Eva Salas, Jean-Paul A. Hobbs, Moisés A. Bernal, W. Brian Simison, Michael L. Berumen, Giacomo Bernardi, Luiz A. Rocha
Ecology and Evolution; 00:125, (2020)
Dascyllus trimaculatus, Hybrid zones, Indo-Pacific, Introgression, Mitochondrial DNA, Phylogeography, RADSeq
Hybrid zones are natural laboratories for investigating the dynamics of gene flow,
reproductive isolation, and speciation. A predominant marine hybrid (or suture) zone
encompasses Christmas Island (CHR) and Cocos (Keeling) Islands (CKE), where 15
different instances of interbreeding between closely related species from Indian
and Pacific Oceans have been documented. Here, we report a case of hybridization
between genetically differentiated Pacific and Indian Ocean lineages of the threespot dascyllus, Dascyllus trimaculatus (Rüppell, 1829). Field observations indicate
there are subtle color differences between Pacific and Indian Ocean lineages. Most
importantly, population densities of color morphs and genetic analyses (mitochondrial DNA and SNPs obtained via RADSeq) suggest that the pattern of hybridization
within the suture zone is not homogeneous. At CHR, both color morphs were present, mitochondrial haplotypes of both lineages were observed, and SNP analyses
revealed both pure and hybrid genotypes. Meanwhile, in CKE, the Indian Ocean color
morphs were prevalent, only Indian Ocean mitochondrial haplotypes were observed,
and SNP analysis showed hybrid individuals with a large proportion (~80%) of their
genotypes assigning to the Indian Ocean lineage. We conclude that CHR populations are currently receiving an influx of individuals from both ocean basins, with a
greater influence from the Pacific Ocean. In contrast, geographically isolated CKE
populations appear to be self-recruiting and with more influx of individuals from the
Indian Ocean. Our research highlights how patterns of hybridization can be different
at scales of hundreds of kilometers, due to geographic isolation and the history of
interbreeding between lineages