Is speciation an unrelenting march to reproductive isolation?

Area of Science:

• Evolutionary biology
• Genomics
• Island biogeography

Background:

• Traditional speciation models emphasize complete reproductive isolation as the endpoint.
• Evidence suggests inter-fertility is common between accepted species, challenging this view.
• Island ecosystems provide unique models for studying diversification.

Discussion:

• Linan et al. (2021) demonstrate gene flow among closely related tree species in the Mascarene Islands.
• These species form nested syngameons with hierarchical interfertility, bridging population and phylogenetic levels.
• Genomic data and complete taxonomic sampling offer deep insights into in situ island diversification.

Key Insights:

• Speciation is a fluid process, not always leading to complete isolation.
• Syngameon dynamics, characterized by inter-fertility, are prevalent across diverse taxa.
• Island clades can evolve as interconnected networks of gene-exchanging lineages.

Outlook:

• Conservation and research should adopt a holistic approach, considering networks of interfertile species.
• Understanding these evolutionary units is crucial for predicting adaptation and innovation.
• Future research should focus on the ecological and evolutionary implications of syngameon dynamics, especially in human-altered landscapes.