Interspecific variation and ontogenetic change in antiherbivore defense in myrmecophytic Macaranga species

The present study examined whether or not coexisting congeneric plant species have different defense strategies against herbivores, and the intensity of defense changes ontogenetically. We focused on nine myrmecophytic Macaranga species and estimated the intensity of non-biotic and biotic defense by the degree of leaf damage in ant-free and ant-occupied plants, respectively. Ant colonization of myrmecophytic Macaranga species occurred in the early stage of plant development (5–50 cm-tall seedlings). Following the colonization, damage by leaf eaters was minimized and stable during the ontogenetic development of the host plants due to protection by ants. In ant-free trees, however, herbivore damage was immense in seedlings and decreased as trees grew. Interspecific comparison of leaf damage and herbivore fauna supported that coexisting congeneric plants differ in their types of non-biotic (chemical/structural) defense: without ant protection, Macaranga beccariana, for example, was somewhat resistant to leaf eaters but susceptible to gall-makers, Macaranga trachyphylla was heavily infested by generalist leaf eaters, and Macaranga winkleri was exploited by ant-predatory birds. Despite these variations in chemical/structural defense, ant-colonized plants were generally well defended by ants against all kinds of herbivores. This suggests that the individual host-specific ant mutualists are well adapted to deter the chemically or structurally adapted herbivores. These results imply that in the history of diversification in the Macaranga–ant–herbivore system, a sequence of mutual counter adaptation took place not only between plants and herbivores but also between ants and herbivores.     

Food bodies and their significance for obligate ant-association in the tree genus Macaranga (Euphorbiaceae)

FIALA, B. & MASCHWITZ, U., 1992. Food bodies and their significance for obligate ant-association in the tree genus Macaranga (Euphorbiaceae). The production of extrafloral nectar and food bodies plays an important role in many tropical ant-plant mutualisms. In Malaysia, a close association exists between ants and some species of the pioneer tree genus Macaranga (Euphorbiaceae). Macaranga is a very diverse genus which exhibits all stages of interaction with ants, from facultative to obligatory associations. The ants nest inside the hollow internodes and feed mainly on food bodies provided by the plants. Food body production had previously been reported only in myrmecophytic Macaranga species, where it is usually concentrated on protected parts of the plants such as recurved stipules. We found that non-myrmecophytic Macaranga species also produce food bodies on leaves and stems, where they are collected by a variety of ants. Levels of food body production differ between facultatively and obligatorily ant-associated species but also among the various non-myrmecophytes. This may be related to the degree of interaction with ants. Food body production starts at a younger age in the myrmecophytic species than in the transitional or non-myrmeccophytic Macaranga. Although food bodies of the non-inhabited Macaranga species are collected by a variety of ants, there is no evidence of association with specific ant species. Our observations suggest that food bodies enhance the evolution of ant-plant interactions. Production of food bodies alone, however, does not appear to be the most important factor for the development of obligate myrmecophytism in Macaranga.     

Non-additive effects of herbivores and pollinators on Erysimum mediohispanicum (Cruciferae) fitness

In this study, the non-additivity of effects of herbivores and pollinator on fitness of the plant Erysimum mediohispanicum (Cruciferae) has been experimentally tested. The abundance and diversity of the pollinator assemblage of plants excluded from and exposed to mammalian herbivores, and the combined effect of pollinators and herbivores on plant reproduction were determined over a period of 2 years. Pollinator abundance was higher and diversity was lower on plants excluded from herbivores. Furthermore, the experimental exclusions demonstrated that both pollinators and herbivores affected plant fitness, but their effects were not independent. Herbivores only had a detrimental effect on plant fitness when pollinators were present. Similarly, pollinators enhanced fitness only when herbivores were excluded. This outcome demonstrates that the importance of pollinators for plant fitness depends on the occurrence of herbivores, and suggests that herbivores may hamper pollinator-mediated adaptation in plants.     

