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Morphological and genetic diversification of Russula floriformis, sp. nov., along the Isthmus of Panama

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Abstract

Species of Russula are ubiquitous members of ectomycorrhizal fungal communities in tropical ecosystems. However, an important part of the total tropical diversity of this genus and its biogeo-graphic patterns is unknown due to the lack of studies on Russula in tropical ecosystems. We combined molecular, morphological, ecological, and biogeographic data to elaborate concepts for two new subspecies of R. floriformis (subsection Substriatinae). Russula floriformis subsp. floriformis and R. floriformis subsp. symphoniae are described as new from montane forest dominated by Quercus and/or Oreomunnea (Fagales) from Colombia and Panama, respectively. Phylogenies were constructed using nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS), D1-D2 domains of nuc 28S rDNA (28S), and partial regions of the second largest subunit of RNA polymerase II (rpb2) and translation elongation factor 1-alpha (tef1). Similar environmental conditions, similar morphology, and an ITS sequence similarity higher than 99% with only three different positions indicate that these two subspecies are closely related. Detailed observations of microscopic structures and analyses of further DNA loci, however, revealed morphological and molecular characteristics that allow distinguishing the two subspecies of R. floriformis. Spatial distribution and phylogenetic proximity of the two Russula subspecies and their ectomycorrhizal hosts, i.e., species of Quercus, suggest that their diversification is a result of comigration, adaptation, and geographic isolation along the Isthmus of Panama during the Pliocene and Pleistocene. ARTICLE HISTORY

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... 1), even when several reference sequences contained additional loci (LSU and rpb1). This result is also evident in earlier studies that used one or a few gene regions where support is lacking for deep nodes (Miller and Buyck 2002;Buyck et al. 2008); this emphasizes the importance of building complete, multilocus phylogenies for studying the evolutionary relationships within Russula, as was done in Looney et al. (2016) and Vera et al. (2021). Our work uncovered apparent misidentifications in public databases such as GenBank and UNITE. ...
... floriforms Vera & Corrales and subsp. symphoniae Manz, F. Hampe & Corrales (Vera et al. 2021), climactic disjunction led to speciation in the R. globispora lineage , and host and ecological differences led to speciation between R. clavipes and R. pascua (Adamčík et al. 2016). In this study, the heterozygous position found in collections of R. altaica from the Rocky Mountains and in collections of R. nana from the Rocky Mountains and Europe were phylogenetically informative and separated these species from the closely related R. gracillima and R. montana, respectively. ...
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... Approximately 3100 species of fungi are known from Panama [8,9]. Among these species, there are nine species of Russula recorded for the entire country [6,[10][11][12]. In contrast to this, a high number of 31 OTUs of Russula spp. ...
... In other lineages of the genus, it is much more complicated to identify undescribed species from Latin America, because recent molecular studies are lacking, the taxonomic concept of oreomunneae (holotype FH- species described only by morphology is unclear and because distribution areas and ecological amplitudes of Russula species in the tropics are unknown. Up to now, 77 Russula species are described from the region [12]. A larger part of these taxa is unlikely to occur in tropical montane forests of the Chiriquí region in Western Panama though, because they are either limited to lowland tropical habitats or associated with Nothofagus spp. in temperate regions of South America. ...
