An update on the physiology of two- and three-toed sloths

FIRST REPORT OF CHEMICAL IMMOBILIZATION AND PHYSIOLOGICAL PARAMETERS FOR FREE-RANGING MANED SLOTH (BRADYPUS TORQUATUS), USING A COMBINATION OF KETAMINE AND MEDETOMIDINE

The maned sloth (Bradypus torquatus) is an endemic and endangered species of two Brazilian states, with much unknown biological information needed to direct conservation actions. Other sloth species have been studied regarding anesthesia; however, there is a lack of anesthesia research for the maned sloth. Anesthetic data were collected from 12 free-range maned sloths that were immobilized for a field examination. Individuals were anesthetized using a combination of ketamine (4.0 mg/kg) and medetomidine (0.03 mg/kg), and antagonized with atipamezole (0.1 mg/kg). Time to induction and recovery were recorded and compared with sex and age classes. After the induction and until antagonist administration, physiological parameters (rectal temperature, heart rate, respiratory rate, and oxygen saturation) were recorded every 10 min during anesthesia and were statistically evaluated over time. Induction was fast (3.21 ± 0.76), but recovery was longer (113.3 ± 18) when compared to other studies. Induction and recovery times were not different across sex or age classes. Rectal temperature, heart rate, and oxygen saturation remained stable throughout the procedure. Respiratory rate significantly decreased over time, from 18.25 ± 7.03 to 13.17 ± 3.66 movements per minute. Our results indicate that the described combination of ketamine and medetomidine is a safe and effective choice for anesthesia of maned sloths.

The organ of vision morphology of the southern two-toed sloth (Choloepus didactylus Linnaeus, 1758; Pilosa, Choloepodidae)

The Choloepus didactylus is a species belonging to the Choloepodidae family of the Folivora suborder. This study concerns the anatomical, morphometrical, histological and histochemical examination of the eye tunics, eyelids and orbital glands in the three adult Choloepus didactylus coming from the Wroclaw Zoological Garden. The cornea consists of four layers since Bowman's membrane was absent. The presence of palisades of Vogt formed from 14/15 to 20/21 layers of epithelial cells was demonstrated. Macroscopically, the tapetum lucidum was not identified, while degenerative choroidal tapetum lucidum cellulosum was found microscopically. The ciliary muscle was found with our histological approach. The pupil was round in shape (post-mortem). The presence of tarsal glands has not been demonstrated in both eyelids. The conjunctiva-associated lymphoid tissue (CALT) has been shown in the upper and lower eyelids. The superficial gland of the third eyelid produced a seromucous secretion. The third eyelid was shaped like a curved arch and composed of hyaline cartilage. The deep gland of the third eyelid was big and multilobar acinar simple with serous character. The lacrimal gland produced mucous secretion. The results of our research indicate that the features of the eye anatomy in the southern two-toed sloth (C. didactylus) are also typical of the Folivora suborder and have common features and differences with Vermilingua.

Aortic branches and rete mirabile of the limbs of two-toed sloth (Choloepus didactylus)

Choloepus didactylus has reduced metabolism and difficulty in thermoregulation owing to its low body mass, and there are few studies related to the vascularization of abdominal and thoracic organs in this species. Therefore, we macroscopically described the arteries that comprise the aortic arch, thoracic aorta, and abdominal aorta. Six specimens were used, and their arterial systems filled with red latex before fixation in 10% formaldehyde, and fragments of the rete mirabile were processed for histological analysis using light and scanning electron microscopy. In these species, the aortic arch had two branches: the brachiocephalic trunk and left subclavian artery. The initial portion of the abdominal aorta presented four different ramifications, besides to the peculiarities of the adrenal, renal, and iliac arteries. Microscopy of the rete mirabile revealed a muscular artery surrounded by smaller muscular arteries, veins, nerves, and lymphatic tissue joined by connective tissue. Thus, the data obtained have clinical and surgical importance, with applicability in procedures involving vascularization of the thoracic and abdominal organs. We suggest that the rete mirabile is an efficient thermoregulatory structure because it allows the accumulation of blood and the countercurrent heat exchange, as there is no blood mixing.

