An introgression breakthrough left by an anthropogenic contact between two ascidians

Area of Science:

• Evolutionary Biology
• Marine Biology
• Genetics

Background:

• Human-driven species translocations can lead to hybridization between isolated taxa.
• The solitary tunicate Ciona robusta, introduced to the North East Atlantic, now co-occurs with native Ciona intestinalis and Ciona roulei.

Purpose of the Study:

• To investigate the genome-wide population structure of native Ciona taxa.
• To explore evidence of recent hybridization and introgression between introduced Ciona robusta and native Ciona intestinalis.

Main Methods:

• Used SNP data from ddRAD-sequencing of 397 individuals across 26 populations.
• Analyzed genome-wide population structure and introgression patterns.

Main Results:

• Confirmed chaotic genetic structure and high similarity between C. roulei and C. intestinalis.
• Discovered a genomic hotspot of long Ciona robusta introgressed tracts within Ciona intestinalis genomes in contact zones.
• Observed recent introgression, restricted to a 1.5 Mb region on chromosome 5, suggesting post-introduction events.

Conclusions:

• Anthropogenic hybridization can facilitate introgression breakthroughs between species nearing the end of the speciation continuum.
• The findings highlight the evolutionary consequences of species translocations and the potential for hybridization in marine environments.