Non-pollinating wasps distort the sex ratio of pollinating fig wasps

In fig wasps, mating occurs among the offspring of one or a few foundress mothers within the fig, from which the mated females disperse to found new broods. Under these conditions, males will compete with each other for mating, and such local mate competition can result in female-biased sex ratios. In addition to pollinating wasps, non-pollinating wasp species are also associated with figs and develop in flower ovaries or parasitize the larvae of primary galling wasps. While studying the fig wasp Pegoscapus tonduzi , which pollinates Ficus citrifolia in Brazil, we examined the influence of non-pollinating fig wasps on the sex ratio of species that pollinate F. citrifolia to determine whether the presence of non-pollinating wasps resulted in a distorted sex ratio. There was a positive relationship between the sex ratio of P. tonduzi and the number of non-pollinating wasps that was independent of the number of foundresses and brood size. In addition, the number of non-pollinating wasps correlated negatively with the number of pollinating females, but was not significantly related to the number of pollinating males. This finding suggested that non-pollinating wasps had a direct effect in distorting the sex ratio of P. tonduzi broods. Our results indicate that the secondary sex ratio may not precisely reflect the primary sex ratio when there is a high infestation of non-pollinating fig wasps.     

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。     

细叶榕榕小蜂群落结构及动态变化

细叶榕为桑科榕属植物,雌雄异株,广泛分布于印度-澳大利亚(Asia-Australasia)榕树植物分布中心区,它既是热带雨林的主要树种,也是庭院和行道绿化的常见树种。通过全年定时、定点、定株观察与采集,对福州2个样地19株细叶榕隐头果内小蜂群落结构及其动态进行研究。全年在两个样地530个隐头果内共收集到小蜂26318只。发现细叶榕隐头果内有17种小蜂,隶属小蜂总科Chalcidoidae中的榕小蜂科(Agaonidae)、隐针榕小蜂亚科(Epichrysomallinae)、金小蜂科(Pteromalidae)、广肩小蜂科(Eurytomidae)和刻腹小蜂科(Ormyridae),其中榕小蜂科的Eupristina verticillata是细叶榕唯一的传粉者,传粉方式为主动传粉,其性比为0.16,具明显偏雌现象;非传粉小蜂中,有翅雄蜂的榕小蜂(Odontofroggatia galili,O.quinifuniculus,O.corneri,Sycophila sp.1,Sycophila sp.2,Meselatus bicolor)的性比(0.46—0.55)较高,无翅雄蜂的榕小蜂(P.taiwanensis,Sycoscaptergajimaru,W.microcarpae)的性比(0.31—0.37)较低,而既具有翅雄蜂又具无翅雄蜂的非传粉榕小蜂(P.okinavensis)性比(0.47)居中。榕小蜂的性比可能与其交配行为策略有关。在细叶榕小蜂群落结构中,传粉小蜂E.verticillata的重要值占绝对优势,非传粉小蜂O.galili和Sycophila sp.2的重要值仅次于传粉小蜂。根据榕小蜂发生数量及连续性,可将细叶榕隐头果中的榕小蜂分为常见种和偶见种,E.verticillata、Odontofroggatia galili、Walkerella microcarpae、Sycophila sp.1、Sycophila sp.2和Philotrypesis okinavensis为常见种,其余11个种为偶见种。传粉小蜂和非传粉小蜂的种类和数量呈现明显的季节性变化。2月至6月期间,每月出现的榕小蜂种类较少,仅3—4种,单果内平均有传粉小蜂48.88只,非传粉小蜂13.64只;7月至翌年1月间,每月出现的榕小蜂种类较多,达6—13种,单果内平均有传粉小蜂24.38只,非传粉小蜂18.89只,表明,7月—翌年1月单果内传粉小蜂数量比较于2—6月极显著降低(P<0.001),而单果内非传粉小蜂数量极显著提高(P=0.001),同时种类也显著增加。雄花期榕小蜂的种类与数量取决于雌花期产卵榕小蜂的种类与数量,而雨量、气温以及雌花期花序果数量对产卵小蜂的数量,以及小蜂产卵行为都可能产生影响。本研究结果可为城市绿化和热带雨林生物多样性保护提供科学依据。     

