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Ecology :非对称性将有利于合作行为演化

来源:昆明动物研究所生态环境中心 2010-05-17 09:37

无论在人类的社会还是自然生物系统中,近代的研究发现合作行为可能是个体间相互作用的基本形式之一。英国科协主席Robert May在2005年的任职演说中,将生物进化过程和人类的社会学中合作关系演化及其系统维持列为进化生物学或社会科学中最为重要的、未被解决的科学问题。从上世纪60年代陆续提出的群选择理论、亲选择理论以及互惠选择等理论认为合作双方由于合作双方之间存在亲缘关系、利益互换或群体间竞争等因素,个体选择合作的策略将总是比其它任何策略的收益都高,合作双方将稳定的合作纳什均衡。然而,后来的试验与观测发现:在几乎所有的合作系统,合作双方实际都存在冲突或竞争,部分个体将会采取欺骗的策略,甚至演化为系统的寄生者。上述经典理论因而无法解释合作系统普遍存在的冲突或投机现象。

中国科学院昆明动物所的王瑞武和云南大学数学系教授李耀堂、博士研究生贺军州等在2004年Nature发表模型的基础上,将经典的鹰-鸽博弈从对称性转化非对称性后,模型惊奇地发现:合作双方的非对称性程度越高,双方的合作频率也将越高。系统中优势方通过对投机的惩罚而奖励诚实合作者,从而维持合作系统地局域稳定性。优势方对合作方或劣势方的惩罚可信性将依赖于合作方从该系统退出成本大小或扩散到其它系统的可能性。其分析发现:经典合作理论与实际观测结果之间的悖论可能是由于经典理论对称性的前提假设不合理所致,现实的合作系统可能是从一个对称性系统演化而来。该理论模型将发表在近期的《中国科学》中。

课题组同时以著名的榕树-榕小蜂之间的合作为模式系统对该思想进行了验证。其实验结果发现:经典的基于对称思想,认为生态位分化维持合作或生态系统稳定性的理论可能是不可信的。其实验结果显示:合作系统内的投机者或寄生物种完全会导致合作的个体或物种灭绝,从而导致榕树与传粉小蜂之间合作关系的解体。然而,投机或寄生物种过度增长又将导致植物惩罚,从而又会致使投机或寄生物种的灭绝,诚实合作的个体或物种又从其它种群中扩散过来,重新建立其种群。当诚实合作者种群数量得以建立并扩张后,投机或寄生者的又可以在合作系统中得到扩散,整个生态或合作系统将通过上述非对称性的相互作用而出现扰动,系统也将通过其内部个体间的非对称性相互作用而维持其合作关系的局域性稳定。

该研究结果同时表明生态学中“岛屿”效应可能通过物种的非对称性相互作用而产生。在生态学理论中, Preston1962年提出“岛屿”理论后,普遍认为“岛屿”效应只能通过空间异质性产生,此项研究结果表明:物种的相互非对称性相互作用也将会导致物种的局域性灭绝,物种分布将因此在某些局域环境的出现“真空”的“斑块”,其它局域或斑块的物种从而迁徙过来填补其分布的空白,合作系统通过物种的非对称性相互作用产生“岛屿”或“斑块”效应,通过“岛屿”或“斑块间的相互移动实现物种间相互关系的混沌性扰动。而这一重要的“岛屿效应”产生机制在过去的生态学研究中完全被忽略了。

这一实验结果由王瑞武和他的两名硕士研究生孙宝发和郑琪合作完成。结果于2010年5月发表在国际著名杂志Ecology上。

该项研究结果将是对老庄哲学思想的一次科学的诠释:任何一个物种或个体的过度增长或扩张反过来将会导致自身灭绝或种群减少。“祸兮福之所倚,福兮祸之所伏”,或“乐极生悲,否去泰来”的思想在生态系统得到验证。(生物谷Bioon.com)

生物谷推荐原文出处:

Ecology  doi: 10.1890/09-1446.1

Diffusive coevolution and mutualism maintenance mechanisms in a fig–fig wasp system
Rui-Wu Wang1,4, Bao-Fa Sun1,2, and Qi Zheng1,3

1 Ecology, Conservation, and Environment Center (ECEC), State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Science, Kunming, Yunnan 650223 China
2 Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Science, Beijing 100101 China
3 School of Medicine, Zhejiang University, Zhejiang 310000 China

In reciprocal mutualism systems, the exploitation events by exploiters might disrupt the reciprocal mutualism, wherein one exploiter species might even exclude other coexisting exploiter species over an evolutionary time frame. What remains unclear is how such a community is maintained. Niche partitioning, or spatial heterogeneity among the mutualists and exploiters, is generally believed to enable stability within a mutualistic system. However, our examination of a reciprocal mutualism between a fig species (Ficus racemosa) and its pollinator wasp (Ceratosolen fusciceps) shows that spatial niche partitioning does not sufficiently prevent exploiters from overexploiting the common resource (i.e., the female flowers), because of the considerable niche overlap between the mutualists and exploiters. In response to an exploiter, our experiment shows that the fig can (1) abort syconia-containing flowers that have been galled by the exploiter, Apocryptophagus testacea, which oviposits before the pollinators do; and (2) retain syconia-containing flowers galled by Apocryptophagus mayri, which oviposit later than pollinators. However, as a result of (2), there is decreased development of adult non-pollinators or pollinator species in syconia that have not been sufficiently pollinated, but not aborted. Such discriminative abortion of figs or reduction in offspring development of exploiters while rewarding cooperative individuals with higher offspring development by the fig will increase the fitness of cooperative pollinating wasps, but decrease the fitness of exploiters. The fig–fig wasp interactions are diffusively coevolved, a case in which fig wasps diversify their genotype, phenotype, or behavior as a result of competition between wasps, while figs diverge their strategies to facilitate the evolution of cooperative fig waps or lessen the detrimental behavior by associated fig wasps. In habitats or syconia that suffer overexploitation, discriminative abortion of figs or reduction in the offspring development of exploiters in syconia that are not or not sufficiently pollinated will decrease exploiter fitness and perhaps even drive the population of exploiters to local extinction, enabling the evolution and maintenance of cooperative pollinators through the movement between habitats or syconia (i.e., the metapopulations).

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