Forelimb indicators of prey‐size preference in the Felidae

The forelimbs, along with the crania, are an essential part of the prey‐killing apparatus in cats. Linear morphometrics of the forelimbs were used to determine the morphological differences between felids that specialize on large prey, small prey, or mixed prey. We also compared the scaling of felid forelimbs to those of canids to test whether prey capture strategies affect forelimb scaling. Results suggest that large prey specialists have relatively robust forelimbs when compared with smaller prey specialists. This includes relatively more robust humeri and radii, relatively larger distal ends of the humerus, and relatively larger articular areas of the humerus and radius. Large prey specialists also had relatively longer olecranon processes of the ulna and wider proximal paws. These characters are all important for subduing large prey while the cat positions itself for the killing bite. Small prey specialists have relatively longer distal limb elements for swift prey capture, and mixed prey specialists had intermediate values with relatively more robust metacarpals. Arboreal felids also had more robust limbs. They had relatively longer proximal phalanges for better grip while climbing, and a relatively short brachial index (radius to humerus ratio). Additionally, we found that felids and canids differ in forelimb scaling, which emphasizes the dual use of forelimbs for locomotion and prey capture in felids. This morphometric technique worked well to separate prey‐size preference in felids, but did not work as well to separate locomotor groups, as scansorial and terrestrial felids were not clearly distinguished. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Radiographs Reveal Exceptional Forelimb Strength in the Sabertooth Cat,Smilodon fatalis

Background

The sabertooth cat, Smilodon fatalis, was an enigmatic predator without a true living analog. Their elongate canine teeth were more vulnerable to fracture than those of modern felids, making it imperative for them to immobilize prey with their forelimbs when making a kill. As a result, their need for heavily muscled forelimbs likely exceeded that of modern felids and thus should be reflected in their skeletons. Previous studies on forelimb bones of S. fatalis found them to be relatively robust but did not quantify their ability to withstand loading.

Methodology/Principal Findings

Using radiographs of the sabertooth cat, Smilodon fatalis, 28 extant felid species, and the larger, extinct American lion Panthera atrox, we measured cross-sectional properties of the humerus and femur to provide the first estimates of limb bone strength in bending and torsion. We found that the humeri of Smilodon were reinforced by cortical thickening to a greater degree than those observed in any living felid, or the much larger P. atrox. The femur of Smilodon also was thickened but not beyond the normal variation found in any other felid measured.

Conclusions/Significance

Based on the cross-sectional properties of its humerus, we interpret that Smilodon was a powerful predator that differed from extant felids in its greater ability to subdue prey using the forelimbs. This enhanced forelimb strength was part of an adaptive complex driven by the need to minimize the struggles of prey in order to protect the elongate canines from fracture and position the bite for a quick kill.     

The geography of diet variation in Neotropical Carnivora

1. Mammalian carnivores (order Carnivora) perform important regulatory functions in terrestrial food webs. Building a comprehensive knowledge of the dietary patterns of carnivorans and the factors determining such patterns is essential for improving our understanding of the role of carnivorans in ecosystem functioning.
2. In the Neotropics, there are 64 extant species of terrestrial Carnivora, but information on their trophic ecology is diffuse. We compiled and analysed the available quantitative dietary data for Neotropical carnivorans, aiming to detect patterns of intraspecific and interspecific dietary variation at a large geographical scale.
3. The resulting database encompasses information on trophic interactions of 37 native carnivoran species from six families across 14 countries. There are clear geographical biases towards southern Brazil, Chile, and Argentina, and a noticeable knowledge gap within the Amazon. Also, most studies are focused on canids and felids, especially Puma concolor, Panthera onca, Cerdocyon thous, Leopardus pardalis, and Chrysocyon brachyurus, whereas for 27 native species, we found no quantitative dietary information.
4. Neotropical carnivorans consume species from at least 651 genera of vertebrates, invertebrates, and plants. We found clear species-specific dietary patterns and marked differences between Neotropical felids and canids. Although predators generally exhibit high levels of consistency in their diets regarding prey body mass, we detected significant intraspecific variation for all species analysed across study sites.
5. Body mass imposes strong constraints on prey use, but biogeographical differences in prey availability and human influence may drive the geographical variation we found. Overall, observed patterns show not only similarities with resource-use patterns found for carnivorans in other continents, such as nestedness driven by body mass, but also differences, such as high levels of frugivory and consumption of invertebrates by canids. Assessing resource-use patterns is the first step towards a better understanding of processes underlying the organisation of trophic interactions, and is imperative for addressing impacts of defaunation on ecosystems and for informing conservation efforts.

