The Effect of Light and Temperature on Plasma Melatonin in Neotenic Tiger Salamanders (Ambystoma tigrinum)

Effects of varying illumination and temperature cycles on circulating melatonin (mel) in neotenic tiger salamanders were investigated in three experiments. In Experiment I animals were maintained for seven days on a 12:12LD illumination regimen with either normal high temperature (20?C) during the photophase, low (10?C) temperature during the scotophase or reversed thermal periods. Animals maintained in a normal temperature and photic regimen had 87.7 and 141.7 pg mel/ml plasma (mean values) measured midphotophase and midscotophase, respectively. Animals in a reversed temperature environment had mean plasma melatonin titers of 100.8 and 91.6 pg mel/ ml at midphotophase and midscotophase. In the second experiment, the effect of continuous high or low temperature was examined while animals were under a 12:12LD illumination regimen. Animals held at continuously low (10?C) temperature had a mean plasma melatonin titer of 87.3 and 125.1 pg/ml at midphotophase and midscotophase respectively. Animals maintained in contin- uously high temperatures (20?C) had mean plasma melatonin titers of 87.7 and 82.0 pg/ml. Finally animals maintained under either continuous light or darkness but an alternating thermal regimen did not display significant differences in plasma melatonin. It was observed that high nocturnal temperature can cause a depression in the amount of melatonin measured in the plasma of neotenic tiger salamanders.