Immobilization of free-ranging Hoffmann's two-toed and brown-throated three-toed sloths using ketamine and medetomidine: a comparison of physiologic parameters

Free-ranging Hoffmann's two-toed sloths (Choloepus hoffmanni; n=26) and brown-throated three-toed sloths (Bradypus variegatus; n=15) were manually captured and immobilized with 2.5 mg/kg ketamine + 0.02 mg/kg medetomidine administered intramuscularly. Physical examinations were conducted on each sloth 10 min after initial injection, and blood, fecal, and ectoparasite samples were collected. Heart rate, respiratory rate, body temperature, indirect systolic blood pressure, and indirect peripheral oxygen saturation were monitored every 5 min for the duration of anesthesia. After 45 min, atipamazole (0.1 mg/kg) was administered intramuscularly, as an antagonist to medetomidine, in order to facilitate recovery. All recoveries were smooth, rapid, and uneventful. Physiologic parameters were compared across time, gender, and species. All sloths, regardless of species and gender, demonstrated a time-dependent decrease in heart rate and blood pressure, and an increase in respiratory rate, during the course of anesthesia. Peripheral oxygen saturation was similar for all sloths over time. There were significant species differences for heart rate (Choloepus > Bradypus), respiratory rate (Choloepus > Bradypus), and systolic blood pressure (Bradypus > Choloepus), while there were significant gender differences for body temperature (males > females) and blood pressure (males > females). Results of this study suggest that the ketamine-medetomidine mixture, as described above, is a safe and effective anesthetic combination in free-ranging two- and three-toed sloths, although peripheral blood pressure should be monitored during anesthesia.     

Form and function of the masticatory musculature in the tree sloths, Bradypus and Choloepus

The tree sloths, Bradypus and Choloepus, show unusual masticatory specializations, compared to each other and to other mammals. Both have an incomplete zygomatic arch with descending jugal process, a complex superficial masseter, a large temporalis and medial pterygoid musculature, and a lateral pterygoid with two heads. In Choloepus the deep masseter and zygomaticomandibularis are typical when compared to other mammals. However, in Bradypus there is an ascending jugal process from which enlarged and vertically oriented deep masseter and zygomaticomandibularis muscles originate. Although both sloths are folivores, the anterior teeth in Choloepus are caniniform, while those of Bradypus have lost such elongation. In both sloths the glenoid cavity is similarly located; however, in Bradypus the craniomandibular joint is raised above the occlusal plane, and the pterygoid flanges are elongated. Prediction of the evolutionary sequence of cranial changes from Choloepus-like (primitive) to Bradypus-like (derived) morphology is based upon the most parsimonious model of masseter-medial pterygoid complex changes for masticatory efficiency improvement. The model proposes that the condylar neck in Bradypus was elongated and that this single change predicated a series of other structural changes. Mandibular movement patterns in both sloths showed anteromedially directed unilateral power strokes as in other mammals. Puncture-crushing, tooth-sharpening, and chewing cycles are distinct in Choloepus, less so in Bradypus. The masticatory rate is slow in sloths compared to other mammals of similar body size, averaging 590 ms per cycle for Choloepus and 510 ms for Bradypus.     

Leishmania herreri sp. n. from sloths and sandflies of Costa Rica.

Leishmania herreri sp. n. is described after isolation in pure culture from blood, viscera and skin of two-toed (Choloepus hoffmanni) and three-toed (Bradypus griseus) sloths from Costa Rica. Also, it was isolated from the following sandflies: Lutzomyia trapidoi, L. ylephiletor and L. shannoni. The amastigote forms were not seen in the final hosts but they were obtained in tissue culture at 33 C. Both promastigotes and amastigotes failed to infect hamsters. The new parasite is isolated frequently in culture, mixed with other hemoflagellates such as L. braziliensis, Endotrypanum sp. and Trypanosoma rangeli.     

