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.     

Behavioural ecology of the Sloth bear (Melursus ursinus)

The Sloth bear ( Melursus ursinus ), which is endemic to the Indian subcontinent and Sri Lanka, has declined in numbers in many areas in recent years probably as the result of over-killing and habitat alteration. In the 544 km² Royal Chitawan National Park in the Nepal terai, we estimated there were a minimum of 55 bears or a crude density of 0˙1/km². During peak concentrations in the lowlying riverine forest/tall grass habitat in March, the ecological density was 0˙5/km².
Cubs still with their mothers comprised 24 % of the 161 bears classified between December 1972 and November 1975. Females comprised 48% of the adults classified. Average size of 24 litters was 1˙6 (1–2). Seventy-two per cent of the observations were of lone individuals. Three (an adult female with two cubs), was the largest group of bears seen. The only extended social group observed was the female-young unit although newly independent siblings may remain together for a short time. Maternal relations, adult interactions, tree marking, ranging, feeding and anti-predatory behaviour are described.
Examination of 139 droppings showed that these bears fed on at least 17 different fruits (47% occurrence), flowers, grass, honey, and six different insects (52% occurrence). Fruits were an important food from March to June with individual species predominating throughout their fruiting season. Termites, including Odontotermes obesus , were in the diet for most of the year. The Sloth bear was not observed preying on mammals and according to other observers, only rarely feeds on carrion. The ecological basis for selected aspects of Sloth bear biology and behaviour is discussed.     

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.     

Comparative Phylogeography of the Atlantic Forest Endemic Sloth (Bradypus torquatus) and the Widespread Three-toed Sloth (Bradypus variegatus) (Bradypodidae, Xenarthra)

The comparative phylogeographic study of the maned sloth (Bradypus torquatus) and the three-toed sloth (Bradypus variegatus) was performed using a segment of mitochondrial DNA (mtDNA) control region. We examined 19 B. torquatus from two regions and 47 B. variegatus from three distant regions of Atlantic forest. This first characterization of molecular diversity indicates a great diversity (B. torquatus: h = 0.901 ± 0.039 and π = 0.012 ± 0.007; B. variegatus: h = 0.699 ± 0.039 and π = 0.010 ± 0.006) and very divergent mitochondrial lineages within each sloth species. The different sampled regions carry distinct and non-overlapping sets of mtDNA haplotypes and are genetically divergent. This phylogeographic pattern may be characteristic of sloth species. In addition, we infer that two main phylogeographic groups exist in the Atlantic forest representing a north and south distinct divergence.     

Challenges of Large Carnivore Conservation: Sloth Bear Attacks in Sri Lanka

Sloth bear (Melursus ursinus) attacks in Sri Lanka present a major challenge to their conservation as human populations grow and compete with bears for space and resources. Bear attacks on humans predominantly affect the rural poor and seem to be increasing in frequency. In 2004, we conducted the first island-wide survey of bear attacks in Sri Lanka. Our main goals were to 1) describe where and when attacks occurred, 2) describe the characteristics and outcome of bear attacks, and 3) evaluate the influence of human group size on the severity of bear attacks. We interviewed 271 individuals attacked by sloth bears between 1938 and 2004. Sloth bears rarely entered village compounds, damaged property, or raided crops; conflicts predominantly involved attacks on people in forests. Most sloth bear attacks took place during daylight hours (0900-1600 h) in the dry season, when humans were likely to engage in forest activities such as honey gathering. Most attacks (80 %) occurred when humans and bears surprised each other at close proximity (<10 m). Most (84 %) victims carried a weapon but 55 % said the attack was too sudden to effectively use the weapon in self-defense. Human injuries included lacerations and puncture wounds, broken limbs, skull fractures, and the loss of scalps, eyes, or other parts of the face. Almost all major injuries resulted from bites. In 61 attacks bears were wounded and in 39 attacks bears were killed. The severity of human injuries depended on human group size; solitary humans experienced more severe injuries than expected, suggesting that the presence of other humans may moderate the bear’s aggression and motivate it to flee. Widespread fear of sloth bears poses a significant challenge to modifying ineffective human responses to bear encounters (e.g., fleeing). Conservation outreach could emphasize that greater human safety may be achieved from remaining in groups and using extreme caution around thickets and rock outcrops likely to be used by bears.     

