Comparative anatomy of the caudate nucleus in canids and felids: Associations with brain size, curvature, cross-sectional properties, and behavioral ecology

The evolutionary history of canids and felids is marked by a deep time separation that has uniquely shaped their behavior and phenotype toward refined predatory abilities. The caudate nucleus is a subcortical brain structure associated with both motor control and cognitive, emotional, and executive functions. We used a combination of three-dimensional imaging, allometric scaling, and structural analyses to compare the size and shape characteristics of the caudate nucleus. The sample consisted of MRI scan data obtained from six canid species (Canis lupus lupus, Canis latrans, Chrysocyon brachyurus, Lycaon pictus, Vulpes vulpes, Vulpes zerda), two canid subspecies (Canis lupus familiaris, Canis lupus dingo), as well as three felids (Panthera tigris, Panthera uncia, Felis silvestris catus). Results revealed marked conservation in the scaling and shape attributes of the caudate nucleus across species, with only slight deviations. We hypothesize that observed differences in caudate nucleus size and structure for the domestic canids are reflective of enhanced cognitive and emotional pathways that possibly emerged during domestication.

Ancient DNA from the Asiatic Wild Dog (Cuon alpinus) from Europe

The Asiatic wild dog (Cuon alpinus), restricted today largely to South and Southeast Asia, was widespread throughout Eurasia and even reached North America during the Pleistocene. Like many other species, it suffered from a huge range loss towards the end of the Pleistocene and went extinct in most of its former distribution. The fossil record of the dhole is scattered and the identification of fossils can be complicated by an overlap in size and a high morphological similarity between dholes and other canid species. We generated almost complete mitochondrial genomes for six putative dhole fossils from Europe. By using three lines of evidence, i.e., the number of reads mapping to various canid mitochondrial genomes, the evaluation and quantification of the mapping evenness along the reference genomes and phylogenetic analysis, we were able to identify two out of six samples as dhole, whereas four samples represent wolf fossils. This highlights the contribution genetic data can make when trying to identify the species affiliation of fossil specimens. The ancient dhole sequences are highly divergent when compared to modern dhole sequences, but the scarcity of dhole data for comparison impedes a more extensive analysis.

Selection and Constraints in the Ecomorphological Adaptive Evolution of the Skull of Living Canidae (Carnivora, Mammalia)

The association between phenotype and ecology is essential for understanding the environmental drivers of morphological evolution. This is a particularly challenging task when dealing with complex traits, such as the skull, where multiple selective pressures are at play and evolution might be constrained by ontogenetic and genetic factors. I integrate morphometric tools, comparative methods, and quantitative genetics to investigate how ontogenetic constraints and selection might have interacted during the evolution of the skull in extant Canidae. The results confirm that the evolution of cranial morphology was largely adaptive and molded by changes in diet composition. While the investigation of the adaptive landscape reveals two main selective lines of least resistance (one associated with size and one associated with functional shape features), rates of evolution along size were higher than those found for shape dimensions, suggesting the influence of constraints on morphological evolution. Structural modeling analyses revealed that size, which is the line of most genetic/phenotypic variation, might have acted as a constraint, negatively impacting dietary evolution. Constraints might have been overcome in the case of selection for the consumption of large prey by associating strong selection along both size and shape directions. The results obtained here show that microevolutionary constraints may have played a role in shaping macroevolutionary patterns of morphological evolution.

Evaluation of the Applicability of Different Age Determination Methods for Estimating Age of the Endangered African Wild Dog (Lycaon Pictus)

African wild dogs (Lycaon pictus) are endangered and their population continues to decline throughout their range. Given their conservation status, more research focused on their population dynamics, population growth and age specific mortality is needed and this requires reliable estimates of age and age of mortality. Various age determination methods from teeth and skull measurements have been applied in numerous studies and it is fundamental to test the validity of these methods and their applicability to different species. In this study we assessed the accuracy of estimating chronological age and age class of African wild dogs, from dental age measured by (i) counting cementum annuli (ii) pulp cavity/tooth width ratio, (iii) tooth wear (measured by tooth crown height) (iv) tooth wear (measured by tooth crown width/crown height ratio) (v) tooth weight and (vi) skull measurements (length, width and height). A sample of 29 African wild dog skulls, from opportunistically located carcasses was analysed. Linear and ordinal regression analysis was done to investigate the performance of each of the six age determination methods in predicting wild dog chronological age and age class. Counting cementum annuli was the most accurate method for estimating chronological age of wild dogs with a 79% predictive capacity, while pulp cavity/tooth width ratio was also a reliable method with a 68% predictive capacity. Counting cementum annuli and pulp cavity/tooth width ratio were again the most accurate methods for separating wild dogs into three age classes (6-24 months; 25-60 months and > 60 months), with a McFadden's Pseudo-R2 of 0.705 and 0.412 respectively. The use of the cementum annuli method is recommended when estimating age of wild dogs since it is the most reliable method. However, its use is limited as it requires tooth extraction and shipping, is time consuming and expensive, and is not applicable to living individuals. Pulp cavity/tooth width ratio is a moderately reliable method for estimating both chronological age and age class. This method gives a balance between accuracy, cost and practicability, therefore it is recommended when precise age estimations are not paramount.