REPRODUCTIVE CYCLE STAGE ASSESSMENT IN THE TWO-TOED SLOTH (CHOLOEPUS HOFFMANNI), PRELIMINARY RESULTS

The number of two-toed sloths (Choloepus hoffmanni) has significantly decreased in the last years. Deepening the knowledge of this tropical mammal's reproductive physiology is essential to improve captive breeding within conservation programs for this species. However, several aspects of its reproductive biology remain unexplored and have not been described sufficiently. The aim of this work was to describe the estrous cycle and reproductive physiology of two adult female C. hoffmanni by vaginal cytology, appearance of the external genitalia, and behavior. Vaginal cytology assay showed that the average duration of the estrous cycle was 15.1 ± 4.53 d. Positive correlations (P < 0.05) were found between the peak presence of superficial cells (estrous phase) and four parameters: aggressive behavior, pursuing behavior, vulvar swelling, and vaginal discharge. This pilot study, conducted on just two animals, forms a basis for a study design that may be employed for a more comprehensive assessment of the two-toed sloth reproductive physiology and behavior.

The behaviour and activity budgets of two sympatric sloths; Bradypus variegatus and Choloepus hoffmanni

It is usually beneficial for species to restrict activity to a particular phase of the 24-hour cycle as this enables the development of morphological and behavioural adaptations to enhance survival under specific biotic and abiotic conditions. Sloth activity patterns are thought to be strongly related to the environmental conditions due to the metabolic consequences of having a low and highly variable core body temperature. Understanding the drivers of sloth activity and their ability to withstand environmental fluctuations is of growing importance for the development of effective conservation measures, particularly when we consider the vulnerability of tropical ecosystems to climate change and the escalating impacts of anthropogenic activities in South and Central America. Unfortunately, the cryptic nature of sloths makes long term observational research difficult and so there is very little existing literature examining the behavioural ecology of wild sloths. Here, we used micro data loggers to continuously record, for the first time, the behaviour of both Bradypus and Choloepus sloths over periods of days to weeks. We investigate how fluctuations in the environmental conditions affect the activity of sloths inhabiting a lowland rainforest on the Caribbean coast of Costa Rica and examined how this might relate to their low power lifestyle. Both Bradypus and Choloepus sloths were found to be cathemeral in their activity, with high levels of between-individual and within-individual variation in the amounts of time spent active, and in the temporal distribution of activity over the 24-hour cycle. Daily temperature did not affect activity, although Bradypus sloths were found to show increased nocturnal activity on colder nights, and on nights following colder days. Our results demonstrate a distinct lack of synchronicity within the same population, and we suggest that this pattern provides sloths with the flexibility to exploit favourable environmental conditions whilst reducing the threat of predation.

Sloth's giant tick (Amblyomma varium) parasitizing free-ranging maned sloth (Bradypus torquatus) in the Atlantic Forest biome, Brazil

Amblyomma varium is a neotropical tick popularly known as the sloth's giant tick, during the adult stage is found almost exclusively on mammals of the Bradypodidae and Megalonychidae families of the superorder Xenarthra. The maned sloth (Bradypus torquatus) is the only sloth species in danger of extinction in Brazil. This species is arboreal and descends to the ground only to perform defecation behavior. This behavior can be the determining factor for infestation and infection by different parasitic agents, including A. varium. This study reported the occurrence of A. varium found parasitizing free-living maned sloths (B. torquatus) in the Atlantic Forest biome of Northeast and Southeast Brazil. A total of 36 individuals were evaluated and more than 50% of the individuals were parasitized by ticks of the species A. varium. This study confirmed the importance of B. torquatus as a host for adults and nymphs of A. varium and reported the variation in length of the spurs on coxa IV of A. varium males.