A molecular phylogeny of two extinct sloths

Xenarthra (Edentata) is an extremely diverse mammalian order whose modern representatives are the armadillos, anteaters, and sloths. The phylogeny of these groups is poorly resolved. This is particularly true for the sloths (phyllophagans), originally a large and diverse group now reduced to two genera in two different families. Both morphological analyses and molecular analyses of rDNA genes of living and extinct sloths have been used with limited success to elucidate their phylogeny. In an attempt to clarify relationships among the sloths, DNA was extracted and mitochondrial cytochrome b gene sequences were determined from representatives of two extinct groups of sloths (Mylodontidae and Megatheriidae), their two living relatives (two-toed sloths [Megalonychidae], three-toed sloths [Bradypodidae]), anteaters and armadillos. A consistent feature of the latter two species was the nuclear copies of cytochrome b gene sequences. Several methods of phylogenetic reconstruction were applied to the sequences determined, and the results were compared with 12S rDNA sequences obtained in previous studies. The cytochrome b gene exhibited a phylogenetic resolving power similar to that of the 12S rDNA sequences. When both data sets were combined, they tended to support the grouping of two-toed sloths with mylodontids and three-toed sloths with megatheriids. The results strengthen the view that the two families of living sloths adapted independently to an arboreal life-style.     

The passage of digesta, particle size, and in vitro fermentation rate in the three-toed sloth Bradypus tridactylus (Edentata: Bradypodidae)

The digestive physiology of six three-toed sloths ( Bradypus tridactylus ) fed exclusively on Cecropia palmata foliage was studied. The mass of digesta in the gut was between 17 and 37% of body mass. This was between 133 and 282% of that expected in an animal of this size, based on published allometric equations. The concentration of total short chain fatty acids in the stomach was similar to that in the fermentative regions of other foregut fermenting herbivores but the rate of fermentation measured in vitro was very slow (6–12 mmol.l^-1.h^-1) and substantially lower than that observed using similar techniques in other small foregut fermenters.
The overall (dose to excretion) mean retention time of particulate and solute digesta markers was about 150 h. Most of this (73%) occurred in the stomach but a substantial proportion (17%) could be attributed to the storage of faeces in the rectum.
The slow rate of passage of digesta through the gut together with the slow rate of fermentation in the stomach is not typical of small foregut fermenting herbivores. However, such a pattern is feasible in Bradypus tridactylus because of the large volume of digesta retained in the gut and the very low metabolic rate of these mammals.     

Dirofilaria macrodemos and D. panamensis spp. n. (Nematoda: Filarioidea) from Central and South Americal sloths

Two new species of Diorfilaria, Dirofilaria macrodemos and Dirofilaria panamensis, are described from the subserosa of Central and South American sloths. Dirofilaria macrodemos, described from the three-toed sloth, Bradypus tridactylus, in Guyana, is characterized and differentiated from other dirofilarias by its length (female 214mm, male 64mm), relatively long tail (female 140 micron, male 110 micron), and the number and distribution of the caudal papillae (7 pairs) in the male. Dirofilaria panamensis, parasite of the two-toed sloth, Cholopeus hoffmanni, in Panama, was previously described as Dirofilaria incrassata by Caballero (1947), but can be distinguished from both D. macrodemos and D. incrassata on the basis of body size (female 66 mm long by 360 micron wide, male 34 mm long by 250 micron wide), tail length (female 80 micron, male 80 micron), and number (6 pairs) of caudal papillae in the male.     

Temporal and spatial resource use by female three-toed sloths and their young in an agricultural landscape in Costa Rica