A chloroplast genealogy of myrmecophytic Macaranga species (Euphorbiaceae) in Southeast Asia reveals hybridization, vicariance and long-distance dispersals

Macaranga (Euphorbiaceae) includes about 280 species with a palaeotropic distribution. The genus not only comprises some of the most prominent pioneer tree species in Southeast Asian lowland dipterocarp forests, it also exhibits a substantial radiation of ant-plants (myrmecophytes). Obligate ant-plant mutualisms are formed by about 30 Macaranga species and 13 ant species of the genera Crematogaster or Camponotus. To improve our understanding of the co-evolution of the ants and their host plants, we aim at reconstructing comparative organellar phylogeographies of both partners across their distributional range. Preliminary evidence indicated that chloroplast DNA introgression among closely related Macaranga species might occur. We therefore constructed a comprehensive chloroplast genealogy based on DNA sequence data from the noncoding ccmp2, ccmp6, and atpB-rbcL regions for 144 individuals from 41 Macaranga species, covering all major evolutionary lineages within the three sections that contain myrmecophytes. A total of 88 chloroplast haplotypes were identified, and grouped into a statistical parsimony network that clearly distinguished sections and well-defined subsectional groups. Within these groups, the arrangement of haplotypes followed geographical rather than taxonomical criteria. Thus, up to six chloroplast haplotypes were found within single species, and up to seven species shared a single haplotype. The spatial distribution of the chloroplast types revealed several dispersals between the Malay Peninsula and Borneo, and a deep split between Sabah and the remainder of Borneo. Our large-scale chloroplast genealogy highlights the complex history of migration, hybridization, and speciation in the myrmecophytes of the genus Macaranga. It will serve as a guideline for adequate sampling and data interpretation in phylogeographic studies of individual Macaranga species and species groups.     

Microsatellite markers for the palaeotropic pioneer tree genus Macaranga (Euphorbiaceae) and their cross‐species transferability

We developed primer sequences for five polymorphic microsatellite loci in the tropical ant‐plant genus Macaranga (Euphorbiaceae). Population genetic parameters were determined on the basis of 30 individuals from each of two Macaranga species in Borneo. Allele numbers per locus ranged from three to 13. Expected and observed heterozygosities ranged from 0.160 to 0.850 and from 0.130 to 0.700, respectively. Four of the five primer pairs cross‐amplify polymorphic PCR products in a wide range of Macaranga species.     

Isolation and characterization of 11 new microsatellite markers for Macaranga (Euphorbiaceae)

We provide primer sequences for 11 new polymorphic microsatellite markers developed in the tropical ant-plant genus Macaranga (Euphorbiaceae), after enrichment cloning of Macaranga tanarius and Macaranga hypoleuca. Allele numbers per locus ranged from two to 16 among 20 accessions of M. tanarius, and from three to 10 among 22 accessions of M. hypoleuca. Observed and expected heterozygosities ranged from 0.150 to 0.900 and from 0.375 to 0.894 in M. tanarius, and from 0.545 to 1.000 and from 0.434 to 0.870 in M. hypoleuca, respectively. Six of the 11 primer pairs successfully cross-amplified polymorphic polymerase chain reaction products in Macaranga winkleri.     

AFLP analysis of phylogenetic relationships among myrmecophytic species of Macaranga (Euphorbiaceae) and their allies

