RADseq population genomics confirms divergence across closely related species in blue coral (Heliopora coerulea)

Background: Heliopora coerulea, the blue coral, is the octocoral characterized by its blue skeleton. Recently, two Heliopora species were delimited by DNA markers: HC-A and HC-B. To clarify the genomic divergence of these Heliopora species (HC-A and HC-B) from sympatric and allopatric populations in Okinawa, Japan, we used a high throughput reduced representation genomic DNA sequencing approach (ezRAD). Results: We found 6,742 biallelic SNPs shared among all target populations, which successfully distinguished the HC-A and HC-B species in both the sympatric and allopatric populations, with no evidence of hybridization between the two. In addition, we detected 410 fixed SNPs linking functional gene differences, including heat resilience and reproductive timing, between HC-A and HC-B. Conclusions: We confirmed clear genomic divergence between Heliopora species and found possible genes related to stress-responses and reproduction, which may shed light on the speciation process and ecological divergence of coral species.