A new species of Oryctina (Loranthaceae) from Guyana

A new species ofOryctina (Loranthaceae) from Guyana,O. atrolineata Kuijt is described and illustrated. It possesses one-flowered inflorescences, the flowers being hexamerous and each subtended by a bract and two minute bracteoles. A peculiarity of the style is a distinctive fusiform, subterminal swelling.Oryctina atrolineata is closely related, and similar to,O. myrsinites (Eichler) Kuijt.     

The effect of nitrogen supply on growth and water-use efficiency of xylem-tapping mistletoes

Xylem-tapping mistletoes are known to have normally a higher rate of transpiration and lower water-use efficiency than their hosts. The relationships between water relations, nutrients and growth were investigated for Phoradendron juniperinum growing on Juniperus osteosperma (a non-nitrogen-fixing tree) and for Phoradendron californicum growing on Acacia greggii (a nitrogen-fixing tree). Xylem sap nitrogen contents were approximately 3.5 times higher in the nitrogen-fixing host than in the non-nitrogen-fixing host. The results of the present study show that mistletoe growth rates were sevenfold greater on a nitrogen-fixing host. At the same time, however, the differences in water-use efficiency between mistletoes and their hosts, which were observed on the non-nitrogen-fixing host did not exist when mistletoes were grown on hosts with higher nitrogen contents in their xylem sap. Growth rates and the accumulation of N, P, K, and Ca as well as values for carbon-isotope ratios of mistletoe tissues support the hypothesis that the higher transpiration rates of mistletoes represent a nitrogen-gathering mechanism.Abbreviation ¹³C carbon-isotope ratio Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday     

Physiology of the interaction of angiosperm parasites and their higher plant hosts

Abstract. Interactions between parasitic angiosperms and their hosts occur at the level of seed germination, haustorial development and resource transfer. Chemicals released from the host function as cues for host recognition, and trigger germination as well as haustorial initiation. Transpiration is a key process regulating solute transfer from host to parasite, and some parasitie plants have unusual stomatal characteristics. Although solute transfer is apoplastic, the haustorium appears to play a role in regulating solute composition. Host responses to infection are reviewed, and it is concluded that competition for water and solutes are unlikely to play a major role in determining reductions in host productivity: metabolic incompatability is suggested to be the major cause of this.     

Mistletoe macroecology: spatial patterns in species diversity and host use across Australia

Mistletoes are parasitic plants, the spatial distributions of which are poorly understood on macroecological scales. Because of their highly unusual life history, investigating mistletoe macroecology may provide new insight into broad‐scale patterns in species distributions. We collated data on the spatial distribution and host use of 65 species of Loranthaceous mistletoes across the continent of Australia, and tested two predictions. First, we predicted mistletoe diversity would be unrelated to productivity (i.e. evapotranspiration and precipitation), as the parasitic lifestyle might relax environmental constraints on their distributions. Second, we predicted that mistletoe host ranges (number of infected host species) would increase in areas with more potential host species. The basis of this prediction is that greater host generality is likely to evolve in regions with greater host diversity because of greater unpredictability in encounter rates with particular host species. Conversely, in regions with fewer potential hosts, randomly dispersing mistletoe propagules are likely to repeatedly encounter particular host species, thus favouring the evolution of host specialization. The results were generally consistent with these predictions. Mistletoe diversity across Australia was weakly associated with environmental conditions, whereas mistletoe host ranges increased significantly with total plant diversity. Macroecological patterns in mistletoes are unusual. In contrast to non‐parasitic plants, mistletoe diversity is poorly correlated with productivity. Host ranges varied predictably across Australia, providing the first quantitative support for the hypothesis that mistletoes in diverse regions tend to be host generalists, whereas mistletoes in depauperate regions tend to be host specialists. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 459–468.     

Parasites on parasites: hyper-, epi-, and autoparasitism among flowering plants

All organisms engage in parasitic relations, as either parasites or hosts. Some species may even play both roles simultaneously. Among flowering plants, the most widespread form of parasitism is characterized by the development of an intrusive organ called the haustorium, which absorbs water and nutrients from the host. Despite this functionally unifying feature of parasitic plants, haustoria are not homologous structures; they have evolved 12 times independently. These plants represent ca. 1% of all extant flowering species and show a wide diversity of life histories. A great variety of plants may also serve as hosts, including other parasitic plants. This phenomenon of parasitic exploitation of another parasite, broadly known as hyper- or epiparasitism, is well described among bacteria, fungi, and animals, but remains poorly understood among plants. Here, we review empirical evidence of plant hyperparasitism, including variations of self-parasitism, discuss the diversity and ecological importance of these interactions, and suggest possible evolutionary mechanisms. Hyperparasitism may provide benefits in terms of improved nutrition and enhanced host–parasite compatibility if partners are related. Different forms of self-parasitism may facilitate nutrient sharing among and within parasitic plant individuals, while also offering potential for the evolution of hyperparasitism. Cases of hyperparasitic interactions between parasitic plants may affect the ecology of individual species and modulate their ecosystem impacts. Parasitic plant phenology and disperser feeding behavior are considered to play a major role in the occurrence of hyperparasitism, especially among mistletoes. There is also potential for hyperparasites to act as biological control agents of invasive primary parasitic host species.     

