Claw Keratin Research Articles

Ontogenetic dependence of Nile crocodile (Crocodylus niloticus) isotope diet‐to‐tissue discrimination factors

The diet of wild Nile crocodiles (Crocodylus niloticus) is difficult to assess because they are cryptic and nocturnal predators that are extremely sensitive to disturbance by observers, and stomach content analysis is challenging, especially in large specimens. Stable light isotope analysis provides a means of assessing their diet, but diet-to-tissue discrimination factors have yet to be established for the species. Isotope ratio (15 N/14 N and 13 C/12 C expressed as δ15 N and δ13 C) analyses of scutes, claws, and blood of farmed crocodiles of different sizes were compared with the isotope values of their lifelong diet, which comprises chickens from a single supplier. Systematic size dependence in the diet-to-tissue discrimination factors for scute collagen, scute keratin, and claw keratin is described in regression relationships against the snout to vent length. Fixed values are presented for erythrocytes and blood plasma because blood was not sampled from juveniles. The diet-to-tissue discrimination factors help assess the diet of wild crocodiles. The diet of crocodiles from Lake Flag Boshielo shows a clear ontogenic shift, as has been seen in other studies, and the results strongly indicate a dependence on the terrestrial food web rather than a fish diet. That this population may exploit a terrestrial diet highlights potential conflicts for conserving Nile crocodiles outside protected areas.

Raman spectroscopy predicts the link between claw keratin and bone collagen structure in a rodent model of oestrogen deficiency

Osteoporosis is a common disease characterised by reduced bone mass and an increased risk of fragility fractures. Low bone mineral density is known to significantly increase the risk of osteoporotic fractures, however, the majority of non-traumatic fractures occur in individuals with a bone mineral density too high to be classified as osteoporotic. Therefore, there is an urgent need to investigate aspects of bone health, other than bone mass, that can predict the risk of fracture. Here, we successfully predicted association between bone collagen and nail keratin in relation to bone loss due to oestrogen deficiency using Raman spectroscopy. Raman signal signature successfully discriminated between ovariectomised rats and their sham controls with a high degree of accuracy for the bone (sensitivity 89%, specificity 91%) and claw tissue (sensitivity 89%, specificity 82%). When tested in an independent set of claw samples the classifier gave 92% sensitivity and 85% specificity. Comparison of the spectral changes occurring in the bone tissue with the changes occurring in the keratin showed a number of common features that could be attributed to common changes in the structure of bone collagen and claw keratin. This study established that systemic oestrogen deficiency mediates parallel structural changes in both the claw (primarily keratin) and bone proteins (primarily collagen). This strengthens the hypothesis that nail keratin can act as a surrogate marker of bone protein status where systemic processes induce changes.

Genomic regression of claw keratin, taste receptor and light-associated genes provides insights into biology and evolutionary origins of snakes

Regressive evolution of anatomical traits often corresponds with the regression of genomic loci underlying such characters. As such, studying patterns of gene loss can be instrumental in addressing questions of gene function, resolving conflicting results from anatomical studies, and understanding the evolutionary history of clades. The evolutionary origins of snakes involved the regression of a number of anatomical traits, including limbs, taste buds and the visual system, and by analyzing serpent genomes, I was able to test three hypotheses associated with the regression of these features. The first concerns two keratins that are putatively specific to claws. Both genes that encode these keratins are pseudogenized/deleted in snake genomes, providing additional evidence of claw-specificity. The second hypothesis is that snakes lack taste buds, an issue complicated by conflicting results in the literature. I found evidence that different snakes have lost one or more taste receptors, but all snakes examined retained at least one gustatory channel. The final hypothesis addressed is that the earliest snakes were adapted to a dim light niche. I found evidence of deleted and pseudogenized genes with light-associated functions in snakes, demonstrating a pattern of gene loss similar to other dim light-adapted clades. Molecular dating estimates suggest that dim light adaptation preceded the loss of limbs, providing some bearing on interpretations of the ecological origins of snakes.

