SAMPLE LABORATORY REPORT
Effect of Urine Treatment on Chow Consumption by Eastern Woodrats
I tested whether eastern woodrats (Neotoma floridana) preferred unsoiled chow to chow that had been treated with urine. The woodrats did not differ in consumption rates between soiled and unsoiled chow. Neither did the woodrats prefer chow that they had soiled over chow that had been soiled by other woodrats. The order in which the food types were presented did not affect the amount of food consumed.
Keywords: food preference, Neotoma, theft deterrence, urine
Many mammals use urine marking as a signal of territoriality or reproductive status (Molteno et al. 1998, Sillero-Zubiri and Macdonald 1998). Woodrats commonly urinate and defecate on their stored food. The reason for this is unknown. Several hypotheses might explain this behavior. One possibility is that urine deters food theft. In laboratory rats and mice, the accessory reproductive glands of dominant males may produce substances that make urine aversive to other males (Gawienowski et al. 1982, Novotny et al. 1990).
Soiling may also act as an olfactory camouflage of food. By depositing urine and feces on food, woodrats may disguise its odor, thus making the food less apparent to other animals. Another theft deterrence hypothesis is that urinating and defecating on food may inoculate the food with microbes. Presumably the animal depositing the wastes has developed a tolerance for these particular microbes because they came from its body. Another animal may not be resistant to the same population of microbes due to individual differences in genetics and prior exposure.
Food soiling may be a form of nitrogen conservation. While energy and carbon can be stored as fat, animals eliminate excess nitrogen and other materials in the form of urine and feces. If the animals require nitrogen later for growth, tissue repair, mounting of an immune response, or other purposes, it may only be available in the form of urine and feces deposited earlier, thus these "waste products" may actually be resources.
This experiment was designed to discover whether woodrats discriminate between fouled food and unsoiled food or between food that they have soiled and food that has been soiled by other woodrats. If woodrats ate equal amounts of the soiled and unsoiled food, the hypothesis that aversion to soiled cached food lowered consumption would be falsified. If the hypothesis that soiling food deters theft is correct, one would predict that food soiled by conspecifics would be consumed to a lesser extant than unsoiled food or self-soiled food.
Materials and Methods
Beginning on Dec. 1, 1995, animals were given 200 g of rat chow and approximately 50 g of fresh apple every three days. The chow was one of three types: chow that had been removed from the woodrat's own cage after being in it for six days (own-soiled), chow that had been removed from the cage of another woodrat after being in it for six days (foreign-soiled), or chow that had not been given to an animal before (unsoiled). All three types had been dried for 12 hours at 63 oC in a Harvest Maid® food dryer (Alternative Pioneering Systems, Inc.) and weighed on an Ohaus Brainweigh® B 300 D electronic balance. The order in which the chow was presented was determined randomly, as was the donor animal for the foreign-soiled chow. On 4, 7, and 10 December, cages were lifted and shaken. The bedding was then stirred and the cage was shaken again until all of the food had fallen from the cage. The food was placed in labeled bags. On 4 and 7 December, the animals were presented with the next test chow and another apple ration. Food removed from cages was then dried and weighed as described above. Data were analyzed using one way analysis of variance in Statistica© for Windows©, version 4.5.
There was no difference in the consumption of the three types of chow by the eastern woodrat (Fig. 1, P=0.84). However, the chow ranked highest for consumption rate was own soiled chow (Mean = 52.1 g, S. E. =3.7), foreign-soiled chow ranked lowest (Mean = 48.8 g, S. E. = 3.9). Consumption of fresh chow was intermediate (Mean = 50.2 g, S. E. = 33.7). The order of presentation had no measurable effect on the consumption of any type of chow.
Fig. 1. Effect of urine on chow consumption by eastern woodrats. Own=self-soiled chow, Foreign=chow soiled by other individuals.
Woodrats in this study did not avoid eating soiled chow. Fresh apple was provided, and the animals were not food-deprived before being presented with the chow, so any chow type could have been safely avoided. Instead, animals showed no difference in consumption rates between unsoiled, self-soiled, and foreign-soiled chows.
These findings are not consistent with the hypothesis that urinating and defecating on food makes it unattractive to conspecifics. However, it is possible that more extensive soiling could have produced a difference in food preference. Another variable is that urine from different animals may vary in its ability to deter theft. Urine from large healthy animals may be more aversive than that from young, unhealthy animals (Novotny et al. 1990). Similarly, target animals may vary in how aversive the urine is based on their own health, size, dominance, and gender.
Gawienowski, A. M., I. J. Berry, and J. Kennelly. 1982. Aversion substance(s) of the rat coagulating glands. Journal of Chemical Ecology 8:379-382.
Molteno, A. J., A. Sliwa, and P. R. K. Richardson. 1998. The role of scent marking in a free-ranging, female black-footed cat (Felis nigripes). Journal of Zoology, 245:35-41.
Novotny, M., S. Harvey, and B. Jemiolo. 1990. Chemistry of male dominance in the house mouse, Mus domesticus. Experimentia 46:109-113.
Sillero-Zubiri, C. and D. W. Macdonald. 1998. Scent-marking and territorial behaviour of Ethiopian wolves Canis simensis. Journal of Zoology, 24:351-361.
Last update: 4/18/02 by Rebecca Burton, Dept. of Biology, Alverno College