榕小蜂温度耐受性及其对种间共存关系的影响

全球已知有约800种榕属(Ficus)植物, 主要分布在热带, 部分种类延伸至亚热带地区。温度是限制榕‒蜂共生系统分布北界的主要因素, 也显著影响榕树及其榕小蜂的繁殖成功, 其中榕小蜂对温度的响应更加敏感。榕小蜂只有在一定的温度范围内才能保持正常的生理机能, 其对温度耐受能力直接影响榕果内小蜂种群数量和群落内种间关系。然而目前对榕小蜂温度耐受性的研究尚少, 榕小蜂的温度耐受能力如何影响榕果内小蜂的共存关系还未见报道。本文研究了分布于西双版纳的2种雌雄同株和1种雌雄异株榕树果内传粉榕小蜂和非传粉小蜂的温度耐受能力。结果表明: 3种传粉榕小蜂对高温的耐受性极差, 相对于雌雄同株的高榕(F. altissima)和聚果榕(F. racemosa)传粉榕小蜂, 雌雄异株的鸡嗉子榕(F. semicordata)传粉榕小蜂对低温有增强的耐受趋势。聚果榕小蜂群落结构显示: 在适宜其生长的西双版纳地区, 传粉榕小蜂的数量占绝对优势, 在温度较低的季节其数量显著减少; 而非传粉榕小蜂呈相反模式, 较强的温度耐受能力使其在低温的雾凉季维持了较高的种群数量。鸡嗉子榕果内非传粉小蜂Sycoscapter trifemmensis相对于Philotrypesis dunia有更强的温度耐受能力, 在种群数量和种间关系上有更多的竞争优势及数量。榕小蜂的温度耐受性差异在物种分布、种间关系的维持和共存上起了重要作用, 本研究结果为阐明榕小蜂种间共存的维持机制提供了科学依据。     

福州大叶榕隐头果内的小蜂群落结构与多样性

对福州2个样地10株大叶榕果内小蜂群落组成和物种多样性进行研究。全年在两个样地267个隐头果内共收集到小蜂13458只。发现大叶榕隐头果内有7种小蜂,隶属小蜂总科Chalcidoidae中的榕小蜂科Agaonidae、金小蜂科Pteromalidae的隐针榕小蜂亚科Epichrysomallinae、锥尾榕小蜂亚科Otitesellinae和延腹榕小蜂亚科Sycoryctinae;广肩小蜂科Eurytomidae、刻腹小蜂科Ormyridae、姬小蜂科Eulophidae,其中榕小蜂科的Platyscapa coronata是大叶榕唯一的传粉者,传粉方式为主动传粉;非传粉榕小蜂的雄性多型现象普遍。传粉与非传粉小蜂的性比明显具有偏雌现象。传粉小蜂性比为0.19±0.07,非传粉小蜂中Camarothorax bismasculinus小蜂性比为0.36±0.10;Walkerella sp.小蜂性比为0.36±0.22,Sycoscapter sp.小蜂性比为0.31±0.22,Sycophila sp.小蜂性比为0.35±0.13。雄性多型现象可能是导致非传粉小蜂性比提高的原因之一。根据各种榕小蜂发生数量及连续性,可将大叶榕隐头果中的榕小蜂分为常见种和偶见种,Platyscapa coronata、Camarothorax bismasculinus、Walkerella sp.、Sycoscapter sp.和Sycophila sp.为常见种,Omyrus sp.和Aprostocetus sp.为偶见种。偶见种的存在对常见种的数量几乎没有影响,偶见种利用的是榕果内未饱和的一部分资源,也可能是榕果为偶见种的发生预留了空间和资源。首次发现姬小蜂科的昆虫寄生在榕果内,且有一定的种群数量,为姬小蜂科昆虫分类及其生物学、生态学特性研究提供了基础资料。在大叶榕小蜂群落结构中,传粉小蜂和非传粉小蜂的种类和数量呈现明显的季节性。冬-春季(12-翌年5月)榕果内小蜂的种类和数量较多,传粉榕小蜂是优势种,其重要值达到0.42,榕果种子结实率高;夏-秋季(6-11月间)小蜂种类和数量略少,Camarothorax bismasculinus和Sycophila sp.是优势种,其重要值分别为0.56和0.28,而传粉小蜂的重要值仅为0.025,此期大叶榕榕果中几乎找不到传粉小蜂,榕果结实率极低,对大叶榕的繁殖利益有较大的负面影响。雨水和高温等不良气候,可能是导致夏-秋季雄花期榕果内的传粉小蜂数量骤减的主要原因。两个实验样地的小蜂群落结构组成没有明显差异,年变化趋势相似。研究结果为城市绿化和热带雨林生物多样性保护提供科学依据。     

