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Lecture 10

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Shawn Lehman

ANT333 Lecture #10 – Dietary Adaptations: Folivory Primate Folivores  Many species are not obligate folivores.  Many species do not consistently combine same kinds of foods in their diets, as many past characterizations would suggest; they often switch between diet categories (e.g., fruit, insects, leaves, etc.).  Thus, many primate species are best characterized as frugivore/folivores or folivore/frugivores. Primate Folivores  Generally, folivores tend to be larger bodied than frugivores &/or insectivores.  However, due to variations in diet, some folivores are relatively small-bodied compared to our preconceived notions of the consequences of body size for folivory.  Next semester, we’ll look at relationship between body size & folivory in greater detail. Examples of Folivory & Body Size in Primates Species % leaves in diet Mean mass (g) Microcebus Murinus 12 62 Lepilemur sp. 70 770 Alouatta senicalus 52 7000 Colobus guereza 60 11500  Body mass is not correlated to folivory Factors Important in Digestion of Plant Material 1. Capacity of the digestive tract 2. Utilization of fermentation end products and microbes 3. Rate of food passage through digestive tract 4. Digestibility of the food 1. Capacity of the digestive tract Digestive Physiology of Herbivores  ~ 50% of organic carbon on earth is tied up in cellulose.  This represents enormous source of energy, but is tied up in indigestable cell wall of cellulose, hemicelluloses, & lignin.  However, vertebrate cells do not produce cellulases necessary to break down this abundant material.  Many microbes do secrete cellulases which allow them to utilize dietary cellulose and other plant wall materials. Digestive Physiology of Herbivores  Relative value of fermentation to an animal's nutrition pretty much depends on size of its fermentation vat.  All herbivores have large digestive tract capacity relative to omnivores & carnivores (~ 24% of body weight)  Fermentation occurs in colon of humans, but our large bowel is rather small and benefit we gain from fermentation is trivial. 1 Folivore Gut Adaptations  Folivores possess specialized fermentation vats as part of their digestive tract.  Two distinct strategies have evolved.  Main difference between the two groups is in positioning of fermentation vat relative to stomach and small intestine:  Foregut (cranial) vs. hindgut (caudal) fermentors  Folivores keep eating to feed microorganisms, so that they stay alive and done die Foregut Fermentors (FGFs)  Multicompartmented section of digestive tract between esophagus and true stomach (e.g., enlarged caecum or stomach).  These forestomachs house very complex ecosystem that supports fermentation (e.g., cattle, sheep, deer).  Primate examples: colobines. Hindgut Fermentors (HGFs)  Similar to humans through stomach and small intestine, but their large intestine (colon), where fermentation occurs, is complex and exceptionally large.  Examples of cecal digestors include horses & rabbits.  Primate examples: Alouatta, Lepilemur, Propithecus 2. Utilization of fermentation end products and microbes Digestive Physiology of Herbivores  Cellulolytic microbes inhabit digestive tract of all animals, allowing animal to siphon off & assimilate end products of fermentation, particularly short chain or volatile fatty acids.  Volatile fatty acids (VFAs), also called low molecular weight organic acids, are readily metabolized, highly oxidized, organic substrates. VFAs--such as acetic, proprionic and butyric acids--are energy source for folivore.  Carbon dioxide & methane = excretion products Digestion & Extraction of Energy from Cellulose  Small intestine only site in digestive tract where simple sugars and amino acids can be absorbed.  FGFs can utilize dietary starch, but very little is absorbed as glucose. Starch & other soluble carbohydrates fermented to volatile fatty acids in forestomach.  What little starch enters small intestine is poorly digested in that organ  Starch fed to HGFs is digested to glucose by amylase & maltase in small intestine, and that glucose is absorbed across epithelium into blood. Foregut vs. Hindgut Fermentation Function Foregut Hindgut Ability to efficiently digest and extract energy from celluloYes Yes Ability to utilize dietary hexose sources* directly No Yes Ability to utilize protein from fermentive microbes Yes No *Glucose , galactose, and fructose, which serve as basic fuel molecules for eukaryotic (nucleic cells) 2 Foregut vs. Hindgut Fermentation  Process & outcome of fermentation is essential
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