Genomic Exaptation and Regulatory Landscape Shifts as Key Mechanisms Enabling Flatworm Terrestrialization

Area of Science:

• Evolutionary Biology
• Genomics
• Animal Adaptation

Background:

• Understanding animal terrestrialization requires exploring genomic adaptations for land life.
• Planarians (Platyhelminthes) provide a unique model, with only one known terrestrial lineage.

Purpose of the Study:

• To investigate the genomic basis of terrestrial adaptation in planarians.
• To identify genetic changes supporting the transition from aquatic to terrestrial environments.

Main Methods:

• Integrated genomics, transcriptomics, and proteomics.
• Analyzed gene gain, differential gene expression under abiotic stress, and selection pressures.
• Compared terrestrial and freshwater planarian species.

Main Results:

• A significant gene gain burst occurred in the lineage leading to terrestrial planarians.
• Terrestrial and freshwater planarians showed distinct stress responses, with terrestrial species utilizing gained orthogroups.
• Terrestrial planarians upregulated ancient genes, while freshwater species downregulated ancestral genes, indicating divergent strategies.

Conclusions:

• Gene gain and co-option, alongside regulatory shifts, were key drivers of planarian terrestrialization.
• Genomic exaptation played a crucial role in the evolution of terrestrial flatworms.
• This study offers a genome-wide perspective on flatworm terrestrialization and broader animal adaptation to land.