The information on ecological behavior of wild sloths is very scarce. In this study we determined the home ranges and resources used by three adult female three-toed sloths (Bradypus variegatus) and their four young in an agricultural matrix of cacao (Theobroma cacao), pasture, riparian forests and living fencerows in Costa Rica. Births occurred during November-December and the young became independent at five to seven months of age. Initially, mothers remained fixed in one or a few trees, but expanded their use of resources as young sloths became independent from them. Mothers initially guided the young to preferred food and cover resources, but they gradually left their young in small nucleus areas and colonized new areas for themselves. Home range sizes for young sloths (up to seven months of age) varied between 0.04-0.6 hectares, while home range sizes for mothers varied from 0.04-25.0 hectares. During the maternal care period, 22 tree species were used, with the most common being Cecropia obtusifolia (30.9%), Coussapoa villosa (25.6%), Nectandra salicifolia (12.1%), Pterocarpus officinalis (5.8%) and Samanea saman (5.4%). However, young sloths used only 20 tree species, with the most common being C. villosa (18.4%), S. saman (18.5%) and N. salicifolia (16.7%). The cacao agroforest was used only by mother sloths and never by their young following separation. However, in the riparian forest, both mother sloths and young used the tree species. A total of 28 tree species were used by the mother sloth; including the food species: C. obtusifolia, C. villosa, N. salicifolia and P. officinalis. However, the young used 18 trees species in this habitat with N. salicifolia and S. saman most commonly used, although they rested and fed during the day in C. obtusifolia, C. villosa and O. sinnuata. The cacao agroforest with adjacent riparian forests and fencerows provides an important habitat type that links the smaller secondary forests and other patches.     

Spatial ecology and conservation of two sloth species in a cacao landscape in limón,Costa Rica

The spatial ecology of sloths was studied in an agricultural landscape in Limón Province, Costa Rica. Two sloth species, the three-toed sloth (Bradypus variegatus) and the two-toed sloth (Choloepus hoffmanni), actively used and traveled through a cacao agroforest and its contiguous living fence rows and riparian forests. This agroecosystem was embedded in an agricultural landscape dominated by banana and pineapple plantations and pastures with dispersed trees. The two-toed sloth (C. hoffmanni) was found in 101 tree species and used 34 for food; the three-toed sloth (B. variegatus) was found in 71 tree species and used 15 for food. Choice of preferred species differed between the two sloth species. Trees commonly used by sloths for food and/or refuge in the cacao agroforest included Erythrina poeppigiana, Cecropia obtusifolia, Leucaena leucocephala; in the living fence rows, Cordia alliodora, Erythrina poeppigiana, Ocotea sinuata and Trophis racemosa; in the riparian forests, Coussapoa villosa, Cecropia obtusifolia, Hura crepitans, Pterocarpus officinalis and Spondias mombin; and in the pastures with dispersed trees, Cordia alliodora, Coussapoa villosa, Erythrina poeppigiana, Ocotea sinuata and Hura crepitans. This study demonstrates the importance of the cacao agroforest as well as arboreal elements in other land uses in providing resources for sloth conservation in a larger agricultural landscape.     

A syndrome of mutualism reinforces the lifestyle of a sloth

Arboreal herbivory is rare among mammals. The few species with this lifestyle possess unique adaptions to overcome size-related constraints on nutritional energetics. Sloths are folivores that spend most of their time resting or eating in the forest canopy. A three-toed sloth will, however, descend its tree weekly to defecate, which is risky, energetically costly and, until now, inexplicable. We hypothesized that this behaviour sustains an ecosystem in the fur of sloths, which confers cryptic nutritional benefits to sloths. We found that the more specialized three-toed sloths harboured more phoretic moths, greater concentrations of inorganic nitrogen and higher algal biomass than the generalist two-toed sloths. Moth density was positively related to inorganic nitrogen concentration and algal biomass in the fur. We discovered that sloths consumed algae from their fur, which was highly digestible and lipid-rich. By descending a tree to defecate, sloths transport moths to their oviposition sites in sloth dung, which facilitates moth colonization of sloth fur. Moths are portals for nutrients, increasing nitrogen levels in sloth fur, which fuels algal growth. Sloths consume these algae-gardens, presumably to augment their limited diet. These linked mutualisms between moths, sloths and algae appear to aid the sloth in overcoming a highly constrained lifestyle.     

