Stress in green iguanas (Iguana iguana): handling and inadequate enclosures
Posted by Erin Chapman on May 19, 2015 in Lizards, Reptiles
A study in 2012[1] looked at stress in green iguanas (Iguana iguana) with regards to handling and inadequate enclosures. Previously stress has been quantified by the glucocorticoids in blood serum. The problem with this method is the theoretical stress produced from the blood draw. Are the resultant stress levels from the experimental values tested or from the stress of the blood draw? This study explores a different method of quantifying stress investigating fecal corticosterone metabolites (FCM). The researchers paired the FCM with a behavioral ethogram to better evaluate stress.
The iguanas were placed in separate wire cages with an elevated tree branch, food, water, and no substrate. Their feces were collected every morning and their behavior observed for an hour each day. An initial acclimation period of 8 days set the base line for stress levels. There were two experimental periods: a handling period of 8 days and an altered environmental period also of 8 days. Handling entailed holding the iguanas with one hand restraining front limb movement and the other restraining hind limb movement for 5 minutes each day. The altered environment in the enclosure restricted access to the tree branch making it so the iguanas were confined to the floor of the cage. There was also an 8 day rest period free of experimental conditions. These 8 day periods were randomized so that some iguanas received the altered environment before the handling. The cycle was repeated so the iguanas experienced each experimental condition twice.
The results show higher FCM under the experimental conditions but no significant difference between them, meaning the stress levels of handling and inadequate enclosures weighs the same when quantified with FCM. However, FCM values were significantly different between iguanas that were handled first then denied the tree branch vs. iguanas that were denied the branch then handled. Iguanas that were put through the altered environmental period first then subjected to handling were much more stressed than iguanas that experienced the reverse order. In addition, all iguanas’ FCM values were higher during the second cycle of experiments.
The ethogram observed iguana behavior during these periods. It was observed that there weren’t any behavioral changes in the handling period when compared to the resting and acclimation periods. During the 8 days of altered environment, however, the iguanas were observed to be standing and hardly closing their eyes. The researchers described this as being more “vigilant”. When observers cleaned cages during this period, aggressive behavior such as head bobbing, dewlap displaying, and tail whipping were directed at the observers.
When the results of the FCM and ethogram are combined, it becomes clear that stress from handling is momentary while stress from living in an inadequate enclosure is constant. In short, it is worse to be living in bad conditions than it is to experience minimal handling. However, because the iguanas that were put through the altered enclosure period first then the handling period experienced much more stress than the other iguanas, it is highly recommended to not handle an iguana that is living in an inadequate enclosure as it has significant impact on the animal’s wellbeing.
In conclusion, stress in captive green iguanas can be minimalized by providing the correct set up and decreasing handling periods. While this study contributes to the knowledge of the betterment of captive care it also opens new pathways to studying stress in iguanas. By proving that quantifying stress through FCM is possible in green iguanas, a less invasive method is now available to study stress in iguanas and, hopefully, other squamates.