Three species of Hapalemur (Primates) coexist in a rainforest in Madagascar, where they subsist on different parts of an unusual food resource, bamboo. These circumstances create an intriguing natural experiment for examining behavioral and morphological variables that contribute to the coexistence of these species on a similar diet. This project will specifically examine relationships between physical parameters of diets and the form and performance of jaws and teeth where food is first encountered. Positive relationships between these factors will support the hypothesis that differences represent feeding adaptations that allow the lemurs to exploit similar resources without being in direct competition. These results can serve as a model for interpreting morphology and dietary reconstruction of extinct primates in the fossil record, while also addressing the extent to which dietary properties influence morphological evolution and adaptation.
Toward these goals, this project will investigate whether the observed dietary differences among Hapalemur species are solely related to behavioral aspects of food choice or whether they are also linked to variation in the form and performance of the masticatory apparatus. Specifically, the project will determine: 1) whether the segregation or overlap of Hapalemur diets can be linked to variation in plant properties, 2) whether these plant properties are correlated with variation in dental and jaw morphology, and 3) whether morphological differences translate into performance differences in biting and chewing behaviors among species. Even though divergence in form is typically used as evidence of adaptive specialization, these morphological differences must result in differential performance if current morphological variation is the result of directional selection. If physical dietary properties, jaw and tooth form, and performance of the masticatory apparatus during chewing and biting are correlated across the lemur species, then this would suggest that differences in the ability to procure specific foods could have contributed to reduction of feeding competition. Fieldwork will involve: 1) observing feeding behaviors to identify exact plant parts eaten and establish individual and species differences in food ingestion and processing; 2) quantifying food properties by testing plant parts eaten and rejected by the lemurs for toughness, hardness, and elastic modulus using a portable mechanical tester; and 3) comparing the morphology and performance of the jaws and teeth of Hapalemur individuals by taking tooth impressions, measuring jaws, quantifying maximum jaw gapes, and estimating maximum bite force capabilities on anesthetized animals.
This project has a strong educational component that involves supporting and training students in the host country. Malagasy students will work with the researchers in all aspects of this project. In addition to providing assistance in the field, each student will be supervised in separate, parallel research projects toward completion of their Master's equivalent degrees. The future conservation of these primates and other rare endemic species will be led by local researchers who must be well-trained. It is the hope of the project investigators to contribute to this effort by exposing students to broad evolutionary questions and fieldwork opportunities that they can then apply to their own research programs.
