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.
Highlights
Based on geometric considerations, volume measurements should scale isometrically with body mass, surface measurements should scale to body mass to the power of 0.67, and length measurements—such as those of intestinal tract sections—should scale to body mass to the power of 0.33 (Calder 1996; Clauss and HummelElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Extended author information available on the last page of the article2005)
The allometric scaling of length measures of all intestinal sections yielded exponents with 95% confidence intervals above the 0.33 scaling exponent expected from geometry (Table 2)
The relative length of the intestinal sections did not change with body mass, suggesting that their proportions remain stable during ontogeny (Table 2; Fig. 5a)
Summary
In contrast to the expected geometric scaling of length measurements, several studies found a higher scaling exponent (positive allometry) for interspecific scaling relationships of various intestinal section lengths with body mass in mammals (Woodall and Skinner 1993; Lavin et al 2008; McGrosky et al 2016, 2019a, b). The length of the intestine must scale more-than-geometrically (with positive allometry) to accommodate geometric volume and surface scaling If this reasoning were correct, we would expect similar scaling at the intraspecific level across ontogeny, because the transition from milk to any other diet likely implies a decrease in diet digestibility, theoretically making short distances between the lumen and surface all the more relevant
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