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.

Methane (CH4) production is a ubiquitous, apparently unavoidable side effect of fermentative fibre digestion by symbiotic microbiota in mammalian herbivores. Here, a data compilation is presented of in vivo CH4 measurements in individuals of 37 mammalian herbivore species fed forage-only diets, from the literature and from hitherto unpublished measurements. In contrast to previous claims, absolute CH4 emissions scaled linearly to DM intake, and CH4 yields (per DM or gross energy intake) did not vary significantly with body mass. CH4 physiology hence cannot be construed to represent an intrinsic ruminant or herbivore body size limitation. The dataset does not support traditional dichotomies of CH4 emission intensity between ruminants and nonruminants, or between foregut and hindgut fermenters. Several rodent hindgut fermenters and nonruminant foregut fermenters emit CH4 of a magnitude as high as ruminants of similar size, intake level, digesta retention or gut capacity. By contrast, equids, macropods (kangaroos) and rabbits produce few CH4 and have low CH4 : CO2 ratios for their size, intake level, digesta retention or gut capacity, ruling out these factors as explanation for interspecific variation. These findings lead to the conclusion that still unidentified host-specific factors other than digesta retention characteristics, or the presence of rumination or a foregut, influence CH4 production. Measurements of CH4 yield per digested fibre indicate that the amount of CH4 produced during fibre digestion varies not only across but also within species, possibly pointing towards variation in microbiota functionality. Recent findings on the genetic control of microbiome composition, including methanogens, raise the question about the benefits methanogens provide for many (but apparently not to the same extent for all) species, which possibly prevented the evolution of the hosting of low-methanogenic microbiota across mammals.

Plains viscachas (Lagostomus maximus) are large South American, fossorial rodents susceptible to diabetic cataracts. Various aspects of their digestive physiology were studied in three different experiments with 9 male and 7 female adult animals and 6 different diets (total n of feeding trials = 35). Viscachas achieved mean retention times of 23-31h, which is of a magnitude also recorded in horses; these did not differ for solute or small particle (<2mm) markers. Secondary marker excretion peaks indicated coprophagy, and were rarer on high-protein as compared to grass hay-only diets. Mean resting metabolic rate was, at 229 kJ/kg0.75/d, lower than expected for a mammal of this size. Digestible energy requirement for maintenance was 445 kJ/kg0.75/d. At 1.6-2.7 L/d, viscachas produced more methane than expected for a hindgut fermenter of their size. On diets that included concentrate feeds, viscachas excreted glucose in their urine, corroborating reports on the susceptibility of this species for diabetes when kept on energy-dense food. Viscachas had a similar apparent digestibility of protein, lipids, and macrominerals as other rodents, rabbits, or domestic horses. This suggests that whether or not a species practices coprophagy does not have a major influence on these measures. Viscachas resemble other hindgut fermenters in their high apparent calcium digestibility. With respect to a digestibility-reducing effect of dietary fiber, viscachas differed from rabbits and guinea pigs but were similar to horses, suggesting that small body size needs not necessarily be linked to lower digestive efficiency on high-fiber diets. three different experiments with 9 male and 7 female adult animals and 6 different diets (total 28 n of feeding trials = 35). Viscachas achieved mean retention times of 23-31h, which is of a 29 magnitude also recorded in horses; these did not differ for solute or small particle (<2mm) viscachas excreted glucose in their urine, corroborating reports on the susceptibility of this 36 species for diabetes when kept on energy-dense food. Viscachas had a similar apparent 37 digestibility of protein, lipids, and macrominerals as other rodents, rabbits, or domestic 38horses. This suggests that whether or not a species practices coprophagy does not have a 39 major influence on these measures. Viscachas resemble other hindgut fermenters in their high 40 apparent calcium digestibility. With respect to a digestibility-reducing effect of dietary fiber, 41 viscachas differed from rabbits and guinea pigs but were similar to horses, suggesting that 42 small body size needs not necessarily be linked to lower digestive efficiency on high-fiber 43 diets. 44 45

1. Per-and polyfluoroalkyl substances (PFAS) are a large group of manufactured chemicals. Since the beginning of their commercial production in the 1950s, PFAS have not only found their way into numerous industrial and commercial applications, but also into the bloodstream of much of the human population, the natural environment and wildlife. Exposure to high levels of PFAS poses a health risk for humans and animals, and may exacerbate the effects of other anthropogenic impacts faced by wildlife species. To gain a comprehensive overview of the abundance and distribution of PFAS research on wildlife species, and to better understand the drivers of this research, we will collate the available literature into a systematic evidence map and perform bibliometric analyses. The systematic mapping will present the distribution of research evidence that exists on PFAS in wildlife.The bibliometric analysis will provide an insight into the historical trends, interdisciplinarity, connectedness and the impact of the individual papers.2. We will conduct a systematic literature search on Scopus, Web of Science and 10 other databases using predefined search strings. We will screen title, abstract and keywords first. We will then screen full-text papers. Two reviewers will be involved in the screening process. We will only consider publications in English, peer-reviewed articles, preprints and theses. We will include papers reportingThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.