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Ectomycorrhizal (ECM) fungi, symbiotic mutualists of many dominant tree and shrub species, exhibit a biogeographic pattern counter to the established latitudinal diversity gradient of most macroflora and fauna. However, an evolutionary basis for this pattern has not been explicitly tested in a diverse lineage. In this study, we reconstructed a mega-phylogeny of a cosmopolitan and hyper-diverse genus of ECM fungi, Russula, sampling from annotated collections and utilizing publically available sequences deposited in GenBank. Metadata from molecular operational taxonomic unit cluster sets were examined to infer the distribution and plant association of the genus. This allowed us to test for differences in patterns of diversification between tropical and extratropical taxa, as well as how their associations with different plant lineages may be a driver of diversification. Results show that Russula is most species-rich at temperate latitudes and ancestral state reconstruction shows that the genus initially diversified in temperate areas. Migration into and out of the tropics characterizes the early evolution of the genus, and these transitions have been frequent since this time. We propose the 'generalized diversification rate' hypothesis to explain the reversed latitudinal diversity gradient pattern in Russula as we detect a higher net diversification rate in extratropical lineages. Patterns of diversification with plant associates support host switching and host expansion as driving diversification, with a higher diversification rate in lineages associated with Pinaceae and frequent transitions to association with angiosperms. This article is protected by copyright. All rights reserved.
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Five new species from Cortinarius sect. Cortinarius are formally described, four from the Americas (Corti-narius palatinus Harrower, sp. nov., Cortinarius atrotomentosus Harrower, sp. nov., Cortinarius altissimus Harrower & T.W. Henkel, sp. nov., Cortinarius neotropicus Harrower, sp. nov.) and one from Australasia (Cortinarius carneipallidus Harrower & E. Horak, sp. nov.) based on molecular, morphological, and ecological circumscription. Additional collections of the Australasian species Cortinarius hallowellensis Wood and Cortinarius kioloensis Wood reveal wider host associations and geographic ranges than previously recorded. Morphological descriptions, photomicrographs and a dichotomous key to all species in Corti-narius sect. Cortinarius are provided. This work raises the number of species in sect. Cortinarius to twelve.
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Quercus forests reach their southern limit of distribution in Colombia, where they are represented by Quercus humboldtii. In the inner slopes of the Western and Eastern cordilleras of Colombia, oak forests are located in areas with annual rainfall between 1260 and 1960 mm. Oak forests can also be found in the eastern slope of the Central cordillera (annual rainfall 2300 mm). Oak forests from massifs of the Caribbean were characterized and grouped in the alliance Billio roseae-Quercion humbodtii. Tovomito werddelianae-Quercetum humboldtii is found in well preserved areas between 750 and 950 m on the wet foothills of the Western cordillera (annual rainfall up to 3000 mm). Wettinio praemorsae-Quercetum humboldtii is found between 1600 and 1800 m.s.l.m.) in the south of the Perija´ mountains (annual rain fall 1600–1800 mm). We did not find a direct relationship between the amount of rainfall and species richness in both the higher strata and the total number of species. Oak forests are distributed from warm climates with temperatures over 248C and 700 m of altitude with precipitation close to 2800 mm/year, to cold climates with temperatures under 108C in altitudes over 3000 m and with annual rainfall between 700 and 3000 mm.
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The linking of North and South America by the Isthmus of Panama had major impacts on global climate, oceanic and atmospheric currents, and biodiversity, yet the timing of this critical event remains contentious. The Isthmus is traditionally understood to have fully closed by ca. 3.5 million years ago (Ma), and this date has been used as a benchmark for oceanographic, climatic, and evolutionary research, but recent evidence suggests a more complex geological formation. Here, we analyze both molecular and fossil data to evaluate the tempo of biotic exchange across the Americas in light of geological evidence. We demonstrate significant waves of dispersal of terrestrial organisms at approximately ca. 20 and 6 Ma and corresponding events separating marine organisms in the Atlantic and Pacific oceans at ca. 23 and 7 Ma. The direction of dispersal and their rates were symmetrical until the last ca. 6 Ma, when northern migration of South American lineages increased significantly. Variability among taxa in their timing of dispersal or vicariance across the Isthmus is not explained by the ecological factors tested in these analyses, including biome type, dispersal ability, and elevation preference. Migration was therefore not generally regulated by intrinsic traits but more likely reflects the presence of emergent terrain several millions of years earlier than commonly assumed. These results indicate that the dramatic biotic turnover associated with the Great American Biotic Interchange was a long and complex process that began as early as the Oligocene-Miocene transition.
