Poikilothermism in the Sloth

Britton, S. W.; Atkinson, William

doi:10.2307/1374287

Cited by 46 publications

(27 citation statements)

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“…The percentage of skin was equal in the adult koala (15.6±1.4% TBM) and sloth (15%; P>0.1) and significantly higher than that of wallabies (7% TBM; P<0.05). The percentage of muscle mass in the adult koala (34%±4.1% TBM) was higher than that in the sloth (23%; P<0.05 ;Beebe 1926;Britton and Atkinson 1938;Goffart 1971;Grand 1978) and lower than that in the wallaby (50%; P<0.005). The ratio of muscle to bone in the hindlimb also reflected this spectrum: adult koala (4.2±0.7) were intermediate to the sloth (2; P<0.05) and the wallaby (6; P<0.05).…”

Section: Resultsmentioning

confidence: 73%

Anatomy and development of the koala, Phascolarctos cinereus : an evolutionary perspective on the superfamily Vombatoidea

Grand¹,

Barboza²

2001

Anatomy and Embryology

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Fifteen koalas (Phascolarctos cinereus)--5 pouched young from 4 to 6.5 months and 10 adults from 5 to 16.5 years--were analyzed for functional parameters (body composition, limb segment and muscle mass, post-cranial skeletal characters) and developmental expressions (growth of body, brain, musculature). These data were compared with a convergent eutherian, the three-toed sloth, Bradypus infuscatus, and with the koala's distant (Macropodid; wallabies) and proximate (Vombatid; wombats) marsupial relatives. Musculoskeletal structures correlated with sitting and climbing; the growth of the young and the physiological demands of adulthood correlated with the low-quality diet of Eucalyptus foliage. The gestalt of the ancestral Vombatoids (pronograde quadrupeds, generalist browsers and social conservatives with low basal metabolism and attenuated development) provided the baseline essential for their locomotor and nutritional divergence into arboreal browsers, the koalas, and fossorial grazers, the wombats.

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Section: Resultsmentioning

confidence: 73%

Anatomy and development of the koala, Phascolarctos cinereus : an evolutionary perspective on the superfamily Vombatoidea

Grand¹,

Barboza²

2001

Anatomy and Embryology

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“…(Carvalho 1960;Montgomery and Sunquist 1975;Chiarello 1998b). Concomitant with their energy-poor diet, they have extremely low metabolic rates and are not fully homeothermic (Britton and Atkinson 1938). Sloths avoid predation largely by avoiding detection, moving very slowly in trees (Brattstrom 1966) throughout small home ranges, which average 1.6 ha (Montgomery and Sunquist 1975;see also Chiarello 1998a).…”

Section: Three-toed Slothsmentioning

confidence: 99%

Dwarfism in Insular Sloths: Biogeography, Selection, and Evolutionary Rate

Anderson

Handley

2002

Evolution

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Abstract. The islands of Bocas del Toro, Panama, were sequentially separated from the adjacent mainland by rising sea levels during the past 10,000 years. Three-toed sloths (Bradypus) from five islands are smaller than their mainland counterparts, and the insular populations themselves vary in mean body size. We first examine relationships between body size and physical characteristics of the islands, testing hypotheses regarding optimal body size, evolutionary equilibria, and the presence of dispersal in this system. To do so, we conduct linear regressions of body size onto island area, distance from the mainland, and island age. Second, we retroactively calculate two measures of the evolutionary rate of change in body size (haldanes and darwins) and the standardized linear selection differential, or selection intensity (i). We also test the observed morphological changes against models of evolution by genetic drift. The results indicate that mean body size decreases linearly with island age, explaining up to 97% of the variation among population means. Neither island area nor distance from the mainland is significant in multiple regressions that include island age. Thus, we find no evidence for differential optimal body size among islands, or for dispersal in the system. In contrast, the dependence of body size on island age suggests uniform directional selection for small body size in the insular populations. Although genetic drift cannot be discounted as the cause for this evolution in body size, the probability is small given the consistent direction of evolution (repeated dwarfism). The insular sloths show a sustained rate of evolution similar to those measured in haldanes over tens of generations, appearing to unite micro-and macroevolutionary time scales. Furthermore, the magnitude and rate of this example of rapid differentiation fall within predictions of theoretical models from population genetics. However, the linearity of the relationship between body size and island age is not predicted, suggesting that either more factors are involved than those considered here, or that theoretical advances are necessary to explain constant evolutionary rates over long time spans in new selective environments.

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“…2), we observed that the environmental variables that presented the largest contributions to defining the potential areas of occurrence for B. tridactylus were minimum temperature of coldest month (64% of contribution), temperature seasonality (11%), mean temperature of coldest quarter (5%), and topography (5%). The climatic variables that limit B. tridactylus occurrence are all related to cold temperatures, which is supported by the fact that sloths are not fully homeothermic (Britton and Atkinson, 1938). …”

Section: Resultsmentioning

confidence: 93%