Morphometric variance, evolutionary constraints and their change through time in Late Devonian Palmatolepis conodonts

Area of Science:

• Paleontology
• Evolutionary Biology
• Geometric Morphometrics

Background:

• Phenotypic variation is crucial for evolution, but selection can alter its structure.
• Understanding how selection regimes influence variance is key to evolutionary studies.

Purpose of the Study:

• To investigate the impact of environmental changes and mass extinctions on phenotypic variation in Palmatolepis conodonts.
• To analyze how adaptive optima shifts reorient the structure of phenotypic variance (P-matrix).

Main Methods:

• Quantified conodont shape using 2D geometric morphometrics.
• Characterized patterns of variance using the variance-covariance matrix (P-matrix) and its first axis (Pmax).
• Analyzed data across the Late Devonian, including the Frasnian/Famennian mass extinction event.

Main Results:

• Environmental oscillations and the Frasnian/Famennian mass extinction caused a shape response and altered the P-matrix and Pmax.
• Post-extinction, Palmatolepis mean shape shifted, accompanied by a reorientation of the P-matrix and Pmax.
• Empirical evidence shows that shifting adaptive optima can reorient phenotypic variation, enhancing evolutionary response.

Conclusions:

• Phenotypic variance is not static; it actively responds to changing selection pressures and adaptive optima.
• The study highlights the dynamic interplay between selection, environmental change, and the evolution of phenotypic variation.
• The P-matrix's variability is a critical factor in adaptation over geological timescales.