While I continue to have several collaborations focused on the role of the gut microbiota in shaping non-human primate ecology and evolution, my current research focuses on comparisons between non-human primates and humans as well as investigations of host-gut microbe dynamics in human populations around the world. In general, these projects focus on the impact of the gut microbiota on host nutrition and health as well as the interaction of host diet, physiology and the gut microbiota. 


The Gut Microbes of Leaf-eating Primates

A variety of primates from distinct taxa including lemurs and apes have developed the ability to consume large amounts leaves. Leaves tend to be high in strutural carbohydrates and secondary metabolites, and as a result, are considered difficult-to-digest. This project examined the composition of the gut microbiota in these primates in an effort to understand the role the gut microbiota has played in the evolutionary transition to a leafy diet. It is likely that marked changes in the gut microbial community were necessary for these primates to process fiber and toxins and to meet nutritional demands. However, it is also likely that differences in gut size and morphology associated with differences in body size and the evolution of a specialized foregut or cecum resulted in different dietary strategies and distinct microbial communities in the hindgut across leaf-eating taxa. My goal was to determine the extent to which the gut microbiota of leaf-eating primates exhibit functional convergence despite these physiological differences. Data analysis is currently being completed, but some evidence of gut microbial convergence in leaf-eating primates has already been uncovered.

Gut Microbes and Howler Intragroup Nutrition

Like most mammals, primates experience temporal variations in diet associated with spatial and seasonal changes food availability. Howler monkeys, in particular, exhibit variable diets across habitats and seasons. They consume fruit and flowers when available but can also survive on a monthly diet of up to 80% leaves. Based on our knowledge of the gut microbiota from laboratory studies, we would expect these diet variations to result in differences in gut microbial community composition across time and space, and subsequently affect howler nutrition and health. Additionally, pregnancy, lactation, and growth increase host nutritional demands. This may be especially true in howler monkeys due to fast growth rates and short interbirth intervals. However, few howler behavioral studies have shown that individuals within a social group consume different amounts of energy and nutrients or change activity patterns to reduce metabolic consumption. Instead, shifts in the gut microbial community may allow individuals to extract different amounts of energy and nutrients from the same diet. 

By integrating field observations with microbial analyses of feces, my dissertation project aimed to quantify and compare monthly and seasonal age- and sex-based variation in foraging behavior and gut microbial community composition in wild, black howler monkeys (Alouatta pigra) in Palenque National Park, Mexico. The four main conclusions of my dissertation were:

1. Despite being considered leaf-eating primates that utilize a diet high in protein and low in energy, howler monkeys prioritize protein intake year-round while foraging. Specifically, they ingest consistent levels of protein regardless of the amount of leaves or ripe fruit in their diet while non-protein energy consumption varies in relation to fruit intake. This suggests that howler monkeys are not as energy limited as previously believed. Additionally, it is possible that although howler monkeys experience reduced energy intake during periods of the year, increased efficiency in the fermentation of fiber by mutualistic gut microbes may provide them with additional energy not accounted for in traditional nutritional analyses.

2. Howler monkey gut microbial community composition shifts temporally in response to changes to the plant parts and plant species consumed, and temporal differences in microbial fermentation are also associated with changes in diet. Therefore, it appears that the howler monkey gut microbial community processes different diets distinctly and may compensate for seasonal variation in the amounts of fiber and nutrients ingested. These data also suggest that the microbial community present in the primate gut allows hosts to undergo temporary shifts in diet with fewer impacts to nutrition and health than would otherwise be expected.

3. Contrary to predictions of bioenergetics models, despite experiencing increased nutritional demands due to processes such as reproduction and growth, adult female and juvenile howler monkeys do not exhibit distinct foraging patterns or activity budgets compared to adult males. Instead, adult female and juvenile howler monkeys differ in overall gut microbial community composition compared to adult males, suggesting that digestive efficiency may differ among age and sex classes, allowing females and juveniles to compensate for increased nutritional demands without major shifts in behavior or diet. These results have important implications for understanding the evolution of life history processes in primates.

4. Howler monkey gut microbial community composition differs across habitats. This appears to be influenced by the plant species being consumed in each habitat. Additionally, howlers in habitats with less dietary diversity exhibit less microbial diversity and experience potential health consequences resulting from changes in energy and toxic by-product generation by microbes. Therefore, despite howler monkeys’ ability to endure temporary changes in diet with few obvious nutritional consequences, long-term changes in diet across space or time incited by factors such as migration, habitat destruction and climate change appear to have serious consequences for both nutrition and health.