Ocular microscopy of Bradypus variegatus

Bradypus variegatus, popularly known as common sloth or brown-throated sloth, is a species with wide geographical distribution in Brazil. Expand on the literature about the species, we aimed to describe the morphology of its eye and its main annexes. For this study, six frozen specimens donated to the Animal Morphological Research Laboratory of the Federal Rural University of Amazonia were used. The specimens were fixed in a 10% aqueous solution of formaldehyde. The structures that constitute the ocular apparatus were identified and described after dissection and histological analysis using light microscopy. The bulbar conjunctiva presented a stratified cuboidal epithelium, with a considerable number of serous glands. The stroma layer and the posterior limiting lamina were found well defined in the species. The corneoscleral meshwork possessed a large opening for drainage of aqueous humour, followed by a wide retinal region, in which a layer of photoreceptors was visualized. Cones and rods could not be discriminated from each other. Microscopy of the medial angle of the eye revealed the cartilage and glands of the third eyelid, and a well-developed lacrimal gland structure. Bradypus variegatus distinguishing features and similarities in comparison with other domestic and wild mammal and bird species already described were investigated, which expounded the limited knowledge that is presently available on the morphology of wild fauna. The data extend the limited knowledge that are presently available on the ocular histology of B. variegatus.

Liver proteome response to torpor in a basoendothermic mammal, Tenrec ecaudatus, provides insights into the evolution of homeothermy

Many mammals use adaptive heterothermy (e.g., torpor, hibernation) to reduce metabolic demands of maintaining high body temperature (T_b). Torpor is typically characterized by coordinated declines in T_b and metabolic rate (MR) followed by active rewarming. Most hibernators experience periods of euthermy between bouts of torpor during which homeostatic processes are restored. In contrast, the common tenrec, a basoendothermic Afrotherian mammal, hibernates without interbout arousals and displays extreme flexibility in T_b and MR. We investigated the molecular basis of this plasticity in tenrecs by profiling the liver proteome of animals that were active or torpid with high and more stable T_b (∼32°C) or lower T_b (∼14°C). We identified 768 tenrec liver proteins, of which 50.9% were differentially abundant between torpid and active animals. Protein abundance was significantly more variable in active cold and torpid compared with active warm animals, suggesting poor control of proteostasis. Our data suggest that torpor in tenrecs may lead to mismatches in protein pools due to poor coordination of anabolic and catabolic processes. We propose that the evolution of endothermy leading to a more realized homeothermy of boreoeutherians likely led to greater coordination of homeostatic processes and reduced mismatches in thermal sensitivities of metabolic pathways.

Flower consumption, ambient temperature and rainfall modulate drinking behavior in a folivorous-frugivorous arboreal mammal

Water is vital for the survival of any species because of its key role in most physiological processes. However, little is known about the non-food-related water sources exploited by arboreal mammals, the seasonality of their drinking behavior and its potential drivers, including diet composition, temperature, and rainfall. We investigated this subject in 14 wild groups of brown howler monkeys (Alouatta guariba clamitans) inhabiting small, medium, and large Atlantic Forest fragments in southern Brazil. We found a wide variation in the mean rate of drinking among groups (range = 0-16 records/day). Streams (44% of 1,258 records) and treeholes (26%) were the major types of water sources, followed by bromeliads in the canopy (16%), pools (11%), and rivers (3%). The type of source influenced whether howlers used a hand to access the water or not. Drinking tended to be evenly distributed throughout the year, except for a slightly lower number of records in the spring than in the other seasons, but it was unevenly distributed during the day. It increased in the afternoon in all groups, particularly during temperature peaks around 15:00 and 17:00. We found via generalized linear mixed modelling that the daily frequency of drinking was mainly influenced negatively by flower consumption and positively by weekly rainfall and ambient temperature, whereas fragment size and the consumption of fruit and leaves played negligible roles. Overall, we confirm the importance of preformed water in flowers to satisfy the howler's water needs, whereas the influence of the climatic variables is compatible with the 'thermoregulation/dehydration-avoiding hypothesis'. In sum, we found that irrespective of habitat characteristics, brown howlers seem to seek a positive water balance by complementing the water present in the diet with drinking water, even when it is associated with a high predation risk in terrestrial sources.