     

Comparisons of canid and felid social systems from an evolutionary perspective

Canids and felids are compared regarding evolutionary history, distribution, habitat preferences, morphology and behaviour. Factors permitting and promoting sociality in both families are discussed, and communication mechanisms within each sensory modality compared. A solitary existence is compatible with felid specializations, the mother and young being the basic social unit. Canid specializations have permitted the development of a pair bond and male provisioning of young. As an adaptation to hunting large herbivorous prey, an increase in size occurred in the felids, but canids developed sophisticated pack-hunting techniques. Group structure in canids is based on long-term affiliations between a pair and matured offspring, while in the lion, the only truly social felid, it is based on a mother and maturing daughters.     

Antibodies to Toxoplasma gondii and Neospora caninum in captive neotropical and exotic wild canids and felids

This study was designed to detect antibodies to Toxoplasma gondii and Neospora caninum in wild captive carnivores maintained in Brazilian zoos. Blood samples were collected from 142 Brazilian wild felids and 19 exotic felids in zoos, and 3 European wolves (Canis lupus) and 94 Brazilian wild canids maintained in captivity in Brazilian zoos of S?o Paulo, Mato Grosso states and Federal District. One hundred and two (63.4%) and 70 (50.3%) of the 161 wild felids tested were seropositive for T. gondii and N. caninum by indirect immunofluorescent assay test (IFAT), respectively. Among sampled wild canids, 49 (50.5%) and 40 (41.2%) animals were seropositive for T. gondii and N. caninum antigens by IFAT, respectively. To our knowledge, this is the first serological detection of antibodies to N. caninum in Brazilian wild captive felids and bush dogs (Speothos venaticus (Lund)).     

Convergence and divergence in prey of sympatric canids and felids: opportunism or phylogenetic constraint?

Since the canids and felids diverged in the mid‐Eocene or earlier, each family has developed a suite of morphological and behavioural adaptations for obtaining and consuming prey. We here distinguish between prey taxa captured and eaten as a result of these phylogenetic adaptations, and those because they are fortuitously encountered, and argue that such supplementary prey, often opportunistically caught, create a buffer between sympatric, and potentially competitive, canids and felids and thus enhance coexistence. We base our analysis on dietary data derived from the stomach contents of four sympatric canid and felid species in the Free State Province, South Africa (canids: Cape fox Vulpes chama and black‐backed jackal Canis mesomelas; felids: African wild cat Felis silvestris lybica and caracal Caracal caracal), and from results of studies on these species elsewhere in southern Africa. The two canid species preyed heavily on invertebrates, and thus opportunistically, while the felids (especially the caracal) concentrated on mammals, prey they are phylogenetically adapted to capture. Only three species of mammalian prey are shared by the four species. The ratio of opportunistically‐to‐phylogenetically mediated prey taxa used (the O/P ratio) differ between the species, with the black‐backed jackal having the most opportunistically caught taxa in its diet, and the caracal the least. As predicted, a comparison of this data with those from dietary studies of the same species carried out elsewhere indicates that the number of opportunistically obtained prey taxa varies more than those resulting from phylogenetic adaptations. The largest canid had the widest food spectrum (35 prey taxa) while the smallest felid had the most restricted one (11 prey taxa). We argue that using the O/P distinction allows a better understanding of changes in food niche breadth of particular species, especially in xeric areas, and gives a better indication of possible exploitative competition for food by sympatric carnivores than when regarding all prey taxa as actively pursued. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 527–538.     

