Ancient Hybridisation Fuelled Diversification in Acropora Corals

Area of Science:

• Marine Biology
• Evolutionary Genetics
• Genomics

Background:

• Introgression, the transfer of genes between species via hybridization and backcrossing, can complicate evolutionary studies.
• The Acropora genus, crucial for reef ecosystems, has an unclear history of pre-diversification introgression.
• Previous divergence-time estimates for Acropora have not accounted for potential introgression impacts.

Purpose of the Study:

• To investigate the existence and extent of ancient introgression within the Acropora coral genus.
• To assess the impact of introgression on phylogenetic reconstruction and divergence-time estimation in Acropora.
• To explore the role of introgression in the evolutionary radiation of Acropora.

Main Methods:

• Analysis of whole-genome protein-coding sequences from multiple Acropora species.
• Inference of introgression events using triplet loci analysis.
• Clustering of nuclear loci using multidimensional scaling to assess phylogenetic heterogeneity.
• Divergence-time estimation using gene groups with varying degrees of introgression.

Main Results:

• Evidence of ancient introgression was detected across Acropora whole-genome sequences.
• Approximately 21.9% of triplet loci showed evidence of introgression, with up to 30.9% genetic contribution before diversification.
• Heterogeneity in nuclear loci clustering led to varied phylogenetic relationships.
• Diversification time was estimated to be middle to late Miocene when accounting for introgression.

Conclusions:

• Ancient introgressive hybridization played a significant role in the genome-wide evolution and radiation of Acropora corals.
• Introgression events occurred prior to Acropora diversification, contributing substantially to their genetic makeup.
• Accurate phylogenetic reconstruction and divergence-time estimates require consideration of introgression's influence.