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Detailed descriptions are given for Russula cartaginis and R. quercophila associated with endemic Quercus in Costa Rica. Both species are compared with the closely resembling and very rare R. eccentrica from southeastern North America and R. imitatrix from northeastern North America. Microscopic features for all four species are here illustrated in more detail for the first time.
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Premise of research. The most important diversity hot spot of genus Quercus (Fagaceae) in America is situated in southern Mexico. From this area down to the Colombian Andes, oak species diversity decreases considerably, but the pattern of species distribution and turnover has not been analyzed. This study aimed at determining geographical patterns of species turnover, species distribution, and endemism for Neotropical Quercus species. Methodology. Occurrence records for 58 oak species belonging to the Quercus and Lobatae sections were obtained. Patterns of species turnover were determined by comparing species composition among latitudinal/longitudinal units. Areas of endemism were determined using weighted networks. The potential distribution of oak species was determined using ecological niche models. Finally, a principal component analysis was used to identify changes in the oak species’ ecological niche across areas. Pivotal results. The species composition analysis indicated that the Tehuantepec Isthmus, the Nicaraguan Depression, and the Panamanian Isthmus represent species turnover points. Nine areas of endemism were recovered, distributed through mountainous ranges from Mexico to Costa Rica. Most of these areas were delimited by the species turnover points detected. Ecological niche modeling indicated that the turnover points represent areas with low climatic suitability for most oak species and represent discontinuities in the distribution of Quercus. Niche comparisons suggest niche differentiation among species distributed in different areas of endemism or on opposite sides of turnover points. Conclusions. The results indicate that the Tehuantepec Isthmus, the Nicaraguan Depression, and the Panamanian Isthmus have acted as important barriers to the dispersal of oak species, influencing species diversity, biogeographic patterns, and niche divergence.
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The fungus/plant root association known as a mycorrhizal symbiosis appears to have evolved in the Devonian. Of the two general morphological types of mycorrhizae among plant families, arbuscular mycorrhizae appear earlier in the fossil record and are more widespread than are ectomycorrhizae. The latter type of symbiosis most likely evolved with the vascular plant progenitors of modern Pinaceae in the Jurassic, but also developed with the ancestors of a dozen or so extant Angiosperm families. The significance of the ectomycorrhizal relationship is evident in that the symbionts profit by acquiring resources from their partners that would otherwise be unavailable. In natural environments where ectomycorrhizal communities exist, the symbiosis may be restricted or not depending on the particular plants and fungi Involved. The presence of an obligate specificity of a particular fungus with a particular plant has a profound consequence on biogeographic distribution.
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Phylogenies are increasingly used in all fields of medical and biological research. Moreover, because of the next generation sequencing revolution, datasets used for conducting phylogenetic analyses grow at an unprecedented pace. RAxML (Randomized Axelerated Maximum Likelihood) is a popular program for phylogenetic analyses of large datasets under maximum likelihood. Since the last RAxML paper in 2006, it has been continuously maintained and extended to accommodate the increasingly growing input datasets and to serve the needs of the user community. I present some of the most notable new features and extensions of RAxML, such as, a substantial extension of substitution models and supported data types, the introduction of SSE3, AVX, and AVX2 vector intrinsics, techniques for reducing the memory requirements of the code and a plethora of operations for conducting post-analyses on sets of trees. In addition, an up-to-date, 50 page user manual covering all new RAxML options is available. The code is available under GNU GPL at https://github.com/stamatak/standard-RAxML. Alexandros.Stamatakis@h-its.org.
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A checklist of the species of Colombian macrofungi cited in the literature is presented. A total of 114 published articles were reviewed. These reported 1219 species of macrofungi belonging to 34 orders and 110 families of Ascomycota and Basidiomycota. Lichens were not included.
