Anuran limbs reflect microhabitat and distal, later-developing bones are more evolutionarily labile

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Developmental biology

Background:

• Tetrapod limb morphology is shaped by selective pressures and constraints.
• Anurans (frogs and toads) offer diverse microhabitat adaptations for studying limb evolution.
• Mammalian studies suggest later-developing bones have fewer constraints and more variation.

Purpose of the Study:

• To investigate how microhabitat, phylogeny, allometry, and developmental timing influence anuran limb bone morphology.
• To test the generality of developmental constraints on limb bone evolution in tetrapods.

Main Methods:

• Microcomputed tomography (micro-CT) scans of 236 anuran species.
• Geometric morphometrics to analyze limb bone shape.
• Phylogenetic comparative methods to assess evolutionary relationships and rates.

Main Results:

• Anuran limb shape is significantly influenced by microhabitat and, to a lesser extent, body size, with a notable phylogenetic signal.
• Distal limb bones exhibit higher evolutionary rates than proximal bones.
• Distal bones show increased selection related to allometry and microhabitat.

Conclusions:

• Developmental constraints are reduced in later-developing limb bones, leading to greater evolutionary lability.
• Microhabitat and allometry are significant drivers of evolutionary change in anuran limb shape.
• The findings suggest that reduced developmental constraints on later-developing bones is a general trend across tetrapods.