Sleeping outside the box: electroencephalographic measures of sleep in sloths inhabiting a rainforest

The functions of sleep remain an unresolved question in biology. One approach to revealing sleep's purpose is to identify traits that explain why some species sleep more than others. Recent comparative studies of sleep have identified relationships between various physiological, neuroanatomical and ecological traits, and the time mammals spend in rapid eye movement (REM) and non-REM sleep. However, owing to technological constraints, these studies were based exclusively on animals in captivity. Consequently, it is unclear to what extent the unnatural laboratory environment affected time spent sleeping, and thereby the identification and interpretation of informative clues to the functions of sleep. We performed the first electroencephalogram (EEG) recordings of sleep on unrestricted animals in the wild using a recently developed miniaturized EEG recorder, and found that brown-throated three-toed sloths (Bradypus variegatus) inhabiting the canopy of a tropical rainforest only sleep 9.63 h d(-1), over 6 h less than previously reported in captivity. Although the influence of factors such as the age of the animals studied cannot be ruled out, our results suggest that sleep in the wild may be markedly different from that in captivity. Additional studies of various species are thus needed to determine whether the relationships between sleep duration and various traits identified in captivity are fundamentally different in the wild. Our initial study of sloths demonstrates the feasibility of this endeavour, and thereby opens the door to comparative studies of sleep occurring within the ecological context within which it evolved.     

Morphology of hair of two- and three- toed sloths (Edentata: Bradypodidae)

Micromorphological differences between hairs of the two-toed sloth (Choloepus hoffmanni) and of the three-toed sloth (Bradypus variegatus) were observed by means of scanning electron microscopy. Hairs of the two-toed had longitudinal grooves which exposed a uniform cortex when viewed in cross section. Hairs of the three-toed sloth have irregular transverse fissures and a cortex that contains scattered fusi. These morphological differences support the placement of the two sloth genera into separate families. Hairs of four other xenarthran species are also illustrated.     

Unexpected Strong Polygyny in the Brown-Throated Three-Toed Sloth

Promiscuous mating strategies are much more common than previously appreciated. So much so, that several authors have proposed that promiscuity is the “rule” rather than the exception in vertebrate mating systems. Decreasing species mobility and increasing habitat fragmentation have both been suggested to reduce the “polygyny potential” of the environment and promote other mating strategies like promiscuity in females. We explored the social and genetic mating system for one of the most sedentary extant mammals, the brown-throated three-toed sloth (Bradypus variegatus), within a highly fragmented Neotropical habitat. Surprisingly, we found that three-toed sloths were strongly polygynous, with males excluding male competitors from their core ranges, and exhibiting strong reproductive skew. Indeed, only 25% of all resident adult males sired offspring and one individual sired half of all sampled juveniles. Paradoxically, a sedentary life-history strategy seems to facilitate polygyny in fragmented landscapes because multiple females can persist within small patches of habitat, and be monopolized by a single male. Our work demonstrates that strong polygyny can arise in systems in which the polygyny potential should be extremely low, and other strategies, including promiscuity, would be favoured. Mating systems can be influenced by a multitude of factor and are dynamic, varying among taxa, over time, and across habitats; consequently, mating systems remain difficult to predict based on general ecological principles.     

Anatomical transformation in mammals: developmental origin of aberrant cervical anatomy in tree sloths

SUMMARY Mammalian cervical count has been fixed at seven for more than 200 million years. The rare exceptions to this evolutionary constraint have intrigued anatomists since the time of Cuvier, but the developmental processes that generate them are unknown. Here we evaluate competing hypotheses for the evolutionary origin of cervical variants in Bradypus and Choloepus , tree sloths that have broken the seven cervical vertebrae barrier independently and in opposite directions. Transitional and mediolaterally disjunct anatomy characterizes the cervicothoracic vertebral boundary in each genus, although polarities are reversed. The thoracolumbar, lumbosacral, and sacrocaudal boundaries are also disrupted, and are more extreme in individuals with more extreme cervical counts. Hypotheses of homologous, homeotic, meristic, or associational transformations of traditional vertebral column anatomy are not supported by these data. We identify global homeotic repatterning of abaxial relative to primaxial mesodermal derivatives as the origin of the anomalous cervical counts of tree sloths. This interpretation emphasizes the strong resistance of the "rule of seven" to evolutionary change, as morphological stasis has been maintained primaxially coincident with the generation of a functionally longer ( Bradypus ) or shorter ( Choloepus ) neck.     

