Feeding ecology and allometry underlie distinct axes of mandible and leg evolution in tropical termites.

Understanding how ecological pressures and allometry contribute to morphological evolution remains a central goal in evolutionary biology. We examined mandible and leg shape in nearly 100 Amazonian termite species using geometric morphometrics and phylogenetic comparative methods. This approach allowed us to assess how feeding ecology and centroid size of body parts contribute to shape variation while accounting for shared evolutionary history across species. We show that mandible shape varies with feeding ecology along a wood-to-soil (humification) gradient, with wood-feeding species exhibiting shorter, more robust mandibles and soil-feeding species showing more elongated forms with a prominent apical tooth. In contrast, leg shape is best explained by leg centroid size and shows limited differentiation across feeding groups. Evolutionary model comparisons indicate that mandible shape is consistent with models suggesting multiple evolutionary optima associated with feeding habit, whereas leg shape is better described by a single optimum. Together, our results indicate that mandible and leg morphology vary along complementary axes: mandibles reflect dietary variation, while legs predominantly scale with size. This illustrates how different processes govern morphological variation in a diverse tropical termite radiation.