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).