Architectural Properties of Sloth Forelimb Muscles (Pilosa: Bradypodidae)

Tree sloths have reduced skeletal muscle mass, and yet they are able to perform suspensory behaviors that require both strength and fatigue resistance to suspend their body mass for extended periods of time. The muscle architecture of sloths is hypothesized to be modified in ways that will enhance force production to compensate for this reduction in limb muscle mass. Our objective is to test this hypothesis by quantifying architecture properties in the forelimb musculature of the brown-throated three-toed sloth (Bradypus variegatus: N = 4). We evaluated architecture from 52 forelimb muscles by measuring muscle moment arm (r _m), muscle mass (MM), belly length (ML), fascicle length (L_F), pennation angle (θ), and physiological cross-sectional area (PCSA), and these metrics were used to estimate isometric force, joint torque, and power. Overall, the musculature becomes progressively more pennate from the extrinsic to intrinsic regions of the forelimb, and the flexors are more well developed than the extensors as predicted. However, most muscles are indicative of a mechanical design for fast joint rotational velocity instead of large joint torque (i.e., strength), although certain large, parallel-fibered shoulder (e.g., m. latissimus dorsi) and elbow (e.g., m. brachioradialis) flexors are capable of producing appreciable torques by having elongated moment arms. This type of functional tradeoff between joint rotational velocity and mechanical advantage is further exemplified by muscle gearing in Bradypus that pairs synergistic muscles with opposing L_F/r _m ratios in each functional group. These properties are suggested to facilitate the slow, controlled movements in sloths. In addition, the carpal/digital flexors have variable architectural properties, but their collective PCSA and joint torque indicates the capability for maintaining grip force and carpal stability while distributing load from the manus to the shoulder. The observed specializations provide a basis for understanding sustained suspension in sloths.     

Mitigating the squash effect: sloths breathe easily upside down

Sloths are mammals renowned for spending a large proportion of time hanging inverted. In this position, the weight of the abdominal contents is expected to act on the lungs and increase the energetic costs of inspiration. Here, we show that three-fingered sloths Bradypus variegatus possess unique fibrinous adhesions that anchor the abdominal organs, particularly the liver and glandular stomach, to the lower ribs. The key locations of these adhesions, close to the diaphragm, prevent the weight of the abdominal contents from acting on the lungs when the sloth is inverted. Using ventilation rate and body orientation data collected from captive and wild sloths, we use an energetics-based model to estimate that these small adhesions could reduce the energy expenditure of a sloth at any time it is fully inverted by almost 13%. Given body angle preferences for individual sloths in our study over time, this equates to mean energy saving of 0.8–1.5% across individuals (with individual values ranging between 0.01 and 8.6%) per day. Given the sloth''s reduced metabolic rate compared with other mammals and extremely low energy diet, these seemingly innocuous adhesions are likely to be important in the animal''s energy budget and survival.     

The effects of posture on blood pressure and heart rate in the three-toed sloth, Bradypus tridactylus

1. In unanesthetized, minimally restrained three-toed sloths, Bradypus tridactylus, the mean arterial pressure was 125/85 mmHg and the heart rate was 83.6 beats/min. There was no significant difference between these parameters whether the animal was erect or supine in the experimental chair. 2. Animals without any restraint had a mean blood pressure of 133/87 mmHg and a heart rate of 78.1 beats/min. There was no significant difference between these parameters whether the animal was seated or suspended from a horizontal bar and there was no significant difference between the minimally restrained and the unrestrained animals. 3. Tilting from the erect to the supine position produced large increases in blood pressure parameters, 37% in systolic and 21% in diastolic, reaching the maximum effect in a mean time of 38 sec. Tilting from the supine to the erect position caused even greater increases in pressure, 43% and 38% respectively, and reaching the maximum also in a mean time of 38 sec. 4. Tilting initially increased the heart rate, in going from erect to supine by 21% in 16 sec and from supine to erect by 23% in 20 sec. 5. In going from erect to supine there was a reflex bradycardia later, 15% below control level with a maximum at 40 sec, and to a lesser degree in going from supine to erect, 9% with maximum at 50 sec.     

