Bryson Voirin

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 sleeps 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.

Evidence that birds sleep in mid-flight

Many birds fly non-stop for days or longer, but do they sleep in flight and if so, how? It is commonly assumed that flying birds maintain environmental awareness and aerodynamic control by sleeping with only one eye closed and one cerebral hemisphere at a time. However, sleep has never been demonstrated in flying birds. Here, using electroencephalogram recordings of great frigatebirds (Fregata minor) flying over the ocean for up to 10 days, we show that they can sleep with either one hemisphere at a time or both hemispheres simultaneously. Also unexpectedly, frigatebirds sleep for only 0.69 h d−1 (7.4% of the time spent sleeping on land), indicating that ecological demands for attention usually exceed the attention afforded by sleeping unihemispherically. In addition to establishing that birds can sleep in flight, our results challenge the view that they sustain prolonged flights by obtaining normal amounts of sleep on the wing.

Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilus welckeri (Chlorophyta, Ulvophyceae).

BackgroundSloths are slow-moving arboreal mammals inhabiting tropical rainforests in Central and South America. The six living species of sloths are occasionally reported to display a greenish discoloration of their pelage. Trichophilus welckeri, a green algal species first described more than a century ago, is widely believed to discolor the animals fur and provide the sloth with effective camouflage. However, this phenomenon has not been explored in any detail and there is little evidence to substantiate this widely held opinion.ResultsHere we investigate the genetic diversity of the eukaryotic community present in fur of all six extant species of sloth. Analysis of 71 sloth hair samples yielding 426 partial 18S rRNA gene sequences demonstrates a diverse eukaryotic microbial assemblage. Phylogenetic analysis reveals that sloth fur hosts a number of green algal species and suggests that acquisition of these organisms from the surrounding rainforest plays an important role in the discoloration of sloth fur. However, an alga corresponding to the morphological description of Trichophilus welckeri was found to be frequent and abundant on sloth fur. Phylogenetic analysis demonstrated the retention of this alga on the fur of sloths independent of geographic location.ConclusionsThese results demonstrate a unique diverse microbial eukaryotic community in the fur of sloths from Central and South America. Our analysis streghtens the case for symbiosis between sloths and Trichophilus welckeri.

Evolutionary Relationships among Extinct and Extant Sloths: The Evidence of Mitogenomes and Retroviruses

Macroevolutionary trends exhibited by retroviruses are complex and not entirely understood. The sloth endogenized foamy-like retrovirus (SloEFV), which demonstrates incongruence in virus–host evolution among extant sloths (Order Folivora), has not been investigated heretofore in any extinct sloth lineages and its premodern history within folivorans is therefore unknown. Determining retroviral coevolutionary trends requires a robust phylogeny of the viral host, but the highly reduced modern sloth fauna (6 species in 2 genera) does not adequately represent what was once a highly diversified clade (∼100 genera) of placental mammals. At present, the amount of molecular data available for extinct sloth taxa is limited, and analytical results based on these data tend to conflict with phylogenetic inferences made on the basis of morphological studies. To augment the molecular data set, we applied hybridization capture and next-generation Illumina sequencing to two extinct and three extant sloth species to retrieve full mitochondrial genomes (mitogenomes) from the hosts and the polymerase gene of SloEFV. The results produced a fully resolved and well-supported phylogeny that supports dividing crown families into two major clades: 1) The three-toed sloth, Bradypus, and Nothrotheriidae and 2) Megalonychidae, including the two-toed sloth, Choloepus, and Mylodontidae. Our calibrated time tree indicates that the Miocene epoch (23.5 Ma), particularly its earlier part, was an important interval for folivoran diversification. Both extant and extinct sloths demonstrate multiple complex invasions of SloEFV into the ancestral sloth germline followed by subsequent introgressions across different sloth lineages. Thus, sloth mitogenome and SloEFV evolution occurred separately and in parallel among sloths.

