Reproductive ecology of dioecious Siparuna (Monimiaceae) in Ecuador–a case of gall midge pollination

The reproductive ecology of the dioecious genus Siparuna , belonging to the primitive family Monimiaceae, was investigated in Ecuador. Thirteen species were studied, and species growing at high altitudes (above 500 m) were compared with species growing at lower altitudes. The genus has specialized flowers pollinated by Cecidomyiidae (Asynapta sp. and other genera) that lay eggs chiefly in male flowers since these are more easily accessible than female flowers due to their morphology. Several traits ensure that pollen transfer is accomplished: 1. long flowering of individuals and single flowers; 2. specific floral morphology (unisexuality, landing platform, restricted pore) allowing the flowers to be visited by Cecidomyiidae seeking egg-laying sites, and 3. a low number of ovules that have to be pollinated in each flower. The low number of ovules per flower results in a high pollen-ovule (P/O) ratio even though pollen production in male flowers is only moderate.
High altitude species had larger flowers, higher pollen-ovule ratios, fewer ovules per female flower, and longer periods of anthesis. Gender differences were seen in the longer functionality of female flowers; the larger numbers of male flowers produced; and the average diameter at breast height (DBH) biased for one of the two sexes depending on the species investigated, with no clear trend in the size distributions of individuals of both sexes. Sex ratios departed significantly from unity both to male and female bias but usually were in favour of males. There were no general differences in the ratio of functional male to female flowers at the time of observation nor in the sizes of male and female flowers. The evolution of unisexual flowers in Siparuna can be explained as a result of the differential predation by larvae: unimportant in male flowers, destructive if occurring in female flowers.     

Effect of microenvironment on development of a gall midge

This study assessed the influence of microenvironment on the establishment and relative reproductive success of the gall-forming midge Rhopalomyia californica Felt on its host plant Baccharis pilularis De Candolle in Marin County, CA. Mesh cages were used to alter the microenvironment, which also allowed us to assess the validity of using these types of experimental manipulations in this system. Temperature, light intensity, wind speed, and stem growth were compared in caged and uncaged B. pilularis plots in two sites during three seasons. Cage presence significantly altered the microenvironment of R. californica but did not affect development. R. californica establishment was greater when growing on host plants with increased stem growth. Season had the largest impact on gall establishment and reproductive success, with the highest establishment and success rates in late winter to early spring, which correlated with the growing period of B. pilularis. These results suggest that the seasonality of R. californica reproductive success is linked to the phenology of its host plant. When the growing conditions for the plant are less than ideal, R. californica performance is stimulated by increased stem growth. Cage presence was not a significant driver of population dynamics because it did not change the environment in an ecologically meaningful way. We therefore assert that the use of cages for experimental manipulations in this study system does not alter R. californica performance.     

Migration and division of cleavage nuclei in the gall midge,Wachtliella persicariae

Summary The control of nuclear division and migration was studied in time-lapse films of the multinucleate egg cell of a gall midge by experimental alterations of the mitotic pattern. During each cleavage cycle, a wave of randomly oriented saltations of yolk particles (WROS) is seen to travel through the ooplasm. This wave proved to be an indispensable prerequisite for the accompanying anaphase wave and for the activation of the nuclear migration cytasters: WROS cycles can occur autonomously without cleavage nuclei being present, but there is no anaphase without a WROS passing the dividing nucleus. WROSs and mitotic waves can be inverted, and the WROS cycles and the cleavage cycles can be desynchronized by temperature grandients or by locally impaired gas exchange. If a nucleus is not ready for anaphase when met by a WROS, it will only divide in the course of the next WROS. WROSs thus indicate autonomous anaphase-triggering waves governing the cleavage divisions. Rhythmic ooplasmic movements continue even if the WROSs as well as the nuclear divisions are inhibited by colchinine. The characteristics of the WROSs support the hypothesis that each of them is the visible effect of a wave of calcium release (similar to that established in vertebrate eggs) which acts locally on the microtubular system and may continue even if the WROSs are suppressed. The correlations between a possible calcium release, WROS activity, microtubule disassembly and nuclear cycle are discussed.     