Canine tooth strength and killing behaviour in large carnivores

Bending strength of upper canine teeth is examined among living canids, felids, hyaenids and several extinct species including sabretooth cats, borophagine dogs and the dire wolf, Canis dirus. The tooth is modelled as a cantilever with an elliptical cross-section. Using beam theory, the bending strength of the upper canine is calculated given a constant force applied to the canine tip. Results indicate that felids and hyaenids have relatively stronger canines than canids, particularly in bending about the anteroposterior (AP) rather than the mediolateral axis. It is suggested that canine shape reflects the forces produced during killing and feeding. As shown by an analysis of jaw muscle moment arms, felids and hyaenids have relatively stronger bites than canids. Moreover, the canines of hyaenids and felids are perhaps more likely to contact bone during feeding and killing and consequently may be subjected to larger and more frequent bending moments about the AP axis. The canines of sabretooth cats are shown to be more similar in shape and strength characteristics to those of living canids than felids, whereas those of the borophagine dogs and the dire wolf are closer to modern hyaenas.     

Evolution of community composition in several carnivore palaeoguilds from the European Pleistocene: the role of interspecific competition

This study focuses on ecological processes such as competition or predation from an evolutionary perspective. First, we attempt to test the idea that species with similar feeding requirements tend to coexist by separating morphologically or behaviourally. Then, the Barton–David test was applied to several carnivore communities (felids and canids) separated in time. Although the preservation bias of the fossil record renders our conclusions tentative, the general equal size–ratio pattern in most of the guilds examined indicates that inter-specific competition for prey species seems to be a good candidate to explain the evolution of guild composition and morphological traits throughout the Pleistocene for the two groups considered, felids and canids.     

Evolution of skull shape in carnivores 1. Representative modern carnivores

Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically.     

In the Pursuit of the Predatory Behavior of Borophagines (Mammalia,Carnivora, Canidae): Inferences from Forelimb Morphology

Here, we perform an ecomorphological study on the major bones (humerus, radius, and ulna) of the carnivoran forelimb using three-dimensional geometric morphometrics. More specifically, we test the association between forelimb morphology and predatory behavior. Our results suggest that the main morphological adaptions of carnivorans to different predatory behaviors relate to: (i) the capacity to perform long and efficient runs as in pounce/pursuit and pursuit predators; (ii) the ability to maneuver as in occasional predators; and (iii) the capacity to exert and resist large loads as in ambushing predators. We used borophagine canids as a case study, given the controversy on the predatory behavior of this extinct subfamily. Our results indicate that borophagines displayed a limited set of adaptions towards efficient running, including reduced joint mobility in both the elbow and the wrist, aspects in which they resemble the living canids. Furthermore, they had forelimbs as powerful as those of the extant ambushing carnivorans (i.e., most felids). This combination of traits suggests that the predatory behavior of borophagines was unique among carnivorans, as it was not fully equivalent to any of the living species.     

Feeding behaviour and bite force of sabretoothed predators

The feeding behaviour of extinct sabretoothed predators (machaeroidines, nimravids, barbourofelids, machairodonts and thylacosmilines) is investigated using beam theory. Because bite force applied along the mandible should be proportional to the external dimension of the mandibular corpus, patterns of variation in these dimensions at interdental gaps will reflect the adaptation of the jaw to specific loads, related to killing methods. Comparison of the mandibular force profiles of sabretooths to those of extant conical‐toothed carnivorans of known feeding behaviour reveals that sabretooths had a powerful bite, as strong or stronger than extant felids of similar mandibular length. Loads exerted at the lower canine were better constrained in the sagittal plane than in extant conical‐toothed carnivorans, indicating that prey was efficiently restrained when the sabre bite was delivered. The mandibular symphysis is generally better buttressed dorsoventrally in dirk‐toothed sabretooths than in scimitar‐toothed sabretooths, implying different killing strategies for the two ecomorphs: dirktooths delivered powerful sabre bites on prey they restrained with their forelimbs, while scimitartooths delivered slashing sabre bites and may have used their incisor battery to subdue their prey. The mandibular symphysis of Smilodon fatalis is less buttressed dorsoventrally than that of other dirk‐toothed sabretooths, possibly as a consequence of the greater torsional stresses induced while feeding rapidly on carcasses in response to intense competition. The mandibular symphysis of Thylacosmilus atrox is better buttressed dorsoventrally in juveniles than in adults, suggesting that young marsupial sabretooths underwent an extended period of parental care as typically observed in modern felids and inferred for eutherian sabretooths. Finally, machaeroidines and the nimravid Nimravus brachyops are exceptional in exhibiting a degree of dorsoventral buttressing of the mandibular symphysis that is intermediate between advanced sabretooths and conical‐toothed felids but similar to the extant Neofelis nebulosa, suggesting that the latter taxon may be close to the ancestral condition of a new sabretooth radiation. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 145 , 393–426.     

