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The complexity of natural communities is the result of interactions among species that coexist within them. Parasitic interactions are among the most common species interaction types, and analysis of parasite-host ranges can advance understanding of how host-parasite pairs structure community interactions across their geographic distributions. Using network analysis and host preference relative index, we analysed host use by the South American mistletoe, Tristerix corymbosus (Loranthaceae), in 22 localities among two biomes: Chilean matorral and temperate forest. The total number of host species recorded was 27, and 40% of these species were non-native. The non-native Populus sp. was shared between biomes. There was a positive relationship between host range and potential host species richness at the studied localities. On average, the mistletoe parasitized each host species relative to its abundance. However, some host species in some localities are more parasitized than expected. Network structure showed a differences in host use between the two biomes: Aristotelia chilensis was central in the temperate forest, with Populus sp. in the Chilean matorral. Host use intensity in the Chilean matorral was higher for non-native species. Tristerix corymbosus has a wide host range and could be considered a generalist parasite across its full geographic distribution, but at local scales, host preferences differed among localities and are related to host coverage. Alterations in community composition, due to natural events or human activities, can modify the availability of possible hosts. Hence, the mistletoe with the described characteristics may be able to change its infection preference while maintaining the interaction functionality.

The high Andean forests of the genus Polylepis (Rosaceae) are threatened by extinction due to anthropogenic effects such as timber extraction, burning, and overgrazing. Some species are also affected by Tristerix chodatianus (Loranthaceae), a hemiparasitic plant which induces progressive host damage. To understand this hemiparasitic process, we evaluated the impact of T. chodatianus on growth and the wood anatomy of Polylepis flavipila using growth rings and digital image processing. We found that P. flavipila has a xeromorphic wood anatomy and that the ecological indices of mesomorphism and vulnerability decrease at higher elevations to avoid embolisms and vessel cavitation. Tristerix chodatianus causes anatomical changes in the host wood, mainly in the last 13 years measured. Alterations include a reduction in the vessel density, and an increase in the vessel diameter and Vulnerability Index, all of which are more evident in downstream sections of parasitized branches. These changes in the xylem tissues increase the vulnerability of the parasitized branches to embolisms and cavitation, thus leading to progressive death of the tree crown. Our study confirms that the analysis of the wood anatomy of parasitized branches can be used to determine the years of colonization of a tree branch by a hemiparasite and that it can be a useful tool to monitor the phytosanitary state of parasitized Polylepis trees.

Premise of research. The New World Loranthaceae correspond to a polyphyletic assembly of hemiparasites that exhibit a high floral diversity in terms of size, merism, groundplan, symmetry, and polli...

There are 11 species of mistletoes in the genus Tristerix (Loranthaceae) endemic to the Andes in South America (1,2). Tristerix verticillatus (Ruiz & Pav.) Barlow & Wiens is distributed on the east side of the Andes from Bolivia to Argentina at high elevations (>1,500 m). On the west side of the Andes, it is only found in Chile where it occurs at low to high elevations (50 to 3,000 m). Along its range, the mistletoe parasitizes more than 25 species, mainly Anarcadiaceae and Rhamnaceae. In February of 2007, it was observed to be parasitizing Schinus fasciculatus (Griseb.) I.M. Johnst. (Anacardiaceae) at two locations in the Sierra de San Luis, Argentina. One location was 6 km south of Las Chacras on Route 31 (32°35′56″S, 65°47′6″W, elevation 1,185 m) and the other was 12 km north of El Trapiche on Route 9 (33°1′21″S, 66°4′11″W, elevation 1,260 m). At these localities, the mistletoe was in full flower and parasitized only one host species, S. fasciculatus. No mortality associated with infection by this mistletoe was observed at either location. Specimens of the mistletoe were collected from both locations and deposited at the Centro Regional Universitario Bariloche Herbarium (BCRU), Río Negro, Argentina. To our knowledge, this is the first report of a Tristerix sp. outside the Andes and extends the eastern distribution of the genus by ≈270 km and also of S. fasciculatus serving as a host for T. verticillatus since previous collections were from other species of Schinus. References: (1) G. C. Amico et al. Am. J. Bot. 94:558, 2007. (2) J. Kuijt, Syst. Bot. Monogr. 19, 1988.

