells were always more common on grey rock than on red rock, and brown shells were usually more common on red than on grey rock, suggesting selection for cryptic colouration. Shell colour frequency differences were also found between replicate samples taken only 5 m apart from the same kind of rock, and between samples from the same kind of rock at the six study sites. These latter differences suggest that selection for camouflage is not the only factor involved in maintaining shell colour polymorphism in this species.     

Structural colour and iridescence in plants: the poorly studied relations of pigment colour

Background

Colour is a consequence of the optical properties of an object and the visual system of the animal perceiving it. Colour is produced through chemical and structural means, but structural colour has been relatively poorly studied in plants.

Scope

This Botanical Briefing describes the mechanisms by which structures can produce colour. In plants, as in animals, the most common mechanisms are multilayers and diffraction gratings. The functions of structural colour are then discussed. In animals, these colours act primarily as signals between members of the same species, although they can also play roles in camouflaging animals from their predators. In plants, multilayers are found predominantly in shade-plant leaves, suggesting a role either in photoprotection or in optimizing capture of photosynthetically active light. Diffraction gratings may be a surprisingly common feature of petals, and recent work has shown that they can be used by bees as cues to identify rewarding flowers.

Conclusions

Structural colour may be surprisingly frequent in the plant kingdom, playing important roles alongside pigment colour. Much remains to be discovered about its distribution, development and function.     

A simple method for measuring colour in wild animals: validation and use on chest patch colour in geladas (Theropithecus gelada)

Adaptive hypotheses about colour variation are widespread in behavioural ecology, and several methods of objective colour assessment have been proposed and validated for use in a wide variety of taxa. However, to date, the most objective and reliable methods of assessing colour are not readily applied to wild animals. In the present study, we present a simple method for assessing colour in unrestrained, wild subjects using digital photography. The method we describe uses a digital camera, a colour standard, and colour analysis software, and can be used to measure any part of the visible colour spectrum. We demonstrate that the method: (1) is accurate and precise across different light conditions; (2) satisfies previous criteria regarding linearity and red, green, and blue equality; and (3) can be independently validated visually. In contrast with previous digital methods, this method can be used under natural light conditions and can be readily applied to subjects in their natural habitat. To illustrate this, we use the method to measure chest colour in wild geladas ( Theropithecus gelada ). Unique among primates, geladas have a red patch of skin on their chest and neck, which, for males, is thought to be a sexually selected signal. Offering some support to this hypothesis, we found differences in chest 'redness' for males across different age groups, with males in their reproductive prime exhibiting the reddest chests.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 231–240.     

Iridescent ultraviolet signal in the orange sulphur butterfly (Colias eurytheme): spatial, temporal and spectral properties

Many of nature's most striking animal colours are iridescent, exhibiting a high degree of spectral purity and strong angular dependence of intensity and hue. Although a growing number of studies have detailed the intricate mechanisms responsible for producing iridescent colours, few attempts have been made to describe their dynamic appearance in ecologically and behaviourally realistic contexts. We suggest that the optical properties unique to iridescent structural colours are important for understanding how they function as signals during behavioural interactions. Using males of the orange sulphur butterfly, Colias eurytheme , which exhibit an iridescent ultraviolet (UV) reflectance on their dorsal wing surfaces, we develop a holistic framework for inferring the appearance of this signal to conspecifics under field conditions that incorporate data on their spectral sensitivity. We show that, during flight, the UV signal is brightest within a wing beat cycle when viewed from directly above the male. Spectral properties of the signal under natural lighting indicate that male wing colour should be readily perceived and distinguished from that of females and from the dark green visual background of UV-absorbing vegetation. Finally, our analyses permit predictions regarding how signal senders and receivers should orientate themselves for maximal transmission and reception of this ultraviolet iridescent signal.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 349–364.     

Habitat use by radio-tagged Namib Desert golden moles (Eremitalpa granti namibensis)

The Namib Desert golden mole (Eremitalpa granti namibensis) is morphologically, physiologically and behaviourally specialized for living in the harsh loose‐sand desert. Ecological studies have relied on visually tracking animals on the surface of sand dunes. A radio tag would allow individuals to be more reliably located, even while under the sand. We developed a radio attachment and gathered preliminary data on winter habitat use by six individuals during 21 days. We compare data from previous studies and suggest that the greater diurnal activity, smaller home ranges, and more restricted movement patterns that we found are related to the unusual thermal and metabolic biology of Eremitalpa.     

Reversible colour change in Arthropoda

The mechanisms and functions of reversible colour change in arthropods are highly diverse despite, or perhaps due to, the presence of an exoskeleton. Physiological colour changes, which have been recorded in 90 arthropod species, are rapid and are the result of changes in the positioning of microstructures or pigments, or in the refractive index of layers in the integument. By contrast, morphological colour changes, documented in 31 species, involve the anabolism or catabolism of components (e.g. pigments) directly related to the observable colour. In this review we highlight the diversity of mechanisms by which reversible colour change occurs and the evolutionary context and diversity of arthropod taxa in which it has been observed. Further, we discuss the functions of reversible colour change so far proposed, review the limited behavioural and ecological data, and argue that the field requires phylogenetically controlled approaches to understanding the evolution of reversible colour change. Finally, we encourage biologists to explore new model systems for colour change and to engage scientists from other disciplines; continued cross‐disciplinary collaboration is the most promising approach to this nexus of biology, physics, and chemistry.     

Home range and movements of the Namib Desert golden mole, Eremitalpa granti namibensis (Chrysochloridae)

Eremitalpa granti namibensis is a small, blind, subterranean insectivore endemic to the Namib desert sand dunes. Unlike most other subterranean mammals, E. g. namibensis lacks a permanent burrow system and is a surface forager. Population density and home range utilization were studied by following surface trails and capture, mark and recapture. Population density was low but stable and home range size large, a reflection of the low food availability in the Namib dune environment. No permanent nests or burrows were found while the pattern of home range utilization was nomadic but circumscribed. Home ranges overlapped with those of neighbouring animals.     

Seasonal colour and antipredator behaviour in Etheostoma (Percidae)

This study examined how colour varies across season and sex in the fantail darter Etheostoma flabellare and the banded darter Etheostoma zonale. Etheostoma flabellare has male‐only parental care and exhibited slight sexual dimorphism in overall colour, with no discernible effect of season on colour; whereas E. zonale does not have parental care and exhibited substantial sexual dimorphism in colour, but only in the breeding season. Additionally, antipredator behaviour of E. zonale was compared between males that were fully coloured during the breeding season and males that were partially coloured at that time, but the effects of colour and season were not consistent across males.