The structure of the mandibular corpus and its relationship to feeding behaviours in extant carnivorans

Assuming some optimization of bone structure to applied mechanical loadings in vivo , different killing and feeding behaviours in carnivores should be reflected in observed differences in cross-sectional shape of their mandibular corpora. Section moduli are used to gauge the magnitudes of bending moments in the mandibular corpus and, when dentary length is controlled, the magnitudes of forces applied to the corpus. Comparisons are made of section moduli at the P₃P₄ and P₄M₁ interdental gaps among canids, felids and hyaenids; in canids only, the M₁M₂ interdental gap was also studied. Local variations in loadings are identified by comparing the section moduli at adjacent loci along the corpus within each family.
The findings of this study show that the precarnassial corpora of canids and hyaenids have greater strength in bending than the corpora of felids of similar body weight. This is taken to reflect relatively greater bending moments under loading in the corpora of canids and hyaenids due, in part, to their elongate dentaries (relative to body weight). Relative to dentary length , however, the precarnassial corpora of felids and hyaenids have much greater strength in bending than the corpora of canids. These scaling relationships appear to reflect the high customary forces (i.e. not moments) applied to the precarnassial corpora of felids and hyaenids with sustained canine killing bites and with bone ingestion using the premolars, respectively. An increase in bending strength of the corpus caudal to the camassial blade in canids is interpreted to be an adaptation for bone-crushing with the postcarnassial molars.     

The effects of locomotion on the structural characteristics of avian limb bones

Despite the wide range of locomotor adaptations in birds, little detailed attention has been given to the relationships between the quantitative structural characteristics of avian limb bones and bird behaviour. Possible differences in forelimb relative to hindlimb strength across species have been especially neglected. We generated cross‐sectional, geometric data from peripheral quantitative computed tomography scans of the humerus and femur of 127 avian skeletons, representing 15 species of extant birds in 13 families. The sample includes terrestrial runners, arboreal perchers, hindlimb‐propelled divers, forelimb‐propelled divers and dynamic soarers. The hindlimb‐propelled diving class includes a recently flightless island form. Our results demonstrate that locomotor dynamics can be differentiated in most cases based on cross‐sectional properties, and that structural proportions are often more informative than bone length proportions for determining behaviour and locomotion. Recently flightless forms, for example, are more easily distinguished using structural ratios than using length ratios. A proper phylogenetic context is important for correctly interpreting structural characteristics, especially for recently flightless forms. Some of the most extreme adaptations to mechanical loading are seen in aquatic forms. Penguins have forelimbs adapted to very high loads. Aquatic species differ from non‐aquatic species on the basis of relative cortical thickness. The combination of bone structural strength and relative cortical area of the humerus successfully differentiates all of our locomotor groups. The methods used in this study are highly applicable to fossil taxa, for which morphology is known but behaviour is not. The use of bone structural characteristics is particularly useful in palaeontology not only because it generates strong signals for many locomotor guilds, but also because analysing such traits does not require knowledge of body mass, which can be difficult to estimate reliably for fossil taxa. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 153 , 601–624.     