歪叶榕非传粉小蜂的繁殖策略及其对榕-蜂共生系统的影响

2004年8月至2005年8月在西双版纳热带植物园内,通过广泛收集歪叶榕榕小蜂标本、非传粉小蜂产卵行为学观察和阻止传粉者入果等实验方法,研究了我国西双版纳热带雨林下的一种榕树——歪叶榕Ficus cyrtophylla的榕小蜂群落组成结构、非传粉小蜂的繁殖策略以及它们对榕-蜂共生系统的影响。结果表明,歪叶榕中除了具有唯一传粉榕小蜂Blastophag sp.以外,还具有3种非传粉小蜂Platyneura sp.、Philotrypesis sp.和Sycoscapter sp.。在歪叶榕榕小蜂群落中,传粉榕小蜂占整个群落总数的92.21%,是群落的最主要组成者;主要的非传粉小蜂是Sycoscaptersp.,占5.78%; 其次是Philotrypesissp.,占1.84%,而Platyneurasp.仅占群落总数的0.17%。歪叶榕中的非传粉小蜂通过各自产卵时间和食性分化的策略来利用榕果中的资源繁殖后代。非传粉小蜂寄生使传粉榕小蜂的总数和其雌蜂数量都显著地降低,但是对传粉小蜂雄蜂数量没有显著影响,从而导致传粉榕小蜂的雄性性比显著地增加。这说明非传粉小蜂在选择寄居宿主时具有明显的倾向性,而且更多地将卵产于含有雌性传粉小蜂的瘿花之中。因此,非传粉小蜂通过减少雌性传粉小蜂的数量而降低了榕树的雄性适合度,从而在一定程度上对榕 蜂共生系统的稳定存在和发展产生了负面影响。     

高榕雌花期传粉榕小蜂和欺骗性小蜂的繁殖特点

榕树及其专一性传粉榕小蜂组成了动植物界最为经典的协同进化关系,传粉榕小蜂演化出欺骗性是非常罕见的。在雌雄同株的高榕隐头果内,共存着一种传粉榕小蜂Eupristina altissima和一种欺骗性的小蜂Eupristina sp.,两种小蜂在雌花期进入隐头果内繁殖,但有不同的繁殖特点。对比研究了两种小蜂从成虫羽化到产卵和传粉这个阶段的雌蜂个体大小、孕卵量及繁殖差异,结果表明:羽化期两种雌蜂的平均个体小,经飞行小个体的雌蜂易死亡,大个体雌蜂到达接受树,但通过苞片通道,一些个体较大的传粉榕小蜂被夹死导致进入果腔的雌蜂相对小,而欺骗性小蜂易通过苞片以至进入果腔的雌蜂个体较大。两种未产卵雌蜂均表现为个体大者孕卵量较多,但两种雌蜂的平均孕卵量没有差异。即使有充足雌花资源产卵,两种雌蜂均未产完所有卵,产卵后两种雌蜂卵巢中的卵量均显著减少,遗留下的卵量两种小蜂间没有差异。传粉榕小蜂只有部分个体传完所携带花粉,并表现为传粉越成功的雌蜂,产卵越多。存在种内竞争时,两种小蜂的产卵量均减少,传粉榕小蜂的传粉效率也降低。在种间竞争背景下,欺骗性小蜂产卵更成功,传粉榕小蜂的产卵和传粉量均受到极大抑制。研究结果说明雌花期隐头果内传粉榕小蜂只适量利用雌花资源产卵繁殖后代,更有效地传粉繁殖榕树种子,这可能是维持榕-蜂互惠系统稳定共存的重要机制之一;欺骗者稳定存在需降低与传粉者的直接竞争,而欺骗者和传粉者分散在不同果内,甚至是不同的树上繁殖是理想的繁殖策略。     