Spontaneous ingestion of water by a free-ranging maned sloth, Bradypus torquatus, in the Ibura National Forest, northeastern Brazil

Water is an important limiting factor in the ecology of many animals, and even in rainforests, arboreal mammals, such as sloths, may have limited access to water sources. Here, we describe the spontaneous ingestion of water by a free-ranging three-toed sloth (Bradypus torquatus). The event occurred in the Ibura National Forest, in northeastern Brazil, where a sub-adult B. torquatus was monitored over three days in January, 2014. On the third day, the sloth was feeding on mature leaves and, at 16:22 h, it began raining heavily. Once the rain ceased, the sloth began to ingest the rainwater trickling down a vertical branch by licking it, and continued to ingest water for approximately 26 minutes. This behaviour indicates that the water was a valuable resource for this sloth, and sheds new light on the previous assumptions that these animals are able to satisfy their water requirements through their diet alone. This observation, together with an overview of the data on the ingestion of water by arboreal mammalian folivores, indicates that the direct ingestion of water may depend on specific local conditions, in particular, the availability of water sources, as well as the specific necessities of the mammal. As the lack of previous records of this behaviour in sloths is likely due to the cryptic behaviour of these animals, this finding highlights the importance of continuous, long-term behavioural monitoring for a more complete understanding of sloth ecology.

Sloths (Bradypus variegatus) as a polygastric mammal

Fermentative herbivorous animals have peculiar conformations of the digestive system. It is known that B. variegatus obtained the capacity for evolutionary adaptation, due to their ecology and eating habits. However, despite the literature on feeding management for this species, there is a lack of published information regarding its gastric morphology, and such information would support a better understanding on the diet and digestion of these individuals. We found seven gastric compartments, which histologically revealed three distinct patterns: an aglandular keratinized fraction (mechanical stomach) and two glandular fractions, one a mucus secretor and the other one composed of acid secreting cells (chemical stomach). With these evidences we understand that these individuals have gastric resemblance to ruminants, with some inherent peculiarities of this species, including the transit of the bolus.

Cross-order host switches of hepatitis C-related viruses illustrated by a novel hepacivirus from sloths

The genealogy of the hepatitis C virus (HCV) and the genus Hepacivirus remains elusive despite numerous recently discovered animal hepaciviruses (HVs). Viruses from evolutionarily ancient mammals might elucidate the HV macro-evolutionary patterns. Here, we investigated sixty-seven two-toed and nine three-toed sloths from Costa Rica for HVs using molecular and serological tools. A novel sloth HV was detected by reverse transcription polymerase chain reaction (RT-PCR) in three-toed sloths (2/9, 22.2%; 95% confidence interval (CI), 5.3-55.7). Genomic characterization revealed typical HV features including overall polyprotein gene structure, a type 4 internal ribosomal entry site in the viral 5'-genome terminus, an A-U-rich region and X-tail structure in the viral 3'-genome terminus. Different from other animal HVs, HV seropositivity in two-toed sloths was low at 4.5 per cent (3/67; CI, 1.0-12.9), whereas the RT-PCR-positive three-toed sloths were seronegative. Limited cross-reactivity of the serological assay implied exposure of seropositive two-toed sloths to HVs of unknown origin and recent infections in RT-PCR-positive animals preceding seroconversion. Recent infections were consistent with only 9 nucleotide exchanges between the two sloth HVs, located predominantly within the E1/E2 encoding regions. Translated sequence distances of NS3 and NS5 proteins and host comparisons suggested that the sloth HV represents a novel HV species. Event- and sequence distance-based reconciliations of phylogenies of HVs and of their hosts revealed complex macro-evolutionary patterns, including both long-term evolutionary associations and host switches, most strikingly from rodents into sloths. Ancestral state reconstructions corroborated rodents as predominant sources of HV host switches during the genealogy of extant HVs. Sequence distance comparisons, partial conservation of critical amino acid residues associated with HV entry and selection pressure signatures of host genes encoding entry and antiviral protein orthologs were consistent with HV host switches between genetically divergent mammals, including the projected host switch from rodents into sloths. Structural comparison of HCV and sloth HV E2 proteins suggested conserved modes of hepaciviral entry. Our data corroborate complex macro-evolutionary patterns shaping the genus Hepacivirus, highlight that host switches are possible across highly diverse host taxa, and elucidate a prominent role of rodent hosts during the Hepacivirus genealogy.