Was Frozen Mammoth or Giant Ground Sloth Served for Dinner at The Explorers Club?

Accounts of woolly mammoths (Mammuthus primigenius) preserved so well in ice that their meat is still edible have a long history of intriguing the public and influencing paleontological thought on Quaternary extinctions and climate, with some scientists resorting to catastrophism to explain the instantaneous freezing necessary to preserve edible meat. Famously, members of The Explorers Club purportedly dined on frozen mammoth from Alaska, USA, in 1951. This event, well received by the press and general public, became an enduring legend for the Club and popularized the notorious annual tradition of serving rare and exotic food at Club dinners that continues to this day. The Yale Peabody Museum holds a sample of meat preserved from the 1951 meal, interestingly labeled as a South American giant ground sloth (Megatherium), not mammoth. We sequenced a fragment of the mitochondrial cytochrome-b gene and studied archival material to verify its identity, which if genuine, would extend the range of Megatherium over 600% and alter our views on ground sloth evolution. Our results indicate that the meat was not mammoth or Megatherium but green sea turtle (Chelonia mydas). The prehistoric dinner was likely an elaborate publicity stunt. Our study emphasizes the value of museums collecting and curating voucher specimens, particularly those used for evidence of extraordinary claims.     

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.     

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.     

Observations on the Endemic Pygmy Three-Toed Sloth,Bradypus pygmaeus of Isla Escudo de Veraguas,Panamá

Our objective was to ascertain the population status of the Pygmy Three-toed Sloth, Bradypus pygmaeus, an IUCN Critically Endangered species, on Isla Escudo de Veraguas, Panama. Bradypus pygmaeus are thought to be folivorous mangrove specialists; therefore we conducted a visual systematic survey of all 10 mangrove thickets on the island. The total mangrove habitat area was measured to be 1.67 ha, comprising 0.024% of the total island area. The population survey found low numbers of B. pygmaeus in the mangrove thickets and far lower numbers outside of them. The connectivity of subpopulations between these thickets on the island is not established, as B. pygmaeus movement data is still lacking. We found 79 individuals of B. pygmaeus; 70 were found in mangroves and 9 were observed just beyond the periphery of the mangroves in non-mangrove tree species. Low population number, habitat fragmentation and habitat loss could lead to inbreeding, a loss of genetic diversity, and extinction of B. pygmaeus.     

Dry Season Diet of the Sloth Bear (Melursus ursinus) in Hadagarh Wildlife Sanctuary,Eastern India

Dry season food habit of sloth bear (Melursus ursinus) in Hadagarh Wildlife Sanctuary was characterized by scat analysis. Importance value index (IVI) of contribution of different food items in the diet of sloth bear was estimated from the undigested food remnants. Percentage of dry weight and IVI score of Ziziphus fruits was highest, termites were the most frequently occurring food item in the diet and percentage of frequency occurrence was equal for both fruits and insects. The present study, as compared to previous studies, suggests that the dietary preference of sloth bear varies according to availability of food and the habitat quality.     

Seed Dispersal by the Sloth Bear (Melursus ursinus) in South India1

Previous studies have shown that sloth bears are mainly myrmecophagous, but in this study, 39 and 83 percent (wet and dry season, respectively) of scats surveyed in South India contained fruits. Seeds from three of six plant species collected from scats germinated faster than seeds not passing through bears; germination percentage was not higher in any of the six species. These results suggest that the sloth bear may play an important role in the population dynamics of fleshy‐fruited species of the region.     

The Narial Anatomy of Extinct and Extant Sloths (Xenarthra,Folivora): Osteological Anomalies in the Extant Two-Toed Sloth Choloepus

Journal of Mammalian Evolution - The skeletal anatomy of the anterior narial region in mammals is complex, comprised of several bony and cartilaginous elements. Because it includes many...     