Scaling and Accommodation of Jaw Adductor Muscles in Canidae

The masticatory apparatus amongst closely related carnivoran species raises intriguing questions about the interplay between allometry, function, and phylogeny in defining interspecific variations of cranial morphology. Here we describe the gross structure of the jaw adductor muscles of several species of canid, and then examine how the muscles are scaled across the range of body sizes, phylogenies, and trophic groups. We also consider how the muscles are accommodated on the skull, and how this is influenced by differences of endocranial size. Data were collected for a suite of morphological metrics, including body mass, endocranial volume, and muscle masses and we used geometric morphometric shape analysis to reveal associated form changes. We find that all jaw adductor muscles scale isometrically against body mass, regardless of phylogeny or trophic group, but that endocranial volume scales with negative allometry against body mass. These findings suggest that head shape is partly influenced by the need to house isometrically scaling muscles on a neurocranium scaling with negative allometry. Principal component analysis suggests that skull shape changes, such as the relatively wide zygomatic arches and large sagittal crests seen in species with higher body masses, allow the skull to accommodate a relative enlargement of the jaw adductors compared with the endocranium. Anat Rec, 299:951-966, 2016. © 2016 The Authors The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology Published by Wiley Periodicals, Inc.

Potential Sources of High Frequency and Biphonic Vocalization in the Dhole (Cuon alpinus)

Biphonation, i.e. two independent fundamental frequencies in a call spectrum, is a prominent feature of vocal activity in dog-like canids. Dog-like canids can produce a low (f0) and a high (g0) fundamental frequency simultaneously. In contrast, fox-like canids are only capable of producing the low fundamental frequency (f0). Using a comparative anatomical approach for revealing macroscopic structures potentially responsible for canid biphonation, we investigated the vocal anatomy for 4 (1 male, 3 female) captive dholes (Cuon alpinus) and for 2 (1 male, 1 female) wild red fox (Vulpes vulpes). In addition, we analyzed the acoustic structure of vocalizations in the same dholes that served postmortem as specimens for the anatomical investigation. All study dholes produced both high-frequency and biphonic calls. The anatomical reconstructions revealed that the vocal morphologies of the dhole are very similar to those of the red fox. These results suggest that the high-frequency and biphonic calls in dog-like canids can be produced without specific anatomical adaptations of the sound-producing structures. We discuss possible production modes for the high-frequency and biphonic calls involving laryngeal and nasal structures.

The late Neopleistocene dhole (Carnivora, Canidae, Cuon alpinus Pallas, 1811) from the Urals

Morphotypic and morphometric analyses of the M2 tooth found in the Late Pleistocene deposits of the Ignatievskaya Cave (southern Urals) demonstrate that this tooth belongs to the dhole (Cuon alpinus Pallas, 1811). This is the first reliable evidence for the presence of the dhole in the Urals. Radiocarbon dating and associated theriofauna allow the tooth to be dated to the first half of the late Neopleistocene or, more precisely, to marine isotope stages (MISs) 3 and 4.

A pathological Late Pleistocene canid from San Sidero (Italy): implications for social- and feeding-behaviour

Evidence of diseases on vertebrate fossil bones can provide detailed information on many aspects of extinct animals. This study focused on pathological craniodental remains (left maxilla and dentary) referred to the canid Cuon alpinus unearthed from a Late Pleistocene karst filling deposit at San Sidero (Apulia, southern Italy). These fossils show clear evidence of a chronic periodontitis that caused the animal's death. Clinical diagnosis of the disease and the timing of its development have been defined on the basis of a veterinary odontostomatology approach, in addition to radiographic and tomographic techniques. From the initiation of the infection until death, a time span of at least 6 months occurred, and three main steps have been defined: (1) the bacterial infections of the buccal cavity turning into severe periodontitis, (2) the fracture of the lower carnassial and (3) the loss of teeth due to the worsening infection that deformed and/or eroded maxillary and mandibular bones and enlarged alveoli. The analysis of the palaeopathology also provides information about the biomechanics of the bite, on the feeding behaviour and on the relationships of injured members in a pack of Late Pleistocene canids.