RENAL EVALUATION IN CHOLOEPUS SPECIES

Two species of sloths in the family Megalonychidae, Hoffmann's (Choloepus hoffmanni) and Linnaeus's (Choloepus didactylus) two-toed sloths, are commonly held in zoological institutions. Despite frequent published reports of urinary tract disease in these species, reports of diagnostics are mostly limited to descriptions of hematology and serum chemistry. In this study, repeated urinalysis, urinary chemistry, serum chemistry, and radiographs were collected opportunistically from six Hoffmann's and five Linnaeus's sloths. Proteinuria, bacteriuria, low urine specific gravity, and crystalluria were common in the absence of other signs of urinary tract pathology.

EVALUATION OF 25-HYDROXYVITAMIN D IN HOFFMANN'S TWO-TOED SLOTHS (CHOLOEPUS HOFFMANNI) USING DRIED BLOOD SPOTS ANALYZED BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Although biochemical analytes have typically been measured using serum or whole blood samples, an increasing number of assays are validated for measurement of analytes from dried blood spots (DBS) on filter paper. DBS techniques are minimally invasive, require only a small sample volume, and simplify processing, storage, and shipment of samples. These qualities make DBS-based assays ideal for sampling of wildlife species in both captive and field settings. In this study, a liquid chromatography-tandem mass spectrometry assay was evaluated for measurement of 25-hydroxyvitamin D in sloths. Paired serum and DBS samples were collected from nine healthy captive Hoffmann's two-toed sloths (Choloepus hoffmanni). Statistical analysis using Passing-Bablok regression analysis, Bland-Altman plots, and the Wilcoxon signed-rank tests found good agreement between 25-hydroxyvitamin D3 measurements in serum and DBS samples. Constant and proportional bias were absent. Results from this study support the use of DBS samples for the evaluation of vitamin D status in Hoffmann's two-toed sloths and provide a foundation for further studies to validate this technique.

Bone cortical compactness in 'tree sloths' reflects convergent evolution

Bone remodeling, one of the main processes that regulate bone microstructure, consists of bone resorption followed by the deposition of secondary bone at the same location. Remodeling intensity varies among taxa, but a characteristically compact cortex is ubiquitous in the long bones of mature terrestrial mammals. A previous analysis found that cortical bone in a few 'tree sloth' (Bradypus and Choloepus) specimens is heavily remodeled and characterized by numerous immature secondary osteons, suggesting that these animals were remodeling their bones at high rate until late in their ontogeny. This study aims at testing if this remodeling is generally present in 'tree sloths', using a quantitative analysis of the humeral cortical compactness (CC) among xenarthrans. The results of the investigation of humeral diaphyseal cross-sections of 26 specimens belonging to 10 xenarthran species including specimens from both extinct and extant species indicate that in 'tree sloths' the CC is significantly lower than in the other sampled xenarthrans. No significant difference was found between the CC of the two genera of 'tree sloths'. Our results are consistent with the hypothesis that the cortical bone of 'tree sloths' in general undergoes intense and balanced remodeling that is maintained until late (possibly throughout) in their ontogeny. In the light of xenarthran phylogeny, low CC represents another convergence between the long-separated 'tree sloth' lineages. Although the exact structural and/or functional demands that are associated with this trait are hitherto unknown, several hypotheses are suggested here, including a relationship to their relatively low metabolism and to the mechanical demands imposed upon the bones by the suspensory posture and locomotion, which was independently acquired by the two genera of 'tree sloths'.

Extreme physiological plasticity in a hibernating basoendothermic mammal, Tenrec ecaudatus