Blood pressure regulation in the three-toed sloth, Bradypus variegatus

The aim of this study was to elucidate the role of the baroreflex in blood pressure control in sloths, Bradypus variegatus, since these animals show labile levels in this parameter. Unanesthetized cannulated sloths were positioned in an experimental chair and the arterial catheter was coupled to a strain gauge pressure transducer. Blood pressure was monitored before, during and after the administration of phenylephrine (0.0625 to 4 microg/kg) and sodium nitroprusside (0.0625 to 2 microg/kg), bringing about changes in mean blood pressure from +/-30 mmHg in relation to control values. The relation between heart rate changes due to blood pressure variation was estimated by linear regression analysis. The slope was considered the reflex baroreceptor gain. The results (means+/-SD) showed that the reflex baroreceptor gain was -0.3+/-0.1 bpm/mmHg (r=0.88) to phenylephrine and -0.5+/-0.1 bpm/mmHg (r=0.92) to sodium nitroprusside, denoting a reduced reflex baroreceptor gain when compared with other mammals, suggesting that in sloths the baroreceptors are minimally involved in the buffering reflex response to these drugs. These findings suggest that the labile blood pressure could be influenced or be a result of this lowering in the reflex baroreceptor gain.     

Sloth Hair as a Novel Source of Fungi with Potent Anti-Parasitic,Anti-Cancer and Anti-Bacterial Bioactivity

The extraordinary biological diversity of tropical forests harbors a rich chemical diversity with enormous potential as a source of novel bioactive compounds. Of particular interest are new environments for microbial discovery. Sloths – arboreal mammals commonly found in the lowland forests of Panama – carry a wide variety of micro- and macro-organisms on their coarse outer hair. Here we report for the first time the isolation of diverse and bioactive strains of fungi from sloth hair, and their taxonomic placement. Eighty-four isolates of fungi were obtained in culture from the surface of hair that was collected from living three-toed sloths (Bradypus variegatus, Bradypodidae) in Soberanía National Park, Republic of Panama. Phylogenetic analyses revealed a diverse group of Ascomycota belonging to 28 distinct operational taxonomic units (OTUs), several of which are divergent from previously known taxa. Seventy-four isolates were cultivated in liquid broth and crude extracts were tested for bioactivity in vitro. We found a broad range of activities against strains of the parasites that cause malaria (Plasmodium falciparum) and Chagas disease (Trypanosoma cruzi), and against the human breast cancer cell line MCF-7. Fifty fungal extracts were tested for antibacterial activity in a new antibiotic profile screen called BioMAP; of these, 20 were active against at least one bacterial strain, and one had an unusual pattern of bioactivity against Gram-negative bacteria that suggests a potentially new mode of action. Together our results reveal the importance of exploring novel environments for bioactive fungi, and demonstrate for the first time the taxonomic composition and bioactivity of fungi from sloth hair.     

High morphological variation of vestibular system accompanies slow and infrequent locomotion in three-toed sloths

The semicircular canals (SCs), part of the vestibular apparatus of the inner ear, are directly involved in the detection of angular motion of the head for maintaining balance, and exhibit adaptive patterns for locomotor behaviour. Consequently, they are generally believed to show low levels of intraspecific morphological variation, but few studies have investigated this assumption. On the basis of high-resolution computed tomography, we present here, to our knowledge, the first comprehensive study of the pattern of variation of the inner ear with a focus on Xenarthra. Our study demonstrates that extant three-toed sloths show a high level of morphological variation of the bony labyrinth of the inner ear. Especially, the variation in shape, relative size and angles of their SCs greatly differ from those of other, faster-moving taxa within Xenarthra and Placentalia in general. The unique pattern of variation in three-toed sloths suggests that a release of selection and/or constraints on their organ of balance is associated with the observed wide range of phenotypes. This release is coincident with their slow and infrequent locomotion and may be related, among other possible factors, to a reduced functional demand for a precise sensitivity to movement.     

Predation by the tayra on the common marmoset and the pale-throated three-toed sloth

Predation on arboreal mammals is rarely observed in the wild. Here we describe the first confirmed observations of predation on a juvenile wild common marmoset (Callithrix jacchus) and on a neonate wild pale-throated three-toed sloth (Bradypus tridactylus) by the mustelid carnivore Eira barbara, the tayra. We discuss predation on both of the prey species and review the nature of predation by the tayra.