Migration and division of cleavage nuclei in the gall midge,Wachtliella persicariae

Summary In the eggs ofWachtliella persicariae the cleavage nuclei move relative to the surrounding ooplasm. This active migration is caused by an organelle whose ultrastructure was studied throughout the mitotic cycle. It consists of a greatly enlarged polar cytaster derived from the mitotic apparatus, linked to the nucleus by 100 Å filaments. The microtubules of the cytaster were found only during periods of active nuclear migration, i.e., from the onset of anaphase to the early prophase of the next mitotic cycle. They are always solitary and follow the course of the astral rays, which are known to temporarily adhere to peripheral structures of the egg cell and to exert tractive forces. In contrast to the cytaster microtubules, the microtubules in the spindle are bundled and persist from early metaphase through late telophase.During ontogenesis the first migration cytaster is built up between 3 and 12 min after oviposition near the anterior egg pole, in the vicinity of the sperm nucleus. In non-inseminated eggs time lapse films show a migration cytaster to develop autonomously in a region free from nuclei, but it does not follow the normal path of the male pronucleus. In several cases the female pronucleus, which remains without a cytaster of its own, was observed to move to the cytaster generated in the absence of the male pronucleus. Whether or not it is adhering to a nucleus, the cytaster divides into two at the correct time, i.e, corresponding to the first cleavage division in fertilized eggs. In some non-inseminated eggs this type of pseudocleavage has been observed to occur repeatedly, giving rise to an increasing number of anucleate cytasters.     

In vitro culture of ovaries of a viviparous gall midge

Summary Ovaries of the viviparous pedogenetic gall midgeHeteropeza pygmaea can be cultured in hemolymph obtained from X-ray-sterilized larvae of the same species. In this culture medium, formation of follicles is essentially the same as in vivo, and sometimes female larvae develop from these follicles. The ovaries of such larvae, in their turn, have been cultured in vitro to produce larvae. In this way, in vitro development from oogonium to larva has been maintained for several generations. When using hemolymph obtained from larvae grown under different conditions, the in vitro cultured ovaries produce a second type of egg which probably is male-determined. Ovarian development in vitro has been studied with differential interference contrast optics and time-lapse cinemicrography. This work was supported by the Swiss National Science Foundation Grant No. 3.2010.73.     

垂叶榕果内寄生瘿蚊的发生规律

在云南西双版纳热带地区,一种还未被描述属和种的瘿蚊寄生于垂叶榕果内的雌花子房里,并膨大形成虫瘿,靠取食花胚组织完成发育.通过2010年定时定点的系统观察和研究瘿蚊的发生规律,结果发现:该种瘿蚊在垂叶榕上发生频率较高,抽样的18批果有17批被瘿蚊寄生,其中有13批果的寄生比率超过了60％,部分甚至达到100％.瘿蚊寄生雌花的平均比率不超过6％,平均每个榕果内有瘿蚊1～40只不等.瘿蚊寄生不仅降低了垂叶榕的种子数,还致命性地影响着传粉榕小蜂的繁殖.在对瘿蚊的羽化、交配行为及其成虫的活动规律观察中,结果显示:寄生在一个榕果里瘿蚊需要5～7d才能羽化完,其羽化高峰期出现在第2～3天;一天内羽化的高峰出现在上午8:00-10:00及晚上20:00-0:00;而羽化后瘿蚊活动高峰期出现在上午8:00-11:00.雄蚊会帮助雌蚊离开榕果并优先获得交配权,雌蚊交配后飞离繁殖自身的榕树,去寻找适合产卵的榕果繁殖后代,雄蚊不离开羽化树,而死在繁殖自身的榕树附近.这些结果为深入研究瘿蚊的防治技术提供了科学依据.     

Correlated evolution in fig pollination

This is the first comparative study of correlated evolution between figs (Ficus species, Moraceae) and their pollinators (Hymenoptera: Agaoninae) based on molecular phylogenies of both lineages. Fig relationships based on the internal transcribed spacer region (ITS) of nuclear ribosomal DNA and pollinator relationships inferred from mitochondrial cytochrome oxidase I (COI) sequences enabled the study of correlated evolution based on molecular phylogenies for the largest set of interacting species ever compared. Comparative methods have been applied to tests of adaptation, but the application of these methods in tests of coadaptation, defined as reciprocal evolutionary change in interacting lineages, has received less attention. I have extended tests of correlated evolution between two traits along a phylogeny to the case of interacting lineages, where two traits may or may not share a common phylogenetic history. Independent contrasts and phylogenetic autocorrelation rejected the null hypothesis that trait correlations within lineages are stronger than trait correlations between interacting lineages. Fig style lengths and pollinator ovipositor lengths, for example, were more highly correlated than were pollinator body size and ovipositor length. Mutualistic interactions between figs and their pollinators illustrate the novel ways in which phylogenies and comparative methods can detect patterns of correlated evolution. The most outstanding evidence of correlated evolution between these obligate mutualists is that interacting trait correlations are stronger than within-lineage allometric relationships.     