Physiological plasticity allows organisms to respond to diverse conditions. However, can being too plastic actually be detrimental? Malagasy common tenrecs, Tenrec ecaudatus, have many plesiomorphic traits and may represent a basal placental mammal. We established a laboratory population of T. ecaudatus and found extreme plasticity in thermoregulation and metabolism, a novel hibernation form, variable annual timing, and remarkable growth and reproductive biology. For instance, tenrec body temperature (Tb) may approximate ambient temperature to as low as 12°C even when tenrecs are fully active. Conversely, tenrecs can hibernate with Tbs of 28°C. During the active season, oxygen consumption may vary 25-fold with little or no changes in Tb. During the Austral winter, tenrecs are consistently torpid but the depth of torpor may be variable. A righting assay revealed that Tb contributes to but does not dictate activity status. Homeostatic processes are not always linked e.g. a hibernating tenrec experienced a ∼34% decrease in heart rate while maintaining constant body temperature and oxygen consumption rates. Tenrec growth rates vary but young may grow ∼40-fold in the 5 weeks until weaning and may possess indeterminate growth as adults. Despite all of this profound plasticity, tenrecs are surprisingly intolerant to extremes in ambient temperature (&lt;8 or &gt;34°C). We contend that while plasticity may confer numerous energetic advantages in consistently moderate environments, environmental extremes may have limited the success and distribution of plastic basal mammals.

FIRST RECORD OF HEMATOLOGIC VALUES IN FREE-LIVING AND CAPTIVE MANED SLOTHS (BRADYPUS TORQUATUS; XENARTHA, BRADYPODIDAE)

Bradypus torquatus is a rare and endemic sloth species from the Atlantic Forest, Brazil. Due to a lack of medical information including hematologic reference parameters for the species, hematologic baseline values were determined using samples from 14 clinically healthy B. torquatus , under captive (n = 7) and free-living (n = 7) conditions in Bahia State, Brazil. Additionally, the morphology of the blood cells is presented, with a demonstration that the Barr body chromosome may assist with sex determination of the species. The Barr body chromosome was present in all seven females and absent in all males. Many erythrocytes were approximately the size of small lymphocytes, with red blood cells exhibiting anisocystosis, normochromia, and apparent macrocytosis, compared with domestic animals. This study provides the first published hematologic values and cell morphology for B. torquatus . However, further studies are suggested using an automated hematology analyzer with larger sample sizes so that reference intervals may be established and hematologic values better understood for sex, habitat type, and age cohorts.

Morfologia e morfometria da traqueia da preguiça (Bradypus variegatus): conhecimentos para procedimentos de emergência

Por ser uma espécie pouco estudada, principalmente do ponto de vista morfológico, objetivou-se conhecer a anatomia da traqueia da preguiça (Bradypus variegatus) a fim de fornecer informações para facilitar a eleição de tubo endotraqueal adequado, máscara laríngea ou cânula de traqueostomia para anestesia e procedimentos de emergência, uma vez que a mesma revelou-se possuidora de uma morfologia especial. Foram investigados 11animais jovens de idades diferentes, sendo quatro machos e sete fêmeas, provenientes do Museu Emilio Goeldi e doados a UFRA. Os exemplares foram perfundidos via intramuscular com solução aquosa de formol a 10% para fins de conservação e posteriormente foram dissecados em nível cervico-torácico, por meio de mesoscopia, expondo-se desde a laringe até os brônquios principais direito e esquerdo ao nível do hilo pulmonar. As traqueias foram divididas em cinco regiões (região cervical, região da primeira flexura, região da segunda flexura, região da terceira flexura e região da carina) as quais foram mensuradas altura e largura, assim como o comprimento traqueal total e parte do material foi submetido à técnicas de rotina histológica. Macroscopicamente, destacou-se a presença de sinuosidades acentuadas em porção médio caudal, contemplando a carina. O comprimento médio traqueal foi de 14,6cm. Microscopicamente, a traqueia era constituída por placas separadas de cartilagem hialina constituindo cada anel, sendo revestido por epitélio estratificado ciliado. Apesar da traqueia da preguiça comum apresentar revestimento padrão encontrado na traqueia de outros animais, na literatura não há registros de outras espécies que tenham morfologia macroscópica nas condições descritas, o que nos leva a sugerir, quando necessário acesso para ventilação de emergência, a prática da IOT e não a de traqueostomia.

