Abstract

1. A comparison of chromic oxide and yttrium oxide as inert markers for determination of digestive efficiency inLithobatespipienstadpoles Sarah Gleason and William Karasov Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, Madison, WI 53706 Abstract The uptake of nutrients, or digestive efficiency, is important for determining an animal’s energy budget, especially those that are sensitive to temperature fluctuations that may affect these processes. Although digestive efficiency is a useful tool, the procedure for its determination has not been extensively studied in Lithobatespipiens tadpoles. No study has been conducted to determine whether chromic oxide or yttrium oxide serve as accurate inert markers that do not affect digestive efficiency. This study will focus on answering these questions by using 3 treatment groups; one control, one treatment using 1% chromic oxide spiked food and the last using 1% yttrium oxide spiked food. Feces of 5 individual tadpoles from each treatment will be collected and pooled into each respective treatment to create one replicate. It is predicted that neither marker will affect digestive efficiency, however yttrium oxide may be a more accurate inert markers because smaller fecal masses are needed. Introduction Typically, inert markers are used to obtain an estimate of digestive efficiency, however the accuracy of these markers needs to be determined. Inert markers are substances that are not assimilated in the organism that are used to directly measure digestive efficiency by comparing marker concentration in food and excreta (Buddington, 1980).There is some controversy over which inert marker will give the most accurate results for digestive efficiency, although chromic oxide is a commonly used marker in aquatic systems (Vendenberg & De La Noue, 2001). Another inert marker, yttrium oxide, has been increasingly used in aquatic studies because lower levels are needed and provide easier detection than chromic oxide (Davies & Gouveia, 2006). This study will evaluate the accuracy of chromic oxide and yttrium oxide as an inert marker in Lithobates (formerly Rana) pipienstadpoles. This will be accomplished by comparing their estimated digestive efficiency calculated from inert markers’ recoveries with results from quantitative measures of food intake and excretion, called the mass balance method. Hypothesis 1 is that the presence of inert markers in the diet has no significant effect on calculated digestive efficiency by mass balance. Hypothesis 2 is that digestive efficiency does not differ significantly when determined using the inert markers vs. when measured by mass balance. The results will determine whether either marker is suitable for determining digestive efficiency in tadpoles. Materials and Methods After four weeks of age, 15 tadpoles from random tanks will be placed into separate containers. There will be 5 tadpoles in each treatment (control, 1% chromic oxide and 1% yttrium,). Each of these groups will serve as one replicate from their respective treatments.The containers will be equipped with 4mm mesh suspended 15mm from the bottom, a design adapted from Peterson and Boulton (1999) to prevent feces from being consumed. A bottle cap will also be placed into each container to serve as a feeding dish. Each tadpole will be given a weighed amount of food that can be eaten in a 2-hour period without any leftovers. The amount of food given will be adjusted over a 3-day period (phase 1) while being fed control food and will be a minimum of 20.0 mg wet mass, based on my preliminary data. Throughout this period, the water will be changed in the containers on a daily basis and feces will be collected by suction filtration to ensure a stable fecal output is achieved.Once the food mass has been adjusted, a 7-day fecal collection period (phase 2) will begin for all treatments. At the same time daily, feces will be collected from the bottom of the containers by suction filtration. Each treatment of 5 tadpoles will have their feces collected on a single filter paper each day which will be placed into the drying oven at 105 °C for at least 24 hours for further analysis. After this 7-day period is over, another 7-day fecal collection will begin with the same group of tadpoles (phase 3). The feces from each tadpole will be collected on a single filter paper over the 7-day period, so each tadpole’s estimated digestive efficiency can be analyzed.After the 7-day fecal collection period is over, the tadpoles in each treatment will be fed again, and then euthanized after the 2-hour feeding period. This will be done to ensure the food being placed into the container is being consumed by its presence in the tadpole’s gut.