Population genetic structure of a major reef-building coral species Acropora downingi in northeastern Arabian Peninsula

Abstract

Current seawater temperatures around the northeastern Arabian Peninsula resemble future global forecasts as temperatures > 35 °C are commonly observed in summer. To provide a more fundamental aim of understanding the structure of wild populations in extreme environmental conditions, we conducted a population genetic study of a widespread, regional endemic table coral species, Acropora downingi, across the northeastern Arabian Peninsula. A total of 63 samples were collected in the southern Arabian/Persian Gulf (Abu Dhabi and Qatar) and the Sea of Oman (northeastern Oman). Using RAD-seq techniques, we described the population structure of A. downingi across the study area. Pairwise G’st and distance-based analyses using neutral markers displayed two distinct genetic clusters: one represented by Arabian/Persian Gulf individuals, and the other by Sea of Oman individuals. Nevertheless, a model-based method applied to the genetic data suggested a panmictic population encompassing both seas. Hypotheses to explain the distinctiveness of phylogeographic subregions in the northeastern Arabian Peninsula rely on either (1) bottleneck events due to successive mass coral bleaching, (2) recent founder effect, (3) ecological speciation due to the large spatial gradients in physical conditions, or (4) the combination of seascape features, ocean circulation and larval traits. Neutral markers indicated a slightly structured population of A. downingi, which exclude the ecological speciation hypothesis. Future studies across a broader range of organisms are required to furnish evidence for existing hypotheses explaining a population structure observed in the study area. Though this is the most thermally tolerant acroporid species worldwide, A. downingi corals in the Arabian/Persian Gulf have undergone major mortality events over the past three decades. Therefore, the present genetic study has important implications for understanding patterns and processes of differentiation in this group, whose populations may be pushed to extinction as the Arabian/Persian Gulf warms.

Physical–biological interactions underlying the connectivity patterns of coral‐dependent fishes around the Arabian Peninsula

“…However, a phylogeographical study of Periophthalmus waltoni , a marine amphibious fish with terrestrial adaptations, revealed two distinct genetic clusters, one represented by the Gulf individuals and the other by individuals from the Sea of Oman. Likewise, genetic investigations involving corals (Howells et al, 2016; Torquato et al, 2021) and sea urchin (Ketchum et al, 2020) showed a genetic discontinuity through the Strait of Hormuz. Indeed, biogeographical survey indicated higher levels of endemism for invertebrates within the Gulf compared to fishes (DiBattista, Roberts, et al, 2016).…”

“…Experiments with Acropora showed that its larval survival strongly declined after the first few days after spawning, with half‐life shorter than 5 days (Graham et al, 2008). Nevertheless, the population differentiation of P. daedalea and A. downingi through the Strait of Hormuz has also been explained by natural selection (Howells et al, 2016) and recent bottlenecks (Torquato et al, 2021), respectively. In turn, the sea urchin ( Echinometra sp.…”

“…The Pleistocene also created conditions to differentiate populations between the Gulf and the Sea of Oman (Torquato et al, 2021). During the glacial maxima, when the sea level lowered at 120 m than the present, the Gulf had its ground almost completely espoused.…”

“…Thus, the populations currently inhabiting this sea were established only in the last few millennia. This scenario of recent founded effect combined with the restricted gene flow between the Gulf and its adjacent Sea of Oman is one of the hypothesis to explain the phylogeographical pattern observed in the region (Torquato et al, 2021).…”

“…The Pleistocene also created conditions to differentiate populations between the Gulf and the Sea of Oman (Torquato et al, 2021).…”