The variation in traits associated with fitness often results in selective pressures, thereby influencing the phenotypic traits observed in populations across diverse environments. The exploration of differences among individuals within and between populations has consistently been a key emphasis in evolutionary biology, seeking to understand how organisms adapt to a range of environments. In this research, I analyzed pelage color variation in the least chipmunk (Tamias minimus). Focusing on intraspecific variation—differences observed within a species—I conducted a quantitative analysis of pelage brightness across populations distributed throughout the range of the least chipmunk. This species is well-suited for this study because of its extensive geographic range, encompassing a variety of environments that span from semi-arid shrub steppe to high-elevation forests. I investigated the relationship between chipmunk habitat, utilizing various environmental variables, and pelage brightness. I predicted that precipitation and temperature would influence the brightness of the pelage, which often corresponds to the ability of an individual to camouflage or thermoregulate in their environment. To test this hypothesis, I photographed 334 museum specimens and measured the mean and standard deviation luminosity (two measurements of brightness) along four dorsal stripes and the head. I then extracted environmental variables using the GPS coordinates for each individual, these included 19 bioclimatic variables, elevation, latitude, net primary productivity and other variables related to geographic location. To examine the influence of environmental factors on the pelage color, I conducted generalized least squares analyses and principal component analyses in R. The initial results of my research indicate that the pelage color of a population is influenced the environment. Most notably, there is a significant correlation between pelage color and precipitation. In habitats with increased precipitation, such as forests, chipmunks tend to exhibit darker colors, whereas in regions with low precipitation, like deserts, individuals often display brighter pelage.

Countershading is defined as the difference in color between an animal’s dorsal and ventral surfaces, and can serve one of two purposes: to aid in background matching or to create a self-cast shadow, causing the animal to appear less three-dimensional to potential predators. Studies on primates show that species with more frequent horizontal postures and smaller body sizes exhibit higher levels of countershading, however, these links between locomotion behavior and coloration have not been explored in the vast majority of mammals. The Sciuridae family encompasses over 280 species, including squirrels, chipmunks, marmots, and beavers, which are characterized by a wide array of coat colors and use of different locomotion strata. Here, I analyze the correlation between Sciuridae countershading and locomotion strata using specimens from the Burke Museum. To test this hypothesis, I am collecting standardized photographs of specimens from the Burke Museum spanning 73 species, along with data on natural history from the literature to categorize species based on locomotion strata and nesting location. I expect to find that primarily terrestrial Sciuridae species will exhibit low levels of countershading, whereas arboreal species will exhibit high levels of countershading. I expect species with intermediate locomotion strata to rely on a combination of patterns and varying countershading levels, as their locomotion is more variable. This research sheds light on countershading trends in small mammals in relation to their locomotion strata, while also taking into account nesting behaviors and phylogenetic relationships. By using specimens from the Burke Museum, my data collection also aids in the digitization of specimens. In the future, I hope to use the results of this study to inform research on predator-prey relationships with respect to coloration and visual distractions, along with how these relationships are affected by the environment.

The diversification of many vertebrates was spurred by the use of novel food resources, and jaw morphology provides clues about the adaptations associated with dietary diversification. The external dimensions along the mandible reflect the strength to resist bite forces, which are associated with the diet's physical properties. Variations between different species may reflect adaptations of the jaw to specific diets. Using the mandibles of 60 Chiroptera species, we quantified the external dimensions at interdental gaps to generate mandibular strength profiles. Insectivores showed the greatest within-guild variation in jaw shape, while nectarivores had noticeably gracile symphyses. Further, insectivorous bats showed deep jaws at the canine, which may be associated with the use for prey capture. At the same time, frugivores have deep jaws at the posterior molars, possibly linked to adaptations for crushing seeds and pulp. When compared to measurements of bite force collected in the field, there was a remarkable and significant correlation between field-gathered and inferred bite force profiles. These results show that mandible strength profiles reflect dietary adaptations in bats, and demonstrate the reliability of this method in inferring the mandibular force profiles from preserved (non-living) specimens. These results indicate that this method can be used to further our understanding of the dietary behavior of species with few living specimens or that are extinct.