Alpova komoviana (Boletales, Paxillaceae), a new sequestrate fungus from Montenegro, with a revised phylogeny of the genus in Europe

A new ectomycorrhizal species, Alpova komoviana, is described from several collections from Montenegro (south-eastern Europe), in association with Alnus incana ssp. incana (Betulaceae). Its interesting basal position in the strictly Alnus-associated Alpova lineage is discussed through morphology and phylogenetic analyses based on ITS, gpd and rpb2 nuclear DNA. ITS sequences of two other taxa are included in the analysis: Alpova rubescens and A. rubescens var. obscuratus; their identity and systematic positions are discussed.     

Ectomycorrhizal fungi associated with ponderosa pine and Douglas-fir: a comparison of species richness in native western North American forests and Patagonian plantations from Argentina

The putative ectomycorrhizal fungal species registered from sporocarps associated with ponderosa pine and Douglas-fir forests in their natural range distribution (i.e., western Canada, USA, and Mexico) and from plantations in south Argentina and other parts of the world are listed. One hundred and fifty seven taxa are reported for native ponderosa pine forests and 514 taxa for native Douglas-fir forests based on available literature and databases. A small group of genera comprises a high proportion of the species richness for native Douglas-fir (i.e., Cortinarius, Inocybe, and Russula), whereas in native ponderosa pine, the species richness is more evenly distributed among several genera. The comparison between ectomycorrhizal species richness associated with both trees in native forests and in Patagonia (Argentina) shows far fewer species in the latter, with 18 taxa for the ponderosa pine and 15 for the Douglas-fir. Epigeous species richness is clearly dominant in native Douglas-fir, whereas a more balanced relation epigeous/hypogeous richness is observed for native ponderosa pine; a similar trend was observed for Patagonian plantations. Most fungi in Patagonian Douglas-fir plantations have not been recorded in plantations elsewhere, except Suillus lakei and Thelephora terrestris, and only 56% of the fungal taxa recorded in Douglas-fir plantations around the world are known from native forests, the other taxa being new associations for this host, suggesting that new tree + ectomycorrhizal fungal taxa associations are favored in artificial situations as plantations.     

Contracting montane cloud forests: a case study of the Andean alder (Alnus acuminata) and associated fungi in the Yungas

Alnus acuminata is a keystone tree species in the Yungas forests and host to a wide range of fungal symbionts. While species distribution models (SDMs) are routinely used for plants and animals to study the effects of climate change on montane forest communities, employing SDMs in fungi has been hindered by the lack of data on their geographic distribution. The well‐known host specificity and common biogeographic history of A. acuminata and associated ectomycorrhizal (ECM) fungi provide an exceptional opportunity to model the potential habitat for this symbiotic assemblage and to predict possible climate‐driven changes in the future. We (1) modeled the present and future distributions of suitable habitats for A. acuminata; (2) characterized fungal communities in different altitudinal zones of the Yungas using DNA metabarcoding of soil and root samples; and (3) selected fungi that were significant indicators of Alnus. Fungal communities were strongly structured according to altitudinal forest types and the presence of Alnus. Fungal indicators of Alnus, particularly ECM and root endophytic fungi, were also detected in Alnus roots. Current and future (year 2050) habitat models developed for A. acuminata predict a 25–50 percent decrease in suitable area and an upslope shift of the suitable habitat by ca. 184–380 m, depending on the climate change scenario. Although A. acuminata is considered to be an effective disperser, recent studies suggest that Andean grasslands are remarkably resistant to forest invasion, and future range contraction for A. acuminata may be even more pronounced than predicted by our models.     