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The increasing aridity during the Last Glacial Maximum (LGM) has been proposed as a major factor affecting Neotropical species. The character and intensity of this change, however, remains the subject of ongoing debate. This review proposes an approach to test contrasting paleoecological hypotheses by way of their expected demographic and genetic effects on Neotropical cloud forest species. We reviewed 48 paleoecological records encompassing the LGM in the Neotropics. The records show contrasting evidence regarding the changes in precipitation during this period. Some regions remained fairly moist and others had a significantly reduced precipitation. Many paleoecological records within the same region show apparently conflicting evidence on precipitation and forest stability. From these data, we propose and outline two demographic/genetic scenarios for cloud forests species based on opposite precipitation regimes: the dry refugia and the moist forests hypotheses. We searched for studies dealing with the population genetic structure of cloud forest and other montane taxa and compared their results with the proposed models. To date, the few available molecular studies show insufficient genetic evidence on the predominance of glacial aridity in the Neotropics. In order to disentangle the climatic history of the Neotropics, the present study calls for a general multi-disciplinary approach to conduct future phylogeographic studies. Given the contradictory paleoecological information, population genetic data on Neotropical cloud forest species should be used to explicitly test the genetic consequences of competing paleoecological models.
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We report a major update of the MAFFT multiple sequence alignment program. This version has several new features, including options for adding unaligned sequences into an existing alignment, adjustment of direction in nucleotide alignment, constrained alignment and parallel processing, which were implemented after the previous major update. This report shows actual examples to explain how these features work, alone and in combination. Some examples incorrectly aligned by MAFFT are also shown to clarify its limitations. We discuss how to avoid misalignments, and our ongoing efforts to overcome such limitations.
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Concerted evolution of the ribosomal DNA array has been studied in numerous eukaryotic taxa, yet is still poorly understood. rDNA genes are repeated dozens to hundreds of times in the eukaryotic genome (Eickbush and Eickbush 2007) and it is believed that these arrays are homogenized through concerted evolution (Zimmer et al., 1980, Dover, 1993) preventing the accumulation of intragenomic, and intraspecific, variation. However, numerous studies have reported rampant intragenomic and intraspecific variation in the rDNA array (Ganley and Kobayashi, 2011, Naidoo et al., 2013, Hughes and Petersen, 2001, Lindner and Banik, 2011, Li et al., 2013; Lindner, Carlsen, et al. 2013; Hughes, Tulloss, et al. 2018), contradicting our current understanding of concerted evolution. The internal transcribed spacers (ITS) of the rDNA cistron are the most commonly used DNA barcoding region in Fungi (Schoch et al. 2012), and rely on concerted evolution to homogenize the rDNA array leading to a “barcode gap” (Puillandre et al. 2012). Here we show that in Boletus edulis Bull., ITS intragenomic variation persists at low allele frequencies throughout the rDNA array, this variation does not correlate with genomic relatedness between populations, and rDNA genes may not evolve in a strictly concerted fashion despite the presence of unequal recombination and gene conversion. Under normal assumptions, heterozygous positions found in ITS sequences represent hybridization between populations, yet through allelic mapping of the rDNA array we found numerous heterozygous alleles to be stochastically introgressed throughout, presenting a dishonest signal of gene flow. Moreover, despite the signal of gene flow in ITS, our organisms were highly inbred, indicating a disconnect between true gene flow and barcoding signals. In addition, we show that while the mechanisms of concerted evolution are ongoing in pseudo-heterozygous individuals, they are not fully homogenizing the ITS array. Concerted evolution of the rDNA array may insufficiently homogenize the ITS gene, allowing for misleading signals of gene flow to persist, vastly complicating the use of the ITS locus for DNA barcoding in Fungi.
