Unexpectedly complex gradation of coral population structure in the Nansei Islands, Japan

Abstract

To establish effective locations and sizes of potential protected areas for reef ecosystems, detailed information about source and sink relationships between populations is critical, especially in archipelagic regions. Therefore, we assessed population structure and genetic diversity of Acropora tenuis, one of the dominant stony coral species in the Pacific, using 13 microsatellite markers to investigate 298 colonies from 15 locations across the Nansei Islands in southwestern Japan. Genetic diversity was not significant among sampling locations, even in possibly peripheral locations. In addition, our results showed that there are at least two populations of A. tenuis in the study area. The level of genetic differentiation between these populations was relatively low, but significant between many pairs of sampling locations. Directions of gene flow, which were estimated using a coalescence‐based approach, suggest that gene flow not only occurs from south to north, but also from north to south in various locations. Consequently, the Yaeyama Islands and the Amami Islands are potential northern and southern sources of corals. On the other hand, the Miyako Islands and west central Okinawa Island are potential sink populations. The Kerama Islands and the vicinity of Taketomi Island are potential contact points of genetic subdivision of coral populations in the Nansei Islands. We found that genetic population structure of A. tenuis in the Nansei Islands is more complex than previously thought. These cryptic populations are very important for preserving genetic diversity and should be maintained.

Influences of the Kuroshio on Interisland Remote Connectivity of Corals Across the Nansei Archipelago in the East China Sea

“…They detected strong historical migration from the Yaeyama Islands (YIs) to Okinawa Island. Zayasu et al () reported from 13 microsatellite markers of A. tenuis sampled at 15 location across the Nansei Archipelago that genetic population structure is complex as gene flow not only occurs from south to north but also from north to south in various locations. Hence, the YIs and the Amami Islands (the islands #3–7 in Table ) are potential northern and southern sources of corals, while Miyako Island (#11) and west central Okinawa Island are potential sink populations.…”

From population connectivity to the art of striping Russian dolls: the lessons from Pocillopora corals

“…Zayasu et al. (2016), studying Acropora tenuis in southwestern Japan, hypothesized the existence of two source populations (two genetic clusters) in both farthest sites of the sampling area and a mix of both clusters in the middle of the sampling area that should be linked to migration from extreme sites to the intermediate ones. A similar pattern was observed in P. damicornis β (Gélin, Fauvelot, Mehn, Bureau, Rouzé & Magalon, 2017) in Reunion Island with both clusters mixed in one intermediate site, evoking a geographic barrier or an asynchronous spawning of the most remote populations.…”

Genetic diversity of farmed and wild populations of the reef‐building coral, Acropora tenuis

“…). For wild locations, 15 sites that had 10 or more colonies of A. tenuis within approximately 3 ha were sampled at depths less than 10 m (Zayasu et al ). For both wild and farmed samples, a branch fragment approximately 2 cm was collected from each colony and preserved in 99% ethanol.…”