四川螺髻山表土和化石孢粉揭示的环境生态意义

通过四川螺髻山（1984、2017年）表土和化石孢粉与植被的关系分析发现：孢粉组合中木本植物含量（91.0%）占绝对优势,松属、冷杉属、青冈属、常绿栎类、落叶栎类、桤木属、杜鹃花科、禾本科和蒿属为主要花粉类型;人工次生林花粉组合能很好地反映母体植被的群落特征,并可指示优势种的存在和人类活动痕迹;针阔混交林花粉组合能较好地反映群落整体特征,花粉类型能与母体植被中优势种较好地对应;常绿阔叶林、针叶林和灌丛草甸的花粉组合难以反映母体植被的群落特征。DCA表明,花粉谱的百分含量,能较好地区分人工扰动植被和天然植被,但人工次生林、常绿阔叶林和针阔混交林之间以及针叶林和灌丛草甸之间未能区分。30年前后表土孢粉组合变化明显,1984年样品以松属、青冈属和桤木属等花粉为主,而2017年采样分析中松属、桤木属花粉占绝对优势。随着人类活动的加强,部分地区松树和桤木大面积飞播或种植,表土孢粉组合对当地植被指示意义与扰动强度呈负相关关系。现生植被与表土孢粉组合的差异能为恢复古植被和古环境提供参考,但原生植被已经被破坏地区的孢粉图谱,就很难作为重建历史时期植被的根据。本研究可以为亚热带山地利用孢粉学恢复第四纪时期植被与气候,探讨人类活动与环境的关系提供理论依据和实践参考。     

Frankia Populations in Soil and Root Nodules of Sympatrically Grown Alnus Taxa

The genetic diversity of Frankia populations in soil and in root nodules of sympatrically grown Alnus taxa was evaluated by rep-polymerase chain reaction (PCR) and nifH gene sequence analyses. Rep-PCR analyses of uncultured Frankia populations in root nodules of 12 Alnus taxa (n?=?10 nodules each) growing sympatrically in the Morton Arboretum near Chicago revealed identical patterns for nodules from each Alnus taxon, including replicate trees of the same host taxon, and low diversity overall with only three profiles retrieved. One profile was retrieved from all nodules of nine taxa (Alnus incana subsp. incana, Alnus japonica, Alnus glutinosa, Alnus incana subsp. tenuifolia, Alnus incana subsp. rugosa, Alnus rhombifolia, Alnus mandshurica, Alnus maritima, and Alnus serrulata), the second was found in all nodules of two plant taxa (A. incana subsp. hirsuta and A. glutinosa var. pyramidalis), and the third was unique for all Frankia populations in nodules of A. incana subsp. rugosa var. americana. Comparative sequence analyses of nifH gene fragments in nodules representing these three profiles assigned these frankiae to different subgroups within the Alnus host infection group. None of these sequences, however, represented frankiae detectable in soil as determined by sequence analysis of 73 clones from a Frankia-specific nifH gene clone library. Additional analyses of nodule populations from selected alders growing on different soils demonstrated the presence of different Frankia populations in nodules for each soil, with populations showing identical sequences in nodules from the same soil, but differences between plant taxa. These results suggest that soil environmental conditions and host plant genotype both have a role in the selection of Frankia strains by a host plant for root nodule formation, and that this selection is not merely a function of the abundance of a Frankia strain in soil.     

Evolutionary drivers of phylogeographical diversity in the highlands of Mexico: a case study of the Crotalus triseriatus species group of montane rattlesnakes

Aim To assess the genealogical relationships of widespread montane rattlesnakes in the Crotalus triseriatus species group and to clarify the role of Late Neogene mountain building and Pleistocene pine–oak forest fragmentation in driving the diversification of Mexican highland taxa. Location Highlands of mainland Mexico and the south‐western United States (Texas, New Mexico, and Arizona). Methods A synthesis of inferences was used to address several associated questions about the biogeography of the Mexican highlands and the evolutionary drivers of phylogeographical diversity in co‐distributed taxa. We combined extensive range‐wide sampling (130 individuals representing five putative species) and mixed‐model phylogenetic analyses of 2408 base pairs of mitochondrial DNA to estimate genealogical relationships and divergence times within the C. triseriatus species group. We then assessed the tempo of diversification using a maximum likelihood framework based on the birth–death process. Estimated times of divergences provided a probabilistic temporal component and questioned whether diversification rates have remained constant or varied over time. Finally, we looked for phylogeographical patterns in other co‐distributed taxa. Results We identified eight major lineages within the C. triseriatus group, and inferred strong correspondence between maternal and geographic history within most lineages. At least one cryptic species was detected. Relationships among lineages were generally congruent with previous molecular studies, with differences largely attributable to our expanded taxonomic and geographic sampling. Estimated divergences between most major lineages occurred in the Late Miocene and Pliocene. Phylogeographical structure within each lineage appeared to have been generated primarily during the Pleistocene. Although the scale of genetic diversity recognized affected estimated rates of diversification, rates appeared to have been constant through time. Main conclusions The biogeographical history of the C. triseriatus group implies a dynamic history for the highlands of Mexico. The Neogene formation of the Transvolcanic Belt appears responsible for structuring geographic diversity among major lineages. Pleistocene glacial–interglacial climatic cycles and resultant expansions and contractions of the Mexican pine–oak forest appear to have driven widespread divergences within lineages. Climatic change, paired with the complex topography of Mexico, probably produced a myriad of species‐specific responses in co‐distributed Mexican highland taxa. The high degree of genetic differentiation recovered in our study and others suggests that the Mexican highlands may contain considerably more diversity than currently recognized.     