Testing the niche variation hypothesis with a measure of body condition

Individual variation and fitness are cornerstones of evolution by natural selection. The niche variation hypothesis (NVH) posits that when interspecific competition is relaxed, intraspecific competition should drive niche expansion by selection favoring use of novel resources and that among‐individual variation should confer a selective advantage. Population‐level niche expansion could be achieved by all individuals using all available resources, or by each individual using a unique combination of resources, thereby increasing among‐individual dietary niche variation. Although individual variation can lead to species‐level evolutionary and ecological change, observed variation does not ensure a beneficial outcome. We used carbon and nitrogen stable isotope analysis of claw keratin and a Bayesian stable isotope mixing model to estimate the summer (July–September) assimilated diet of individual female black Ursus americanus and brown U. arctos bears. We quantified variation in dietary niche in both populations, and assessed diet relative to percentage body fat. We hypothesized that if the NVH held, percentage body fat would be similar for individuals of the same species across much of the dietary range of observed proportional salmon contributions to individual bear diets. Although we found greater differences in dietary niches between than within species, we observed greater among‐individual dietary variation in the brown bear population. Moreover, we found that within each species individual female bears achieved similar ranges of percentage body fat at various levels of salmon in the diet. Our results provide support for the NVH. Linking individual dietary niches to measures of physiological condition related to fitness can offer new insights into eco‐evolutionary processes related to food resource use.

Tracking animal movement by comparing trace element signatures in claws to spatial variability of elements in soils

Biogeochemical markers in ecology have provided a useful means for indicating geographic origin and movement patterns of species on various temporal and spatial scales. We used trace element analysis to resolve spatial and habitat-specific environmental gradients in elemental distributions that could be used to infer geographic origin and habitat association in a model terrestrial carnivore: American badger (Taxidea taxus jacksoni). To accomplish this, we generated element base-maps using spatial principal component analysis, and assessed habitat-specific signatures using multivariate statistics from soil element concentrations in southwestern Ontario, Canada. Using canonical correlation analysis (CCA) we also test whether element variability in the claw keratin of a terrestrial carnivore could be explained by the chemical variability in the soils of the local environment. Results demonstrated that trace element signatures in soils vary locally with land use practices and soil texture type and broadly with the underlying geology. CCA results suggest that chemical profiles in claws can be linked to the surrounding chemical environment, providing evidence that geographic patterns in mammalian movement can be discerned on the basis of claw chemistry. From this, we conclude that geographic assignment of individuals based on element profiles in their tissues and referenced against soil elemental distributions would be coarse (at a spatial scale of 100–1000km, depending on the chemical heterogeneity of the landscape), but could be used to assess origin of highly mobile animals or habitat association of individuals. Compared to stable isotope analysis, the assessment of trace elements can provide a much greater level of detail in backcasting animal movement pathways.

Trace Elements in Claw Keratin as Temporally Explicit Indicators of Geographic Origin in Terrestrial Mammals

Biogeochemical markers in ecology are useful for indicating geographic origin and movement patterns of species on various temporal and spatial scales. By assessing these markers in a tissue that is chemically inert once formed (e.g., claws) and is grown incrementally (i.e., deposited in layers), changes in an individual's foraging environment would be captured in the chemical signatures in these tissues. To determine whether trace elements can be used as a marker to track movement in terrestrial carnivores, we resolved multi-elemental data at a fine spatial scale in the claw keratin of a model species (Taxidea taxus) using high resolution laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS). The unique chemical signatures we detected in claws suggested that these chemical variations were, in part, a reflection of the chemical environment and were not be attributable to sex or random deposition. Neighbouring claw samples were not more chemically related than distant ones, which suggests that local differences in chemical composition (e.g., habitat type) may have a stronger influence on claw chemistry than large-scale patterns in trace element variation associated with underlying geology. Our findings illustrated that temporallyexplicit chemical profiles in the blade horn keratin of mammalian claws may be used to examine endogenous uptake of trace element signatures from the local environment and serve as tool to assist in reconstructing animal movement pathways.

