Divergence in ecologically adaptive traits may be maintained across small spatial scales, even with ongoing geneflow between closely related species. Selective gradients that occur across narrow ecological boundaries may present sharp transitions in resources for organisms, of which they may be differentially adapted. For mammal herbivores, dietary resources are often constrained between acquiring nutrients and limiting exposure to plant toxins. Consequently, mammal herbivores may navigate this balance through a combination of metabolic processes, including their own detoxification mechanisms as well as those of their gut microbiome. Understanding how these mechanisms are maintained in the presence of ongoing geneflow between closely related taxa may provide important insight into the role of ecologically adaptive traits in the evolution and maintenance of diversity. We used DNA metabarcoding coupled with chemical analysis of woodrat fecal samples to investigate differences in dietary ecology, gut microbiome, and metabolome in two closely related woodrat species and their hybrids that occur across a sharp environmental gradient: Neotoma bryanti (Bryant’s woodrat) and Neotoma lepida (Desert woodrat). Seasonal fecal samples were collected from traps during spring and summer months of 2017 and 2018. We used trnL and 16S metabarcoding to reconstruct diet and gut microbiome from trap collected fecal samples. From the same samples, LC-MS was also used to characterize fecal chemistry.
Results/Conclusions
We found that while some plants are consumed by both species of woodrat, dietary composition remains distinct across this hybrid zone. Specifically, Frangula californica (California coffeeberry) made up ~30-40% of the diet of N. bryanti, while Prunus fasciculata (desert almond) contributed ~60-65% of the diet of N. lepida. Importantly, both of these plants are known to produce potentially toxic secondary compounds. We found the gut microbiome of woodrat species was distinct across this hybrid zone. Furthermore, the gut communities of individuals of hybrid ancestry exhibited intermediate composition that was associated with habitat. Similar patterns were reflected in fecal chemistry. We also found seasonal variation in diet, microbiome, and metabolome, with some degree of seasonal convergence in resources between woodrat species. Our findings add to a growing understanding of how mammal herbivores respond to changes in resource availability, both spatially and temporally, and establish a framework for studying how ecological adaptations may be generated and maintained even in the presence of gene flow.