榕-传粉榕小蜂间的专一性与协同进化

共生体系的长期维持引发了一系列进化问题, 特别是共生双方的相互适应、协同进化成为进化理论的一大挑战。榕和传粉榕小蜂是目前所知的专性最强的共生体系之一, 两者异常丰富的物种组成以及宿主多样的生活型为以上问题的研究提供了理想的体系。早期认为榕与其传粉小蜂间均为狭义协同进化, 一对一原则在该体系中具有普适性。然而近年来发现越来越多的例外, 特别是宿主转移现象在某些地区、某些榕属类群中的普遍存在, 使榕及其传粉小蜂间严格的物种专一性及协同进化发生在物种水平的观点受到质疑, 最近提出了一个新的协同进化模式来解释榕与其传粉小蜂的对应关系。榕与传粉小蜂间的进化模式说明两者间既有狭义的协同进化, 也有发散协同进化关系, 从而导致它们之间物种专一性不同。目前, 两种协同进化模式在该系统中的相对重要性仍存在很大争议, 不同地区、不同榕属类群中两者的物种专一性程度和产生原因可能有很大差异, 榕与传粉榕小蜂系统的复杂性决定了不能将某些地区和某些类群的结论简单扩展, 有关该体系协同进化主导模式的正确评判有待于对不同地区和不同榕属类群对应传粉小蜂的物种组成、来源方式, 以及共生双方的系统发生关系进行更广泛、更深入的研究。     

聚果榕传粉榕小蜂传粉与产卵之间的权衡

【目的】榕树(Ficus)依赖专性榕小蜂(Agaonidae)传粉,同时为传粉榕小蜂提供繁衍后代的场所,两者形成动植物间经典的协同进化关系。在雌花期果内,榕小蜂需在有限的存活时间内完成传粉和产卵,而传粉榕小蜂如何在传粉与产卵之间进行权衡仍然是悬而未解的问题。本研究旨在明确传粉榕小蜂——一种栉颚榕小蜂Ceratosolen sp.在雌雄同株的聚果榕Ficus racemosa雌花期果内的行为活动及繁殖模式。【方法】借助测微尺测量聚果榕榕果雌花花柱长度与传粉榕小蜂(Ceratosolen sp.)产卵器长度,通过显微视频记录传粉榕小蜂在雌花期果内搜索、传粉及产卵行为;结合单果控制性引蜂试验,测定不同阶段榕小蜂个体大小、孕卵量、携粉量,以及雄花期最终繁殖的榕小蜂后代和榕果种子数量。【结果】聚果榕雌花花柱长度存在树间变异,榕小蜂产卵器长度比绝大多数的雌花花柱长,说明该小蜂可以产卵于大部分的雌花子房里。通常个体大的榕小蜂孕卵量更多,但个体大小与携粉量之间相关性不显著。观察发现,榕小蜂进入雌花期榕果内,前6 h集中产卵,可产下孕卵量的95%,平均搜索用时27 s,产卵用时46 s,此期间传粉行为少...     

木瓜榕传粉榕小蜂与一种非传粉榕小蜂核型比较分析

【目的】为了明确木瓜榕传粉榕小蜂Ceratosolen emarginatus Mayr及另外一种寄生于木瓜榕雌果内的非传粉小蜂Platyneura sp.染色体核型特征和差异。【方法】本研究采用小牛血清培养脑神经节的方法对寄生于木瓜榕Ficus auriculata Loureiro的两种小蜂进行了染色体核型比较分析。【结果】木瓜榕传粉小蜂的染色体数目为2n(♀)=10,染色体臂指数NF值为20,整个染色体组包含5对中着丝粒染色体,核型类别属Stebbins-1A型;非传粉小蜂Platyneura sp.的染色体数目为2n=12,染色体臂指数NF值为24,染色体组全部为中着丝粒染色体,核型类别属Stebbins-1A型。【结论】两种小蜂除染色体类型和核型类别相同,在其他染色体特征方面均表现出差异。结合前人和本研究结果,我们推测两种小蜂之间染色体核型可能发生了由传粉者向非传粉者的演化,即发生了染色体数目由少到多的演化。     

