榕树–榕小蜂协同进化中的非对称性相互作用及其集合种群效应

在协同进化研究中,传统观点认为物种之间的相互作用是对称性的,在进化过程中将形成一个稳定的均衡状态或进化稳定策略。然而,近来的观测和实验数据表明,物种间的协同进化可能存在非对称性相互作用,而且这种非对称性可能造成集合种群效应(metapopulation effect)或形成非均衡状态(例如混沌,chaos)。本文利用"榕树–榕小蜂"这一经典的协同进化模式系统来介绍协同进化过程中的非对称性相互作用,以及这种非对称性如何产生集合种群效应。在榕–蜂共生系统中,栖身于榕果中的榕小蜂除了传粉小蜂之外,还有一些"投机"的非传粉小蜂。非传粉小蜂比传粉小蜂具有更强的竞争力,而榕树则可惩罚不合作的非传粉蜂,同时奖励合作的传粉小蜂,从而形成了复杂的非对称性种间相互作用。在某个斑块生境中,非传粉小蜂通过竞争作用排斥传粉小蜂,然而随着非传粉小蜂在蜂群中的比例不断升高,榕树惩罚作用(如落果等)常常会导致整个非传粉蜂群的数量急剧下降,甚至局域性灭绝。随后,其他斑块的传粉小蜂则迁移过来填补空白。然而,随着传粉小蜂种群的数量增长,该斑块又会集聚更多的投机性非传粉小蜂,进而诱发榕树再次进行惩罚。这样的非对称性相互作用导致了非传粉小蜂、传粉小蜂以及榕树种群的集合效应,其种群大小呈现周期性的"此消彼长"式的循环。     

聚果榕榕果小蜂种群分布格局及其生境和季节差异比较

采用多个指数对西双版纳地区聚果榕榕果小蜂的种群分布格局进行了检测,并重点运用基于方差/均值比率法的t值测度比较了其生境和季节差异.结果表明,6种聚果榕榕果小蜂的种群分布格局皆呈聚集分布;传粉小蜂聚集强度在生境序列上,原始雨林≈严重干扰地段中度干扰地段,在季节序列上,雨季>干热季>雾凉季;非传粉小蜂不同种类不同性别随着生境和季节变化皆表现出明显的聚集强度差异.对各种聚集强度变化的发生机理与其对聚果榕传粉者互惠共生体进化稳定性进行了讨论,认为保护榕树、保护榕树和传粉昆虫互惠共生体的重点应放在保护其原始森林生境方面.     

聚果榕榕果小蜂种群分布格局及其生境和季节差异比较

采用多个指数对西双版纳地区聚果榕榕果小蜂的种群分布格局进行了检测,并重点运用基于方差／均值比率法的t值测度比较了其生境和季节差异．结果表明,6种聚果榕榕果小蜂的种群分布格局皆呈聚集分布;传粉小蜂聚集强度在生境序列上,原始雨林≈严重干扰地段>>中度干扰地段。在季节序列上,雨季>干热季>雾凉季;非传粉小蜂不同种类不同性别随着生境和季节变化皆表现出明显的聚集强度差异。对各种聚集强度变化的发生机理与其对聚果榕-传粉者互惠共生体进化稳定性进行了讨论,认为保护榕树、保护榕树和传粉昆虫互惠共生体的重点应放在保护其原始森林生境方面。     

