Microbial Fermentation in Juvenile and Adult Pond Slider Turtles, Trachemys scripta

Herbivorous reptiles use microbial gut symbionts to digest plant material. These symbionts ferment cell wall components, producing short-chain fatty acids (SCFA), which the host uses as an energy source. In reptiles, fermentation usually occurs in the large intestine; however, the freshwater Florida Red-Bellied Cooter, Pseudemys nelsoni, has both small and large intestine fermentation. Although small intestine fermentation has not been found in other chelonians, no other freshwater turtles have been examined. We measured SCFA concentrations in the digestive tracts of juvenile and adult Pond Sliders, Trachemys scripta. Like many other turtles, T. scripta experiences an ontogenetic diet shift from carnivory to herbivory, and it is unknown whether juveniles can digest plant material. We determined whether (1) this species harbors small intestine fermentation, (2) juveniles possess SCFA concentrations comparable to other herbivorous reptiles, and (3) a change in relative fermentation chamber capacity accompanies the diet shift. We fed turtles a plant diet for five weeks and then measured SCFA concentrations in their gastrointestinal tracts and the mass of gastrointestinal tract contents. Both juveniles and adults had SCFA concentrations comparable to other herbivorous reptiles; however, they did not have significant small intestine fermentation. Additionally, there was no difference between the relative masses of juvenile and adult fermentation chamber contents. Therefore, the ontogenetic diet shift in T. scripta is not accompanied by a change in relative gut capacity.