Ecology and Neurophysiology of Sleep in Two Wild Sloth Species

STUDY OBJECTIVES Interspecific variation in sleep measured in captivity correlates with various physiological and environmental factors, including estimates of predation risk in the wild. However, it remains unclear whether prior comparative studies have been confounded by the captive recording environment. Herein we examine the effect of predation pressure on sleep in sloths living in the wild. DESIGN Comparison of two closely related sloth species, one exposed to predation and one free from predation. SETTING Panamanian mainland rainforest (predators present) and island mangrove (predators absent). PARTICIPANTS Mainland (Bradypus variegatus, five males and four females) and island (Bradypus pygmaeus, six males) sloths. INTERVENTIONS None. MEASUREMENTS AND RESULTS Electroencephalographic (EEG) and electromyographic (EMG) activity was recorded using a miniature data logger. Although both species spent between 9 and 10 h per day sleeping, the mainland sloths showed a preference for sleeping at night, whereas island sloths showed no preference for sleeping during the day or night. Standardized EEG activity during nonrapid eye movement (NREM) sleep showed lower low-frequency power, and increased spindle and higher frequency power in island sloths when compared to mainland sloths. CONCLUSIONS In sloths sleeping in the wild, predation pressure influenced the timing of sleep, but not the amount of time spent asleep. The preference for sleeping at night in mainland sloths may be a strategy to avoid detection by nocturnal cats. The pronounced differences in the NREM sleep EEG spectrum remain unexplained, but might be related to genetic or environmental factors.

Biology and Conservation of the Pygmy Sloth, Bradypus pygmaeus

The pygmy three-toed sloth (Bradypus pygmaeus) has garnered much interest since being described in 2001 as a new species, which occurs on a single island, Escudo de Veraguas, Panama. Recent work has found that the species has a highly diverse eukaryotic community in its hair, activity, and sleep patterns markedly different from other three-toed sloths in the region, and that some individuals live in nonmangrove areas as well as in the mangroves on the island. This critically endangered species is being threatened by several factors, including habitat degradation due to timber harvesting, increased development, and collecting. An accurate understanding of the ecological needs of pygmy sloths is imperative to forming a comprehensive and successful conservation strategy.

The curious case of Bradypus variegatus sloths: Populations in threatened habitats are biodiversity components needing protection

Studying Neotropical wild populations is of particular interest. While this region is facing an escalating habitat degradation, it also has remarkable biodiversity levels, whose origin we are only beginning to understand. A myriad of processes might have had idiosyncratic effects on its numerous species. Within the hottest Neotropical biodiversity hotspot, the Atlantic Forest (AF), species and genetic diversities are organized latitudinally, with decreasing diversity levels southwards. Bradypus variegatus, the brown-throated three-toed sloth, was one of the first species observed to present such pattern. Moreover, within AF, B. variegatus populations seem to be geographically isolated and genetically differentiated. Whether AF B. variegatus isolation, differentiation, and loss of genetic diversity are historical or contemporary (anthropogenic-driven), result from species-specific or general historical events, and if this is of conservation concern remains unclear. Here, we combine micro-evolutionary, multilocus, and high-throughput sequencing approaches to detail the processes responsible for the patterns of genetic diversity on B. variegatus populations in AF, and further understand AF biogeographic history. Few studies made use of similar approaches on Neotropical biodiversity. Our results agree with recent re-interpretations on the AF refugia model and support a species-specific refugium in southern AF, characterized by a metapopulation formation. Finally, we present compelling evidences of the need for conservation actions on AF B. variegatus populations, by comparing genetic diversity levels between populations of different Bradypus species. As far as we know, this is the most comprehensive assessment on Bradypus nuclear DNA diversity.

Why Do Sloths Poop on the Ground

The bizarre ground-based defecation behavior of two- and three-toed sloths remains one of the most paradoxical and humorous mysteries in canopy biology. Both two-toed (Choloepus sp.) and three-toed (Bradypus sp.) sloths defecate and urinate only once every 4–8 days in the wild. Although all other arboreal mammals release their excrement from the forest canopy, all sloths climb down from the treetops and relieve themselves on the forest floor. In the canopy, sloths have few predators, but on the ground, sloths expose themselves to great variety of predators. There must be some defining reason behind this high-risk behavior.