聚果榕传粉榕小蜂传粉与产卵之间的权衡

【目的】榕树(Ficus)依赖专性榕小蜂(Agaonidae)传粉,同时为传粉榕小蜂提供繁衍后代的场所,两者形成动植物间经典的协同进化关系。在雌花期果内,榕小蜂需在有限的存活时间内完成传粉和产卵,而传粉榕小蜂如何在传粉与产卵之间进行权衡仍然是悬而未解的问题。本研究旨在明确传粉榕小蜂——一种栉颚榕小蜂Ceratosolen sp.在雌雄同株的聚果榕Ficus racemosa雌花期果内的行为活动及繁殖模式。【方法】借助测微尺测量聚果榕榕果雌花花柱长度与传粉榕小蜂(Ceratosolen sp.)产卵器长度,通过显微视频记录传粉榕小蜂在雌花期果内搜索、传粉及产卵行为;结合单果控制性引蜂试验,测定不同阶段榕小蜂个体大小、孕卵量、携粉量,以及雄花期最终繁殖的榕小蜂后代和榕果种子数量。【结果】聚果榕雌花花柱长度存在树间变异,榕小蜂产卵器长度比绝大多数的雌花花柱长,说明该小蜂可以产卵于大部分的雌花子房里。通常个体大的榕小蜂孕卵量更多,但个体大小与携粉量之间相关性不显著。观察发现,榕小蜂进入雌花期榕果内,前6 h集中产卵,可产下孕卵量的95%,平均搜索用时27 s,产卵用时46 s,此期间传粉行为少见,花粉筐中携带花粉量亦无明显变化;榕小蜂进果后6-24 h,主要执行传粉,其行为主动,连贯高效,单次传粉用时平均为2 s,最终可传完携粉量的80%。控制引蜂试验也证实榕小蜂进入榕果内前6 h主要执行产卵繁殖后代,之后6-24 h主要执行传粉以繁殖榕树种子。【结论】在雌雄同株的聚果榕雌花期榕果内,榕小蜂先产卵、后传粉。本研究首次展示了传粉榕小蜂在聚果榕雌花期榕果内的产卵和传粉行为,并获得与行为相匹配的产卵量和传粉繁殖量,反映了具主动传粉行为的榕小蜂在传粉和产卵之间存在时间和数量上的权衡。     

环纹榕传粉榕小蜂的传粉模式

榕小蜂的传粉结构、 传粉行为以及寄主榕树的花药胚珠比是判断榕-蜂互惠系统传粉模式的重要依据。本研究于2010年8月至2011年6月对位于云南西双版纳地区的试验样树环纹榕Ficus annulata进行观察, 对出榕果的环纹榕传粉榕小蜂Deilagaon annulatae进行电镜扫描和室内显微镜下对其进行行为观察。电镜扫描显示： 环纹榕传粉榕小蜂D. annulatae位于胸部的花粉筐消失, 具一片可粘附花粉的毛区, 提示其属于被动传粉的种类。传粉行为观察发现, 该蜂没有主动采集花粉的行为, 显然存在的花粉刷已丧失了主动收集花粉的功能。寄主植物环纹榕F. annulata属于典型的自动散粉让榕小蜂沾附花粉的榕树种类。环纹榕传粉榕小蜂D. annulatae是西双版纳热带地区已知58种传粉榕小蜂中唯一体色为黄色的种类, 该蜂偏爱在低温的夜晚出蜂。除了传粉榕小蜂, 一种金小蜂Lipothymus sp.也在雌花期进入榕果内繁殖, 并且其数量显著高于环纹榕传粉榕小蜂D. annulatae (P<0.0001)。自然单果的繁殖中, 环纹榕传粉榕小蜂的数量显著高于种子数量, 呈现出榕-蜂互惠系统中罕见的传粉榕小蜂主导的局面。综合榕-蜂的传粉特征显示, 环纹榕F. annulata及其传粉榕小蜂D. annulatae互惠系统是被动传粉的模式。     

