Selection for increased tibia length in mice alters skull shape through parallel changes in developmental mechanisms

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Skeletal Biology

Background:

• Vertebrate skeletal growth, including cranial base and limb bones, relies on endochondral ossification regulated by growth plates.
• Conserved mechanisms across growth plates can lead to size and shape covariation, potentially causing non-adaptive skeletal trait changes.

Purpose of the Study:

• To investigate cranial shape changes in the Longshanks mouse model, selectively bred for extended tibiae.
• To explore the developmental basis of correlated morphological changes between limb and cranial base skeletons.

Main Methods:

• Utilized micro-computed tomography (micro-CT) for high-resolution skeletal imaging.
• Applied geometric morphometrics to quantitatively analyze cranial shape variations.

Main Results:

• Longshanks mouse skulls exhibited a stepwise increase in length, accompanied by flattening and narrowing.
• These cranial shape alterations mirrored changes observed in the tibia, suggesting shared developmental pathways.
• Cranial base growth plate development in Longshanks mice was implicated as the source of these morphological changes.

Conclusions:

• Developmental overlap between distant skeletal elements can induce indirect, non-adaptive morphological changes.
• These findings have significant implications for understanding the evolutionary history and interpretation of vertebrate skeletal form.