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Numerous lineages of mushroom-forming fungi have been subject to bursts of diversification throughout their evolutionary history, events that can impact our ability to infer well-resolved phylogenies. However, groups that have undergone quick genetic change may have the highest adaptive potential. As the second largest genus of mushroom-forming fungi, Russula provides an excellent model for studying hyper-diversification and processes in evolution that drives it. This study focuses on the morphologically defined group – Russula subsection Roseinae. Species hypotheses based on morphological differentiation and multi-locus phylogenetic analyses are tested in the Roseinae using different applications of the multi-species coalescent model. Based on this combined approach, we recognize fourteen species in Roseinae including the Albida and wholly novel Magnarosea clades. Reconstruction of biogeographic and host association history suggest that parapatric speciation in refugia during glacial cycles of the Pleistocene drove diversification within the Roseinae, which is found to have a Laurasian distribution with an evolutionary origin in the Appalachian Mountains of eastern North America. Finally, we detect jump dispersal at a continental scale that has driven diversification since the most recent glacial cycles.
Article
Since 2007, the quality of Russula descriptions has improved and the use of molecular support for species delimitation and the number of published new species has increased. However, the description style is not consistent and has regional or author-specific patterns. Most recent publications still favour descriptions of spores compared to hymenium and pileipellis elements, and usually only the spore size is provided with statistical support. This study proposes standards for descriptions of the microscopic structure of Russula species (Russulaceae, Agaricomycetes). We present the description template, the template measurements table, the specific terminology and the essential chemical reagents. The proposed standards were tested by mycologists from 11 countries who met at the Russula Microscopy Workshop in Slovakia. Descriptions of 26 species from 9 countries and four continents were prepared, among them R. amarissima, R. castanopsidis, R. seperina and R. subtilis are re-described and 15 species are introduced as new: R. abietiphila, R. amerorecondita, R. aurantioflava, R. echidna, R. flavobrunnescens, R. fluvialis, R. fortunae, R. garyensis, R. gemmata, R. laevis, R. madrensis, R. olivaceohimalayensis, R. purpureogracilis, R. sancti-pauli and R. wielangtae. Seven descriptions for candidate new species are provided without a formal name assignment. Pairwise comparison of species described in this study with available similar descriptions of related species suggests that microscopic characters from all parts of the basidiomata can be equally important for species recognition and they deserve the same treatment including number of measurements and statistics. The majority of recent studies does not recognise differences between the pileus margin and centre, but more than one-third of the species described in this study show distinct differences between the pileus areas, emphasizing the importance to specify the origin of pileipellis observations. This study proved that there is frequently insufficient difference in the ITS barcode between closely related species and that it is necessary to use more genetic markers combined with ecological and geographical data.
Article
Using specimens collected from subtropical pine-fagaceous mixed forests and phylogenetic analysis of DNA sequence data of ITS, 28S rDNA, rpb2 and tef1, we describe two new species, R. maguanensis and R. substriata, in R. subg. Heterophyllidia, subsect. Substriatinae subsect. nov. Russula maguanensis and R. substriata are similar to Indian R. shingbaensis in the tuberculate-striate pileus and spores with isolated warts but have more vividly coloured pileus and associate with pines and/or fagaceous trees rather than with Abies. In our multi-gene phylogeny, the new subsection and a representative of tropical African R. subsect. Aureotactinae compose one of the four major clades of R. subg. Heterophyllidia, the three remaining ones corresponding to R. sect. Heterophyllae, R. sect. Ingratae and R. subsect. Cyanoxanthinae. The overall characters of this new section combine those of some other sections in the same subgenus: mostly tuberculate-striate but more vivid pileus, spores with isolated warts, orthochromatic pileipellis with abundant erect aggregate mucronate pileocystidia in the suprapellis but absent in the subpellis and numerous cystidioid hyphae at the bottom of subpellis and trama beneath it. It differs from its sister clade R. subsect. Aureotactinae in lacking the intense yellowing of surface and context of their fruiting bodies and having pileal cystidioid elements clearly separated by the loose tissue of subpellis from the pileocystidia at the pileus surface. In order to compare our two new species with recently described Asian species and investigate their geographical distributions, we produced an ITS genealogy including also environmental sequences. This ITS genealogy suggests that R. subsect. Substriatinae includes at least seven potential species, shows an amphi-pacific distribution and its members associate with at least four families of host trees.
