| Description |
Herbivory is the most common feeding strategy among mammals. The dietary niches of herbivores are largely determined by toxic plant secondary chemicals (PSCs) that alter the physiology of herbivores. Decades of ecological research have revealed that the detoxification systems of herbivores are adapted to metabolize PSCs and allow herbivores to consume toxic plants. However, the gastrointestinal tract may represent an earlier line of defense for herbivores. I have been studying interactions between the gastrointestinal tract of mammalian herbivores and PSCs. My research has focused on the desert woodrat (Neotoma lepida), which specializes on toxic creosote bush (Larrea tridentata). I first investigated how digestive enzymes of woodrats respond to toxic PSCs. Creosote bush is covered in a phenolic-rich resin that inhibits digestive enzymes, which may in turn limit nutrient and energy availability to herbivores. I found that desert woodrats upregulate digestive enzyme activity when feeding on PSCs, presumably to overcome inhibition. These adaptations may be important for allowing woodrats to feed on toxic diets. Next, I tested a longstanding hypothesis that gut microbes metabolize plant toxins and allow the ingestion of chemically defended plants. Woodrats have a semisegmented stomach that has been hypothesized to harbor a gut microbial community. I first characterized the microbial ecology of the woodrat gut by measuring the stomach pH of rodent species with and without stomach segmentation. Next, I conducted microbial inventories of woodrat feces to demonstrate that woodrats harbor diverse and novel microbial communities, which they maintain in captivity. Further, I conducted inventories and various measurements on foregut contents to demonstrate that the foregut harbors a dense and active microbial community. Finally, I tested interactions between PSCs and gut microbes. I found that PSCs greatly alter the microbial community structure of the woodrat gut. Additionally, I conducted a series of experiments consisting of whole-organism feeding trials, microbiome removal and microbial transplants to demonstrate that microbes can enhance tolerance to toxins. This work demonstrates that the gastrointestinal tract is a site of adaptation and detoxification for mammalian herbivores. Further, it shows that microbial detoxification represents an accelerated mechanism by which herbivores may rapidly adapt to PSCs. |
