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.
Data collection. An example of the habitat in which lizards were collected (A), the trackway filming setup where sprint performance data were collected (B), and an example of the body shape landmarks used for the geometric morphometric analysis (C).
Habitat. Bar plot of proportion of individuals found in each habitat type for juvenile and adult lizards. Shading represents different habitat types.
Box plots for juvenile and adult maximum relative sprint speed (SVL/s). The midlines represent the mean, the two hinges represent the first and third quartiles, and the whiskers extend to the maximum or minimum value or to 1.5* the interquartile range. Outliers are represented by black dots.
Box plots for juvenile and adult limb lengths. (A) Forelimb and (B) hindlimb length relative to body length measured as a proportion of snout–vent length. Note, we tested the limb lengths measured in cm, but we have chosen to visualize limb lengths as %SVL to better visualize the interaction between SVL and limb length that is tested by the ANCOVAS used in our analysis. The midlines represent the mean, the two hinges represent the first and third quartiles, and the whiskers extend to the maximum or minimum value or to 1.5* the interquartile range.
Contributor Notes
Associate Editor: J. M. Davenport