Contrasting patterns of fig wasp communities along Mt. Wilhelm,Papua New Guinea

The fig (Moraceae) and pollinating fig wasp (Agaonidae) mutualism is best known as a model system for the study of coevolution in plant–pollinator interactions and its central role in shaping vertebrate communities in tropical forests. Figs also host myriad antagonistic parasitic fig wasps which impose costs on both partners threatening mutualism stability. Spatiotemporal variation in parasitic wasp abundance is a key factor in mitigating these effects. Because fig wasps are temperature sensitive and likely vary in their ability to traverse environmental gradients, we expect community assemblages and abundance of both pollinating and non-pollinating fig wasps to respond to changes along an elevational gradient. In the present study, we compare the fig wasp communities and abundance of three fig species growing along the slopes of the Mount Wilhelm altitudinal gradient in Papua New Guinea. We quantified wasps from over 100 male fig trees and calculated seed set for 55 female trees along each of the species’ distribution on the transect. Our results show that the abundance of both pollinating and non-pollinating fig wasps follow a mid-elevation peak, consistent with fig species richness found in the same transect. The patterns, however, are different according to the host's species distribution. Seed set remained relatively constant along the gradient for all species with some decrease along higher elevations, potentially affecting connectivity along the gradient. As suggested for insects in general, temperature and habitat diversity appear to play a fundamental role in the species richness and abundance of fig wasps.     

Measuring the discrepancy between fecundity and lifetime reproductive success in a pollinating fig wasp

Lifetime reproductive success in female insects is often egg‐ or time‐limited. For instance in pro‐ovigenic species, when oviposition sites are abundant, females may quickly become devoid of eggs. Conversely, in the absence of suitable oviposition sites, females may die before laying all of their eggs. In pollinating fig wasps (Hymenoptera: Agaonidae), each species has an obligate mutualism with its host fig tree species [Ficus spp. (Moraceae)]. These pro‐ovigenic wasps oviposit in individual ovaries within the inflorescences of monoecious Ficus (syconia, or ‘figs’), which contain many flowers. Each female flower can thus become a seed or be converted into a wasp gall. The mystery is that the wasps never oviposit in all fig ovaries, even when a fig contains enough wasp females with enough eggs to do so. The failure of all wasps to translate all of their eggs into offspring clearly contributes to mutualism persistence, but the underlying causal mechanisms are unclear. We found in an undescribed Brazilian Pegoscapus wasp population that the lifetime reproductive success of lone foundresses was relatively unaffected by constraints on oviposition. The number of offspring produced by lone foundresses experimentally introduced into receptive figs was generally lower than the numbers of eggs carried, despite the fact that the wasps were able to lay all or most of their eggs. Because we excluded any effects of intraspecific competitors and parasitic non‐pollinating wasps, our data suggest that some pollinators produce few offspring because some of their eggs or larvae are unviable or are victims of plant defences.     

高榕隐头果内小蜂群落的动态变化

高榕隐头果内的小蜂群落是我国目前所知榕小蜂群落中最为丰富多样的群落。通过600个果内78063号小蜂标本的分类、统计,在高榕果内共有25种榕小蜂,隶属于7科、14属,其中两种为传粉小蜂,23种为非传传粉小蜂。在榕小蜂群落中,传粉小蜂优势度较为明显,除1月份为18.42%外,其余月份均达51.62%以上,有时甚至达100%。在单个榕果内,小蜂的种类和数量呈现较大变幅,有1~8种,普遍寄生2~4种;榕小蜂数量从1~561只/果不等,寄生100~200只/果较多。1年中不同小蜂出现的相对频度差异也较大,E up ristina sp.和Sy coscap ter sp.2每月都出现,有的非传粉小蜂仅于特定月份出现,并且数量极少。榕小蜂的丰富度随着月份而变化,变幅3~19种,并于1月、4月和8月出现3个高峰。自然群落中,传粉小蜂与非传粉小蜂的数量变化呈显著负相关;多样性指数与传粉小蜂比例呈显著负相关,与非传粉小蜂比例呈显著正相关,而且都具较高的拟合优度。通过3个不同生境样地的多样性指数、丰富度和均匀度比较,结果表明:在人为干扰较严重的样地内,3项指标都较低,除均匀度指标未达显著外,多样性指数和丰富度均达显著水平。但生境对传粉小蜂和非传粉小蜂的影响却不相同,非传粉小蜂会随生境的恶化而迅速消亡,而传粉小蜂的种群则急速膨大,占领全部生境。反之,随着生境的改善,传粉小蜂的种群数量将有所下降,而非传粉小蜂的种类和数量将增加。     

