Morphology of the gastrointestinal tract in primates: Comparisons with other mammals in relation to diet

Abstract

Three categories of dietary adaptation are recognized--faunivory, frugivory, and folivory--according to the distinctive structural and biochemical features of animal matter, fruit, and leaves respectively, and the predominance of only one in the diets of most species. Mammals subsisting mainly on animal matter have a simple stomach and colon and a long small intestine, whereas folivorous species have a complex stomach and/or an enlarged caecum and colon; mammals eating mostly fruit have an intermediate morphology, according to the nature of the fruit and their tendency to supplement this diet with either animal matter or leaves. The frugivorous group are mostly primates: 50 of the 78 mammalian species, and 117 of the 180 individuals included in this analysis are primates. Coefficients of gut differentiation, the ratio of stomach and large intestine to small intestine (by area, weight, and volume), are low in faunivores and high in folivores; the continuous spread of coefficients reflects the different degrees of adaptation to these two dietary extremes. Interspecific comparisons are developed by allowing for allometric factors. In faunivores, in which fermentation is minimal, the volume of stomach and large intestine is related to actual body size, whereas these chambers are more voluminous in larger frugivores and mid-gut fermenting folivores; fore-gut fermenters show a marked decrease in capacity with increasing body size. Surface areas for absorption are related to metabolic body size, directly so in frugivores; area for absorption is relatively less in larger faunivores and more in large folivores, especially those with large stomachs. Indices of gut specialization are derived from these regressions by nonlinear transformation, with references to the main functional features of capacity for fermentation and surface area for absorption. These are directly comparable with the dietary index, derived from quantitative feeding data displayed on a three-dimensional graph, with all species within a crescentic path from 100% faunivory through 55--80% frugivory to 100% folivory, perhaps illustrating, at least for primates, the evolutionary path from primitive insectivorous forms through three major ecological grades.

The human adaptations to meat eating: a reappraisal

“…Taking into account the fact that a part of the data has been recorded in zoos, and the possibility that net energy rather than gross energy intake was used for some species, these considerations highlight, once again, the necessity for humans to find energy in an easily digestible form. Similarly, the "coefficient of gut differentiation" (after correcting the mismatch in the figures' legends of the published paper) do not support the claim that of human beings are closer to cats and dogs than to monkeys and apes; clearly, this type of measurement does not take into account the allometric factor, necessary when comparing species with different body sizes (Chivers and Hladik, 1980). The link between a high quality diet (eventually including animal matter), and the enlargement of the brain characterizing hominid evolution, previously highlighted by several authors (Martin, 1983;Foley and Lee, 1991;Leonard and Robertson, 1997) can be the result of a behavioral change, followed or not by morphological adaptation (i.e.…”

“…To support their hypothesis, Aiello and Wheeler (1995) refer to a set of measurements of the intestinal tract of primates published by one of us (Hladik, 1977;Chivers and Hladik, 1980) -with some adjustmentscompared to human intestinal tract measurements (data from Aschoff et al, 1971). However, the sample they used to determine non-human primate gut weight includes species of primates with partly folivorous diets rich in fiber.…”

“…The absorptive areas vary according to body length (L), scaled to L2.64, L2.37 and L1.98, respectively for folivores, frugivores and faunivores (that is a large range of morphological variation, between L2 and L3 ). We (Chivers and Hladik, 1980) proposed a geometrical model to explain the functional effect of allometry so that animals with high-quality diet (faunivores, and to a lesser extent, frugivores) show a reduced absorptive area when compared to folivores; assuming, of course, a constant flux per unit mucosal area for all species. Thus, in humans, a clear-cut adaptation to meat eating would imply that the gut allometric relationship coincides with that of the "faunivores", having the lowest absorptive area.…”

“…Functional body size (10-3L3) is plotted along a logarithmic scale (L= nose to anus for animals; sitting height for humans). (taken from Chivers and Hladik, 1980; With relation to the energy needs, primate feeding strategies vary from a type involving low-energy cost / low energy yield (i.e. for most folivore±frugivore), to a type involving the opposite, namely high energy expenditure / high energy intake, such as in baboons and chimpanzees (Hladik, 1981).…”

“…Functional body size (10-3L3) is plotted along a logarithmic scale (L= nose to anus for animals; sitting height for humans). (taken from Chivers and Hladik, 1980; Figure 2. Allometric relationships between cranial capacity and body weight in different categories of primates and insectivorous mammals (after R.D.…”