New combinations are here proposed for Maracanthus costaricensis (Kuijt) Kuijt [≡ Oryctina costaricensis Kuijt] and Passovia pedunculata (Jacq.) Kuijt [≡ Loranthus pedunculatus Jacq.]. Five new species of Loranthaceae from South America are also described and illustrated: Psittacanthus longiflorus Kuijt from Peru, Struthanthus cajamarcanus Kuijt from Peru, S. ophiostylus Kuijt from Peru, S. truncatus Kuijt from Colombia, and Tristerix divaricatus Kuijt from Peru. The name Passovia pedunculata is neotypified.

A new, large-flowered species of Tristerix, T. rhodanthus, is described and illustrated from Bolivia

The mistletoe Tristerix corymbosus (Loranthaceae) is present in the temperate forest and Chilean matorral biomes of Chile and northwest Patagonia. The closely related cactus-specific species, T. aphyllus, occurs only in the matorral biome. The population structure of these mistletoes was examined to determine whether the distribution of haplotypes corresponds mostly to geographic zone, biome, or other biotic factors. Samples from 108 individuals in 26 localities of T. corymbosus and 13 individuals in four localities of T. aphyllus were collected. Sequences were obtained from two chloroplast genome regions: the atpB-rbcL spacer and the trnL-F region. Haplotypes were analyzed using parsimony and Bayesian trees as well as parsimony networks. All methods placed the haplotypes in four clades, one of which corresponded to T. aphyllus and the others to T. corymbosus. Within T. corymbosus, the different clades did not correlate with biome, geographical region, host, or any apparent morphological feature of the mistletoe. The morphologically distinct cactus parasite T. aphyllus likely arose in sympatry from an unspecialized tree parasite, T. corymbosus, after a host switch. The present day haplotype distribution is complex and resulted from post-glaciation migrations from multiple Pleistocene refugia.

Loranthaceae (73 genera and ca. 900 species) comprise mostly aerial hemiparasitic plants. Three monotypic genera considered relicts are root parasites. The family is diverse in tropical areas, but representatives are also found in temperate habitats. Previous classifications were based on floral and inflorescence morphology, karyological information, and biogeography. The family has been divided into three tribes: Nuytsiae, Elytrantheae (subtribes Elytranthinae and Gaiadendrinae), and Lorantheae (subtribes Loranthinae and Psittacanthinae). Nuytsiae and Elytrantheae are characterized by a base chromosome number of x = 12, whereas subtribes Loranthinae (x = 9) and Psittacanthinae (x = 8) numbers are derived via aneuploid reduction. To elucidate the phylogeny of the family, we analyzed sequences from five genes (nuclear small and large subunit rDNA and the chloroplast genes rbcL, matK, and trnL-F) representing most genera using parsimony, likelihood, and Bayesian inference. The three root parasites, Nuytsia, Atkinsonia, and Gaiadendron, are supported as successive sister taxa to the remaining genera, resulting in a monophyletic group of aerial parasites. Three major clades are resolved each corresponding to a subtribe. However, two South American genera (Tristerix and Notanthera) and the New Zealand genus Tupeia, which were previously classified in subtribe Elytranthinae, are weakly supported as part of a clade representing the South American subtribe Psittacanthinae.

Floral diversification in Loranthaceae reaches its highest peak in the Andes. The flowers of the exclusively Andean genus Tristerix exhibit tubular and vividly coloured flowers pollinated by hummingbirds. We studied inflorescence and flower morphoanatomy of the two Colombian species, T. longebracteatus and the highly endangered T. secundus . Both species have terminal racemes with up to 26 ebracteolate flowers, of which the proximal one opens and sets fruits first. The slightly irregular calyx initiation is followed by the simultaneous initiation of petals and the successive initiation of stamens. Anthesis is fenestrate, explosive, and triggered by the tension of the style against the abaxial petals, a mode so far not reported in Loranthaceae . Anthetic petals spread symmetrically in T. longebracteatus and asymmetrically in T. secundus . Nectar is produced by a supraovarial disk and by the petal mesophyll. Floral lifespan lasts up to 20 days. The hummingbirds Eriocnemis vestita and Pterophanes cyanopterus are the likely pollinators of T. secundus . Morphological traits are inconclusive to support one of the two competing sister group relationships that involve Tristerix , as the lack of cataphylls in renewal shoots links Ligaria and Tristerix , whereas the terminal inflorescences support its relationship with Desmaria and Tupeia .