Article
The family Russulaceae is considered an iconic lineage of mostly mushroom-forming basidiomycetes due to their importance as edible mushrooms in many parts of the world, and their ubiquity as ectomycorrhizal symbionts in both temperate and tropical forested biomes. Although much research has been focused on this group, a comprehensive or cohesive synthesis by which to understand the functional diversity of the group has yet to develop. Interest in ectomycorrhizal fungi, of which Russulaceae is a key lineage, is prodigious due to the important roles they play as plant root mutualists in ecosystem functioning, global carbon sequestration, and a potential role in technology development toward environmental sustainability. As one of the most species-diverse ectomycorrhizal lineages, the Russulaceae has recently been the focus of a dense sampling and genome sequencing initiative with the Joint Genome Institute aimed at untangling their functional roles and testing whether functional niche specialization exists for independent lineages of ectomycorrhizal fungi. Here we present a review of important studies on this group to contextualize what we know about its members' evolutionary history and ecosystem functions, as well as to generate hypotheses establishing the Russulaceae as a valuable experimental system.
Book
Two rather different elements combine to explain the origin of this volume: one scientific and one personal. The broader of the two is the scientific basis-the time for such a volume had arrived. Geology had made remarkable progress toward an understanding of the phys­ ical history of the Caribbean Basin for the last 100 million years or so. On the biological side, many new discoveries had elucidated the distributional history of terrestrial orga­ nisms in and between the two Americas. Geological and biological data had been combined to yield the timing of important events with unprecedented resolution. Clearly, when each of two broad disciplines is making notable advances and when each provides new insights for the other, the rewards of cross-disciplinary contacts increase exponentially. The present volume represents an attempt to bring together a group of geologists, paleontologists and biologists capable of exploiting this opportunity through presentation of an interdisciplinary synthesis of evidence and hypothesis concerning interamerican connections during the Cretaceous and Cenozoic. Advances in plate tectonics form the basis for a modern synthesis and, in the broadest terms, dictate the framework within which the past and present distributions of organisms must be interpreted. Any scientific dis­ cipline must seek tests of its conclusions from data outside of its own confines.
Article
Detailed illustrated descriptions are given for Russula panamae sp.nov, Russula aucarum, R. puiggarii and R. venezueliana, all of which are reported for the first time from Panamá. For Russula venezueliana and R. aucarum, it is also the first record since their original description. Taxonomy, systematic position, and related species are discussed for each species. Russula ochrostraminea is probably a synonym of R. venezueliana and section Delicoarchaeae is considered a possible synonym of subsection Lactarioideae or of section Metachromaticae.
Article
Species ofRussulasubsect.Xerampelinaeare notoriously difficult to identify and name and have not been subject to molecular study. A group of species, referred to here as theR. clavipescomplex, growing in association withSalix,BetulaandPopulusas well as coniferous tree species from temperate to arctic and alpine habitats, were examined. Analyses of the nuc rDNA internal transcribed spacer (ITS) region and a numerical analysis of morphological characters were used. TheR. clavipescomplex is a monophyletic group withinRussulasubsect.Xerampelinae, according to molecular results. The complex includes three species:R. nuoljaeis a phylogenetically and morphologically well-supported species while the other two,R. clavipesandR. pascua, are similar based on ITS data and morphology but separate based on their ecology.Russula pseudoölivascensis conspecific withR. clavipes Several combinations of characters traditionally used in the taxonomy ofR.subsect.Xerampelinaeare inappropriate for species delimitation in this group and the adequacy of the ITS for species identification in this group is discussed. Detailed microscopic observations on the type collection ofR. nuoljaeare presented and illustrated, along with a key to the European members ofR.subsect.Xerampelinae.
