Variation in Dental Morphology and Dietary Breadth in Primates and Their Kin

Sympatric animals may consume diets of differing breadths as a strategy to reduce competition. Studying patterns of dietary breadth in extinct taxa is difficult because available data are generally limited to morphology. Dental topographic analysis (DTA) is useful for comparing occlusal morphology and allows for examination of dietary adaptations in extinct taxa. What remains unknown is how dental morphology, quantified using DTA, covaries with dietary breadth. The niche variation hypothesis (NVH) posits that taxa with broader ecological niches will be characterized by greater variability in morphology relative to specialized taxa. Therefore, we predict that taxa with greater dietary breadth will have more varied dental morphology compared to specialists as a result of the molar morphology of specialists being under greater genetic control relative to generalists, with specialists requiring teeth specially adapted to efficiently process a smaller range of food sources. We measured curvature, complexity, and relief of the M2 of 3 pairs of closely related euarchontan mammals (primates and treeshrews), with each taxon within a pair categorized as a generalist or specialist. Our results indicate that generalists do not consistently show greater variability in dental morphology compared to specialists among primates, but that atelids and treeshrews do generally follow the predictions of the NVH, with the caveat that our treeshrew sample is small. This suggests that while dietary specialists may be under greater genetic constraint with respect to their molar topography, a link between dietary breadth and dental form is not clear. Our study demonstrates that variation in dental topography does not necessarily reflect dietary breadth and highlights the fact that it is difficult to categorize even the most specialized primates (i.e. bamboo lemurs) as "dietary specialists." The niche variation hypothesis (NVH) suggests that generalist species will be characterized by greater variability in morphology relative to specialists. We test this hypothesis as it relates to dietary breadth and molar form (dental topography) in primates and their close relatives. We find variable support for the NVH, and suggest that a link between molar form and dietary breadth is not clear, and that categorizing primates as "generalists" or "specialists" minimizes the complexity of their diets. Los animales simpatricos pueden consumir dietas de diferentes amplitudes como estrategia para reducir la competicion. Es dificil estudiar los patrones de amplitud dietetica en taxones extintos debido a que los datos disponibles generalmente estan limitados tan solo a morfologia. El analisis topografico dental (DTA; dental topographic analysis) es util para comparar morfologias oclusales y permite examinar las adaptaciones dieteticas en taxones extintos. Lo que aun permanece sin saber es como la morfologia dental, cuantificada con el uso de DTA, covaria con el rango dietetico. La hipotesis de variacion de nicho (NVH; niche variation hypothesis) plantea que taxones con nichos ecologicos mas amplios se caracterizaran por tener una mayor variabilidad morfologica en comparacion con taxones mas especializados. Por eso, predecimos que los taxones con una mayor amplitud dietetica tendran una morfologia dental mas variada comparada con especialistas como resultado de que la morfologia molar de los especialistas este bajo mayor control genetico que la de los generalistas, dado que los especialistas requieren dientes especialmente adaptados para procesar eficientemente una menor amplitud de alimentos. Medimos la curvatura, la complejidad y el relieve del M2 de tres pares de Euarchontas evolutivamente cercanos (primates y tupayas) y simpatricos, con cada taxon en cada par categorizado como generalista o especialista. Nuestros resultados indican que los generalistas no muestran, consistentemente, mayor variabilidad en la morfologia dental en comparacion con los especialistas dentro de los primates, aunque los atelidos y las tupayas generalmente si que siguen las predicciones de la NVH, aunque admitiendo que nuestra muestra de tupayas es pequena. Esto sugiere que mientras que puede ser que los especialistas dieteticos esten bajo una mayor restriccion genetica con respecto a su topografia molar, la conexion entre amplitud dietetica y forma dental no es clara. Nuestro estudio demuestra que la variacion en topografia dental no se refleja necesariamente en amplitud dietetica y recalca el hecho de que es dificil categorizar incluso los primates mas especializados (por ejemplo, los lemures del bambu) como "especialistas dieteticos."