The palaeotropic pioneer tree genus Macaranga Thouars (Euphorbiaceae) is characterized by various types of mutualistic interactions with specific ant partners (mainly Crematogaster spp.). About 30 species are obligate ant-plants (myrmecophytes). We used amplified fragment length polymorphism (AFLP) markers to assess phylogenetic relationships among 108 Macaranga specimens from 43 species, including all available taxa from the three sections known to contain myrmecophytes. Eight primer combinations produced 426 bands that were scored as presence/absence characters. Banding patterns were analyzed phenetically, cladistically and by principal coordinates analysis. Monophyly of section Pruinosae is clearly supported. There is also good evidence for a monophyletic section Pachystemon that includes the puncticulata group. The monophyly of section Winklerianae and relationships between the three sections remain ambiguous. Section Pachystemon is subdivided into four well-supported monophyletic subclades that presumably correspond to taxonomic entities.We acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG Fi606/4-1, DFG We1830/2-1, 4-1 and 4-2), which in part was granted in the frame of the DFG-SPP 1127 Radiations: origins of biological diversity. Part of the plant material was kindly supplied by Dr. H. Feldhaar (University of Würzburg), Dr. U. Moog (University of Kassel) and Dr. F. Slik (Leiden University Branch, Nationaal Herbarium Nederland). We thank the University of Malaysia (Dr. Rosli b. Hashim) and Taman Taman Sabah (Datuk Lamri Ali; Dr. J. Nais) for permits and logistic support, and EPU for permission to conduct research in Malaysia.     

Slippery ant-plants and skilful climbers: selection and protection of specific ant partners by epicuticular wax blooms in Macaranga (Euphorbiaceae)

 In many ant-plant species of the genus Macaranga in South-East Asia, conspicuous blooms of epicuticular wax crystals cover the stem surface. We found that many ant species were unable to walk on these surfaces. Only the specific ant partners of glaucous Macaranga host plants were capable of moving on the slippery stems without difficulty. Therefore, the epicuticular coatings of Macaranga myrmecophytes appear to have a selective function and protect the associated ants against competitors. The epicuticular aggregates function as a physical barrier; no evidence of chemical repellence was found. The extent to which ”foreign” ant species are excluded from a tree strongly depends on inclination, diameter and length of the glaucous stem sections. The particular growth form of some glaucous Macaranga ant-plants enhances the influence of the wax barriers. The ant associates of glaucous and glossy Macaranga ant-plants (genera Crematogaster and Camponotus) differ strongly in their capacity to adhere to the glaucous stems. For this reason, the wax blooms in Macaranga can act as an ecological isolation mechanism for the sympiotic ants. Within the genus Macaranga, we find a high correspondence between the occurrence of glaucousness and obligatory ant association (50% in ant-plants; 6.7% in non-myrmecophytes). The genus Macaranga thus represents one of the few cases known so far where epicuticular wax crystals are likely to have evolved in relation to insects. Received: 2 January 1997 / Accepted: 9 June 1997     

Leaf damage effects on leaf expansion timing in Mallotus japonicus (Euphorbiaceae)

For many plant species, biotic factors determining the timing of leaf expansion have not been elucidated sufficiently. We investigated the effects of leaf damage on the timing of leaf defoliation and on the timing of leaf expansion in Mallotus japonicus (Euphorbiaceae). The degree of leaf herbivory of M. japonicus in the field was examined in summer, with subsequent investigation of the date of leaf defoliation in autumn and that of leaf expansion the following spring. Effects of artificial leaf damage on the timing of leaf defoliation and of leaf expansion were also examined in a greenhouse. In the field, the degree of leaf herbivory sustained by M. japonicus did not affect the timing of defoliation. However, the timing of leaf expansion the next spring advanced earlier, concomitantly with the increase of leaf damage during the previous year. Fifty per cent artificial leaf damage in M. japonicus saplings in summer had no marked effect on the timing of leaf defoliation in autumn. However, the effects of leaf damage on the timing of leaf expansion were apparent the following spring: the damaged plants expanded new leaves ca. 8 days earlier than control plants did. Plants that showed earlier leaf expansion tended to have a higher shoot/root ratio. Our results demonstrate that the plants advance the timing of their leaf expansion in response to leaf damage sustained during the previous year, suggesting that the shoot/root ratio is a determining factor.     