钝叶榕果实内繁殖的两种榕小蜂与寄主榕树间的协同进化

 榕树(Ficus)及其传粉榕小蜂(Agaonidae)构成了高度专一的互惠共生体系。榕树的果实(以下简称榕果)内也寄生着一些非传粉小蜂。 绝大多数非传粉小蜂在榕果外把产卵器刺入果壁产卵到果腔内, 只有极少数种类能够进入果腔内产卵。在西双版纳地区, 钝叶榕(Ficus curtipes)上的杨氏榕树金小蜂(Diaziella yangi)类似于传粉者钝叶榕小蜂(Eupristina sp.), 它也是进入榕果内产卵繁殖后代的, 这就为比 较研究榕果内产卵小蜂与寄主榕树间的关系提供了材料。该文从形态学、行为学和生态学角度比较研究了这两种进入榕果内产卵的小蜂与寄主 钝叶榕之间的作用关系, 研究结果显示: 1)杨氏榕树金小蜂与钝叶榕小蜂的雌蜂头部形状存在趋同进化; 2)两种小蜂的产卵器的平均长度都比 雌花花柱长, 因而能把卵产在子房里; 3)钝叶榕小蜂从瘿花出来需要3~5 h, 交配需要17~19 min, 杨氏榕树金小蜂从瘿花出来只需18~20 min, 交配时间为20~30 s; 4)在自然群落中, 大约90%的雌花期榕果里都只进一只杨氏榕树金小蜂和一只钝叶榕小蜂, 杨氏榕树金小蜂能通过传粉来 增加榕树种子数量, 但对钝叶榕小蜂种群的繁衍造成了极显著的负面影响; 5)两种小蜂于同一时期进入榕果内繁殖, 子代同期成熟羽化, 发育 期与榕树雄花的发育期同步。研究表明: 进入榕果内繁殖的两种小蜂与寄主榕树之间存在着协同进化关系, 杨氏榕树金小蜂为榕树有效地传粉, 这可能是一个由寄生者向互惠方向进化的实例。     

榕树-榕小蜂互惠合作系统中的非对称性博弈

榕树及其传粉榕小蜂是自然界中目前所知道的关系最为紧密的互利共生系统之一。随着研究的深入, 越来越多的证据发现榕树-传粉榕小蜂之间互惠合作的过程中存在着复杂的竞争和对抗关系, 例如榕树与传粉榕小蜂之间对公共资源的竞争、传粉欺骗与宿主对传粉者的惩罚、榕树与传粉小蜂之间的“军备竞赛”等。在相互竞争或者对抗关系中, 双方表现出非对称性相互作用。其非对称性关系主要表现出如下3个特征: (1)收益不对称, 即榕树(宿主)与传粉榕小蜂(共生体)之间在资源利用等方面的实力不对称; (2)榕树与传粉榕小蜂之间的信息不对称; (3)进化速率不对称。这些非对称的相互作用可能导致种群的波动、榕树与传粉榕小蜂相互适应和进化策略的变化。因此, 理解榕树与传粉榕小蜂之间的非对称交互作用有助于理解为什么合作和冲突在互利共生关系中经常能同时存在, 也将有助于解释榕树-传粉榕小蜂种间相互关系和物种的多样性。     

不同繁育系统的榕树雌花的花柱长度和繁殖率比较

多年来, 不同繁育系统的榕树(Ficus spp.)的进化问题引起生物学家们极大的兴趣。前人通过对不同繁育系统榕树雌花的花柱长度、传粉榕小蜂产卵器长度和繁殖率的比较, 推测榕树的雌雄异株是由雌雄同株进化而来的。为验证这一推论, 选取雌雄同株的垂叶榕(Ficus benjamina)和钝叶榕(F. curtipes)以及雌雄异株的斜叶榕(F. tinctoria)和鸡嗉子榕(F. semicordata), 进行了雌花花柱长度、传粉榕小蜂产卵器长度及繁殖率的比较。研究结果显示: 1)两种雌雄同株榕树的传粉榕小蜂(Eupristina koningsbergeri和Eupristina sp.)的产卵器长度, 显著长于两种雌雄异株榕树的传粉榕小蜂(Liporrhopalum gibbosae和Ceratosolen gravelyi)产卵器的长度, 且雌雄同株榕树雌花花柱长度的变异大于雌雄异株雌花花柱长度的变异; 2)两种雌雄同株榕树的雌花花柱长度呈单峰分布, 且花柱长度的变异大于传粉榕小蜂产卵器长度的变异; 两种雌雄异株榕树花序的雌花花柱长度呈双峰分布, 雌花花柱长度的变异也大于传粉榕小蜂产卵器的长度变异; 3)两种雌雄同株榕树的传粉榕小蜂产卵器长度能到达雌花子房的比例更高, 可更有效地产生瘿花, 而雌雄异株榕树产生种子的优势更强。研究表明: 在传粉榕小蜂产卵器长度及花序雌花花柱分布方面, 雌雄异株榕树有着明显的优势, 但在繁殖率方面没有绝对优势。因此, 前人从雌花花柱分布及繁殖率比较而做出榕树进化的推测并不正确。要真正解决榕树的进化问题, 需要多学科、多指标的综合分析和深入研究。     

