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Herbivorous reptiles and body mass: Effects on food intake, digesta retention, digestibility and gut capacity, and a comparison with mammals


Franz, R; Hummel, J; Müller, Dennis W H; Bauert, M; Hatt, Jean-Michel; Clauss, Marcus (2011). Herbivorous reptiles and body mass: Effects on food intake, digesta retention, digestibility and gut capacity, and a comparison with mammals. Comparative Biochemistry and Physiology - Part A: Molecular and Integrative Physiology, 158(1):94-101.

Abstract

Differences in the allometric scaling between gut capacity (with body mass, BM1.00) and food intake (with BM0.75) should theoretically result in a scaling of digesta retention time with BM0.25 and therefore a higher digestive efficiency in larger herbivores. This concept is an important part of the so-called ‘Jarman-Bell principle’ (JBP) that explains niche differentiation along a body size gradient in terms of digestive physiology. Empirical data in herbivorous mammals, however, do not confirm the scaling of retention time, or of digestive efficiency, with body mass. Here, we test these concepts in herbivorous reptiles, adding data of an experiment that measured food intake, digesta retention, digestibility and gut capacity in 23 tortoises (Testudo graeca, T. hermanni , Geochelone nigra, G. sulcata, Dipsochelys dussumieri) across a large BM range (0.5-180 kg) to a literature data collection. While dry matter gut fill scaled to BM1.07 and dry matter intake to BM0.76, digesta mean retention time (MRT) scaled to BM0.17; the scaling exponent was not significantly different from zero for species > 1 kg. Food intake level was a major determinant of MRT across reptiles and mammals. In contrast to dietary fibre level, BM was not a significant contributor to dry matter digestibility in a General Linear Model. Digestibility coefficients in reptiles depended on diet nutrient composition in a similar way as described in mammals. Although food intake is generally lower and digesta retention longer in reptiles than in mammals, digestive functions scale in a similar way in both clades, indicating universal principles in herbivore digestive physiology. The reasons why the theoretically derived JBP has little empirical support remain to be investigated. Until then, the JBP should not be evoked to explain niche differentiation along a body size axis in terms of digestive physiology.

Abstract

Differences in the allometric scaling between gut capacity (with body mass, BM1.00) and food intake (with BM0.75) should theoretically result in a scaling of digesta retention time with BM0.25 and therefore a higher digestive efficiency in larger herbivores. This concept is an important part of the so-called ‘Jarman-Bell principle’ (JBP) that explains niche differentiation along a body size gradient in terms of digestive physiology. Empirical data in herbivorous mammals, however, do not confirm the scaling of retention time, or of digestive efficiency, with body mass. Here, we test these concepts in herbivorous reptiles, adding data of an experiment that measured food intake, digesta retention, digestibility and gut capacity in 23 tortoises (Testudo graeca, T. hermanni , Geochelone nigra, G. sulcata, Dipsochelys dussumieri) across a large BM range (0.5-180 kg) to a literature data collection. While dry matter gut fill scaled to BM1.07 and dry matter intake to BM0.76, digesta mean retention time (MRT) scaled to BM0.17; the scaling exponent was not significantly different from zero for species > 1 kg. Food intake level was a major determinant of MRT across reptiles and mammals. In contrast to dietary fibre level, BM was not a significant contributor to dry matter digestibility in a General Linear Model. Digestibility coefficients in reptiles depended on diet nutrient composition in a similar way as described in mammals. Although food intake is generally lower and digesta retention longer in reptiles than in mammals, digestive functions scale in a similar way in both clades, indicating universal principles in herbivore digestive physiology. The reasons why the theoretically derived JBP has little empirical support remain to be investigated. Until then, the JBP should not be evoked to explain niche differentiation along a body size axis in terms of digestive physiology.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:05 Vetsuisse Faculty > Veterinary Clinic > Department of Small Animals
Dewey Decimal Classification:570 Life sciences; biology
630 Agriculture
Language:English
Date:2011
Deposited On:23 Dec 2010 16:52
Last Modified:07 Dec 2017 04:36
Publisher:Elsevier
ISSN:1095-6433
Publisher DOI:https://doi.org/10.1016/j.cbpa.2010.09.007
PubMed ID:20850560

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