Browsing by Subject "Lemurs"

Host fitness is impacted by trillions of bacteria in the gastrointestinal tract (GIT) that facilitate development of the intestines and brain, digest fiber, and defend against pathogenic invasion. Gut microbes are closely tied to host development and, by extension, the components of life history. Yet, because microbes are capable of lateral gene transfer across vast phylogenetic distances, scientists have struggled to determine whether the taxonomic (microbiota) or genetic (microbiome) composition of a microbial community plays a greater role in its symbiosis with the host. The overarching theme of this dissertation is to explore the interplay between the phylogeny and phenotype of both host and its microbiome. By using 16S rRNA gene amplicon sequencing, metagenomic sequencing, and metabolomics to compare gut microbial communities associated with captive hosts, we are able to identify which microbial community features are correlated with specific host factors. First we compared gut colonization in infants across three lemur species with different diets and gut morphologies. Next we used metagenomic sequencing and nuclear magnetic resonance (NMR) spectroscopy to assess the suite of metabolic pathways and products associated with each host species. Both studies suggest that fiber is a critical dietary component associated with key features of microbial colonization in healthy infants. We next compared bacterial lineages shared between lemurs and bamboo specialists to assess which specific classes of microbial membership are impacted by host phylogeny versus diet. Finally, we compared secondary colonization trajectories to assess the impact of Cryptosporidium, an intestinal pathogen that seasonally infects captive sifakas at the Duke Lemur Center. We find that, while diet predictably shapes community structure and function during colonization, disease incurs age-related impacts on each individual’s microbiome uniquely.

Primates in the wild face complex foraging decisions where they must assess the most valuable of different potential resources to exploit, as well recall the location of options that can be widely distributed. While differences in diet and ecology have long been thought to be an important factor influencing brain evolution in primates, it is less well understood what psychological abilities animals actually use when making foraging decisions. This dissertation examines cognitive domains that play a crucial role in supporting foraging behaviors--spatial memory and decision-making--by integrating both psychological and biological approaches to behavior. In particular, the research presented here examines multiple species of primates to address the cognitive skills that different animals use to solve foraging problems (at the proximate level of analysis), as well as why some species appear to solve such problems differently than other species (at the ultimate level of analysis).

The first goal of the dissertation is to compare closely-related species that vary in ecological characteristics, in order to illuminate how evolution shapes the cognitive skills used in foraging contexts. This component focuses on comparisons between chimpanzees (Pan troglodytes) and bonobos (Pan paniscus), humans' closest extant relatives. In addition, this component reports comparisons amongst strepsirrhines (Lemur catta, Eulemur mongoz, Propithecus coquereli, and Varecia subsp.) to model cognitive evolution in a taxonomic group with greater ecological diversity than Pan. The first two chapters test the hypothesis that more frugivorous species exhibit more accurate spatial memory skills, first by comparing apes' spatial memory abilities (Chapter 2), and then by comparing four species of lemurs on a related set of spatial memory tasks (Chapter 3). In subsequent chapters, I examine apes' decision-making strategies to test the hypothesis that chimpanzees are more willing to pay decision-making costs than are bonobos, due to differences in their feeding ecology. I focus on preferences about the timing of payoffs (Chapter 4); preferences about risk, or the variability in payoffs (Chapters 4 and 5); and preferences about ambiguity, or knowledge about available options (Chapter 6).

The second goal of the dissertation is to compare the psychological mechanisms that human and nonhuman great apes use for foraging, in order to identify potentially human-unique cognitive abilities. In terms of spatial memory, I examine whether other apes also exhibit human-like patterns of spatial memory development (Chapter 2). In terms of decision-making, I examine whether apes exhibit a suite of human-like biases when making value-based choices. In particular, I test whether emotional and motivational processes, which are critical components of human decision-making, also play a role in apes' choices (Chapters 4); whether apes are sensitive to social context when making economic decisions (Chapter 5); and whether apes are sensitive to their degree of knowledge when making choices under uncertainty (Chapter 6). Finally, I directly compare human and ape preferences on a matched task to assess whether humans use any unique psychological abilities when making decisions about risk (Chapter 7). In sum, this dissertation links studies of mechanism with hypotheses about function in order to illuminate the evolutionary roots of human's unique cognitive phenotype.