Abstract
Species delimitation of corals is one of the most challenging issues in coral reef ecology and conservation. Morphology can obscure evolutionary relationships, and molecular datasets are consistently revealing greater within-species diversity than currently understood. Most phylogenetic studies, however, have examined narrow geographic areas and phylogeographic expansion is required to obtain more robust interpretations of within- and among- species relationships. In the case of the blue coral Heliopora, there are currently two valid species (H. coerulea and H. hiberniana) as evidenced by integrated genetic and morphological analyses in northwestern Australia. There are also two distinct genetic lineages of H. coerulea in the Kuroshio Current region that are morphologically and reproductively different from each other. Sampling from all Heliopora spp. across the Indo-Pacific is essential to obtain a more complete picture of phylogeographic patterns. To examine phylogenetic relationships within the genus Heliopora, we applied Multiplexed inter simple sequence repeat (ISSR) Genotyping by sequencing (MIG-seq) on > 1287 colonies across the Indo-West Pacific. Maximum likelihood phylogenetic trees indicated the examined Heliopora samples comprise three genetically distinct groups: H. coerulea group, H. hiberniana group, and a new undescribed Heliopora sp. group with further subdivisions within each group. Geographic structuring is evident among the three species with H. hiberniana group found in the Indo-Malay Archipelago and biased toward the Indian Ocean whilst Heliopora sp. was only found in the Kuroshio Current region and Singapore, indicating that this taxon is distributed in the western Pacific and the Indo-Malay Archipelago. Heliopora coerulea has a wider distribution, being across the Indian Ocean and western Pacific. This study highlights the effectiveness of phylogenetic analysis using genome-wide markers and the importance of examining populations across their distribution range to understand localized genetic structure and speciation patterns of corals.
Highlights
Coral reef ecosystems have the highest biodiversity of all marine ecosystems (Fisher et al, 2015) and are important in terms of their scientific, economic, and social value (Moberg and Folke, 1999; Spalding et al, 2001; Cesar et al, 2003)
Phylogenetic and population genetic analyses using genomewide single nucleotide polymorphisms (SNPs) by MIG-seq showed that the Indo-West Pacific Heliopora was divided into three groups: H. coerulea group, distributed in the Indo-West Pacific and including HCB in the Kuroshio Current region; H. hiberniana group distributed mainly in the Indian Ocean including the type locality of H. hiberniana in northwestern Australia; and a new undescribed Heliopora sp. group distributed mainly in the Western Pacific Ocean, including HC-A in the Kuroshio Current region (Figures 1, 2 and 3A; Supplementary Table 1)
The new undescribed Heliopora sp. group was distributed mainly in the Western Pacific (Japan and Taiwan) and Singapore in this study, while H. hiberniana group was distributed mainly in the Indian Ocean. Such uneven geographical distributions imply the origin of Heliopora sp. group could be in the Pacific Ocean and that of H. hiberniana could be in the Indian Ocean, but this remains to be tested with a dated phylogeny
Summary
Coral reef ecosystems have the highest biodiversity of all marine ecosystems (Fisher et al, 2015) and are important in terms of their scientific, economic, and social value (Moberg and Folke, 1999; Spalding et al, 2001; Cesar et al, 2003). Genetic information based on several molecular markers has shown morphology can conceal cryptic evolutionary relationships (Richards et al, 2013) and it is increasingly common for genetically distinct cryptic species or lineages to be found within widespread coral species (e.g., Nakajima et al, 2012; Pinzón et al, 2013; Warner et al, 2015) Such discordance between morphology and genetics has led to confusion regarding the species boundaries in many groups (e.g., Acropora, van Oppen et al, 2001; Marquez et al, 2002, Pocillopora, Flot et al, 2008; Souter, 2010; Schmidt-Roach et al, 2013). Such ambiguity threatens to undermine effective biodiversity conservation efforts and prevents the true complexity of coral reef ecosystems from being properly understood
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