Stat Michael, Morris Emily, Gates Ruth D
Hawaii Institute of Marine Biology/School of Ocean and Earth Science and Technology, University of Hawaii, 46-007 Lilipuna Road, Kaneohe, HI 96744, USA.
Proc Natl Acad Sci U S A. 2008 Jul 8;105(27):9256-61. doi: 10.1073/pnas.0801328105. Epub 2008 Jun 30.
Symbioses are widespread in nature and occur along a continuum from parasitism to mutualism. Coral-dinoflagellate symbioses are defined as mutualistic because both partners receive benefit from the association via the exchange of nutrients. This successful interaction underpins the growth and formation of coral reefs. The symbiotic dinoflagellate genus Symbiodinium is genetically diverse containing eight divergent lineages (clades A-H). Corals predominantly associate with clade C Symbiodinium and to a lesser extent with clades A, B, D, F, and G. Variation in the function and interactive physiology of different coral-dinoflagellate assemblages is virtually unexplored but is an important consideration when developing the contextual framework of factors that contribute to coral reef resilience. In this study, we present evidence that clade A Symbiodinium are functionally less beneficial to corals than the dominant clade C Symbiodinium and may represent parasitic rather than mutualistic symbionts. Our hypothesis is supported by (i) a significant correlation between the presence of Symbiodinium clade A and health-compromised coral; (ii) a phylogeny and genetic diversity within Symbiodinium that suggests a different evolutionary trajectory for clade A compared with the other dominant Symbiodinium lineages; and (iii) a significantly lower amount of carbon fixed and released by clade A in the presence of a coral synthetic host factor as compared with the dominant coral symbiont lineage, clade C. Collectively, these data suggest that along the symbiotic continuum the interaction between clade A Symbiodinium and corals may be closer to parasitism than mutualism.
共生现象在自然界中广泛存在，且存在于从寄生到互利共生的连续统一体中。珊瑚与甲藻的共生关系被定义为互利共生，因为双方通过营养物质的交换从这种关联中受益。这种成功的相互作用是珊瑚礁生长和形成的基础。共生甲藻属Symbiodinium在基因上具有多样性，包含八个不同的谱系（A - H分支）。珊瑚主要与C分支的Symbiodinium共生，在较小程度上与A、B、D、F和G分支共生。不同珊瑚 - 甲藻组合的功能和相互作用生理学的变化几乎未被探索，但在构建有助于珊瑚礁恢复力的因素的背景框架时，这是一个重要的考虑因素。在本研究中，我们提供的证据表明，与占主导地位的C分支Symbiodinium相比，A分支Symbiodinium对珊瑚的功能益处较少，可能代表寄生而非互利共生的共生体。我们的假设得到以下几点支持：（i）A分支Symbiodinium的存在与健康受损的珊瑚之间存在显著相关性；（ii）Symbiodinium内部的系统发育和遗传多样性表明，与其他主要的Symbiodinium谱系相比，A分支具有不同的进化轨迹；（iii）与占主导地位的珊瑚共生体谱系C分支相比，在存在珊瑚合成宿主因子的情况下，A分支固定和释放的碳量显著更低。总体而言，这些数据表明，在共生连续统一体中，A分支Symbiodinium与珊瑚之间的相互作用可能更接近寄生而非互利共生。
