Adaptive evolution of plastron shape in emydine turtles.

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Herpetology

Background:

• Morphological variation is shaped by ecological pressures, evolutionary history, and biophysical constraints.
• Understanding these influences is key to studying trait evolution and natural selection.

Purpose of the Study:

• To investigate the factors contributing to plastron (ventral shell) shape variation in emydine turtles.
• To disentangle the roles of function, phylogeny, and habitat in shaping turtle morphology.
• To evaluate evolutionary models explaining observed patterns of plastron shape.

Main Methods:

• Geometric morphometrics was used to quantify shape variation in emydine turtle plastra.
• Path analysis was employed to determine the influence of function, phylogeny, and habitat on shape.
• Evolutionary models were fitted to the shape data to assess selective landscapes.

Main Results:

• The presence of a plastral hinge was the primary driver of morphological variance.
• Phylogeny and habitat were also found to correlate significantly with plastron shape.
• The distribution of shape variance best fit an evolutionary model with two adaptive zones: kinetic and rigid plastra.

Conclusions:

• Plastral kinesis imposes strong mechanical constraints, leading to a relatively simple adaptive landscape for emydine turtle plastron shape.
• Phylogenetic history and habitat are secondary factors influencing plastron morphology.
• The evolution of plastron shape is largely dictated by the functional dichotomy of hinged versus rigid ventral shells.