Interaction between the black yeast Aureobasidium pullulans and the gall midge Lasioptera ephedricola in gall formation on the desert shrub Ephedra trifurca

Galls produced by the cecidomynd Lastoptera ephedncola on Ephedia trifurca always have a black ring associated with them while galls produced by the congener L ephedrae never do Black ring material after microscopic examination and culture proved to be Aureobasidium pullulans In addition to lacking black ring material neither L ephedrae galls nor healthy stems consistently yielded Aureobasidium on culture Gall and larva size measurements indicated that continued larval presence is not necessary for gall development, suggesting fungus initiated gall formation However inoculation of healthy stems with Aureobasidium caused lesions hut not galls The mycelium m galls did not appear grazed and neither larvae nor pupae contained Aureobasidium propagules suggesting that larvae do not feed directly on fungi These data also suggest that there is no trans-pupal passage of fungus from larvae or pupae to adults Newly emerged females do not carry fungal propagules suggesting that thcy are not inoculated upon exiting the gall Gall position leaf culture and stem culture data suggest that the fungus is picked up from leaves prior to oviposition     

Effects of gall midge infestation on plant growth and growth regulating substances

The biological association between plant and gall-inducing insects can be characterized by growth and developmental abnormalities of the plant tissues caused by the feeding activities of the insects. The relationship between Wachtliella persicariae L. (Diptera: Cecidomyiidae) and Polygonum amphibium L. has been studied.The gall-making larvae settle only on the undifferentiated parts of the leaf and prevent the normal unfolding of the lamina; and there is a close developmental synchronization between the two organisms.The essential reaction of the leaf tissue to the continuous feeding activity of the larvae is primarily a disturbance of the normal development, characterized by an imbalance in growth-regulating substances. Bioassays showed greater amounts of auxin-like substances in the galled tissues. The way in which feeding behaviour, feeding activity and nutritional physiology possibly interfere with the growth-regulating factors of the leaf is discussed.The resulting abnormal leaf growth and development is essential for the normal growth and development of the larvae.

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Zusammenfassung Die biologische Verbindung zwischen Pflanzen und gallenerzeugenden Insekten kann durch Wachstums-und Entwicklungsabnormalitäten der Pflanzengewebe gekennzeichnet werden, welche durch die Fraßtätigkeit der Insekten hervorgerufen werden. Hier wurde die Beziehung zwischen Wachtliella persicariae (Diptera: Cecidomyiidae) und Polygonum amphibium untersucht.Die gallenerzeugende Larve siedelt sich nur auf undifferenzierten Teilen des Blattes an und verhindert die normale Entfaltung der Lamina; es besteht eine enge Synchronisation der Entwicklung beider Organismen.Die wesentliche Reaktion des Blattgewebes auf die fortdauernde Fraßaktivität der Larve stellt zunächst eine Störung der normalen Entwicklung dar, die durch ein Ungleichgewicht der Stoffe charakterisiert ist, die das Pflanzenwachstum kontrollieren. Biotests ergaben in den vergallten Geweven größere Beträge auxinartiger Stoffe. Der Weg, auf dem Fraßverhalten, Fraßaktivität und Ernährungsphysiologie mit den wachstumkontrollierenden Faktoren des Blattes ineinandergreifen, wird diskutiert.Das entstehende anomale Blattwachstum und seine Entwicklung sind für das normale Wachstum und die Ontogenese der Larve wesentlich.

     

Deceit pollination and the effect of deforestation on reproduction in dioecious Schisandra sphenanthera (Schisandraceae) in central China

The fruits of Schisandra sphenanthera (dioecious) are used to produce ‘Nan-Wuweizi',an important Chinese medicine.However,long-term exploitation and habitat destruction have threatened these plants in ...     

Intermittent mass blooming, midnight anthesis and rockbee pollination in Pterocarpus santalinus (Fabaceae)

Pterocarpus santalinus blooms massively in the dry season. Flowering is not continuous during the season and mass bloom recurs only on certain days with 2–5 days interval or sometimes there may be little flowering in between two days of massive bloom. A tree may have five such occasions of mass bloom. At the inflorescence level such intermittent flowering occurs also. The flowers open at the mid of night and are bright yellow in colour. They are typically papilionaceous flag blossoms and thus zygomorphic. They are homogamous and are visited by the rockbee Apis dorsata at moonlit nights or otherwise at dawn and up to 0730 h. The flowers permit several effective visits by the rockbee and as long as the pressure of the bee continues the stamens and stigma project from the keel and permit sternotribic pollination. Controlled pollinations show fruit formation after autogamy (25%), geitonogamy (60%) and xenogamy (85%). Staggered anther dehiscence minimises pollen discounting. Flower bud, flower and fruit abortions occur on a large scale. Natural fruiting is very low compared to the mass bloom. Compatibility to geitonogamy and autogamy may function as a reproductive assurance mechanism. The natural habitat of P. santalinus has a hot dry climate, and the nocturnal flowering and foraging of the rockbee at that time during moonlit nights appear to be an adaptation to avoid the adverse effects of daytime high temperatures.     

