Differences between Juveniles and Adults in Habitat Use, Sprint Performance, and Morphology in the Desert Horned Lizard, Phrynosoma platyrhinos

As animals develop, demands on their physical form often change in response to ecological pressures. Structures associated with locomotion and habitat use can be particularly affected. Due to their smaller size, juvenile animals are often under selection to evade a larger and more diverse set of predators compared to adults of the same species. Adult Desert Horned Lizards, Phrynosoma platyrhinos, use a dorsoventral “shielding” as an anti-predator strategy to gape-limit potential predators. Because this strategy is likely size-dependent, we anticipated that juvenile lizards likely use different anti-predator strategies that would result in differences in habitat use, sprint performance, and morphology between age groups. We found differences in sprint speed and morphology, but not habitat use. Juvenile lizards had proportionally longer forelimbs and faster relative sprint speeds, potentially making juveniles more maneuverable than adults, though more work is needed to confirm this relationship. Our results suggest that selection for shielding behavior may constrain body shape throughout development, while shifts in limb lengths during development can enable juvenile lizards to evade their wider set of potential predators.