Oocyte maturation in the sloth's giant tick Amblyomma varium (Acari: Ixodidae) in an ecological context

The sloth's giant tick Amblyomma varium Koch, which is a neotropical species that inhabits tropical rainforests, is the largest tick reported to date. The adult stage of this tick parasitizes mammals from the families Bradypodidae and Magalonychidae (Xenarthra) nearly exclusively. This study aimed to describe morphological and histological features of the reproductive system and the oocyte maturation process of this tick species. The ovary of A. varium is a long single tubular organ that is horseshoe-shaped, winding and arranged in the posterior part of the body. Two oviducts are connected to the ovary on each side; these thicken at certain region forming the uterus (common oviduct), followed by a muscular connecting tube, vagina and genital aperture. A large number of oocytes at different stages of development are attached to the ovary wall by the pedicel, as they reach maturity they are released into the ovary lumen and from there to the genital aperture. These oocytes develop simultaneously and asynchronically along the ovary. Amblyomma varium oocytes were classified into five development stages (i.e., I-V), and specific characteristics were observed; the processes of yolk and chorion deposition begin early in oocytes stage II, and oocytes V exhibit a very thick chorion and eggs of a large size. These characteristics are likely adaptations that enhance the survival and the reproductive success of this extremely host-specific tick, which is limited to a particular environment.

The distributional ecology of the maned sloth: environmental influences on its distribution and gaps in knowledge

The maned sloth Bradypus torquatus (Pilosa, Bradypodidae) is endemic to a small area in the Atlantic Forest of coastal Brazil. It has been listed as a threatened species because of its restricted geographic range, habitat loss and fragmentation, and declining populations. The major objectives of this study were to estimate its potential geographic distribution, the climatic conditions across its distributional range, and to identify suitable areas and potential species strongholds. We developed a model of habitat suitability for the maned sloth using two methods, Maxent and Mahalanobis Distance, based on 42 occurrence points. We evaluated environmental variable importance and the predictive ability of the generated distribution models. Our results suggest that the species distribution could be strongly influenced by environmental factors, mainly temperature seasonality. The modeled distribution of the maned sloth included known areas of occurrence in the Atlantic Forest (Sergipe, Bahia, Espírito Santo, and Rio de Janeiro), but did not match the observed distributional gaps in northern Rio de Janeiro, northern Espírito Santo or southern Bahia. Rather, the model showed that these areas are climatically suitable for the maned sloth, and thus suggests that factors other than climate might be responsible for the absence of species. Suitable areas for maned sloth were located mainly in the mountainous region of central Rio de Janeiro throughout Espírito Santo and to the coastal region of southern Bahia. We indicate 17 stronghold areas and recommended survey areas for the maned sloth. In addition, we highlight specific areas for conservation, including the current network protected areas. Our results can be applied for novel surveys and discovery of unknown populations, and help the selection of priority areas for management and conservation planning, especially of rare and relatively cryptic species directed associated with forested habitats.

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.

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.

Paws for thought: comparative radiologic anatomy of the mammalian forelimb

All mammals share a remarkably similar skeleton based on a common template. This commonality is particularly well illustrated by the versatile pentadactyl limb, upon which all mammalian limbs are based. For most mammals, the primary function of the forelimb is locomotion. The forelimb has been successfully adapted in mammals of all sizes and in terrestrial, arboreal, aquatic, and airborne environments. In primates, the forelimbs have developed such that speed and stamina have been sacrificed for an increased range of movement, which in turn has provided increased manual dexterity. For instance, chimpanzee hands are pronated and the fingers are flexed, and the phalanges are longer and exhibit much more robust insertion areas for flexor tendons. Ungulates (hoofed mammals), on the other hand, have evolved to maximize speed and stamina in quadrupedal locomotion. The two main orders of ungulates have elongated phalanges and metacarpals; all ungulates have lost the first metacarpal. The cat family represents some of the most highly evolved predators. Cats' forelimbs are designed for speed, power, and acceleration rather than for stamina; they maintain all five metacarpals and phalanges, although the first digit is relatively small.

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.