Testing the potential for conflicting selection on floral chemical traits by pollinators and herbivores: predictions and case study

1.  There are myriad ways in which pollinators and herbivores can interact via the evolutionary and behavioural responses of their host plants.
2.  Given that both herbivores and pollinators consume and are dependent upon plant-derived nutrients and secondary metabolites, and utilize plant signals, plant chemistry should be one of the major factors mediating these interactions.
3.  Here we build upon a conceptual framework for understanding plant-mediated interactions of pollinators and herbivores. We focus on plant chemistry, in particular plant volatiles and aim to unify hypotheses for plant defence and pollination. We make predictions for the evolutionary outcomes of these interactions by hypothesizing that conflicting selection pressures from herbivores and pollinators arise from the constraints imposed by plant chemistry.
4.  We further hypothesize that plants could avoid conflicts between pollinator attraction and herbivore defence through tissue-specific regulation of pollinator reward chemistry, as well as herbivore-induced changes in flower chemistry and morphology.
5.  Finally, we test aspects of our predictions in a case study using a wild tomato species, Solanum peruvianum , to illustrate the diversity of tissue-specific and herbivore-induced differences in plant chemistry that could influence herbivore and pollinator behaviour, and plant fitness.     

The reproductive biology and effective pollinators of the endangered beardtonguePenstemon penlandii (Scrophulariaceae)

Penland's beardtongue, a rare endemic plant of the Colorado Plateau, displays a mixed breeding system. Plants are partially self-compatible but set more fruits when cross-pollinated than when self-pollinated. Fruit production is significantly increased by pollinators. However, in two years of study there was no indication that fruit set was being limited by inadequate pollinator visitation. Pollinator effectiveness was judged by correlating bee behavior at the flowers with analysis of the pollen carried on bee bodies. The most important pollinators were native megachilid bees, particularly in the genusOsmia. The bees that pollinate Penland's beardtongue are essential to its reproduction and must be preserved along with this rare plant.     

Choice,performance and heritability of performance of specialist and generalist insect herbivores towards cacalol and seneciphylline,two allelochemicals of Adenostyles alpina (Asteraceae)

We compared the effects of a sesquiterpene (ST, cacalol) and a pyrrolizidine alkaloid (PA, seneciphylline), both occurring in Adenostyles alliariae, on food choice and performance of specialist and generalist insect herbivores which are all known to feed or live on A. alliariae. In choice experiments we investigated whether the compounds were preferred, deterrent or had no effect. All specialist species Aglaostigma discolor (Hymenoptera, Tenthredinidae), Oreina cacaliae (Coleoptera, Chrysomelidae) and O. speciosissima avoided feeding when confronted with the combination of compounds. Only larvae of A. discolor avoided the single ST treatment as well. Larvae of the generalist species Callimorpha dominula (Lepidoptera, Arctiidae), Cylindrotoma distinctissima (Diptera, Tipulidae) and Miramella alpina (Caelifera, Acrididae) generally avoided feeding from PA, ST and PAST treatments. The only exception were caterpillars of C. dominula which were indiscriminate towards PA when naive, and preferred to feed on the PA treatment when they had experienced the compound before. Performance, measured as the growth of larvae on the different treatments in a no choice situation over a period of 10–17 days, was not different between treatments in the specialist leaf beetles O. cacaliae and O. speciosissima. Their avoidance of the combination treatment in the choice experiments had no obvious effect on growth when forced to feed from the treatment. In the generalist C. dominula only the high concentration combination treatment (PAST) reduced growth of the larvae due to decreased consumption. In C. distinctissima we found reduced growth in all treatments except one (PA3%). Poor growth performance in C. distinctissima was due to postingestive physiological effects of all treatments and additionally to consumption reduction in high‐dose ST treatments. Genetic variability (broad sense heritability) of growth performance metabolism varied in accordance with the specialization degree of the species. O. cacaliae, the most specialized species, had no significant heritability; O. speciosissima, the less specialized specialist, had a heritability of 0.46; C. dominula, the PA adapted generalist species, had a heritability of 0.64; C. distinctissima, the generalist with no apparent adaptations, had a heritability of 0.84.     

