Ascidians are known to harbour bacterial symbionts in their tunics. In particular, the ascidian genus Lissoclinum can host abundant and diverse cyanobacterial associates. Here, we determined the diversity and host-specificity of cyanobacteria inhabiting 28 ascidian samples corresponding to eight Lissoclinum species: L. bistratum, L. midui, L. patella, L. punctatum, and L. timorense from Japan, L. aff. fragile and L. verrilli from the Bahamas, and L. perforatum from Spain and Chile. Cyanobacterial symbionts were characterized using both partial 16S rRNA gene sequences and sequences obtained for the entire 16S-23S rRNA internal transcribed spacer region (ITS). We found that both host species and geographic location played a role in structuring ascidian-cyanobacterial symbioses. Broad biogeographic trends included the dominance of Prochloron symbionts in Japanese ascidians and the presence of a novel cyanobacterial lineage in L. aff. fragile hosts from the Bahamas. Within each geographic region, a high degree of host-specificity was observed, where similar symbionts were recovered from ascidian hosts across multiple collection locations. Further, our analysis revealed the existence of nine distinct Prochloron clades in Japan, some of which corresponded to particular host species and sampling sites. For L. aff. fragile, further differences were observed between cyanobacterial symbionts in ascidians from reef and mangrove habitats. Our results showed high host-specificity in ascidian-cyanobacterial symbioses characterized by cryptic diversity and structured by host identity, location and habitat.

中文翻译：

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Lissoclinum 属群落海鞘中蓝藻共生体的生物地理学和宿主特异性

众所周知，海鞘在它们的外衣中含有细菌共生体。特别是，海鞘属 Lissoclinum 可以容纳丰富多样的蓝藻伙伴。在这里，我们确定了栖息在 28 个海鞘样本中的蓝藻的多样性和宿主特异性，这些样本对应于八种 Lissoclinum 物种：L. bistratum、L. midui、L. patella、L. punctatum 和 L. timorense 来自日本，L. aff。来自巴哈马的脆弱和 L. verrilli，以及来自西班牙和智利的 L. perforatum。使用部分 16S rRNA 基因序列和为整个 16S-23S rRNA 内部转录间隔区 (ITS) 获得的序列表征蓝细菌共生体。我们发现宿主物种和地理位置在构建海鞘-蓝藻共生中都发挥了作用。广泛的生物地理趋势包括日本海鞘中 Prochloron 共生体的主导地位以及 L. aff 中存在新型蓝藻谱系。来自巴哈马的脆弱宿主。在每个地理区域内，都观察到了高度的宿主特异性，其中从多个收集位置的海鞘宿主中回收了相似的共生体。此外，我们的分析揭示了日本存在九个不同的 Prochloron 进化枝，其中一些对应于特定的宿主物种和采样地点。对于 L. aff。脆弱的，在来自珊瑚礁和红树林栖息地的海鞘中的蓝藻共生体之间观察到了进一步的差异。我们的研究结果表明，海鞘-蓝藻共生具有高度的宿主特异性，其特征是隐秘的多样性，并由宿主身份、位置和栖息地构成。