Gross morphometric study of the eyeball and tongue of the Nigerian local dog

This study investigates the morphometry of two sense organs, the eyeball and tongue, of the Nigerian local dog (11 males, 14 females), all aged 2 years and above. The samples were grouped according to gender and weight (up to 12 kg or above that weight). The average values obtained for the weights of the left and right eyeballs and the tongue were 3.77 +/- 0.51 g, 3.68 +/- 0.74 g and 2.96 +/- 0.38 g respectively, while the length of the tongue, its thickness and width at the root and apex were 14.20 +/- 2.29 cm, 0.87 +/- 0.30 cm, and 0.21 +/- 0.05 cm respectively. The circumferences of the eyeballs (antero-posterior, mediolateral and peri-orbital) were all found to be higher in females, except the antero-posterior circumference of left eye, in spite of heavier eyeballs in males. Also, the females showed a wider rima oris and higher values for most of the tongue measurements. A positive correlation existed between the weight of the animal and that of the head and tongue, while a negative correlation was observed between the body weight and the weight of the eyeballs. This report highlights the presence of sexual dimorphism and mild lateral asymmetry in this rarely reported breed of dog. The data obtained from this study may find application in feeding physiology, ophthalmic clinical manipulations and comparative anatomy.

Similarities of the neuronal circuit for the induction of fictive vomiting between ferrets and dogs

Previous studies suggested that the following neuronal circuit participates in the induction of vomiting by afferent vagal stimulation in decerebrated paralyzed dogs: (1) afferent fibers of the vagus nerve, (2) neurons of the solitary nucleus (NTS), (3) neurons of the prodromal sign center near the semicompact part of the nucleus ambiguus (scAMB), (4) neurons of the central pattern generator in the reticular area adjacent to the compact part of nucleus ambiguus (cAMB), (5) respiratory premotor neurons in the caudal medulla, (6) motor neurons of the diaphragm and abdominal muscles. However, the commonality of this neuronal circuit in different species has not yet been clarified. Thus, this study was conducted to clarify this point. This study clarified for the first time that fictive vomiting in decerebrated paralyzed ferrets could be induced by vagal stimulation, and could be identified by centrifugal activity patterns of the phrenic and abdominal muscle nerves. The distributions of c-Fos immunoreactive neurons in the NTS, scAMB and cAMB areas in ferrets that exhibited fictive vomiting were denser than those in ferrets that did not. Application of the nonNMDA receptor antagonist into the 4th ventricle produced the reversible suppression of fictive vomiting. The NK1 receptor immunoreactive puncta were found in the reticular area adjacent to the scAMB. Microinjections of NK1 receptor antagonist into the reticular areas on both sides abolished fictive vomiting. All these results in the ferrets are identical with results previously obtained in dogs and cats. Therefore, this suggests that the above neuronal circuit commonly participates in the induction of emesis in these animal species.

Retrograde labeling reveals extensive distribution of genioglossal motoneurons possessing 5-HT2A receptors throughout the hypoglossal nucleus of adult dogs

Inspiratory hypoglossal motoneurons (IHMNs) innervate the muscles of the tongue and play an important role in maintaining upper airway patency. However, this may be reduced during sleep and by sedatives, potent analgesics, and volatile anesthetics. The genioglossal (GG) muscle is the main protruder and depressor muscle of the tongue and contributes to upper airway patency during inspiration. In vitro data suggest that serotonin (5-hydroxytryptamine, 5-HT), via the 5-HT(2A) receptor (5-HT(2A)R) subtype, plays a key role in controlling the excitability of IHMNs. The distribution of GG motoneurons (GGMNs) within the hypoglossal (XII) nucleus has not been studied in the adult dog. Further, it is uncertain whether the 5-HT(2A)R is located on GGMNs in the adult dog. We therefore used the cholera toxin B (CTB) subunit as a retrograde tracer to map the location of GGMNs in combination with immunofluorescent labeling to determine the presence and colocalization of 5-HT(2A)R within the XII nucleus in adult mongrel dogs. Injection of CTB into the GG muscle resulted in retrogradely labeled cells in a compact column throughout the XII nucleus, extending from 0.75 mm caudal to 3.45 mm rostral to the obex. Fluorescence immunohistochemistry revealed extensive 5-HT(2A)R labeling on CTB-labeled GGMNs. Identification of the 5-HT(2A)R on GGMNs in the XII nucleus of the adult dog supports in vitro data and suggests a physiological role for this receptor subtype in controlling the excitability of GGMNs, which contribute to the maintenance of upper airway patency.