Genetic Variation,Structure, and Gene Flow in a Sloth Bear (Melursus ursinus) Meta-Population in the Satpura-Maikal Landscape of Central India

Sloth bears (Melursus ursinus) are endemic to the Indian subcontinent. As a result of continued habitat loss and degradation over the past century, sloth bear populations have been in steady decline and now exist only in isolated or fragmented habitat across the entire range. We investigated the genetic connectivity of the sloth bear meta-population in five tiger reserves in the Satpura-Maikal landscape of central India. We used noninvasively collected fecal and hair samples to obtain genotypic information using a panel of seven polymorphic loci. Out of 194 field collected samples, we identified 55 individuals in this meta-population. We found that this meta-population has moderate genetic variation, and is subdivided into two genetic clusters. Further, we identified five first-generation migrants and signatures of contemporary gene flow. We found evidence of sloth bears in the corridor between the Kanha and Pench Tiger Reserves, and our results suggest that habitat connectivity and corridors play an important role in maintaining gene flow in this meta-population. These corridors face several anthropogenic and infrastructure development threats that have the potential to sever ongoing gene flow, if policies to protect them are not put into action immediately.     

<Emphasis Type="Italic">Baraguatherium takumara</Emphasis>, <Emphasis Type="Bold">Gen. et Sp. Nov., the Earliest Mylodontoid Sloth (Early Miocene) from Northern South America</Emphasis>

We report a new genus and species of sloth, based on a partial mandible and associated femur, from the early Miocene of Venezuela. Baraguatherium takumara, gen. et sp. nov., represents the earliest member of the Mylodontoidea recognized from northern South America. Phylogenetically and morphologically, Baraguatherium possesses some plesiomorphic characters: a vasodentine layer in the core of the tooth similar to Octodontotherium, Paroctodontotherium, and Orophodon; molariforms parallel to the long axis of the toothrow; teeth with a very thin layer of cementum; mf1-mf3 series of similar size and bilobate; mf3 conspicuously piriform; and occlusal surface of tooth beveled, which places it at the base of the Mylodontidae clade. Baraguatherium was found in continental deposits that also preserve abundant wood and leaves associated with a near shore marine complex, indicating that Baraguatherium lived in a coastal tropical forest in the early Miocene in northern South America. The presence of a vasodentine layer in the core of the tooth is quite similar to Octodontotherium, Paroctodontotherium, and Orophodon and allows assignment of this new taxon to the Mylodontoidea.     

Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands/Savannas in South America

We describe a new taxon of mylodontid sloth from the late Oligocene (Deseadan South American Land Mammal “age”), Salla Beds of Bolivia. This taxon, Paroctodontotherium calleorum, new genus and species, is one of the oldest known sloths, but it is surprisingly derived. It is referable to the Mylodontidae and, with just a little doubt, to the Mylodontinae. It shares a number of derived characteristics with other mylodontids and even mylodontines. These include: a relatively low temporomandibular joint; a relatively short zygomatic process of the squamosal; an elongated, narrow braincase; anteriorly diverging toothrows; broad muzzle; and greatly enlarged external nares. The relative width of the muzzle of Paroctodontotherium is as great as any Pleistocene mylodontid except the giant grazer, Lestodon. We review and critique methods of estimating diets of extinct sloths and propose a hypothesis in regard to the feeding ecology of Paroctodontotherium. Based upon its broad muzzle, the degree of tooth wear, and its presence in a habitat dominated by hypsodont herbivores, we propose that Paroctodontotherium was a bulk feeder that foraged near ground level. Grasses were likely a major component of its diet. The addition of this new taxon, along with other recently discovered taxa, illustrates that late Oligocene sloths had much greater diversity than recognized just a decade ago. This diversity is evident in species richness, variations in body sizes, dental morphologies, and means of locomotion. We regard this relatively sudden sloth radiation as a significant component of the Eocene-Oligocene faunal turnover and was related to the development of more open habitats of post-Eocene South America.