Many broadly‐dispersing corals acquire their algal symbionts (Symbiodiniaceae) “horizontally” from their environment upon recruitment. Horizontal transmission could promote coral fitness across diverse environments provided that corals can associate with divergent algae across their range and that these symbionts exhibit reduced dispersal potential. Here we quantified community divergence of Cladocopium algal symbionts in two coral host species (Acropora hyacinthus, Acropora digitifera) across two spatial scales (reefs on the same island, and between islands) across the Micronesian archipelago using microsatellites. We find that both hosts associated with a variety of multilocus genotypes (MLG) within two genetically distinct Cladocopium lineages (C40, C21), confirming that Acropora coral hosts associate with a range of Cladocopium symbionts across this region. Both C40 and C21 included multiple asexual lineages bearing identical MLGs, many of which spanned host species, reef sites within islands, and even different islands. Both C40 and C21 exhibited moderate host specialization and divergence across islands. In addition, within every island, algal symbiont communities were significantly clustered by both host species and reef site, highlighting that coral‐associated Cladocopium communities are structured across small spatial scales and within hosts on the same reef. This is in stark contrast to their coral hosts, which never exhibited significant genetic divergence between reefs on the same island. These results support the view that horizontal transmission could improve local fitness for broadly dispersing Acropora coral species.

中文翻译：

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在多个空间尺度上的两个棘足珊瑚寄主的枝形蕨群落多样性

许多分布广泛的珊瑚在募集时从其环境“水平”获得了藻类共生体（Symbiodiniaceae）。水平传播可以促进珊瑚在各种环境中的适应性，但前提是珊瑚可以在其整个范围内与不同藻类相关联，并且这些共生体显示出降低的传播潜力。在这里，我们使用微卫星技术在密克罗尼西亚群岛的两个空间尺度（同一个岛上以及两个岛之间的礁石）上，对两个珊瑚寄主物种（Acropora hyacinthus，Acropora digitifera）中的角藻藻共生体进行了群落多样性定量分析。我们发现两个宿主与两个遗传学上不同的锁兰属内的多种多基因座基因型（MLG）相关谱系（C40，C21），确认鹿角珊瑚主机与一系列的相关联Cladocopium跨越该区域共生体。C40和C21都包含多个携带相同MLG的无性血统，其中许多跨越宿主物种，岛屿内甚至不同岛屿上的珊瑚礁。C40和C21均表现出中等的宿主专业性，并且在整个岛屿上均存在差异。此外，在每个岛屿中，藻类共生菌群落均由寄主物种和礁石位点显着聚集，突显出与珊瑚相关的枝形兰属群落的结构跨越较小的空间尺度，并在同一礁石的宿主内。这与它们的珊瑚寄主形成了鲜明的对比，后者从未在同一岛上的珊瑚礁之间表现出显着的遗传差异。这些结果支持水平传播可以提高当地的健身为广泛分散的观点鹿角珊瑚物种。