鸡嗉果榕榕小蜂产卵时序与种群数量分析

榕树与传粉榕小蜂的互惠共生体系被多种非传粉榕小蜂利用。在同一个榕果中,具有较高种群密度的传粉榕小蜂和多种非传粉榕小蜂生存在一起并相互作用。通过野外观察和采样分析的方法,对鸡嗉果榕内5种榕小蜂（传粉榕小蜂Ceratosolen gravelyi;非传粉榕小蜂Apocrypta sp., Philotrypesis dunia, Platyneura cunia和Sycoscaptertr ifemmensis）的产卵行为进行了研究。结果证明,鸡嗉果榕内生活的各种榕小蜂通过比较严格的产卵时序在榕果内产卵以占领不同的生态位,这反映了这些榕小蜂各自的生物学特性。自然种群数量分析表明,单个非传粉榕小蜂物种的种群数量几乎不与传粉榕小蜂种群数量呈负相关,而所有非传粉榕小蜂物种的种群个体总量与传粉榕小蜂的种群个体数呈正相关,这可能是多个物种共存于单个榕果内的进化适应。     

垂叶榕上16种榕小蜂的种群动态

传粉榕小蜂和榕树的互利共生是传粉昆虫与植物间协同进化的典范。在榕果(榕树的隐头状花序)内,还生活着多种非传粉榕小蜂。这些生活在密闭榕果内由传粉榕小蜂和非传粉榕小蜂组成的群落对研究群落生态学有很大价值。然而,对生存在单一榕树的榕果内的所有榕小蜂的种群动态了解很少,特别是缺少相对长期的连续数据。通过野外近3a观察和采样,研究了垂叶榕榕小蜂群落结构和榕小蜂的种群动态。共记录榕小蜂16种;各种榕小蜂根据发生规律可分为常见种和偶见种,Eupristina koningsbergeri,Philotrypesis sp.1,Philotrypesis sp.4,Philotrypesis sp.5,Sycoscapter sp.1,Walkerella benjamini,Walkerella sp.1,Sycophila sp.2,Sycobia sp.2为常见种;Sycobia sp.1,Acophila sp.1,Sycophila sp.1,Ormyrus sp.1等为偶见种。每种榕小蜂在单果上的数量随季节呈波动变化,季节对榕小蜂群落的多样性和均匀性无显著影响。除了传粉榕小蜂外,Sycoscapter sp.1也是优势种类之一。传粉榕小蜂的数量与非传粉榕小蜂总数间呈显著负相关。传粉榕小蜂与非传粉榕小蜂几乎都呈负相关,而与Walkerella sp.1在数量上呈显著正相关。Sycobia sp.2与Sycophila sp.2在同一瘿中出现,数量上呈显著正相关。但其它非传粉榕小蜂种类在数量上的相关性较为复杂,可能是造成各种榕小蜂数量波动的一个原因。     

基于集合种群理论框架的榕树-榕小蜂互惠系统动力学模型

互惠共生指双方物种都能通过对方增加适合度的种间关系。榕树与榕小蜂的传粉关系是自然界中典型的互惠共生系统,这种互惠关系发生在榕果中,也就是榕果是种间作用的场所,榕小蜂在其中传粉和产卵。由此,可以把榕果看作榕小蜂的生境斑块,利用集合种群理论框架构建榕树与榕小蜂互惠关系的动力学模型,研究这个互惠系统的稳定性和续存条件。由于这里的生境斑块(榕果)的动态变化性(榕果产生和掉落),模型不同于传统的生境斑块固定不变的集合种群模型,增加了描述生境动态的维度。模型表明:(1)榕果产生率足够大(大于一个阈值)是榕树与榕小蜂互惠系统能够续存的必要条件;(2)榕树和榕小蜂互惠系统存在双稳态现象(Allee效应),这个互惠系统续存需要种群大小超过一个阈值,换言之,种群大小低于这个阈值时,系统必然灭绝;(3)榕果产生率增加使榕小蜂种群增加,但不会影响未被占据的榕果数量。我们的模型不但可用来研究榕树与榕小蜂互惠系统的动力学性质,而且也是集合种群理论斑块动态化的发展。     

