4. CONCLUSIONS
A combination of metagenomic, metabarcoding, and stable isotope data
provided new insights into the diet of Phyllotis mice living at
extreme elevations that far surpass known vegetation limits. Stable
isotope data revealed that Phyllotis vaccarum maintains a mainly
omnivorous diet in all elevational zones, and elevational variation in
diet reflects variation in vegetation composition and the extent to
which the mice rely on animal prey. Estimates of trophic position based
on isotopic data indicated that mice collected near apparent vegetation
limits (~5100 m) on the flanks of Llullaillaco rely more
heavily on animal prey than mice from lower elevations. Metagenomic and
metabarcoding analyses of gut contents from the mouse from the summit of
Llullaillaco (6739 m) revealed a strictly herbivorous diet. The absence
of animal DNA suggests that mice at extreme elevations do not subsist on
wind-blown arthropods or other animal material. The detection of DNA
from lichen-associated fungi indicate that Phyllotis mice living
above known vegetation limits may supplement their diet with saxicolous
lichens, as observed for other arctic and alpine mammals during periods
of food scarcity in the winter. However, measured δ15N
levels indicate that lichen is not an important dietary staple in mice
native to any of the surveyed elevational zones. The metagenomic and
metabarcoding data also produce a scientific conundrum: the gut contents
of a mouse captured at 6739 m elevation contained DNA from several
families of native plants that are not known to occur above
elevational distributions of both the plants and the mice. It is
possible that some of the plants identified in the diet of the summit
mouse exist at higher elevations than previously supposed, but they
exist beneath the snowpack or in other cryptic microhabitats.