THE EFFECTS OF TEMPERATURE ON FOOD PASSAGE TIME THROUGH THE DIGESTIVE-TRACT IN NOTOPHTHALMUS-VIRIDESCENS

Movement of food through digestive tracts of red-spotted newts from southern Ohio was studied to better understand seasonal changes in energy processing. To determine minimum food passage time through the gastrointestinal tract, blood-worms marked with carbon black were consecutively intubated five times to one group of newts at 25 C and twice to a second group at 5 C. Minimum food passage time at 25 C averaged 33 h, with no significant differences among the five feedings. The newts tested at 5 C required an average of 220 h for the passage of food, with significant differences between the two feedings: 157 h for the first and 284 h for the second. Other newts, intubated with worms labeled with iron powder, were X-rayed at periodic intervals to investigate passage of food through the digestive tract. Full stomachs were completely evacuated in 2 d at 25 C, with a half evacuation time of 20 h, but only after 15 d or more at 5 C, with a half evacuation time of 55 h. Maximal amounts of food in the intestines were attained by 20 h at 25 C, but were achieved only after 3 d at 5 C. Evacuation of labeled food from the intestines was completed in about 40 h at 25 C, whereas most of the food was still in the intestines after 15 d at 5 C. It appears that newts are able to process food in all seasons; however, passage time is greatly influenced by temperature.