Ontogenetic Diet Shifts and Digestive Constraints in the Omnivorous Freshwater Turtle Trachemys scripta

Abstract

Many reptiles undergo an ontogenetic diet shift from carnivory to herbivory. In this study, we used the yellow-bellied slider turtle, Trachemys scripta, as a model to evaluate whether juvenile turtles are carnivorous because physiological constraints preclude herbivory. We conducted feeding trials in which we fed juvenile and adult turtles a duckweed plant, Lemna valdiviana, or a freshwater grass shrimp, Palaemontes paludosus, for 5 wk. During the trials, we measured mass-specific intake, digestibility, and digestible intake for both size classes, as well as juvenile growth. At the end of the trials, we measured the nutrient composition of the juvenile turtles. Juveniles fed shrimp grew 3.2 times faster than those fed duckweed and had equivalent lipid stores. Digestive processing in juveniles was extremely efficient on the shrimp diet, with higher mass-specific intakes than adults and very high digestibilities (97%). Juveniles digested duckweed as well as adults did; however, their intake of this diet was limited, possibly by the time required for fermentation. We concluded that although juveniles can process plant material, an animal diet allows for greater juvenile growth, which in turtles is linked to higher survivorship and increased future reproductive success.

Anatomical and Physiological Changes Associated with a Recent Dietary Shift in the LizardPodarcis sicula

“…;Rocha 1998;Spencer et al 1998;Durtsche 2000;Fialho et al 2000;Bouchard and Bjorndal 2006; but see Cooper and Vitt 2002 on the generality of this phenomenon). At least in some of the species studied, this ontogenetic dietary shift is accompanied by changes in digestive efficiency (Durtsche 2004;Bouchard and Bjorndal 2006). Reptiles living in a seasonal environment have been described as regulating their digestive apparatus according to activity or prey availability (Latif et al 1967;Tracy and Diamond 2005;Naya et al 2008;Iglesias et al 2009).…”

“…Many reptiles shift toward a more herbivorous diet as they age (Kennett and Tory 1996;Bjorndal 1997Í? ;Rocha 1998;Spencer et al 1998;Durtsche 2000;Fialho et al 2000;Bouchard and Bjorndal 2006; but see Cooper and Vitt 2002 on the generality of this phenomenon). At least in some of the species studied, this ontogenetic dietary shift is accompanied by changes in digestive efficiency (Durtsche 2004;Bouchard and Bjorndal 2006).…”

Comparative Digestive Physiology

“…In some groups such as ruminant mammals, insects, amphibians, and fish, these are also accompanied also by dramatic changes in GI structure. The reviews by Buddington and colleagues in the early 1990s (49, 50, 54) summarized results for about 12 vertebrate species, and additional work in the past 15 years has resulted in many more studies of developmental changes in digestion and features of digestive physiology, as well as an expanded list of species including more than a dozen fish species (see below), six amphibian species, a turtle (35), five avian species, and a dozen mammals. The latter class has been most intensively studied, and reviews of work in that group (148, 208, 354, 461) provide some major themes that apply as well to other groups.…”

Does the exotic invader turtle, Trachemys scripta elegans, compete for food with coexisting native turtles?

“…As the introduced exotic crayfish were a very abundant feeding resource in El Acebuche, adult turtles increased their inges-tion in detriment to the more common ingestion of plants usually reported in most adult turtles (Parmenter and Avery, 1990;Bouchard and Bjorndal, 2006). However, the carnivorous diet of juveniles was mainly composed of smaller prey, such as odonates, which probably are easier to capture for small turtles than crayfish.…”