Head shape evolution in Tropidurinae lizards: does locomotion constrain diet?

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Functional morphology

Background:

• Complex systems, like vertebrate skulls, face conflicting selective pressures due to multiple functions (locomotion, feeding, defense).
• The Tropidurinae lizard cranial system exemplifies this, with potential conflicts between adaptations for arboreal locomotion and processing hard prey.

Purpose of the Study:

• To investigate the influence of conflicting selective pressures, specifically diet versus locomotion, on the evolutionary trajectory of head shape in Tropidurinae lizards.
• To determine whether habitat use or dietary adaptations are the primary drivers of cranial morphology evolution in this group.

Main Methods:

• Quantified body size and six head shape variables from preserved specimens of 23 Tropidurinae species.
• Gathered data on diet and substrate usage from existing literature.
• Employed factor analysis and independent contrast analysis to assess evolutionary patterns and covariation.

Main Results:

• No phylogenetic signal was detected in the morphological data, suggesting strong adaptive evolution.
• Factor and independent contrast analyses revealed significant adaptive co-variation between head shape and the consumption of hard prey.
• Contrary to expectations, habitat use (e.g., vertical structures) did not significantly influence or constrain head shape evolution.

Conclusions:

• Head shape evolution in Tropidurinae lizards is primarily driven by dietary adaptations, particularly the need to process hard prey.
• Locomotory or habitat-related selective pressures appear to play a minimal role in shaping cranial morphology within this lizard subfamily.
• The study highlights the power of diet as a selective force in the adaptive radiation of complex morphological systems.