琼花生殖器官结构及传粉昆虫的观察

为了探讨影响琼花Viburnum macrocephalum f.keteleeri有性生殖的因素,对其生殖生物学和传粉生物学进行了研究。研究内容主要包括琼花花部特征、生殖器官解剖结构、花粉活力、花粉胚珠比(P/O)、繁育系统、传粉形式、传粉昆虫和花粉管生长路径等。结果表明:(1)琼花聚伞花序由大型不孕花和小型可孕花组成,可孕花雌雄蕊发育正常,雄蕊5枚,雌蕊1枚,干型柱头,单子房,倒生胚珠;不孕花的雌雄蕊在发育早期正常,而在花期时退化。雄蕊退化表现为雄蕊消失、花丝缩短或消失或花药大小不一;而雌蕊退化表现为雌蕊缩小或柱头开裂;有时雌雄蕊也存在瓣化现象。(2)自然条件下,单花花粉活性在散粉4–5d后明显下降,居群花粉活力在4月25日–28日开始显著下降。(3)花粉胚珠比P/O值为12800–18700,属专性异交型;繁育系统为异株异花授粉,属虫媒传粉植物。(4)可孕花大量散粉时间为9:00–16:00,昆虫访花高峰时段为11:00–15:00,访花昆虫中以蝶类和蜂类为主,蝶类访花频率最高。(5)落置柱头的花粉萌发率较高,花粉粒授粉后1h左右开始萌发,花粉管从柱头乳突细胞的间隙穿入花柱,沿花柱中央引导组织生长,18h左右进入子房,20h左右从珠孔进入胚囊。讨论了琼花的不孕花形成、花部结构适应、花型演化趋势、低结实率和花粉管生长特点。     

Epiphytes on the rocky intertidal red alga RhodomelaLarix (Turner) C. Agardh: Negative effects on the host and food for herbivores?

The diversity of epiflora and fauna associated with a dominant turf-forming alga was examined in intertidal communities on the central Oregon coast. Epiphytes associated with the red alga, Rhodomelalarix (Turner) C. Agardh, were examined by surveying intertidal areas for the presence of epiphytes, and by following changes in epiphyte cover in marked quadrats of R. larix. The alga is host for at least 17 species of sessile plants and animals. To determine the role of some of the larger epiphytes in the community, Rhodomela plants were marked and monitored and herbivore feeding was examined. Data suggest that epiphytes decrease the growth rate of their host, increase the probability of axis breakage and decrease reproductive output. Epiphytes provide food for littorine snails and gammarid amphipods that live in the beds of the plant. Amphipods were found to decrease epiphyte cover on R. larix in laboratory tanks, suggesting that these herbivores may have beneficial effects on the host plant.     

Formation and structure of food bodies in Cordia nodosa (Boraginaceae)

Cordia nodosa Lamark (Boraginaceae) is a myrmecophyte (i.e., plants housing ants in hollow structures) that provisions associated ants with food bodies (FBs) produced 24 h a day. Distributed over all the young parts of the plants, they induce ants to forage continually and so to protect the plants. Metabolites are stored in the inner cells of C. nodosa FBs as they form. In addition the peripheral cells have an extrafloral nectary-like function and secrete a substance that covers the FBs. The amalgam of these two functions, distinct in other known cases, is discussed taking into account the origin of FBs and extrafloral nectaries.     

不同食料植物对棉古毒蛾生长发育和繁殖的影响

在恒温(28±1)℃、恒湿(80±5)%RH条件下,研究了莲雾、芒果、荔枝、龙眼、毛叶枣、木菠萝等6种食料植物对棉古毒蛾的生长发育和繁殖的影响。结果表明,棉古毒蛾能在这6种食料植物上完成其世代循环。其发育历期、雌蛹重、存活率、成虫繁殖力和寿命等,在6种寄主植物间均存在显著差异,其中莲雾和芒果是最适宜的寄主植物,荔枝和龙眼是不适宜的寄主植物。