Deleterious Mutations of a Claw Keratin in Multiple Taxa of Reptiles

We have recently shown that homologs of mammalian hair keratins are expressed in the claws of the green anole lizard, Anolis carolinensis. To test whether reptilian hair keratin homologs are functionally associated with claws, we investigated the conservation of the prototypical reptilian hair keratin homolog, hard acidic keratin 1 (HA1), in representative species from all main clades of reptiles. A complete cDNA of HA1 was cloned from the claw-forming epidermis of the lacertid lizard Podarcis sicula, and partial HA1 gene sequences could be amplified from genomic DNA of tuatara, lizards, gekkos, turtles, and crocodiles. In contrast, the HA1 gene of the limbless slow worm, Anguis fragilis, and of two species of turtles contained at least one deleterious mutation. Moreover, an HA1 gene was undetectable in the softshell turtle, snakes, and birds. Mapping the presence and absence of HA1 onto the phylogenetic tree of sauropsids suggested that the HA1 gene has been lost independently in several lineages of reptiles. The species distribution of HA1 is compatible with the hypothesis of a primary function of HA1 in claws but also shows that the formation of reptilian claws does not strictly depend on this keratin.

Variability in the growth patterns of the cornified claw sheath among vertebrates: implications for using biogeochemistry to study animal movement

We review the role of biogeochemical signatures, such as stable isotopes and trace elements, in the cornified claw tissue as a means of studying movement and foraging behaviour of vertebrates because this approach is noninvasive and can capture contemporary and historic signatures. Because biogeochemical techniques are still relatively new in studies of animal movement, we are only beginning to understand how the growth patterns of the cornified claw sheath may affect our ability to interpret the biogeochemical signals in these tissues. To move towards resolving this, we review the morphology of the epidermal cornified claw sheath in several taxa that illustrate substantial variation in growth patterns both between taxa and between individual distinct claw regions. For instance, in mammalian claws, deposition of keratinizing cells from the epidermis is nonlinear because the claw tip is composed of old and new cornified epidermal cells, whereas the cornified blade horn covering the claw’s lateral walls is deposited continuously and without assortment, providing unbroken time-series data. We also consider patterns of growth in mammalian hooves, as well as reptilian, avian, and amphibian cornified claw sheaths, and address the need for expanded research in this field. We conclude this synthesis by describing a noninvasive technique for monitoring growth rates in a model mammal, the American badger ( Taxidea taxus (Schreber, 1777)), and provide guidelines for future sampling of claw keratin, which will improve our ability to back-calculate the time of biogeochemical integration into this tissue.

The influence of hydration on the tensile and compressive properties of avian keratinous tissues

Despite recent research exploring the elastic properties of avian keratins, data on failure properties are less common in the literature. In this paper we present data on the failure properties and moduli of both avian feather and claw keratin in tension and the modulus of claw keratin in compression. Increased water content acts to decrease stiffness and strength but to increase strain at failure. The modulus of claw did not differ significantly when tested under tension and compression.