Locomotor correlates of the scapholunar of living and extinct carnivorans

The relationship of carpal morphology to ecology and habitat is under studied in carnivorans and more generally in mammals. Here, we use 3D-scanning techniques to assess the usefulness of a carpal bone, the scapholunar, in carnivorans to reflect ecology and habitat, and to reconstruct the ecology of five extinct carnivorans from two fossil sites: Rancho La Brea and Natural Trap Cave. We 3D-scanned scapholunars and measured articular surface areas and angles between articular facets using GeoMagic and Rhino 3D-software. We analyzed the difference in these metrics using multivariate analysis of variance and discriminant function analysis. Results show that the scapholunar reflects ecological signal, with clear groupings of cursorial carnivorans and grappling/climbing carnivorans; however, phylogenetic signal was also present in the results with hyaenids, canids, and large felids in distinct morphospaces. Extinct species Miracinonyx trumani (American cheetah) and Smilodon fatalis (sabertooth cat) showed surprising results with M. trumani grouping with pantherines instead of Acinonyx or Puma, suggesting it runs but still retains the ability to grapple prey. S. fatalis groups with pantherines, but also shows some unique adaptations, suggesting it had a different range of wrist motion than living cats. Overall, the scapholunar is a good indicator of ecology and functional morphology and can be another tool to use in modern and fossil carnivorans to reconstruct extinct ecologies and locomotor behaviors.     

Chromosomal localization of satellite DNA sequences among 22 species of felids and canids (Carnivora)

In situ hybridization was carried out using cloned satellite DNAs from the domestic cat and domestic dog as probes to metaphase chromosomes from 12 species of felids and 10 species of canids. Autoradiographic silver grains along metaphase chromosomes were counted and analyzed with regard to the mean number of grains per cell in each species, their chromosomal location, and their presence or absence on specific autosomes or sex chromosomes, where known. Among the felids and canids there was a 7.6- and 8.9-fold statistically significant difference, respectively, in the mean number of grains per cell between the species having the minimum and maximum values. Among the felids, most grains occurred on the telomeres of D- and E-group chromosomes, although departures from this general pattern also occurred. For example, the Asian golden cat and the Bornean bay cat showed substantial labeling at the centromeric region of chromosome A1, and a number of species showed some labeling at the short-arm telomeres of B-group chromosomes. Among the canids, about 90% of all grains were located at autosomal centromeres, and grains were absent from the sex chromosomes. Grains are usually distributed at chromosomal locations that stain C-band positive; however, certain C-band-positive regions without grains probably do not contain the particular satellites studied here.     

Evolution of heterochromatin-associated satellite DNA loci in felids and canids (Carnivora)

Cloned satellite DNAs that hybridize primarily to C-band-positive regions of felid and canid chromosomes were used to probe the organization of satellite families in the genomes of 16 species of felids and 15 species of canids. Southern-blot and quantitative dot-blot experiments demonstrated that satellite families within the great cats (panthera lineage) vary considerably in regard to amount and/or sequence mismatch and vary some-what in regard to restriction patterns. Satellite families within the canids appeared to be more uniform in regard to both amount/sequence and restriction patterns, although some canid species did differ significantly from the consensus in both respects. Even though intrafamilial satellite restriction patterns were generally similar, every species could be shown to have a unique, characteristic pattern.     

Mid-Pliocene Carnivora from the Woranso-Mille Area,Afar Region,Ethiopia

The Woranso-Mille paleontological study area, located in the central Afar region of Ethiopia, is one of the most important Pliocene sites in eastern Africa. Since the Woranso-Mille Research Project began its investigation in 2005, more than 7,500 mammalian fossils, including hominins, have been collected from 80 vertebrate localities. This paper provides a preliminary assessment of the Woranso-Mille carnivoran record, a record that is of great interest given the high level of species richness of African carnivorans during the middle Pliocene. Craniodental and postcranial material of canids, lutrine mustelids, viverrids, herpestids, machairodontine and feline felids, and hyaenids has been recovered. Thus, this diverse fauna includes not only the largest carnivorans from this time period (e.g., Enhydriodon and Homotherium), but also some of the smallest, including mongooses, civets, genets, and felids, some of which represent new species. However, the diversity of small taxa does not yet approach that found in the roughly contemporaneous Upper Laetolil Beds of Tanzania. In contrast, lutrine mustelids are better represented at Woranso-Mille than at Kanapoi (Kenya) or Laetoli (Tanzania), which is to be expected given the diversity of habitats represented at these sites. While more material from these sites and others are necessary to truly understand the increased diversity within the early to middle Pliocene eastern African carnivoran guild, it is clear that the material from Woranso-Mille has the potential to fill many of the gaps in our knowledge of carnivorans during this time period.     

