Sorting of ancestral polymorphism and its impact on morphological phylogenetics and macroevolution

Area of Science:

• Evolutionary Biology
• Paleontology
• Developmental Biology

Background:

• Intraspecific phenotypic variation is crucial for adaptation and speciation.
• Understanding how this variation influences macroevolutionary patterns is essential.
• Previous models have not fully incorporated polymorphism.

Purpose of the Study:

• To introduce and test a novel model of morphological evolution that includes polymorphism.
• To investigate the interplay between intraspecific variation and macroevolutionary processes.
• To reconstruct phylogenetic relationships within the Cretaceous echinoid genus Micraster.

Main Methods:

• Development of a stochastic model of phenotypic character state gain/loss (anagenesis) and sorting during speciation (cladogenesis).
• Computer simulations to explore model behavior.
• Application of the model to empirical data from the fossil genus Micraster.

Main Results:

• The model successfully reconstructs contentious phylogenetic relationships within Micraster with strong statistical support.
• Observed a pattern of variation accumulation in early lineages, followed by sorting into descendants.
• Demonstrated that variation is maintained in some lineages and lost in others without full replenishment.

Conclusions:

• The model provides a framework for understanding how intraspecific variation shapes macroevolutionary trajectories.
• The findings link population-level processes maintaining variation to clade-level radiation and decline.
• This research highlights the importance of considering polymorphism in evolutionary studies.