Intraspecific macroscopic digestive anatomy of ring-tailed lemurs (Lemur catta), including a comparison of frozen and formalin-stored specimens

Abstract

Digestive tract measurements are often considered species specific, but little information exists on the degree to which they change during ontogeny within a species. Additionally, access to anatomical material from nondomestic species is often limited, with fixed tissues possibly representing the only available source, though the degree to which this material is representative in terms of dimensions and weight is debatable. In the present study, the macroscopic anatomy of the digestive tract (length of intestinal sections, and tissue weights of stomach and intestines) of 58 Lemur catta [ranging in age from 1 month (neonates) to 25 years], which had been stored frozen (n = 27) or fixed in formalin (n = 31), was quantified. Particular attention was paid to the caecum and the possible presence of an appendix. The intraspecific allometric scaling of body mass (BM)0.46[0.40;0.51] for total intestine length and BM0.48[0.41;0.54] for small intestine length was higher than the expected geometric scaling of BM0.33, and similar to that reported in the literature for interspecific scaling. This difference in scaling is usually explained by the hypothesis that, to maintain optimal absorption, the diameter of the intestinal tube cannot increase geometrically. Therefore, geometric volume gain of increasing body mass is accommodated for by more-than-geometric length scaling. According to the literature, not all L. catta have an appendix. No appendix was found in the specimens in the present study. The proportions of length measurements did not change markedly during ontogeny, indicating that the proportions of the foetus are representative of those of the adult animal. By contrast, width and tissue-mass scaling of the caecum indicated disproportionate growth of this organ during ontogeny that was not reflected in its length. Compared to overall intraspecific variation, the method of storage (frozen vs. formalin) had no relevant impact on length or weight measurements.

Mammalian intestinal allometry, phylogeny, trophic level and climate

“…Intestinal anatomy has varying degrees of flexibility in different species; this has particularly been investigated in small mammals [53], whereas there is less evidence in larger mammals [54]. In a recent study on the intra-specific variation of intestinal length measurements linked to material stored frozen or in formalin, no difference between the methods was evident [55]. However, given probable differences between individual studies, it is recommended that the present data compilation is used to investigate broad patterns across many species, but should not form the basis of a comparison of a specific pair of species.…”

Gastrointestinal morphology and ontogeny of foregut‐fermenting primates

“…Indeed, comparisons of intestine length measurements between frozen ( n = 3) and formalin‐fixed material ( n = 3) indicated some degree of shortening during formalin storage (Hume, Jazwinski, & Flannery, 1993). However, based on a comparison with a larger sample size of Lemur catta intestines stored either frozen ( n = 27) or fixed in formalin ( n = 31), the method of preservation does not have a relevant impact on length or weight measurements (Clauss et al, 2021), suggesting little effects of storage method on our results. This is also supported by the generally good data fit with literature data based on specimens not fixated in formalin (Figure 13).…”

“…Lemur catta intestines stored either frozen (n = 27) or fixed in formalin (n = 31), the method of preservation does not have a relevant impact on length or weight measurements (Clauss et al, 2021), suggesting little effects of storage method on our results. This is also supported by the generally good data fit with literature data based on specimens not fixated in formalin (Figure 13).…”

“…The challenge of combining milk feeding with a composite stomach anatomy may also make foregut fermenters peculiar in the ontogeny of their digestive tract. Mammals that rely, as adults, on hindgut fermentation only can have the respective anatomical structures developed even before birth, even though they may somewhat increase disproportionately in size when used due to plant food ingestion (reviewed in Clauss et al, 2021). This is because a hindgut fermentation site will not interfere with auto‐enzymatic milk digestion, being located after the small intestine where the latter takes place.…”

Diet and stomach characteristics of feral piglets (Sus scrofa): Implications for farmed piglets

“…The entire stomach (tissue and contents) of each individual was collected and stored in 5% formalin. We assumed that the weights determined after storage in formaldehyde would only marginally differ from fresh weights as determined for the farmed piglets (Clauss et al, 2021; Fraser, 1985; Kanerva et al, 1983).…”