2.2 Dissection of gastrointestinal tract
For the mouse captured on the summit of Volcán Llullaillaco (UACH8291), we extracted DNA from contents of the stomach for metagenomic sequencing and DNA metabarcoding. We also dissected the lower gastrointestinal tract into 13 adjoining sections, the cecum and 12 consecutive segments of the colon, ordered from the outlet of the cecum to the rectum (Figure 2), and we extracted DNA from the contents of each section for additional DNA metabarcoding analysis. This approach allowed us to examine temporal changes in the mouse’s diet, as determined by gut passage times: the stomach and cecum contain food items ingested within a few hours of its capture, while the colon sections and rectum potentially contain food ingested within the previous two or three days. The metagenomic sequencing represents an unbiased approach to characterize the stomach contents of the mouse while the metabarcoding analysis is designed to test specific hypotheses about the animal’s diet (arthropod fallout, interspecific coprophagy, lichenivory, or herbivory at elevations that surpass assumed vegetation limits).