La fonction thyroidienne chez l'unau (Choloepus hoffmanni Peters)

Lemaire, M; Goffart, M; Closon, J; Winand, R

doi:10.1016/0016-6480(69)90191-9

Cited by 14 publications

(6 citation statements)

References 40 publications

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“…However, the low metabolism of Choloepus is associated with low thyroid activity (Lemaire et al. ; no data available to our knowledge for Bradypus ). In mammals, the multifunctional thyroid hormones are essential for both the regulation of metabolism (Brent, ), and the development and maintenance of bones (Gorka et al.…”

Section: Discussionmentioning

confidence: 99%

Bone cortical compactness in ‘tree sloths’ reflects convergent evolution

2018

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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'.

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Section: Discussionmentioning

confidence: 99%

Bone cortical compactness in ‘tree sloths’ reflects convergent evolution

2018

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“…are only 34–56% of the value expected for an average mammal of comparable body mass. This low metabolism is matched by a low thyroid activity as compared with other eutherian mammals (Lemaire et al., ), along with comparatively low, and fluctuating body temperatures that range between 30.2 and 34.2 °C (Ozorio de Almeida and Branco de Fialho, ; Montgomery and Sunquist, ; Oliveira et al., ; Merrit, ). However, depending on ambient temperature body temperature can even vary between 29.4 and 40.6 °C as recorded in six free‐ranging individuals (Montgomery and Sunquist, ).…”

Section: Introductionmentioning

confidence: 99%

Digestive physiology, metabolism and methane production of captive Linné's two‐toed sloths (Choloepus didactylus)

Vendl

Frei

Dittmann

et al. 2015

Animal Physiology Nutrition

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Sloths are renowned for their low metabolic rate, low food intake and low defecation frequency. We investigated factors of digestive physiology and energy metabolism in four captive individuals (mean body mass 10.0 ± SD 3.7 kg) of a hitherto mostly unstudied sloth species, Linné's two-toed sloth (Choloepus didactylus), in a 2-week digestion recording and 23-h respiration experiment on animals fed a standard zoo diet of vegetables and starchy components. Dry matter intake, defecation frequency and particle mean retention time (MRT) in the gastrointestinal tract (GIT) were 12 ± 3 g/(kg(0.75) day), once every 5 days and >140 h in three individuals, but 53 g/(kg(0.75) day), daily and 82 h in one individual that was apparently compensating for a period of weight loss prior to the experiment. In all animals, solute marker was eliminated at a faster rate than the particle marker, indicating 'digesta washing' in the sloths' GIT. The overall metabolic rate calculated from oxygen consumption matched the metabolisable energy intake in three individuals [173 ± 22 vs. 168 ± 44 kJ/(kg(0.75) day)] but not in the fourth one [225 vs. 698 kJ/(kg(0.75) day)], supporting the interpretation that this animal was replenishing body stores. In spite of the low food intake and the low-fibre diet (209 ± 26 g neutral detergent fibre/kg dry matter), methane production was rather high accounting for 9.4 ± 0.8% of gross energy intake (2.7% in the fourth individual), which exceeded literature data for ruminants on forage-only diets. These results corroborate literature reports on low intake, low defecation frequency, low metabolic rate and long MRT in other sloth species. The long MRT is probably responsible for the comparatively high methane production, providing more opportunity for methanogenic archaea than in other non-ruminant mammals to produce significant amounts of methane.

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“…2013) may be driven by low thyroid activity (reported for Choloepus ; Lemaire et al. 1969). Thyroid hormones regulate metabolism (Brent 2012) and bone growth (Gorka et al.…”

Section: Discussionmentioning

confidence: 99%

Evolution of bone cortical compactness in slow arboreal mammals

2020

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Convergent evolution is a major topic in evolutionary biology. Low bone cortical compactness (CC, a measure of porosity of cortical bone) in the extant genera of “tree sloths,” has been linked to their convergent slow arboreal ecology. This proposed relationship of low CC with a slow arboreal lifestyle suggests potential convergent evolution of this trait in other slow arboreal mammals. Femoral and humeral CC were analyzed in “tree sloths,” lorisids, koala, and extinct palaeopropithecids and Megaladapis, in comparison to closely related but ecologically distinct taxa, in a phylogenetic framework. Low CC in “tree sloths” is unparalleled by any analyzed clade and the high CC in extinct sloths suggests the recent convergence of low CC in “tree sloths.” A tendency for low CC was found in Palaeopropithecus and Megaladapis. However, lorisids and the koala yielded unexpected CC patterns, preventing the recognition of a straightforward convergence of low CC in slow arboreal mammals. This study uncovers a complex relationship between CC and convergent evolution of slow arboreality, highlighting the multifactorial specificity of bone microstructure.

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La fonction thyroidienne chez l'unau (Choloepus hoffmanni Peters)

Cited by 14 publications

References 40 publications

Bone cortical compactness in ‘tree sloths’ reflects convergent evolution

Bone cortical compactness in ‘tree sloths’ reflects convergent evolution

Digestive physiology, metabolism and methane production of captive Linné's two‐toed sloths (Choloepus didactylus)

Evolution of bone cortical compactness in slow arboreal mammals

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