PHYLOGEOGRAPHY OF GRACILARIA TIKVAHIAE (GRACILARIACEAE,RHODOPHYTA): A STUDY OF GENETIC DISCONTINUITY IN A CONTINUOUSLY DISTRIBUTED SPECIES BASED ON MOLECULAR EVIDENCE1

Gracilaria tikvahiae, a highly morphologically variable red alga, is one of the most common species of Gracilariaceae inhabiting Atlantic estuarine environments and the Intracoastal Waterway of eastern North America. Populations of G. tikvahiae at the extremes of their geographic range (Canada and southern Mexico) are subjected to very different environmental regimes. In this study, we used two types of genetic markers, the chloroplast‐encoded rbcL and the nuclear internal transcribed spacer (ITS) region, to examine the genetic variability within G. tikvahiae, for inferring the taxonomic and phylogenetic relationships between geographically isolated populations, and to discuss its distributional information in a phylogeographic framework. Based on rbcL and ITS phylogenies, specimens from populations collected at the extreme distributional ranges reported for G. tikvahiae are indeed part of the same species; however, rbcL‐ but not ITS‐based phylogenies detected phylogenetic structure among the ten G. tikvahiae different haplotypes found in this study. The four distinct rbcL lineages were identified as 1) a Canadian–northeast U.S. lineage, 2) a southeast Florida lineage, 3) an eastern Gulf of Mexico lineage, and 4) a western Gulf of Mexico lineage. We found no evidence for the occurrence of G. tikvahiae in the Caribbean Sea. Observed phylogeographic patterns match patterns of genetic structures reported for marine animal taxa with continuous and quasicontinuous geographic distribution along the same geographic ranges.     

Temporal variation of Bistorta vivipara‐associated ectomycorrhizal fungal communities in the High Arctic

Ectomycorrhizal (ECM) fungi are important for efficient nutrient uptake of several widespread arctic plant species. Knowledge of temporal variation of ECM fungi, and the relationship of these patterns to environmental variables, is essential to understand energy and nutrient cycling in Arctic ecosystems. We sampled roots of Bistorta vivipara ten times over two years; three times during the growing‐season (June, July and September) and twice during winter (November and April) of both years. We found 668 ECM OTUs belonging to 25 different ECM lineages, whereof 157 OTUs persisted throughout all sampling time‐points. Overall, ECM fungal richness peaked in winter and species belonging to Cortinarius, Serendipita and Sebacina were more frequent in winter than during summer. Structure of ECM fungal communities was primarily affected by spatial factors. However, after accounting for spatial effects, significant seasonal variation was evident revealing correspondence with seasonal changes in environmental conditions. We demonstrate that arctic ECM richness and community structure differ between summer (growing‐season) and winter, possibly due to reduced activity of the core community, and addition of fungi adapted for winter conditions forming a winter‐active fungal community. Significant month × year interactions were observed both for fungal richness and community composition, indicating unpredictable between‐year variation. Our study indicates that addressing seasonal changes requires replication over several years.     

Comparative phylogenies and host specialization in the alder ectomycorrhizal fungi Alnicola, Alpova and Lactarius (Basidiomycota) in Europe

Background  

Mycorrhizal fungi form intimate associations with their host plants that constitute their carbon resource and habitat. Alnus spp. (Betulaceae) are known to host an exceptional species-poor and specialized ectomycorrhizal (ECM) fungal community compared to other tree species, but the host-specificity pattern and its significance in terms of fungal diversification and speciation remain poorly documented. The degree of parallel speciation, host switching, and patterns of biogeography were explored in the historical associations between alders and three ECM taxa of Basidiomycetes: Alnicola (Agaricales), Alpova (Boletales), and Lactarius (Russulales). The aim was to develop an evolutionary framework on host specificity and diversification of Basidiomycetes in this highly specialized plant-fungus symbiosis.     