Article
Neotropical montane forests are often dominated by ectomycorrhizal (EM) tree species, yet the diversity of their EM fungal communities remains poorly explored. In lower montane forests in western Panama, the EM tree species Oreomunnea mexicana (Juglandaceae) forms locally dense populations in forest otherwise characterized by trees that form arbuscular mycorrhizal (AM) associations. The objective of this study was to compare the composition of EM fungal communities associated with Oreomunnea adults, saplings, and seedlings across sites differing in soil fertility and the amount and seasonality of rainfall. Analysis of fungal nrITS DNA (nuclear ribosomal internal transcribed spacers) revealed 115 EM fungi taxa from 234 EM root tips collected from adults, saplings, and seedlings in four sites. EM fungal communities were equally species-rich and diverse across Oreomunnea developmental stages and sites, regardless of soil conditions or rainfall patterns. However, ordination analysis revealed high compositional turnover between low and high fertility/rainfall sites located ca. 6 km apart. The EM fungal community was dominated by Russula (ca. 36 taxa). Cortinarius, represented by 14 species and previously reported to extract nitrogen from organic sources under low nitrogen availability, was found only in low fertility/high rainfall sites. Phylogenetic diversity analyses of Russula revealed greater evolutionary distance among taxa found on sites with contrasting fertility and rainfall than was expected by chance, suggesting that environmental differences among sites may be important in structuring EM fungal communities. More research is needed to evaluate whether EM fungal taxa associated with Oreomunnea form mycorrhizal networks that might account for local dominance of this tree species in otherwise diverse forest communities.
Article
Microscopical characters of type specimens for five species in Russula subgenus Heterophyllidia: R. albiduliformis Murrill, R. flocculosa Burl., R. maculosa Murrill, R. heterosporoides Murrill and R. subgraminicolor Murrill are described in detail. Taxonomy, systematic placement and nomenclatural aspects are discussed. Both R. heterosporoides Murrill and R. subgraminicolor Murrill are likely good species of subsection Virescentinae, whereas the other three species are more difficult to place with precision, but show affinities with both Virescentinae and Heterophyllinae.
Article
The isolation of South America from Central America and Africa during the Tertiary Period left a strong imprint on the flora of the Neotropics. South American Eocene through Miocene fossil assemblages, both pollen and macrofossils, document a rich tropical flora on the continental margins, and represent some of the only data on pre-landbridge lowland taxa in South America. Lowland Miocene floras from Amazonia are remarkably similar in their high diversity to Amazonian floras today based on lists of dominant families. Recent geophysical data on the uplift of the northern Andes show a strong correlation between uplift and the development and diversification of montane forests in Colombia and Venezuela. The emergence of a continuous landbridge at 3 Ma between Central and South America is well documented and is demonstrated by the arrival of temperate elements in South American highlands and concurrent appearance of South American taxa in Central America. There is no evidence for displacement of lowland tropical plants in South America by northern immigrants, which appears to stand in contrast to the published record for mammals. The mix of taxa in extant Mexican tropical floras derived from tropical South America, tropical Central America, and from remnants of northern tropical Eocene floras is strong evidence for the impact that the landbridge through the Panamanian isthmus had on the neotropical flora. The early appearance of low-elevation savannas is inferred from an increase in grass pollen in the middle Pliocene of Panama; however, widespread savannas are not indicated by pollen data from the Central American region. Rather, beginning in the latest Miocene Epoch and continuing up to the Quaternary, a mix of tropical rainforest and mixed tropical woodlands is suggested for the lowlands, based on pollen evidence. Accumulating data on temperature changes during the late Tertiary and Quaternary Periods points to low-latitude temperature fluctuations of up to 6 degrees C. Proposals of accompanying widespread rainfall fluctuations are more equivocal. Rainfall probably varied regionally, resulting in a mosaic of habitats controlled by river migration, sea level fluctuations. local dryness, and local uplift. Zones postulated as refugia provide testable hypotheses using neoecological and paleoecological data. The paleoecological data to test three hypotheses are still limited taxonomically and spatially. It is important to stress that the effect of the isolation of South American neotropical floras has not been erased in the 3 million years since their connection with Central America. New data front middle and late Miocene floras in South America will be critical in determining the degree to which the composition of South American floras has been influenced by immigration of plants from the better-known Central American area to the north.