The alteration and transformation of the areas surrounding native forests due to anthropogenic disturbance can result in differences near this newly created boundary, termed 'edge effects'. Our study describes the consequences of edge creation over two successive stages in the life cycle of a hemi-parasitic mistletoe (Tristerix corymbosus), which determine its reproductive success, in temperate austral forests. We assessed how flower production and pollinator visits change with distance to the nearest forest edge and how these changes affect fruit set, fruit and seed size, and fruit removal by seed dispersers. Edge effects were dominated by fruit removal, which increased with the distance to the edge, height in the canopy and fruit availability. As a result, plant reproduction (in terms of seeds produced and fruits removed, which putatively leads to higher seed dispersal) decreased strongly near to forest edges. In contrast, visitation rates of the main pollinator (the hummingbird) were unaffected by edges, and their strong effects on fruit set (including the alleviation of quality pollen limitation arising in the forest interior) might be mitigating the decrease in bumblebee visitation near to forest edges. Synthesis. Our study shows clearly how secondary and tertiary responses to forest edges acted in opposite directions (increasing or decreasing plant reproductive performance), highlighting the need to study several successive processes that impact upon plant fitness under disturbance. Preserving relatively large patches of old-growth forest with low perimeter/area ratios would be key to the habitat requirements of the main disperser and pollinator and thus for mistletoe reproductive performance. © 2013 The Authors. Journal of Ecology © 2013 British Ecological Society., Funding by the BBVA Foundation (project DOSEL) and the Basque Country Government (pre-doctoral fellowship for A.M.) made this study possible. A.R.L. received funding from the JAEDOC program of the Spanish Research Council (CSIC)

Nectar robbing may have an indirect negative effect on plant reproduction by discouraging legitimate pollinator species from visiting robbed flowers. In this study, we set up a 2 × 2 factorial design with nectar-robbing ants and hummingbird pollination to test for non-additive effects on fruit set, seed mass, and seed germination of the leafless mistletoe Tristerix aphyllus (Loranthaceae). Even though ants caused conspicuous damage at the base of the floral tubes, nectar availability was reduced by only 8 % in the presence of ants. The green-backed firecrown Sephanoides sephaniodes was insensitive to the presence of ants. Rather, the bird responded to flower number and the presence or the absence of damage, but not to the extent of damage within inflorescences. As hummingbirds were largely insensitive to variation in nectar robbing, the interaction ant × hummingbird had no effect on plant-reproductive success. Thus, the factorial experiment did not provide evidence for indirect negative effects of nectar robbing on plant reproduction. These results suggest that indirect effects of nectar robbers on pollinator behaviour may occur under a more restricted set of conditions than those previously considered. We suggest that the low amount of nectar removed by nectar-robbing ants was insufficient for hummingbirds to avoid robbed flowers, which restricted the potential for non-additive effects.

Phylogenies can provide valuable information on biotic and abiotic factors associated with speciation. We examined species relationships in Tristerix (Loranthaceae), a genus of 11 species with an Andean distribution from Colombia to Chile. A previous classification divided Tristerix into subgenera Tristerix (two species) and Metastachys (nine species). We tested this classification by generating a molecular phylogeny of the genus using nuclear ribosomal DNA ITS and chloroplast atpB-rbcL intergenic spacer and trnL-F regions. All partitions generally gave congruent trees, thus a combined analysis was conducted. Tristerix was composed of a northern clade (six species) and a southern clade (four species). Tristerix verticillatus and T. penduliflorus (Metastachys) were strongly supported as members of the (southern) subgenus Tristerix clade. Speciation appears to be correlated with the emergence of matorral and cloud forest biomes and is driven by interactions with pollinators and seed dispersers. Tristerix aphyllus is sister to T. corymbosus of the matorral, not to neighboring temperate forest populations, thus rendering the latter species paraphyletic. This ecological speciation event may have occurred in sympatry. Tristerix provides excellent examples of how, during the orography of the Andes, many dynamic and interacting ecological factors have influenced their speciation.