The gut of the African bush elephant is a scaled-up version of that of herbivorous rats

Everyone knows that elephants are herbivores, and that the African bush elephant (Loxodonta africana) is the largest land mammal in Earth.

However, what may be more poorly appreciated is that various rat-like spp. of rodents, including some coexisting with elephants, are likewise specialised for eating mainly green matter. This means that L. africana shares the same foraging guild as e.g. Otomyinae (https://animaldiversity.org/accounts/Otomyinae/).

In this framing, elephants are essentially scaled-up versions of rodents, in which the odd features of the megaherbivores can be viewed as allometric compensations for the effects of gravity on body size.

The following surprising finding is based on my own analyses.

Allometry hardly affects the gut of Loxodonta africana, relative to rodents (whether herbivorous or omnivorous).

In both cases, the gastrointestinal tract is about 5-fold the length of the head and body, from tip of nose to base of tail.

The main chambers, viz. stomach and caecum, together constitute about 6% of body mass, in both cases. In both cases, the stomach is slightly less capacious than the caecum, which is the widest part of the hindgut.

Although the colon also contributes to fermentation of the food, it is no wider in L. africana than in the rodents, relative to body length as defined.

The small intestine is proportionately slightly shorter in L. africana than in the rodents, compensating by a slightly greater proportional width.

SOURCES OF INFORMATION

Perrin and Curtis (1980, https://www.semanticscholar.org/paper/Comparative-morphology-of-the-digestive-system-of-Perrin-Curtis/a53e273875e006770c2ca71c93eb1d8ac6df5188 and https://www.tandfonline.com/doi/pdf/10.1080/02541858.1980.11447680)

Clemens and Maloiy (1982, https://profiles.uonbi.ac.ke/gmaloiy/publications/clemens-et-and-maloiy-gmo1982-digestive-physiology-three-east-african-herbivore and https://zslpublications.onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1982.tb02066.x and https://agris.fao.org/agris-search/search.do?recordID=US201302578413).

The following is my comparison of gut proportions of the African bush elephant and the mean for 19 spp. of rodents sympatric with it. Length of head and body excludes the tail, but includes the proboscis of L. africana; it was measured along the curvature of the back.

Length of gut relative to head and body: L. africana 5.0, rodents 4.74
Mass of stomach relative to body mass (%): L. africana 2.2-2.9, rodents 2.74
Mass of caecum relative to body mass (%): L. africana 2.7-3.2, rodents 3.3
Length of small intestine relative to hindgut: L. africana 1.4, rodents 1.76
Width of small intestine relative to length of head and body: L. africana 0.019, rodents 0.01
Width of colon relative to length of head and body: L. africana 0.078, rodents 0.095
Width of caecum relative to colon: L. africana 1.8, rodents 1.8.

DISCUSSION

I conclude that the African bush elephant and omnivorous rodents with which it coexists agree in:

• the length of the gastrointestinal tract as a percentage of full body length: about 500% in each case,
• the full mass of the caecum as a percentage of body mass: about 3% in each case,
• the width of the caecum as a percentage of the width of the colon: about 170% in each case,
• the length of the small intestine as a percentage of the length of the hindgut: approximately similar, viz. 140-190%,
• the width of the small intestine as a percentage of the full length of head and body: approximately similar, viz. 1-2%, and
• the width oftbe colin as a percentage of the full length of head and body: approximately similar, viz. 5-10%.

This suggests that L. africana is, in these aspects of its anatomy, just a scaled-up version of the rodents, as opposed to being subject to the allometric principles that have shaped the bodies as a whole. This is remarkable in view of the 40 thousand-fold difference in body masses.

However, this does not apply to the stomach, which is proportionately larger in L. africana than in the rodents.

Posted on 12 November, 2022 09:35 by milewski