Mechanisms and evolution of deceptive pollination in orchids

The orchid family is renowned for its enormous diversity of pollination mechanisms and unusually high occurrence of non-rewarding flowers compared to other plant families. The mechanisms of deception in orchids include generalized food deception, food-deceptive floral mimicry, brood-site imitation, shelter imitation, pseudoantagonism, rendezvous attraction and sexual deception. Generalized food deception is the most common mechanism (reported in 38 genera) followed by sexual deception (18 genera). Floral deception in orchids has been intensively studied since Darwin, but the evolution of non-rewarding flowers still presents a major puzzle for evolutionary biology. The two principal hypotheses as to how deception could increase fitness in plants are (i) reallocation of resources associated with reward production to flowering and seed production, and (ii) higher levels of cross-pollination due to pollinators visiting fewer flowers on non-rewarding plants, resulting in more outcrossed progeny and more efficient pollen export. Biologists have also tried to explain why deception is overrepresented in the orchid family. These explanations include: (i) efficient removal and deposition of pollinaria from orchid flowers in a single pollinator visit, thus obviating the need for rewards to entice multiple visits from pollinators; (ii) efficient transport of orchid pollen, thus requiring less reward-induced pollinator constancy; (iii) low-density populations in many orchids, thus limiting the learning of associations of floral phenotypes and rewards by pollinators; (iv) packaging of pollen in pollinaria with limited carry-over from flower to flower, thus increasing the risks of geitonogamous self-pollination when pollinators visit many flowers on rewarding plants. All of these general and orchid-specific hypotheses are difficult to reconcile with the well-established pattern for rewardlessness to result in low pollinator visitation rates and consequently low levels of fruit production. Arguments that deception evolves because rewards are costly are particularly problematic in that small amounts of nectar are unlikely to have a significant effect on the energy budget of orchids, and because reproduction in orchids is often severely pollen-, rather than resource-limited. Several recent experimental studies have shown that deception promotes cross-pollination, but it remains unknown whether actual outcrossing rates are generally higher in deceptive orchids. Our review of the literature shows that there is currently no evidence that deceptive orchids carry higher levels of genetic load (an indirect measure of outcrossing rate) than their rewarding counterparts. Cross-pollination does, however, result in dramatic increases in seed quality in almost all orchids and has the potential to increase pollen export (by reducing pollen discounting). We suggest that floral deception is particularly beneficial, because of its promotion of outcrossing, when pollinators are abundant, but that when pollinators are consistently rare, selection may favour a nectar reward or a shift to autopollination. Given that nectar-rewardlessness is likely to have been the ancestral condition in orchids and yet is evolutionarily labile, more attention will need to be given to explanations as to why deception constitutes an 'evolutionarily stable strategy'.     

水稻对稻瘿蚊为害补偿力与经济阈值研究

１９９４－１９９８年针对水地稻瘿蚊为害补偿力及经济阈值进行了研究,结果表明：⑴水稻对稻瘿蚊为害具有较强的补偿能力,但基本属于不足补偿,不同标葱梯度其补偿力不同,每造成１％的标葱引起的产量损失远小于１％,其补偿率一般在５５％－８０％之间,产量损失及其损失率与标葱数呈极显正相关,有效穗和产量补偿率与标葱数则呈显负相关;⑵在相同受害程度下,密植损失大,补偿力小,而稀植损失小,补偿能力大,秧苗期补偿效     

Flower visitation and pollination efficiency of some North European butterflies

Summary Nectar plant utilization by butterflies was compared with the abundance of flowering plants on some SW Swedish meadows. The transportation of pollen grains by individual butterflies was analysed using a scanning electron microscope.For the majority of plant species, butteflies were of minor importance as pollinators. Some flowers with protruding sexual organs, e.g. Knautia arvensis, when heavily utilized by butterflies, might also be pollinated by these.For Dianthus deltoides and Viscaria vulgaris, butterfly pollination was found to be important.Several butterfly species, e.g. Plebicula amanda, visited legumes regularly. In spite of this, legume pollen was rarely transported by the butterflies. This suggests these butterflies act as nectar robbers among the legumes.     

The dual origin of the nurse chamber in the ovarioles of the gall midge,Heteropeza pygmaea

Summary By following the lineage of the primordial germ cell and the mesoderm cells during the ontogeny of the gall midge,Heteropeza pygmaea, it has been determined that the nurse chamber of the polytrophic ovarioles of this insect is derived from the descendants of these cells. Such a dual origin for the nurse chamber of an insect ovary is the first of its kind to be reported.