Fecal estradiol and progesterone metabolite levels in the three-toed sloth (Bradypus variegatus)

The present study was carried out to assess the possibility of measuring fecal steroid hormone metabolites as a noninvasive technique for monitoring reproductive function in the three-toed sloth, Bradypus variegatus. Levels of the estradiol (E2) and progesterone (P4) metabolites were measured by radioimmunoassay in fecal samples collected over 12 weeks from 4 captive female B. variegatus sloths. The validation of the radioimmunoassay for evaluation of fecal steroid metabolites was carried out by collecting 10 blood samples on the same day as defecation. There was a significant direct correlation between the plasma and fecal E2 and P4 levels (P < 0.05, Pearson's test), thereby validating this noninvasive technique for the study of the estrous cycle in these animals. Ovulation was detected in two sloths (SL03 and SL04) whose E2 levels reached 2237.43 and 6713.26 pg/g wet feces weight, respectively, for over four weeks, followed by an increase in P4 metabolites reaching 33.54 and 3242.68 ng/g wet feces weight, respectively. Interestingly, SL04, which presented higher levels of E2 and P4 metabolites, later gave birth to a healthy baby sloth. The results obtained indicate that this is a reliable technique for recording gonadal steroid secretion and thereby reproduction in sloths.

Molecular trees of trypanosomes incongruent with fossil records of hosts

Molecular trees of trypanosomes have confirmed conventionally accepted genera, but often produce topologies that are incongruent with knowledge of the evolution, systematics, and biogeography of hosts and vectors. These distorted topologies result largely from incorrect assumptions about molecular clocks. A host-based phylogenetic tree could serve as a broad outline against which the reasonability of molecular phylogenies could be evaluated. The host-based tree of trypanosomes presented here supports the " invertebrate first " hypothesis of trypanosome evolution, supports the monophyly of Trypanosomatidae, and indicates the digenetic lifestyle arose three times. An area cladogram of Leishmania supports origination in the Palaearctic during the Palaeocene.

The effect of feeding on the respiratory activity of the sloth

The aim of the present study was to confirm whether feeding influences the resting breathing rate and to observe possible alterations in blood gas and pH levels produced by feeding in unanesthetized sloths (Bradypus variegatus). Five adult male sloths (4.1 +/- 0.6 kg) were placed daily in an experimental chair for a period of at least 4 h for sitting adaptation. Five measurements were made for each sloth. However, the sloths one, two and five were studied once and the sloths three and four were studied twice. Breathing rate was determined with an impedance meter and the output signal was digitized. Arterial blood samples were collected for blood gas analysis with a BGE electrolytes analyzer and adjusted for the animal's body temperature and hemoglobin content. The data are reported as mean +/- SD and were collected during the resting period (8:00-10:00 h) and during the feeding period (16:00-18:00 h). The mean breathing rate increased during mastication of ymbahuba leaves (rest: 5.0 +/- 1, feeding: 10 +/- 1 bpm). No significant alterations were observed in arterial pH (rest: 7.42 +/- 0.05, feeding: 7.45 +/- 0.03), PCO2 (rest: 35.2 +/- 5.3, feeding: 33.3 +/- 4.4 mmHg) or PO2 (rest: 77.5 +/- 8.2, feeding: 78.4 +/- 5.2 mmHg) levels. These results indicate that in unanesthetized sloths 1) feeding evokes an increase in breathing rate without a significant change in arterial pH, PCO2 or PO2 levels, and 2) the increase in breathing rate produced by feeding probably is due to the act of mastication.

Acute disseminated toxoplasmosis in a captive three-toed sloth (Bradypus tridactylus)

Fatal toxoplasmosis was diagnosed in a captive three-toed sloth (Bradypus tridactylus), an arboreal species of the tropical rainforests of South and Central America. In view of its specialized lifestyle and ecosystem and its low metabolic rate, B. tridactylus would seem to warrant further investigation in respect of its susceptibility to Toxoplasma gondii.

Sloth biology: an update on their physiological ecology, behavior and role as vectors of arthropods and arboviruses

This is a review of the research undertaken since 1971 on the behavior and physiological ecology of sloths. The animals exhibit numerous fascinating features. Sloth hair is extremely specialized for a wet tropical environment and contains symbiotic algae. Activity shows circadian and seasonal variation. Nutrients derived from the food, particularly in Bradypus, only barely match the requirements for energy expenditure. Sloths are hosts to a fascinating array of commensal and parasitic arthropods and are carriers of various arthropod-borne viruses. Sloths are known reservoirs of the flagellate protozoan which causes leishmaniasis in humans, and may also carry trypanosomes and the protozoan Pneumocystis carinii.