Article
Based on recently collected specimens, four new records of the Russulaceae are presented for Panama: Russula aff. densissima, R. luteotacta, R. mexicana and Lactarius aff. lilacinus. R. aff. densissima is reported for the first time for the Americas. The Panamanian specimens of R. luteotacta, R. mexicana and L. aff. lilacinus are the most southern records for the Americas. All species are described and illustrated. A discussion of their known distribution, delimitation from morphologically similar species, and their taxonomy is added, where applicable.
Article
Fog interception and rainfall were measured at 14 stations across the Central Cordillera in western Panamá. Fog interception and rainfall were measured monthly during 1988–1989 with artificial fog catchers and rain gauges, respectively. Fog interception was highest on ridges and increased with increasing altitude. Fog interception contributed between 2.4 and 60.6% of the total water input, depending on altitude and exposure to the prevailing winds. Absolute amounts of annual fog interception ranged from 142 to 2295 mm. Although low clouds were more frequent in montane forests, clouds close to the ground also occurred in the lowlands. During the study period, there was a gradient of increasing total rainfall from the Caribbean (3355 mm) to the Pacific side (5759 mm) of the Central Cordillera. Nevertheless, rainfall was more seasonal on the leeward side of the mountain range. Seasonal variation in fog intereption was different from rainfall patterns and no correlation was found between monthly (or annual) rainfall and fog interception. The results of this study showed the importance of montane forests for the preservation of water sources, particularly along ridges of the Fortuna drainage basin that provides more than 50% of the electricity of the Republic of Panamá.
Article
We have designed two taxon-selective primers for the internal transcribed spacer (ITS) region in the nuclear ribosomal repeat unit. These primers, ITS1-F and ITS4-B, were intended to be specific to fungi and basidiomycetes, respectively. We have tested the specificity of these primers against 13 species of ascomycetes, 14 of basidiomycetes, and 15 of plants. Our results showed that ITS4-B, when paired with either a ‘universal’ primer ITS1 or the fungal-specific primer ITS1-F, efficiently amplified DNA from all basidiomycetes and discriminated against ascomycete DNAs. The results with plants were not as clearcut. The ITS1-F/ITS4-B primer pair produced a small amount of PCR product for certain plant species, but the quantity was in most cases less than that produced by the ‘universal’ ITS primers. However, under conditions where both plant and fungal DNAs were present, the fungal DNA was amplified to the apparent exclusion of plant DNA. ITS1-F/ITS4-B preferential amplification was shown to be particularly useful for detection and analysis of the basidiomycete component in ectomycorrhizae and in rust-infected tissues. These primers can be used to study the structure of ectomycorrhizal communities or the distribution of rusts on alternate hosts.
Article
The “Great American Biotic Interchange” (GABI) is regarded as a defining event in the biogeography of the Americas. It is hypothesized to have occurred when the Isthmus of Panama closed ca three million years ago (Ma), ending the isolation of South America and permitting the mixing of its biota with that of North America. This view of the GABI is based largely upon the animal fossil record, but recent molecular biogeographic studies of plants that show repeated instances of long-distance dispersal over major oceanic barriers suggest that perhaps the land bridge provided by the isthmus may have been less necessary for plant migration. Here we show that plants have significantly earlier divergence time estimates than animals for historical migration events across the Isthmus of Panama region. This difference in timing indicates that plants had a greater propensity for dispersal over the isthmus before its closure compared with animals. The GABI was therefore asynchronous for plants and animals, which has fundamental implications for the historical assembly of tropical biomes in the most species-rich forests on the planet.