福州大叶榕隐头果内榕小蜂的分类

通过对福州两个样地大叶榕雄花期隐头果进行定时、定点采集,观察与鉴定,从546个花序果内共收集到榕小蜂33641头,隶属于小蜂总科中的7个科(亚科)7个属的11个种,其中传粉小蜂为榕小蜂科的Platyscapa coronata,其余10种非传粉小蜂分别隶属于隐针榕小蜂亚科Epichrysomallinae,金小蜂科Pteromalidae的锥尾榕小蜂亚科Otitesellinae和延腹榕小蜂亚科Sycoryctinae,广肩小蜂科Eurytomidae,刻腹小蜂科Ormyridae和姬小蜂科Eulophidae。传粉小蜂和非传粉小蜂的种类和数量呈现明显的季节性。冬-春季(12-翌年5月)榕果内小蜂的种类和数量较多,传粉榕小蜂是优势种;夏-秋季(6-11月间)小蜂种类和数量略少,Camarothorax bismasculinus和Sycophila sp.1是优势种。在非传粉小蜂中,Camarothorax、Sycophila、Otitesella、Sycoscapter等4个属的榕小蜂为常见种,而Ormyrus和Aprostocetus等2个属的榕小蜂为偶见种。根据小蜂的形态特征制定大叶榕隐头果中榕小蜂种类检索表,本实验为榕小蜂分类、榕-蜂协同进化研究,以及非传粉小蜂对榕-蜂共生体系的影响等研究提供科学依据。     

Ecology of a fig ant–plant

Mutualistic interactions are embedded in networks of interactions that affect the benefits accruing to the mutualistic partners. Figs and their pollinating wasps are engaged in an obligate mutualism in which the fig is dependent on the fig pollinator for pollination services and the pollinator is dependent on fig ovules for brood sites. This mutualism is exploited by non-pollinating fig wasps that utilise the same ovules, but do not provide a pollination service. Most non-pollinating wasps oviposit from outside the inflorescence (syconium), where they are vulnerable to ant predation. Ficus schwarzii is exposed to high densities of non-pollinating wasps, but Philidris sp. ants patrolling the syconia prevent them from ovipositing. Philidris rarely catch wasps, but the fig encourages the patrolling by providing a reward through extra-floral nectaries on the surface of syconia. Moreover, the reward is apparently only produced during the phase when parasitoids are ovipositing. An ant-exclusion experiment demonstrated that, in the absence of ants, syconia were heavily attacked and many aborted as a consequence. Philidris was normally rare on the figs during the receptive phase or at the time of day when wasp offspring are emerging, so predation on pollinators was limited. However, Myrmicaria sp. ants, which only occurred on three trees, preyed substantially on pollinating as well as non-pollinating wasps. F. schwarzii occurs in small clusters of trees and has an exceptionally rapid crop turnover. These factors appear to promote high densities of non-pollinating wasps and, as a consequence, may have led to both a high incidence of ants on trees and increased selective pressure on fig traits that increase the payoffs of the fig–ant interaction for the fig. The fig receives no direct benefit from the reward it provides, but protects pollinating wasps that will disperse its pollen.     

Oogenesis and ovarian morphology in pollinating and non-pollinating fig wasps: evidence from adult and immature stages

Hymenopteran insects have meroistic polytrophic ovaries characterised by trophocytes associated with oocytes inside the follicles. In pro-ovigenic species, all oocytes mature before emergence and no trace of oogenesis is visible in adult females. Pro-ovigeny is a rare condition among Hymenoptera, but common in pollinating fig wasps. In the present investigation, we studied adult and pupa females of three fig wasp species with different trophic strategies. We demonstrated that females of Pegoscapus aerumnosus and Idarnes spp. have an unusual ovarian organisation (i.e. each ovariole has only one mature egg and no oocyte) that has led to misleading interpretation of fig wasp reproductive anatomy. The ovaries of these studied species have several ovarioles, recognisable by the presence of nuclei of tunica propria cells surrounding them. Each adult wasp ovariole had one mature egg. None of the pupae had mature eggs, but all of them had follicles with oocytes in different developmental stages. The studied fig wasps are pro-ovigenic, irrespective of their trophic strategy, since there were no signs of ovigeny in adult females. We discuss ecological and phylogenetic factors that could play a role in fig wasps reproductive strategies.     

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.     