非传粉小蜂对榕-蜂共生系统的影响

榕-蜂共生系统是桑科榕属(Ficus)植物与传粉榕小蜂专一互惠形成的生态学关系。但是,也有一些非传粉的小蜂出现在这个系统中,对榕-蜂共生系统可能产生较大的影响。西双版纳的聚果榕(Ficus racemosa)树上主要有5种非传粉小蜂,分别在榕果发育的不同阶段从果外向果内产卵。在传粉榕小蜂进果之前的花前期,Platyneura testace、Apocrypta sp.和P. mayri这3种非传粉小蜂先后到果外产卵繁殖后代,对榕-蜂共生系统造成显著影响,尤其是影响传粉榕小蜂的繁殖。在传粉榕小蜂进果之后的间花期,P. mayri、A. westwoodi和P. agraensis这3种非传粉小蜂相继到果外产卵,它们虽然能减少种子形成和传粉榕小蜂繁殖的数量,但最终没有对榕-蜂共生系统造成显著的影响。造瘿类的P. mayri可在花前期和间花期产卵繁殖,在花前期产卵时它主要是影响传粉榕小蜂的繁殖,而在间花期产卵时它则更多地是影响种子的生产。     

传粉榕小蜂与榕树的繁衍

榕树传粉现象被广泛地作为研究协同进化特别是互惠共生的重要模式之一。本文总结了榕果与传粉榕小蜂的有关研究,试图解释其形态结构之间的相互适应,总结传粉榕小蜂的传粉行为,探讨传粉榕小蜂在雌雄同株及雌雄异株榕树上的传粉模式,讨论传粉榕小蜂的寄主专一性,并展望中国在榕小蜂方面的研究前景。     

薜荔榕小蜂产卵和传粉行为

薜荔榕小蜂Blastophaga pumilae是薜荔的传粉昆虫,栖息于薜荔隐头花序中,在其生物学行为中以钻入花序产卵或传粉最为关键。研究表明：薜荔榕小蜂钻入花序平均费时69.48 min,标准差13.26 min;伤残程度很高并能在伤残的情况下完成产卵或传粉;卵的尾丝能起标识作用避免重复产卵;进入雌花序的小蜂具逃离花序的行为但不能实现;1只小蜂平均产528个卵或为1 072.4朵雌花授粉。     

榕树-榕小蜂的物种共形成

榕树-榕小蜂的互惠共生是植物与其传粉者间相互作用的最极端的特例,几乎每一种榕树均由榕小蜂科的一种特定昆虫传粉,而它们的小蜂也只能在此特定榕树种的花内养育它们的幼虫,构成了高度的种专一性(一对一原则).因此榕树及其传粉昆虫间的相互作用被看作是专性互惠共生的最极端特例,也引起人们对它们共趋异及物种形成的诸多推测.对目前榕树一榕小蜂的物种共形成的研究进行了回顾与阐述,希望能对全面认识这对完美的共生伙伴及物种共形成机制提供一些启示.     

榕树传粉昆虫榕小蜂染色体制备方法研究

榕树与其传粉昆虫榕小蜂之间具有高度专一的互惠共生关系,榕小蜂为榕树传粉的同时又在榕果内营寄生生活,直至完成其整个生活史,因此一直以来对榕小蜂的染色体研究存在很大困难。本文以对叶榕Ficus hispida传粉榕小蜂Ceratosolen solmsi和鸡嗉子榕F.semicordata传粉榕小蜂C.gravelyi为材料,摸索出一套适合于榕树传粉昆虫榕小蜂染色体研究的详细、有效的技术和方法。应用该法对对叶榕传粉榕小蜂C.solmsi和鸡嗉子榕传粉榕小蜂C.gravelyi的染色体核型进行了研究,结果表明两种榕小蜂的染色体核型特征非常相似,具有相同的染色体数目2n(♀)=10,染色体类型全部为中着丝粒染色体,臂数NF=20。此外,在相对长度方面两者也没有明显的差异。最后与Imai等1988年研究蚂蚁染色体时提出的方法进行了比较。利用本文介绍的方法进行榕小蜂染色体制备,操作过程简单、重复性强,不仅能够得到大量的染色体分裂相,而且染色体细胞界限明确、形态清晰、分散良好。     