榕树及其传粉榕小蜂的系统发育和协同进化研究现状及展望

榕属(Ficus)是有花植物中最大的木本属,全世界有750多种.榕树及其传粉榕小蜂形成的种类专一的互惠共生系统,长期以来被作为研究共生系统比较生物学和协同进化的模式材料.虽然从20世纪90年代才开始对榕树一榕小蜂体系开展分子系统发育研究,但由于这个体系的特殊性和分子技术的快速发展,越来越多的学者开始利用分子学手段来研究榕一蜂共生系统的一系列生物学问题.本文总结了近年来对榕树及其传粉榕小蜂开展的系统发育及协同进化方面的研究,并分析了中国此方面的研究现状,对未来的研究趋势和前景进行了展望.     

New insight into the phylogenetic and biogeographic history of genus Ficus: Vicariance played a relatively minor role compared with ecological opportunity and dispersal

Studies on the evolution of tropical taxa emphasize the role ofvicariance and the break-up of Gondwana in explaining modern distributions.Earlier studies on figs (Ficus spp.) support this view.In the current study,we used an expanded sample (208 spp.) and improved molecular dating techniques to reconstruct the phylogenetic and biogeographic history of Ficus.Consistent with previous studies,our biogeographic analysis indicated that the ancestor of Ficus was present in Gondwana.However,a relaxed clock analysis relying on uncorrelated rates in BEAST suggested that the Neotropical section Pharmacosycea split-off in South America 86.67 Mya,and that other Ficus lineage ancestors originated in India.Most of the basal lineages appeared to have diverged following KT extinction,then rapidly diversified after India collided with continental Asia.The Afrotropical species most likely evolved initially in the Indian subcontinent then dispersed to Africa,either in the late Cretaceous of Madagascar or even later,following the Eocene collision of India with Asia.The Neotropical section Americana,either islandhopped to South America or took a northern route to the Americas through Europe prior to the terminal Eocene global cooling event.Ficus may have arrived in eastern Malesia following the collision of India with Asia,then widely dispersed thereafter.Given the wide ranges in our date estimates,several other scenarios are possible.However,contrary to earlier reports,our analyses suggest that vicariance played a relatively minor role compared with ecological opportunity and dispersal in the diversification of genus Ficus.     

Moving your sons to safety: galls containing male fig wasps expand into the centre of figs, away from enemies

Figs are the inflorescences of fig trees (Ficus spp., Moraceae). They are shaped like a hollow ball, lined on their inner surface by numerous tiny female flowers. Pollination is carried out by host-specific fig wasps (Agaonidae). Female pollinators enter the figs through a narrow entrance gate and once inside can walk around on a platform generated by the stigmas of the flowers. They lay their eggs into the ovules, via the stigmas and styles, and also gall the flowers, causing the ovules to expand and their pedicels to elongate. A single pollinator larva develops in each galled ovule. Numerous species of non-pollinating fig wasps (NPFW, belonging to other families of Chalcidoidea) also make use of galled ovules in the figs. Some initiate galls, others make use of pollinator-generated galls, killing pollinator larvae. Most NPFW oviposit from the outside of figs, making peripherally-located pollinator larvae more prone to attack. Style length variation is high among monoecious Ficus spp. and pollinators mainly oviposit into more centrally-located ovules, with shorter styles. Style length variation is lower in male (wasp-producing) figs of dioecious Ficus spp., making ovules equally vulnerable to attack by NPFW at the time that pollinators oviposit. We recorded the spatial distributions of galled ovules in mature male figs of the dioecious Ficus hirta in Southern China. The galls contained pollinators and three NPFW that kill them. Pollinators were concentrated in galls located towards the centre of the figs, NPFW towards the periphery. Due to greater pedicel elongation by male galls, male pollinators became located in more central galls than their females, and so were less likely to be attacked. This helps ensure that sufficient males survive, despite strongly female-biased sex ratios, and may be a consequence of the pollinator females laying mostly male eggs at the start of oviposition sequences.     

