Frade P R, De Jongh F, Vermeulen F, van Bleijswijk J, Bak R P M
Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands.
Mol Ecol. 2008 Jan;17(2):691-703. doi: 10.1111/j.1365-294X.2007.03612.x. Epub 2007 Dec 20.
Symbiotic algae in coral species distributed over a large depth range are confronted with major differences in light conditions. We studied the genetic variation of Symbiodinium in the coral genus Madracis over depth (5-40 m) and at two different colony surface positions. Using polymerase chain reaction-denaturing gradient gel electrophoresis ITS2 nuclear ribosomal DNA analyses, we consistently identified three symbiont genotypes with distributions that reveal patterns of host specificity and depth-based zonation. ITS2 type B7 Symbiodinium is the generalist type, occurring in all zooxanthellate Madracis corals and at all depths. Type B13 is restricted to the shallow water specialist Madracis mirabilis. Type B15 is typical of deep reef environments and replaces B7 in the depth generalist Madracis pharensis. Contrasting with variation over depth, we found strong functional within-colony uniformity in symbiont diversity. Relating symbiont distributions to measured physical factors (irradiance, light spectral distribution, temperature), suggests depth-based ecological function and host specificity for Symbiodinium ITS2 types, even among closely related coral species.
分布在较大深度范围内的珊瑚物种中的共生藻面临着光照条件的巨大差异。我们研究了深度（5 - 40米）以及两个不同群体表面位置下，鹿角杯形珊瑚属珊瑚中虫黄藻的遗传变异。使用聚合酶链反应 - 变性梯度凝胶电泳ITS2核糖体DNA分析，我们始终鉴定出三种共生体基因型，其分布揭示了宿主特异性和基于深度的分区模式。ITS2 B7型虫黄藻是通用型，存在于所有有虫黄藻的鹿角杯形珊瑚中，且在所有深度均有出现。B13型仅限于浅水特化种美丽鹿角杯形珊瑚。B15型是深礁环境的典型类型，在深度广适种法氏鹿角杯形珊瑚中取代了B7型。与深度变化形成对比的是，我们发现共生体多样性在群体内部具有很强的功能一致性。将共生体分布与测量的物理因素（辐照度、光谱分布、温度）相关联，表明即使在亲缘关系密切的珊瑚物种中，虫黄藻ITS2类型也具有基于深度的生态功能和宿主特异性。