榕果挥发物对传粉榕小蜂的吸引作用

榕树 /榕小蜂专一性共生系统的维持 ,与榕树开花期释放的特殊的挥发性化合物以及榕小蜂对其寄主榕树的化学识别和定位紧密相关。研究选取了西双版纳地区常见的 3种榕树 ,即对叶榕 Ficus hispida、木瓜榕 F.auriculata和鸡嗉子榕F.semicordata的榕果作为实验材料 ,利用野外诱捕实验、室内生物检测实验检测传粉榕小蜂 Hymenoptera:ChalcidoidaeAgaonidae对 12种信息化合物及榕果的二氯甲烷浸提物的趋向性反应 ,研究不同榕属植物的传粉榕小蜂对相同的信息化合物的反应差异 ,以及传粉榕小蜂受不同发育时期榕果浸提物吸引的显著性程度。诱捕实验中对叶榕小蜂 Ceratosolen solmsimarchali对香叶醇的趋向性反应显著 ,大果榕小蜂 C.emarginatus对接受期榕果浸提物和芳樟醇都有明显的趋向性反应 ,而对间花期榕果浸提物则无显著反应。嗅觉仪生物检测实验中 ,鸡嗉果榕小蜂 C.gravelyi对香叶醇和松油醇都表现出显著的趋向性反应。结果表明 ,对叶榕、鸡嗉子榕传粉榕小蜂对 12种信息化合物的反应存在一定的差异 ,木瓜榕传粉榕小蜂对香叶醇和木瓜榕接受期榕果浸提物的趋向性反应比间花期榕果强得多     

Chemical composition of volatiles from the syconia of Ficus microcarpa and host recognition behavior of pollinating fig wasps

Aims Chemical communication plays a key role in host plant recognition of pollinators. There are two recognized types of chemical communication between syconia and their pollinating fig wasps: one is “generalization”, of which the wasps respond to the relative ratio of multiple compounds, and the other is “specialization”, of which the key signal is a single uncommon, possibly unique, compound. The aims of this study were to identify the chemical composition of volatiles from the syconia of Ficus microcarpa at different developmental phases, and to determine if the signaling between F. microcarpa and its pollinating fig wasp, Eupristina verticillata, is of generalized type, or of specialized type.Methods The volatiles from syconia of F. microcarpa were extracted using solid-phase micro extraction (SPME) at different developmental phases (pre-female, female (before and after pollination), interfloral, male and postfloral phases) and the chemical compounds were identified by gas chromatography mass spectrometry (GC-MS). We then tested the behavioral responses of E. verticillata to fresh syconia at different developmental phases using two-choice olfactometers.Important findings There were 21 volatile compounds identified from the syconia at different developmental phases, which were mainly fatty acid derivatives, terpenoids and aromatic compounds. The components of the volatiles apparently differed among the developmental stages. The contents of terpenoids declined, but the contents of fatty acid derivatives increased, from before the pollination to after the pollination. Especially, the characteristic compounds of 2-heptanone and 3-octanone before the pollination disappeared, D-limonene decreased after the pollination, but copanene, cyclohexane and 2-hexenal increased. The results of the two-choice olfactometer experiment showed that the pollinating fig wasps had higher selection ratio to chemicals found in the female phase syconia than those in other phases; whereas the volatile compounds from the male phase syconia had the function pushing the pollinating fig wasps to leave the natal syconia so that there existed the “push-pull” responses by fig wasps to volatiles released by their host syconia. We conclude that there are multiple chemical compounds playing the roles in host recognition of pollinating fig wasp E. verticillata. The mutualistic relationship between F. microcarpa and E. verticillata is maintained by the chemical communication of “generalization” strategy.     