Ectomycorrhizal fungal community structure across a bog-forest ecotone in southeastern Alaska

We examined the ectomycorrhizal (ECM) fungal community across a bog-forest ecotone in southeastern Alaska. The bog and edge were both characterized by poorly drained Histosols and a continuous layer of Sphagnum species, ericaceous shrubs, Carex species, and shore pine [Pinus contorta Dougl. ex Loud. var. contorta]. The forest had better-drained Inceptisols and Spodosols, a tree community comprised of western hemlock [Tsuga heterophylla (Raf.) Sarg.], yellow cedar (Thuja plicata Donn ex D. Don.), Sitka spruce [Picea sitchensis (Bong.) Carr.] and shore pine, and an understorey of ericaceous shrubs and herbs. ECM root tip density (tips cm^–3 soil) was significantly greater in the forest than the edge or bog and ECM colonization was significantly different in all three plant communities. The below ground ECM fungal taxa were analyzed using molecular techniques (PCR-RFLP and DNA sequencing). Three ECM fungal taxa, Suillus tomentosus (Kauffman) Singer, Cenococcum geophilum Fr.:Fr, and a Russula species, differed in relative frequency, yet were among the four most frequent in all three plant communities. Although differences in ECM fungal richness were observed across plant communities, unequal sampling of ECM roots due to root density and colonization differences confounded richness comparisons. Using resampling procedures for creating taxon-accumulation curves as a function of sampled ECM roots revealed similarities in cumulative ECM fungal taxa richness across the ecotone.     

Dispersal of the Cotton Boll Weevil (Coleoptera: Curculionidae) in South America: Evidence of RAPD Analysis

RAPD technique provides useful information on the geographic origin and dispersal of the boll weevil Anthonomus grandis in South America. Nine populations from Argentina, Brazil, Paraguay, Mexico and USA were analyzed. Weevils were captured on native plants (Misiones province, Argentina) and on cotton cultures, except the sample from the United States (USDA laboratory-reared colony). A sample of the ‘Peruvian square weevil’, A. vestitus, from Ecuador, was included in the analysis in order to compare interspecific variation. The four primers used in the analysis revealed 41 ‘anonymous loci’. The neighbor-joining tree based on Nei's distances and values of Nm (migrants per generation), indicate that genetic similarity between samples from Tecomán (Mexico) and Puerto Iguazú (Argentina), is higher than among remaining South American populations. This result supports an hypothesis of natural occurrence of the boll weevil in South America, prior to extensive cotton cultivation. Population outbreaks of the species would be associated with increase of agricultural lands. This revised version was published online in August 2006 with corrections to the Cover Date.     

Invertebrate Assemblages Associated with Root Masses of <Emphasis Type="Italic">Eichhornia crassipes</Emphasis> (Mart.) Solms-Laubach 1883 in the Alvarado Lagoonal System,Veracruz, Mexico

This paper describes the spatial and temporal variation of aquatic invertebrate assemblages associated with root masses of Eichhornia crassipes collected at 12 sites between July 2000 and June 2002 in the Alvarado Lagoonal System (ALS), Veracruz, Mexico. A total of 96 taxa were registered; acari showed the highest species richness with 15 taxa followed by decapods (14), mollusks (12), amphipods (9), and isopods (7). Freshwater organisms represented 44% of the total taxa, 53% belonged to estuarine taxa, and marine taxa 3%. The isopod Munna sp. was the dominant taxon throughout the entire study period, followed by Ephemeroptera, Hyalella azteca, Chydorus sp., Physella sp., Podura aquatica, and Fossaria sp. during the low salinity period (July–September 2001, 1.6–3.8 psu), and Neritina virginea, Cassidinidea ovalis, Macrobrachium acanthurus and Melita longisetosa during the high salinity period (March–May 2001 9.7–12.7 psu and April–May 2002, 8.2–8.9 psu). A spatial gradient of species richness and diversity was registered for the freshwater organisms. Additionally, the spatial and temporal patterns of invertebrate densities could be explained due to the movements of Eichhornia crassipes mats through the system, and the temporal variation of environmental variables such as salinity, dissolved oxygen, and turbidity.     