两栖榕在人工湿地的生长特性及其对污水的净化效果

研究了两栖榕在潜流型人工湿地的生长特性及其对污水的净化效果。一年多的实验表明,生长在人工湿地的两栖榕具有发达的侧根和不定根,保持正常的净光合速率,蒸腾速率,根系活力生长速率。两栖榕人工湿地对TN,TP,CODCr和BOD5的去除率分别为54．2％、40．9％、72．4％和74．3％,与无植物系统相比较,去除率分别提高了17％、12％、10％和11％,此外,两栖榕人工湿地系统中,水力停留时间对去除率果有一定影响。     

Traditional nutritional analyses of figs overestimates intake of most nutrient fractions: a study of ficus perforata consumed by howler monkeys (Alouatta palliata mexicana)

There continue to remain uncertainty concerning the nutritional importance of figs (Ficus spp.) in the primate diet. Although studies have been performed on the nutritional analysis of fig pulp and seed fractions separately, there has not been an attempt to quantify the contribution of animal matter within figs. Here we report nutritional values of figs (Ficus perforata) (Urostigma) consumed by a troop of howler monkeys (Alouatta palliata mexicana). Separate nutritional assays were performed on the pulp, seed, and animal fraction. Whole-fig analyses significantly exaggerate the concentrations of all nutrients (lipids especially) as seeds, which represent a large proportion of the fig (45%), cannot be digested. Animal matter only represents 1% of the fig, and augments fig protein and lipid content by 0.44 and 0.30%, respectively. This represents the 11 and 9% of the fraction available for digestion. Differences in fig consumption were observed between age and sex classes (P=0.04) and periods of the day (P=0.001); females consumed more figs than males and the highest consumption of figs was observed in the afternoon. F. perforata figs may be an important component of the howler monkeys diet owing to their high content of water and calcium.     

种间专性协同进化关系对榕属分类的影响

榕与榕小蜂的专性共生系统为人们提供了研究生物协同进化规律和进化历史的完美范例,已成为国际上研究植物与昆虫相互作用的一个热点。这也给仅根据外部形态等传统方法进行的榕属经典分类带来了极大的影响和冲击。为了进一步研究榕属的系统与进化,介绍了该属分类学研究的历史、主要分类系统和存在的问题,并对今后榕属分类的发展趋势进行展望。     

Ficus (Moraceae) and Hymenoptera (Ghalcidoidea): Figs and their pollinators

Attempts are made to meet discrepancies between the botanical classification of Ficus and the zoological classification of its pollinators. They are discussed as Ficus elastica , subgen. Pharmacosycea , subsect. Palaeomorphe , dioecism in Ficus , the Ceratosolen complex, and sect. Conosycea. It seems from the botanical side that the evolution of Ficus into subgenera and sections preceded that of its insects into genera. On the whole there are no grounds for reclassification of Ficua , but leaf structure indicates that some rearrangement of the species of subgen. Urostigma sect. Conosycea may be needed to fit the entomology. Ficus asperiuscula poses a problem in sect. Sycidium.     

Convergence and coevolution in a mutualism: evidence from a molecular phylogeny of Ficus

Abstract.— The interaction between Ficus (Moraceae) and their pollinating wasps (Chalcidoidea: Agaonidae; more than 700 species-specific couples) is one of the most specialized mutualisms found in nature. Both partners of this interaction show extensive variation in their respective biology. Here we investigate Ficus life-history trait evolution and fig/fig wasp coadaptation in the context of a well-resolved molecular phylogeny. Mapping out variations in Ficus life-history traits on an independently derived phylogeny constructed from ribosomal DNA sequences (external and internal transcribed spacer) reveals several parallel transitions in Ficus growth habit and breeding system. Convergent trait evolution might explain the discrepancies between morphological analyses and our molecular reconstruction of the genus. Morphological characters probably correlate with growth habit and breeding system and could therefore be subject to convergent evolution. Furthermore, we reconstruct the evolution of Ficus inflorescence characters that are considered adaptations to the pollinators. Our phylogeny reveals convergences in ostiole shape, stigma morphology, and stamen:ovule ratio. Statistical tests taking into account the phylogenetic relationship of the species show that transitions in ostiole shape are correlated with variation in wasp pollinator head shape, and evolutionary changes in stigma morphology and stamen:ovule ratio correlate with changes in the pollination behavior of the associated wasp. These correlations provide evidence for reciprocal adaptations of morphological characters between these mutualistic partners that have interacted over a long evolutionary time. In light of previous ecological studies on mutualism, we discuss the adaptive significance of these correlations and what they can tell us about the coevolutionary process occurring between figs and their pollinators.     