鸡嗉子榕内传粉小蜂与非传粉小蜂的繁殖稳定共存机制研究

【目的】榕-蜂系统是自然界协同进化和互利共生的典型模型,榕-蜂之间如何实现繁殖分配从而实现稳定共存一直是倍受研究者关注的问题,但对传粉小蜂和非传粉小蜂的繁殖稳定共存研究较少。【方法】本文选取分布在西双版纳地区的雌雄异株榕树鸡嗉子榕Ficus semicordata的雄果,通过对榕果内唯一的传粉小蜂Ceratosolen gravelyi Grandi以及4种非传粉小蜂Philotrypesis dunia Joseph,Apocrypta sp.,Platyneura sp.,Sycoscapter trifemmensis Joseph的产卵时序进行了观察,并对5种小蜂的种群数量进行统计,以及对每种小蜂产卵小花的空间分布、瘿花体积等特征进行了研究。【结果】发现:5种小蜂在产卵时间上存在分离,且传粉小蜂的种群数量远大于其他4种非传粉小蜂的种群数量之和。5种小蜂的瘿花特征也存在差异:瘿花的子房大小不同,且花梗长度即分布空间也有差异,传粉小蜂最接近果腔而非传粉小蜂则更多地利用中层和内层的小花。【结论】结果说明在鸡嗉子榕有限的空间内,5种小蜂通过产卵时间和生长空间的分离,实现了减少竞争以及长期共存的特征,维持了榕-蜂系统的稳定性。     

大果榕亚组三种榕树传粉榕小蜂核型研究

研究了木瓜榕(Ficus auriculata Loureiro)、苹果榕(F.oligodon Miquel)及未知榕(Ficus sp.)3种榕树传粉榕小蜂的核型。结果表明:3种榕树对应的传粉榕小蜂具有非常相似的核型,染色体数目相同为2n=10,染色体全部为中着丝粒染色体;核型公式2n=2X=10=10M,核型均为Stebbins-1A型。以臂比不对称性系数Dc和相对长度不对称性系数Dt作二维散点图,Ceratosolen emarginatus Mayr(木瓜榕传粉榕小蜂)和C.emarginatus Mayr(苹果榕传粉榕小蜂)具有非常相近的核型不对称系数,核型不对称性大于Ceratosolen sp.(未知榕传粉榕小蜂),显示出两者更近的亲缘关系,而Ceratosolen sp.(未知榕)与前两者亲缘关系较远。此外,比较了Ceratosolen属和Blastophaga属在核型方面的差异,认为染色体数目包括染色体形态能够作为准确区分Ceratosolen属和Blastophaga属的依据,并对Ceratosolen属的核型进化进行了初步探讨。     

Egg deposition patterns of fig pollinating wasps: implications for studies on the stability of the mutualism

1. Fig pollinating wasps (Agaonidae) enter Ficus inflorescences (figs), oviposit in some of the flowers, and pollinate in the process. Each larva completes its development within a single flower. In most cases, an inflorescence entered by a wasp will represent its only egg‐laying site. The mechanisms that prevent pollinating wasps from exploiting all the flowers inside a fig are not understood. In this study, hypotheses about flower use by pollinating fig wasps were tested by investigating egg deposition patterns in three species. 2. Either one or three wasps were introduced into figs. The figs were then harvested. Serial sections allowed assessment of the presence or absence of a wasp egg in a sample of flowers in each fig. The overall proportion of flowers with eggs and the spatial distribution of eggs were then compared in single wasp figs and three foundress figs. 3. In all species, the proportion of flowers with a wasp egg increased with foundress number but less than three‐fold. 4. In all species, at least in single foundress figs, flowers near the fig cavity were more likely to receive a wasp egg than were flowers near the fig wall. 5. In two species, when the number of foundresses was multiplied by three, there was an increase in the use of flowers near the fig wall, while in the third species, the increase was spread evenly among flowers. 6. Factors affecting wasp egg deposition patterns and the potential of investigating such patterns for studying the stability of the mutualism are discussed.     

