Ambrosio Louis J, Baeza J Antonio
Department of Biological Sciences, Clemson University, Clemson, South Carolina, United States of America.
Smithsonian Marine Station at Fort Pierce, Fort Pierce, Florida, United States of America.
PLoS One. 2016 Feb 24;11(2):e0148285. doi: 10.1371/journal.pone.0148285. eCollection 2016.
Host monopolization theory predicts symbiotic organisms inhabiting morphologically simple, relatively small and scarce hosts to live solitarily as a result of territorial behaviors. We tested this prediction with Tunicotheres moseri, an endosymbiotic crab dwelling in the atrial chamber of the morphologically simple, small, and relatively scarce ascidian Styela plicata. As predicted, natural populations of T. moseri inhabit ascidian hosts solitarily with greater frequency than expected by chance alone. Furthermore, laboratory experiments demonstrated that intruder crabs take significantly longer to colonize previously infected compared to uninfected hosts, indicating as expected, that resident crabs exhibit monopolization behaviors. While territoriality does occur, agonistic behaviors employed by T. moseri do not mirror the overt behaviors commonly reported for other territorial crustaceans. Documented double and triple cohabitations in the field coupled with laboratory observations demonstrating the almost invariable success of intruder crabs colonizing occupied hosts, suggest that territoriality is ineffective in completely explaining the solitary social habit of this species. Additional experiments showed that T. moseri juveniles and adults, when searching for ascidians use chemical cues to avoid hosts occupied by conspecifics. This conspecific avoidance behavior reported herein is a novel strategy most likely employed to preemptively resolve costly territorial conflicts. In general, this study supports predictions central to host monopolization theory, but also implies that alternative behavioral strategies (i.e., conflict avoidance) may be more important than originally thought in explaining the host use pattern of symbiotic organisms.
宿主独占理论预测，由于领地行为，栖息在形态简单、相对较小且数量稀少的宿主中的共生生物会独自生活。我们用莫氏突眼蟹对这一预测进行了测试，莫氏突眼蟹是一种内共生蟹，生活在形态简单、体型小且相对稀少的皱瘤海鞘的围鳃腔中。正如预测的那样，莫氏突眼蟹的自然种群在海鞘宿主中独自栖息的频率高于仅由随机因素预期的频率。此外，实验室实验表明，与未感染的宿主相比，入侵蟹在先前已被感染的宿主上定殖所需的时间要长得多，这正如预期的那样，表明常驻蟹表现出独占行为。虽然确实存在领地行为，但莫氏突眼蟹所采用的争斗行为并不反映其他领地性甲壳类动物通常报道的明显行为。在野外记录到的双重和三重同居现象，再加上实验室观察表明入侵蟹几乎总能成功地在已被占据的宿主上定殖，这表明领地行为并不能完全解释该物种的独居社会习性。额外的实验表明，莫氏突眼蟹的幼体和成体在寻找海鞘时会利用化学信号来避开被同种个体占据的宿主。本文报道的这种同种回避行为是一种新颖的策略，很可能是为了先发制人地解决代价高昂的领地冲突。总体而言，这项研究支持了宿主独占理论的核心预测，但也意味着，在解释共生生物的宿主利用模式时，替代行为策略（即冲突避免）可能比原先认为的更为重要。