Diversity of Boll Weevil Populations in South America: A Phylogeographic Approach

A phylogeographic approach was conducted to assess the geographic structure and genetic variation in populations of the boll weevil Anthonomus grandis, which is the most harmful insect pest of cotton in the Americas. COI and COII mitochondrial gene sequences were analyzed to test a former hypothesis on the origin of the boll weevil in Argentina, Brazil and Paraguay, using samples from Mexico and USA as putative source populations. The analysis of variability suggests that populations from South American cotton fields and nearby disturbed areas form a phylogroup with a central haplotype herein called A, which is the most common and widespread in USA and South America. The population from Texas has the A haplotype as the most frequent and gathers in the same group as the South American populations associated with cotton. The sample from Tecomán (México) shows high values of within-nucleotide divergence, shares no haplotype in common with the South American samples, and forms a phylogroup separated by several mutational steps. The sample from Iguazú National Park (Misiones Province, Argentina) has similar characteristics, with highly divergent haplotypes forming a phylogroup closer to the samples from cotton fields, than to the Mexican group. We propose that in South America there are: populations with characteristics of recent invaders, which would be remnants of “bottlenecks” that occurred after single or multiple colonization events, probably from the United States, and ancient populations associated with native forests, partially isolated by events of historical fragmentation.     

Frankia bacteria in Alnus rubra forests: genetic diversity and determinants of assemblage structure

To quantify the genetic diversity of Frankia bacteria associated with Alnus rubra in natural settings and to examine the relative importance of site age, management, and geographic location in structuring Frankia assemblages in A. rubra forests, root nodules from four A. rubra sites in the Pacific Northwest, USA were sampled. Frankia genetic diversity at each site was compared using sequence-based analyses of a 606 bp fragment of the nifH gene. At a 3% sequence similarity cutoff, a total of 5 Frankia genotypes were identified from 317 successfully sequenced nodules. Sites varied in the total number of genotypes present, but were typically dominated by only one or two genotypes. Phylogenetic analyses showed that all of the A. rubra-Frankia genotypes grouped with other Alnus-infective Frankia. Analysis of similarity (ANOSIM) and chi-square analyses indicated that Frankia assemblages were more strongly influenced by site age/management than geographic location. This study demonstrates that the Frankia assemblages in A. rubra forests have low genotype diversity, but that genotype abundance can differ significantly in forests of different age/management history.     

Restriction Fragment Length Polymorphism Analyses of the Plasmid DNAs in Strains of Xanthomonas campestris pv. vesicatoria from Different Geographic Areas

Restriction fragment length polymorphisms (RFLPs) of plasmid DNAs in Xanthomonas campestris pv. vesicatoria were analysed using 77 strains from the United states, Argentina, Australia, Taiwan, and Korea. One or more plasmids were detected in all tested strains, irrespective of geographic origin, host plant from which isolated, or chemical resistance. All Korean strains contained a few plasmids of similar high molecular weight, whereas some small plasmids occured only in strains from the United States, Argentina, and Taiwan. After digesting total plasmid DNAs with each of four restriction endonucleases, 18 fragments with sizes from about 1 to 23 kb were visualized. Seventy-seven strains of diverse geographic origins, with different levels of resistance to streptomycin and copper, were classified into the 14 RFLP groups based on the restriction endonuclease digestion patterns of their plasmid DNAs. Strains belonging to each group shared DNA fragments of identical size, suggesting the possible presence of similar plasmids in these strains. A 5.8-kb EcoRI plasmid DNA probe prepared from the United States strain 81-23 hybridized to EcoRI plasmid digests from all tested strains. Other plasmid DNA fragments of the strain81-2,3 used as probes had no homology to plasmid DNA fragments from several strains around the world. The variation in hybridization profiles of plasmid DNA was very similar to the results obtained by RFLP analysis of plasmid DNA digested by four restriction enzymes. Most of the Korean strains tested were highly sensitive to streptomycin and copper, whereas most strains from other geographic areas showed a high level of resistance to one or two of the chemicals. Cluster analysis of genetic distance between the strains based on the data obtained generated the dendrograms that separated all Korean strains from the other strains, suggesting that plasmid DNA of the Korean strains may be genetically very different from those of the others.     