A molecular phylogeny of the Canidae based on six nuclear loci

We have reconstructed the phylogenetic relationships of 23 species in the dog family, Canidae, using DNA sequence data from six nuclear loci. Individual gene trees were generated with maximum parsimony (MP) and maximum likelihood (ML) analysis. In general, these individual gene trees were not well resolved, but several identical groupings were supported by more than one locus. Phylogenetic analysis with a data set combining the six nuclear loci using MP, ML, and Bayesian approaches produced a more resolved tree that agreed with previously published mitochondrial trees in finding three well-defined clades, including the red fox-like canids, the South American foxes, and the wolf-like canids. In addition, the nuclear data set provides novel indel support for several previously inferred clades. Differences between trees derived from the nuclear data and those from the mitochondrial data include the grouping of the bush dog and maned wolf into a clade with the South American foxes, the grouping of the side-striped jackal (Canis adustus) and black-backed jackal (Canis mesomelas) and the grouping of the bat-eared fox (Otocyon megalotis) with the raccoon dog (Nycteruetes procyonoides). We also analyzed the combined nuclear + mitochondrial tree. Many nodes that were strongly supported in the nuclear tree or the mitochondrial tree remained strongly supported in the nuclear + mitochondrial tree. Relationships within the clades containing the red fox-like canids and South American canids are well resolved, whereas the relationships among the wolf-like canids remain largely undetermined. The lack of resolution within the wolf-like canids may be due to their recent divergence and insufficient time for the accumulation of phylogenetically informative signal.     

Traditional Versus Multivariate Methods for Identifying Jaguar,Puma, and Large Canid Tracks

ABSTRACT The jaguar (Panthera onca) and puma (Puma concolor) are the largest felids of the American Continent and live in sympatry along most of their distribution. Their tracks are frequently used for research and management purposes, but tracks are difficult to distinguish from each other and can be confused with those of big canids. We used tracks from pumas, jaguars, large dogs, and maned wolves (Chrysocyon brachyurus) to evaluate traditional qualitative and quantitative identification methods and to elaborate multivariate methods to differentiate big canids versus big felids and puma versus jaguar tracks (n = 167 tracks from 18 zoos). We tested accuracy of qualitative classification through an identification exercise with field-experienced volunteers. Qualitative methods were useful but there was high variability in accuracy of track identification. Most of the traditional quantitative methods showed an elevated percentage of misclassified tracks (≥20%). We used stepwise discriminant function analysis to develop 3 discriminant models: 1 for big canid versus big felid track identification and 2 alternative models for jaguar versus puma track differentiation using 1) best discriminant variables, and 2) size-independent variables. These models had high classification performance, with <10% of error in the validation procedures. We used simpler discriminant models in the elaboration of identification keys to facilitate track classification process. We developed an accurate method for track identification, capable of distinguishing between big felids (puma and jaguar) and large canids (dog and maned wolf) tracks and between jaguar and puma tracks. Application of our method will allow a more reliable use of tracks in puma and jaguar research and it will help managers using tracks as indicators of these felids' presence for conservation or management purposes.     

Characterization of dinucleotide microsatellite loci and confirmation of sexing primers for the bush dog (Speothos venaticus)

Bush dogs (Speothos venaticus) are small, threatened canids from Central and South America. The ability to conduct population-level studies using noninvasive genetic samples would provide important information on this poorly understood species. We characterized eight dinucleotide microsatellite loci using samples from 15 captive bush dogs. Allelic diversity ranged from 2 to 5 alleles per locus, and observed heterozygosity ranged from 0.267 to 0.933. All loci were in Hardy-Weinberg equilibrium and no evidence of genotypic linkage disequilibrium was found. We determined that DBX6 and DBY7, two canid-specific molecular sexing primers, accurately indicate the sex of individual bush dog samples.