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Deep time perspective on turtle neck evolution: chasing the Hox code by vertebral morphology.

Christine Böhmer1, Ingmar Werneburg2,3,4

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Summary
This summary is machine-generated.

Turtle neck retraction evolved through distinct modes, influenced by Hox gene expression and vertebral morphology. Genetic shifts explain cervical vertebrae evolution and the fixed count in turtles.

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Area of Science:

  • Evolutionary Biology
  • Developmental Genetics
  • Comparative Anatomy

Background:

  • Turtles exhibit unique neck retraction abilities, classified into three modes: stem turtles, Pleurodira (side-necked), and Cryptodira (hidden-necked).
  • Despite a conserved vertebral count, the turtle cervical column shows significant functional and morphological regionalization.
  • Hox genes are crucial for vertebral morphology differentiation, suggesting genetic variations among turtle groups and other land vertebrates.

Purpose of the Study:

  • To investigate morphological modularity in turtle necks by correlating Hox gene expression with vertebral shape.
  • To reconstruct the hypothetical ancestral Hox gene code pattern for the entire turtle clade.
  • To understand the evolutionary genetics underlying turtle neck diversity and the fixed cervical vertebra count.

Main Methods:

  • Reconstruction of evolutionary genetics in deep time.
  • Correlation of anterior Hox gene expression with quantifiable vertebral shape in living and extinct turtles.
  • Comparative analysis with mammalian axial patterning.

Main Results:

  • Identified shifts in HoxA-5 spatial expression related to reduced cervical ribs in modern turtles.
  • Linked HoxB-5 expression to lower morphological differentiation in anterior cervical vertebrae of Cryptodira.
  • Reconstructed the ancestral Hox code pattern for turtles.

Conclusions:

  • The evolution of axial patterning in turtles involves specific Hox gene expression shifts.
  • The fixed count of eight cervical vertebrae in turtles is linked to the development of the turtle shell.
  • Genetic and morphological analyses provide insights into the deep evolutionary history of turtle necks.