Hydration sensitivity of ostrich claw keratin

In a recent paper [1] I reported the first measurements of the elastic properties of the keratinous covering of the ostrich claw. Of course, as well as having to transmit and withstand the substantial [2] forces during locomotion the claw material too must resist abrasive wear from contact with substrates. Ostriches (Struthio camelus L.) naturally inhabit arid desert or savannah regions of the African continent, however since antiquity [3] they have become extensively domesticated and now occur in temperate environments where the climate is cooler and more damp. Indeed, it has been shown that ostriches will alter their behavior when faced with a cold, damp northern European climate [4]. Under such conditions it is likely that the claw material will absorb water from the environment and its water content will increase. We know that increasing the water content of the α-keratin, from which the claws and hairs of mammals are composed, leads to reduced stiffness, strength and hardness [5–8] but toughness is highest at intermediate hydration levels [9]. We do not have a comparable body of literature relating to the β-keratin occurring in birds; only one study has identified that increased water content leads to decreases in stiffness and strength of feather keratin [10]. The effect of two levels of hydration on microhardness and Young’s modulus was determined on samples of claw keratin from six ostriches. For microhardness testing small cubes (∼9 mm3) were tested after polishing with 600 and 1200 grit “wet and dry” paper and a final napping with 0.5 micron diamond cutting paste. Vickers microhardness tests were carried out using a Zwick 3212 test machine with a test load of 20 g. Indenter descent time and dwell time of 15 s were allowed and a 45 s period allowed prior to measuring the indentation. Specimens were first tested “dry” (conditioned at 50% RH) and then “wet” after 72 h immersion in distilled water. Six specimens were tested, their hardness being the mean of ten indentations at random points over their surfaces. The tensile Young’s modulus was determined for specimens having a cross-sectional area of approximately 1 mm2 and a mean length of 9.77 (SEM = 0.37) mm. Specimens for testing “wet” and “dry” were cut from adjacent areas of claw to minimise the effect of any regional variation in properties. Tests were conducted by using a Davenport-Nene test machine and were loaded using a low test speed (1 mm min−1). The test machine and grips had been calibrated for compliance and a correction factor applied to measured

The structure and expression of a gene encoding chick claw keratin

A cDNA library was constructed from embryonic chick claw mRNA and a claw keratin (cKer)-encoding clone was isolated and sequenced. Subsequently, a genomic clone, containing four cKer-encoding genes (cKer) was isolated and one of the genes (cKer1) was completely sequenced. The cKerl gene appears to be differentially expressed in the keratinizing tissue appendages of the embryonic chick, being abundantly expressed in the claw and at a low level in feather tissue. Comparison of the deduced amino acid (aa) sequence of the cKer to those of feather (fKer) and scale keratins (sKer) showed that the regions conserved between fKer and sKer are also found in the cKer. The glycine-rich as repeat region characteristic of sKer is also present in a shortened form in the cKer sequence. Like the fKer genes (fKer) and the feather histidine-rich protein-encoding gene (HRP), the cKer1 gene also contains one intron which interrupts the 5'-noncoding region at an equivalent position to that found in the fKer and HRP genes. Genomic Southern analysis using the cKer cDNA as a probe indicated the presence of several related genes in the chick genome.

Variations in some inorganic components and physical properties of claw keratin associated with claw disease in the British Friesian cow

Horn hardness, water content and mineral composition were measured in the feet of 42 Friesian cows, 27 with no history and 15 with a history of lameness. Water content and magnesium concentration increased with age, potassium concentration was lower in the hooves of pregnant animals, but none of the variates was affected by lactation. Horn hardness was related to composition, the harder keratin of the claw wall containing more calcium, copper, zinc and phosphorus and lower concentrations of water, sodium, potassium and iron than the heel. Zinc concentration was lower in the horn of lame animals but those of magnesium and copper were increased. Mineral composition varied significantly with respect to the position of the horn in the claw (heel, sole or wall). The results are discussed with regard to the function of the horn constituents.

The tryptophan-rich keratin protein fraction of claws of the lizard Varanus gouldii

1. 1. Claw keratin of the lizard, Varanus gouldii, is composed mainly of 13,000 m r proteins rich in glycine and cystine. This study deals with a tryptophan-rich group of about 20 constituent proteins comprising about one-third of the mass. 2. 2. As S- carboxymethylkerateines , these proteins were separated by fractional precipitation and gel filtration, then characterized by amino acid analysis, end group analysis, electrophoresis and ultracentrifugation. 3. 3. It is considered that the majority of lizard claw proteins are more closely allied to those of avian beak and claw than feather proteins. 4. 4. Claw keratin also contains minor proteins which resemble mammalian keratin high-tyrosine proteins.

Effects of High Air Temperature on the Bill and Claw Keratin Structures of the Tree Sparrow

Effects of High Air Temperature on the Bill and Claw Keratin Structures of the Tree Sparrow