Non‐pollinating cheater wasps benefit from seasonally poor performance of the mutualistic pollinating wasps at the northern limit of the range of Ficus microcarpa

1. Species interactions in tightly bound ecological mutualisms often feature highly specialised species' roles in which competitive exclusion may preclude multi‐species coexistence. Among the 800 fig (Ficus) species, it was originally considered that each was pollinated by their own wasp (Agaonidae). However, recent investigations show that this ‘one‐to‐one’ rule often breaks down, as fig species regularly host multiple agaonids but in ways suggesting that competitive processes still mediate biodiversity outcomes. 2. A phenological survey was conducted of the fig–fig wasp pair, Ficus microcarpa and its associated pollinating wasp, alongside its sister species, the cheating wasp, in Xishuangbanna, China. 3. Reproductive output underwent extreme seasonal variation. Seed and pollinator production fell markedly during cooler, drier months, although high levels of fig production continued. However, this resource was predominantly utilised by the cheater species, which offers no pollination services. Pollinators and cheaters rarely co‐occur, suggesting that temporal coexistence is constrained by competition for access to figs. 4. The overall findings indicate periodic rearrangements of mutualism dynamics, probably resulting from a strongly seasonal environment. Sympatric co‐occurrence may result from a window of opportunity for a functionally divergent agaonid, potentially due to constraints on the main pollinator in adapting to variable year‐round conditions that prevent competitive exclusion.     

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。     

Genetic and physiological data suggest demographic and adaptive responses in complex interactions between populations of figs (Ficus pumila) and their pollinating wasps (Wiebesia pumilae)

To study interactions between host figs and their pollinating wasps and the influence of climatic change on their genetic structures, we sequenced cytoplasmic and nuclear genes and genotyped nuclear microsatellite loci from two varieties of Ficus pumila, the widespread creeping fig and endemic jelly fig, and from their pollinating wasps, Wiebesia pumilae, found in Taiwan and on nearby offshore islands. Great divergence in the mitochondrial cytochrome c oxidase subunit I (mtCOI) with no genetic admixture in nuclear markers indicated that creeping‐ and jelly‐fig wasps are genetically distinct. Compared with creeping‐fig wasps, jelly‐fig wasps also showed better resistance under cold (20 °C) than warm (25 and 30 °C) conditions in a survival test, indicating their adaptation to a cold environment, which may have facilitated population expansion during the ice age as shown by a nuclear intron and 10 microsatellite loci. An excess of amino acid divergence and a pattern of too many rare mtCOI variants of jelly‐fig wasps as revealed by computer simulations and neutrality tests implied the effect of positive selection, which we hypothesize was associated with the cold‐adaptation process. Chloroplast DNA of the two fig plants was completely segregated, with signs of genetic admixture in nuclear markers. As creeping‐ and jelly‐fig wasps can pollinate creeping figs, occasional gene flow between the two figs is thus possible. Therefore, it is suggested that pollinating wasps may be playing an active role in driving introgression between different types of host fig.     

One fig to bind them all: host conservatism in a fig wasp community unraveled by cospeciation analyses among pollinating and nonpollinating fig wasps

The study of chalcid wasps that live within syconia of fig trees (Moraceae, Ficus ), provides a unique opportunity to investigate the evolution of specialized communities of insects. By conducting cospeciation analyses between figs of section Galoglychia and some of their associated fig wasps, we show that, although host switches and duplication have evidently played a role in the construction of the current associations, the global picture is one of significant cospeciation throughout the evolution of these communities. Contrary to common belief, nonpollinating wasps are at least as constrained as pollinators by their host association in their diversification in this section. By adapting a randomization test in a supertree context, we further confirm that wasp phylogenies are significantly congruent with each other, and build a "wasp community" supertree that retrieves Galoglychia taxonomic subdivisions. Altogether, these results probably reflect wasp host specialization but also, to some extent, they might indicate that niche saturation within the fig prevents recurrent intrahost speciation and host switching. Finally, a comparison of ITS2 sequence divergence of cospeciating pairs of wasps suggests that the diversification of some pollinating and nonpollinating wasps of Galoglychia figs has been synchronous but that pollinating wasps exhibit a higher rate of molecular evolution.