Fine-Scale Differentiation in Diet and Metabolomics of Small Mammals Across a Sharp Ecological Transition

Abstract

Sharp ecological boundaries often present animals with abrupt transitions in various resources, including the availability of food, potentially creating strong selective gradients. Yet little is known concerning how animals respond to abrupt shifts in resources, especially when gene flow may limit local adaptation. Here, we used DNA metabarcoding and untargeted metabolomics of fecal samples to begin characterizing the foraging ecology of two closely related rodents (Neotoma bryanti and N. lepida) across a sharp ecological boundary. We find abrupt transitions in diet and metabolomic signatures that coincide with the rapid habitat transition. Further, we show that individuals have habitat-specific diets that are dominated by distinctly toxic plants that likely require different metabolic processing. Our approach allows detailed characterization of diet and metabolic processing of food plants, which can provide evolutionary ecologists and wildlife biologists much needed insight into the nutritional and physiological ecology of the systems they study and manage.

Differences in dietary composition and preference maintained despite gene flow across a woodrat hybrid zone

“…Our measures of diet composition in this study were largely consistent with those previously described in Matocq et al (2020). Their measure of diet occurred during the summer of 2013, an extreme drought year, wherein Neotoma bryanti consumed a high level of F. californica (RRA = 0.52) and N. lepida consumed large amounts of P.…”

“…fasciculata (RRA = 0.59; Matocq et al, 2020). During spring of a wet year (2016; this study), when more vegetation diversity was available, N. bryanti reduced consumption of the "difficult" F. californica relative to summer (RRA spring = 0.35, RRA summer = 0.51).…”

“…Bold indicates statistical significant p values. Lastly, we considered diet composition of N. bryanti and N. lepida in this study (2016, a wet year) relative to that found previously (2013, a dry year; Matocq et al, 2020). We compare RRA values as consumption of plant food was not modeled for 2013 data.…”

“…In contrast, P. fasciculata contains cyanogenic glycosides, also highly toxic once cyanide is released from the parent compound (Vetter, 2000). Chemical analysis of plants from the Kelso Valley have shown that F. californica and P. fasciculata contain chemical peaks consistent with the anthraquinone, emodin, in F. californica and the cyanogenic glycoside, prunasin, in P. fasciculata (Matocq et al, 2020). Given the potential toxicity of these plants, why do woodrats eat so much of them?…”

“…These hybridization events lead to approximately 14% of individuals across the study site having hybrid ancestry, with backcrossing and introgression in both parental directions (Shurtliff et al, 2014; J. P. Jahner, T. L. Parchman, M. D. Matocq, unpublished data). Previous diet analyses (Matocq et al, 2020;Shurtliff et al, 2014) suggest that N. bryanti and N. lepida consume distinct diets in the hill and flats, respectively. As such, this system offers an opportunity to investigate dietary choices across a sharp ecotone, as well as the potential role of dietary differences in limiting interspecific contact and hybridization.…”