Histological Comparisons of Parasitism by Schistonchus spp. (Nemata: Aphelenchoididae) in Neotropical Ficus spp.

Syconia (enclosed infructescences) infested with host-specific species of Schistonchus (Aphelenchoididae) were collected from six species of Ficus (Moraceae) native to Florida or Panama. They were sectioned and histologically examined to assess the effects of parasitism. Parasitism by Schistonchus spp. was associated with hypertrophied cells, tissue necrosis, and the presence of an exudate in all species. Occasional hypertrophy of the outer epidermal cells occurred on seed florets, wasp florets, and on the endothecial cells of male florets in F. aurea (subgenus Urostigma) from Florida. Aberrations of the inner mesocarp occurred under the hypertrophied cells on seed florets. In F. laevigata (subgenus Urostigma) from Florida, Schistonchus sp. infested immature male florets and was associated with hypertrophy of endothecial cells, epidermal cells of the anther filaments, and anthers. Schistonchus sp. also caused aberrations of the anther filament, anthers, and pollen. Ficus poponoei (subgenus Urostigma) and F. glabrata (subgenus Pharmacosycea), both from Panama, had hypertrophied outer epidermal cells on seed florets. Ficus poponoei also had Schistonchus sp. within the pedicel of an aborted floret, with hypertrophy of the cortical parenchyma. Ficus trigonata (subgenus Urostigma) from Panama had hypertrophy of the outer epidermis of seed florets. When the outer epidermis on these florets was missing, the inner mesocarp was hypertrophied. Ficus maxima (subgenus Pharmacosycea) from Panama had hypertrophy on the outer epidermis of seed and aborted florets. Schistonchus spp. were not found in wasp larvae or pupae in any of the Ficus spp. examined. Hypertrophy was never observed in the absence of Schistonchus spp.     

Molecular phylogenies of fig wasps: partial cocladogenesis of pollinators and parasites

Figs (Ficus spp., Moraceae) and their pollinating wasps form an obligate mutualism, which has long been considered a classic case of coevolution and cospeciation. Figs are also exploited by several clades of nonpollinating wasps, which are parasites of the mutualism and whose patterns of speciation have received little attention. We used data from nuclear and mitochondrial DNA regions to estimate the phylogenies of 20 species of Pleistodontes pollinating wasps and 16 species of Sycoscapter nonpollinating wasps associated with Ficus species in the section Malvanthera. We compare the phylogenies of 15 matched Pleistodontes/Sycoscapter species pairs and show that the level of cospeciation is significantly greater than that expected by chance. Our estimates of the maximum level of cospeciation (50 to 64% of nodes) are very similar to those obtained in other recent studies of coevolved parasitic and mutualistic associations. However, we also show that there is not perfect congruence of pollinator and parasite phylogenies (for any substantial clade) and argue that host plant switching is likely to be less constrained for Sycoscapter parasites than for Pleistodontes pollinators. There is perfect correspondence between two terminal clades of two sister species in the respective phylogenies, and rates of molecular evolution in these pairs are similar.     

Factors Influencing Realized Sex Ratios in Fig Wasps: Double Oviposition and Larval Mortalities

Pollinator fig wasps (Agaonidae) are a model system for studies of sex ratio evolution. They lay their eggs in galled ovules within figs. Only one adult emerges from each gall, suggesting that only one egg is always laid per ovule, but if double oviposition occurs then the assumption that adult (realised) sex ratios of fig wasps are representative of primary sex ratios may be violated. Many galls also fail to produce any wasps. If they initially contained eggs then differential mortality rates may also modify realized sex ratios. We investigated whether Kradibia (= Liporrhopalum) tentacularis foundresses in Ficus montana figs avoid laying in ovules that already contain eggs. Comparisons of oviposition frequencies and wasp emergence frequencies showed that most galls that failed to produce wasps will have had eggs laid in them, but few occupied ovules contained two eggs. Realised sex ratios therefore do not necessarily reflect primary sex ratios in this species, but double oviposition is not responsible.