桑寄生植物繁殖物候研究概述

桑寄生植物是一类自身可以进行光合作用的半寄生性灌木, 作为森林和林地的关键性资源可为鸟类等动物分类群提供重要的食物资源和巢址, 并影响当地的生物多样性。桑寄生植物隶属于檀香目, 包括5科88属约1,600种, 除极地、部分高寒和干旱沙漠地区外均有分布。桑寄生植物繁殖物候的研究对于了解“寄主植物-桑寄生植物-传粉/种子散布者系统”中物种相互作用网络的维持机制、生态系统结构的稳定性具有重要意义。本文综述了桑寄生植物在景观、群落和种群尺度上繁殖物候的表现类型, 发现桑寄生植物主要通过繁殖物候异步的方式延长物候期, 维持与传粉/种子散布者持久的互惠关系以保障自身种群的繁衍。该领域经过近年的发展, 已从单一地描述繁殖物候的表现类型到探究系统中寄主植物、传粉/种子散布者以及桑寄生植物自身生物学特性等因素的分析。通过前人的研究发现桑寄生植物繁殖物候对于该系统内相互作用的双方或多方有重要的适应意义, 今后首先应该对桑寄生植物的基础生物学背景进行研究, 然后还应加强实验验证, 进行多因素综合分析等来探讨桑寄生植物繁殖物候的生态学意义。     

Unravelling host-mediated effects on hemiparasitic Mexican mistletoe Psittacanthus calyculatus (DC.) G. Don traits linked to mutualisms with pollinators and seed dispersers

Aims While the influence of mistletoe–host interactions on each other’s evolution is well-recognized, the role of interactions between mistletoes and its mutualistic pollinators and seed dispersers mediated by host species is relatively unexplored.     

Interactions among fire, insects and pathogens in coniferous forests of the interior western United States and Canada

1 Natural and recurring disturbances caused by fire, native forest insects and pathogens have interacted for millennia to create and maintain forests dominated by seral or pioneering species of conifers in the interior regions of the western United States and Canada. 2 Changes in fire suppression and other factors in the last century have altered the species composition and increased the density of trees in many western forests, leading to concomitant changes in how these three disturbance agents interact. 3 Two‐ and three‐way interactions are reviewed that involve fire, insects and pathogens in these forests, including fire‐induced pathogen infection and insect attack, the effects of tree mortality from insects and diseases on fuel accumulation, and efforts to model these interactions. 4 The emerging concern is highlighted regarding how the amount and distribution of bark beetle‐caused tree mortality will be affected by large‐scale restoration of these fire‐adapted forest ecosystems via prescribed fire. 5 The effects of fire on soil insects and pathogens, and on biodiversity of ground‐dwelling arthropods, are examined. 6 The effects of fire suppression on forest susceptibility to insects and pathogens, are discussed, as is the use of prescribed fire to control forest pests.     

Epiphytes in human settlements in rural Panama

Background: An ever-increasing proportion of tropical ecosystems are affected by on-going land-use changes, stressing the importance of understanding how organisms cope with biotic and abiotic challenges outside their natural habitat. An important group in the tropics are vascular epiphytes, whose response to human disturbance is poorly understood.

Aims: Creating a baseline data set of epiphyte diversity in human settlements and assessing differences with assemblages of less disturbed habitats.

Methods: We surveyed the vascular epiphyte assemblages in 25 settlements of south-west Panama along a rainfall gradient. We tested how epiphyte assemblages were affected by human disturbance and climate by comparing our data to that of pastures and forest.

Results: Almost half (238 of 499) of all studied trees hosted at least one epiphyte. Altogether, 10,700 epiphytes of 56 species were found. Rainfall strongly affected both composition and diversity of epiphyte assemblages, whereas geographic proximity did not. In settlements, the species pool was considerably smaller than in pastures and undisturbed forest; however, settlements’ diversity was only significantly lower compared to pastures.

Conclusions: Epiphyte assemblages in settlements had a diminished species pool but diversity per tree was comparable to less disturbed habitats. Unsurprisingly, rainfall seems to be the main determinant of epiphyte diversity in rural settlements.