Diet Study with Gastric Lavage

Rings and syringes for gastric lavage.

With only two weeks left in El Yunque, Puerto Rico, the two projects that Travis Ingram and I are doing will soon come to a close. Travis has already written about one project, the enclosure experiment. The second is a diet survey of six species (Anolis evermanni, A. stratulus, A. cristatellus, A. gundlachi, A. pulchellus, and A. krugi) that are sympatric in the area around where we are staying. The goal is to quantify diet overlap between these species. To obtain the stomach contents, we use a nonlethal method known as gastric lavage. I chose this method unsure of how it would turn out because, before this trip, Travis and I had had very little practice performing gastric lavage. My hope was that we could take this technique that we had read about and practiced a few times in the lab and become good enough at it to do it potentially hundreds of times in the field.

To perform gastric lavage on anoles, we use a syringe to flush water into the lizards’ stomachs, and as the water comes back out of the mouth again, it carries with it any food that was in the stomach. We select the size of the syringe and the amount of water used to flush based on the size of the lizard. If you can see in the picture, the tips of the syringes are covered in rubber, so as not to injure the lizard as the syringe is inserted into the stomach. We use plastic rings made of sections of small test tubes (also in the picture) to keep the lizard’s mouth open during the process. We slowly and carefully rinse water through the lizard’s stomach, and then we store the stomach contents in ethanol.

Afterwards, we mark and release the lizards where we caught them. If done properly, gastric lavage is an efficient way to sample anole diets without harming the lizards. Numerous times I have seen marked anoles as I pass through an area where we have caught and released them several weeks before, so the lizards seem to survive very well after undergoing gastric lavage. Overall, I would definitely recommend this technique to anyone interested in studying anole diets because in addition to not harming the lizards, it can be done quickly enough to enable large amounts of sampling in a couple of weeks.