Molecular taxonomy of Hyrcanian Alnus using nuclear ribosomal ITS and chloroplast trnH-psbA DNA barcode markers

The taxonomy and phylogeny of Hyrcanian Alnus (eight taxa) were investigated using sequence data from the nuclear ribosomal ITS and the chloroplast trnH-psbA intergenic spacer. The mean nucleotide compositions of the ITS region were completely equal for two main Hyrcanian taxa, and the ITS1 region had fewer variable sites than the ITS2 region. Two relatively distinct types of ITS2 were identified for two main clades of Hyrcanian Alnus, the A. subcoradata complex and A. glutinosa. Two recently described species, A. dolichocarpa and A. djavanshirii, did not show any diagnostic sites and had a similar pattern with A. subcordata. Three recognized subspecies of A. glutinosa were distributed in the A. incana complex. In the analysis of trnH-psbA sequence data, the three subgenera of Alnus were poorly resolved relative to one another. Alnus glutinosa had minimal sequence divergence from A. incana and A. tenuifolia, and A. subcordata had a minimum distance from A. cordata and A. orientalis. A maximum pairwise distance also was observed between Hyrcanian species (A. glutinosa and A. subcordata) with A. pendula and A. sieboldiana, respectively. Ultimately, the molecular phylogeny of Alnus based on two DNA barcode markers was not congruent with recent morphological classifications, so additional DNA markers should be explored for identifying Alder taxa in the Hyrcanian forest.     

Relationship between topographic heterogeneity and vegetation patterns in a Californian salt marsh

Questions: Are species richness and species abundances higher in the presence of tidal creeks? Do species richness and species abundances vary with plot size? Location: Intertidal plain of Volcano Marsh, Bahia de San Quintin, Mexico. Methods: We analysed vegetation patterns in large areas (cells) with tidal creeks (+creek) and without (‐creek). We surveyed vegetation cover, microtopography, habitat type, and distance to creeks in nested plots of five sizes, 0.1, 0.25, 1, 2.5, and 10 m². Results: Species richness, frequency, cover, and assemblages differed between ±creek cells. Richness tended to be higher in +creek cells, and cover and frequency of individual species differed significantly between ±creek cells. We found consistent patterns in vegetation structure across plot sizes. We encountered 13 species that occurred in 188 unique assemblages. The most common assemblage had six species: Batis maritima, Frankenia salina, Salicornia bigelovii, S. virginica, Salicornia spec. and Triglochin concinna. This assemblage occurred in ±creek cells and at all spatial scales. Of the most common assemblages all but one were composed of multiple species (3–9 species/plot). Conclusions: The persistence of vegetation patterns across a 100‐fold range in spatial scale suggests that similar environmental factors operate broadly to determine species establishment and persistence. Differences in assemblage composition result from variation of frequency and cover of marsh plain species, particularly Suaeda esteroa and Monanthochloe littoralis. The recommendation for restoration of Californian salt marshes is to target (and plant) multi‐species assemblages, not monocultures.     

Declines in littoral species richness across both spatial and temporal nutrient gradients: a palaeolimnological study of two taxonomic groups

1. Using a palaeolimnological approach in shallow lakes, we quantified the species richness responses of diatoms and Cladocera to phosphorus enrichment. We also examined differences in species richness responses between littoral and pelagic assemblages of our focal communities. To address both spatial and temporal relationships, our study includes an analysis of both surface sediments from 40 lakes and of a lake sediment record spanning c. 120 years. The objective of our study was to determine whether similar species richness patterns occurred across trophic levels, as well as along spatial and temporal gradients. 2. We found that both diatom and Cladocera species richness estimates significantly declined with increasing phosphorus across space and through time. When the assemblages were subdivided according to known habitat preferences, littoral biodiversity maintained a negative trend, whereas pelagic species richness tended to show no relationship with phosphorus. 3. Negative productivity–diversity patterns have been observed across almost all palaeolimnological studies that span large productivity gradients. This congruence in patterns is most likely due to the similarity in data collection methods and in focal communities studied. The contrasting responses between littoral and pelagic assemblages may be explained by the differences in physical habitat and the pool of taxa in each of these environments. Consistent with the literature, we found statistical support for the idea that littoral diversity declines could be explained by an interaction between macrophytes and nutrients along strong trophic gradients. The general lack of a diversity response in our pelagic assemblages could be attributable to the limited pool of subfossil taxa. The response of the pelagic diatom could also be related to their broad range of nutrient tolerances. 4. The observed negative response of species richness to phosphorus enrichment, particularly in the littoral assemblages, has implications for ecosystems functioning because communities with reduced biodiversity often are less resilient to anthropogenic change.     

Into and out of the tropics: global diversification patterns in a hyperdiverse clade of ectomycorrhizal fungi

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 hyperdiverse 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.