Relative investment in egg load and poison sac in fig wasps: Implications for physiological mechanisms underlying seed and wasp production in figs

Fig pollinating wasps and most non-pollinator wasps apply secretions from their poison sacs into oviposited flowers that appear necessary to the formation of the galls that their developing offspring consume. Thus, both eggs and poison sac secretions appear to be essential for wasp reproduction, but the relative investment in each is unknown. We measured relative investment in poison sac and egg production in pollinating and non-pollinating wasps associated with seven species of monoecious Panamanian figs representing both active and passive pollination syndromes. We then collected similar data for four fig hosts in China, where some wasp species in the genus Eupristina have lost the ability to pollinate (“cheaters”). All wasps examined possessed large poison sacs, and we found a strong positive correlation between poison sac size and absolute egg production. In the Panamanian species, the relative poison sac to egg investment was highest in the externally ovipositing non-pollinator wasps, followed by active pollinators, then by passive pollinators. Further, pollinator wasps of fig species with demonstrated host sanctions against “cheating” wasps showed higher investment in the poison sac than wasps of species without sanctions. In the Chinese samples, relative investment in the poison sac was indistinguishable between pollinators and “cheaters” associated with the same fig species. We suggest that higher relative investment in poison sac across fig wasp species reflects higher relative difficulty in initiating formation of galls and subsequently obtaining resources from the fig. We discuss the implications for the stability of the fig–wasp mutualism, and for the ability of non-pollinators to exploit this mutualism.     

Restructuring of a mutualism following introduction of Australian fig trees and pollinating wasps to Europe and the USA

Figs and fig-pollinating wasps are obligate mutualists that require each other to complete sexual reproduction. However, landscapers can establish populations of fig trees outside their native ranges by propagation through exported seeds, seedlings or cuttings. Once mature, these trees could be colonized by pollinating wasps and/or various non-pollinating wasps that also develop in figs. In recent decades, the Australian endemic Ficus rubiginosa has been planted widely in the Mediterranean region and in parts of the USA. Observation of ripe fruit production suggested that a pollination mutualism has been re-established by pollinating wasps colonizing trees in the plant’s introduced range. We therefore used sampling of pollinators from mainland Spain, Tenerife and California (USA) and molecular studies to characterize the restructured mutualism and compare it with the native range. In the native range, the plant is pollinated by five wasp species that form the Pleistodontes imperialis complex. However, all wasps in the introduced ranges belonged to just one of these species (P. imperialis sp. 1). Moreover, their mtDNA diversity was close to zero and the sequences clearly link them with the native southern population of this species. None of the?>?20 non-pollinating wasp species from the native range were found in the introduced ranges. In summary, the restructured mutualism has been dramatically simplified, lacking all non-pollinating wasps and all but one pollinator species from the native range. Moreover, the one pollinator species to establish successfully shows a drastic reduction in genetic diversity relative to its source population.     

榕树高度专性共生体系内影响传粉蜂子代繁殖的因素

为探讨影响传粉蜂子代数量及性比的因素,以广州地区分布的粗叶榕(Ficus hirta Vahl)及其传粉小蜂爪哇榕小蜂(Valasia javana Mayr)为材料,采用自然收蜂与控制放蜂试验进行研究。结果表明,果内的榕小蜂群落随季节更替发生显著变化,非传粉蜂的介入、季节差异使雌蜂间的干扰强度不同,导致传粉蜂子代数量发生变化,其中雌蜂间的干扰会使传粉蜂性比显著升高,而非传粉蜂的介入对传粉蜂性比的影响不大,传粉蜂仍能正常地进行繁殖。另外,传粉蜂在雌花期雄花序内的产卵和存活时间一般较短,约为15 h;传粉蜂子代在干、湿季的雄花序内的发育时间差异显著,干季时间长,湿季时间短。这表明传粉榕小蜂进化出了适应广州地区季节变化的繁殖策略。     

Figs,pollinators, and parasites: A longitudinal study of the effects of nematode infection on fig wasp fitness

Mutualisms are interactions between two species in which the fitnesses of both symbionts benefit from the relationship. Although examples of mutualism are ubiquitous in nature, the ecology, evolution, and stability of mutualism has rarely been studied in the broader, multi-species community context in which they occur. The pollination mutualism between figs and fig wasps provides an excellent model system for investigating interactions between obligate mutualists and antagonists. Compared to the community of non-pollinating fig wasps that develop within fig inflorescences at the expense of fig seeds and pollinators, consequences of interactions between female pollinating wasps and their host-specialist nematode parasites is much less well understood. Here we focus on a tri-partite system comprised of a fig (Ficus petiolaris), pollinating wasp (Pegoscapus sp.), and nematode (Parasitodiplogaster sp.), investigating geographical variation in the incidence of attack and mechanisms through which nematodes may limit the fitness of their wasp hosts at successive life history stages. Observational data reveals that nematodes are ubiquitous across their host range in Baja California, Mexico; that the incidence of nematode infection varies across seasons within- and between locations, and that infected pollinators are sometimes associated with fitness declines through reduced offspring production. We find that moderate levels of infection (1–9 juvenile nematodes per host) are well tolerated by pollinator wasps whereas higher infection levels (≥10 nematodes per host) are correlated with a significant reduction in wasp lifespan and dispersal success. This overexploitation, however, is estimated to occur in only 2.8% of wasps in each generation. The result that nematode infection appears to be largely benign – and the unexpected finding that nematodes frequently infect non-pollinating wasps – highlight gaps in our knowledge of pollinator-Parasitodiplogaster interactions and suggest previously unappreciated ways in which this nematode may influence fig and pollinator fitness, mutualism persistence, and non-pollinator community dynamics.     

垂叶榕榕小蜂群落及种间互作网络季节动态

群落中的物种相互作用构成了复杂的生态网络。有关物种的数量和组成的季节性动态变化已有较多的研究, 但是对于生态网络的动态变化知之甚少。揭示生态网络的动态变化对于理解群落的稳定性以及群落的动态变化过程和机理具有重要意义。本研究以垂叶榕(Ficus benjamina)榕小蜂群落为研究对象, 分别在西双版纳的干季和雨季采集了榕小蜂的种类和数量信息。比较了两个季节榕小蜂群落的动态变化以及共存网络的参数(例如网路直径、连接数、嵌套性和群落矩阵温度)变化。结果显示: 雨季榕果内传粉榕小蜂Eupristina koningsbergeri所占比例高于干季, 传粉榕小蜂的种群数量也高于干季, 而在干季非传粉榕小蜂的种类增加(干季15种小蜂, 雨季14种)。从榕树-传粉榕小蜂互利共生系统的适合度来看, 干季非传粉小蜂的增加对传粉榕小蜂和榕树的适合度是不利的。在干季, 共存网络物种间的连接数(干季0.95, 雨季0.47)多于雨季, 群落矩阵温度(干季23.24, 雨季2.64)也显著高于雨季。表明干季榕小蜂群落组成及种间关系较雨季更为复杂而多样, 高的矩阵温度暗示群落受到的干扰更大。     

榕小蜂的产卵模式及其对子代性比的影响

于2007年4月—2007年7月在中国科学院西双版纳热带植物园,通过干预控制榕小蜂产卵的方法研究了聚果榕的传粉榕小蜂Ceratosolen fusciceps和非传粉小蜂Platyneura mayri及垂叶榕的非传粉小蜂Acophila sp.1和Wakerella benjamini等的产卵顺序。对传粉榕小蜂,在完成放蜂后不同间隔时间向榕果内注入乙醚杀死小蜂;对非传粉榕小蜂,在放蜂后不同间隔时间将其从纱网袋内全部放出,从而控制了各种榕小蜂的产卵时间。到榕果成熟后,收集了榕果内的小蜂,并分析比较各种榕小蜂在不同产卵时间下的子代性比。结果表明：Ceratosolen fusciceps、P. mayri和Acophila sp.1在产卵的最初时间内倾向于产下更多的雄性后代,而随后的时间内则产下更多的雌性伴随少量的雄性后代,这样的产卵顺序导致子代性比随着母代产卵时间的延长而下降,榕小蜂后代雌性比例显著高于雄性。同时,子代榕小蜂数量随母代产卵时间的延长而增加,这在一定程度上解释了单头繁殖雌蜂的子代性比随子代数量的增加而减少的现象。而Wakerella benjamini在产卵顺序上是随机的,在其开始产卵后的不同时间段内子代性比都接近于50%。这一结果表明榕小蜂的产卵顺序与母代产卵时间的长短对子代性比有极为重要的影响。