Rangewide analysis of fungal associations in the fully mycoheterotrophic Corallorhiza striata complex (Orchidaceae) reveals extreme specificity on ectomycorrhizal Tomentella (Thelephoraceae) across North America

Fully mycoheterotrophic plants offer a fascinating system for studying phylogenetic associations and dynamics of symbiotic specificity between hosts and parasites. These plants frequently parasitize mutualistic mycorrhizal symbioses between fungi and trees. Corallorhiza striata is a fully mycoheterotrophic, North American orchid distributed from Mexico to Canada, but the full extent of its fungal associations and specificity is unknown. Plastid DNA (orchids) and ITS (fungi) were sequenced for 107 individuals from 42 populations across North America to identify C. striata mycobionts and test hypotheses on fungal host specificity. Four largely allopatric orchid plastid clades were recovered, and all fungal sequences were most similar to ectomycorrhizal Tomentella (Thelephoraceae), nearly all to T. fuscocinerea. Orchid-fungal gene trees were incongruent but nonindependent; orchid clades associated with divergent sets of fungi, with a clade of Californian orchids subspecialized toward a narrow Tomentella fuscocinerea clade. Both geography and orchid clades were important determinants of fungal association, following a geographic mosaic model of specificity on Tomentella fungi. These findings corroborate patterns described in other fully mycoheterotrophic orchids and monotropes, represent one of the most extensive plant-fungal genetic investigations of fully mycoheterotrophic plants, and have conservation implications for the >400 plant species engaging in this trophic strategy worldwide.     

Evidence for specificity to Glomus group Ab in two Asian mycoheterotrophic Burmannia species

Nonphotosynthetic mycorrhizal plants, so‐called mycoheterotrophic plants, have long attracted the curiosity of botanists and mycologists. Recent advances in molecular methods based on fungal‐specific PCR amplification have dramatically enhanced the identification of their host mycorrhizal fungi. However, studies investigating the fungal hosts of arbuscular mycorrhizae‐forming mycoheterotrophs are still limited in Asia, which is known as one of the diversity hot spots of mycoheterotrophs that parasitize arbuscular mycorrhizae (AM). Therefore, we aimed to reveal the mycorrhizal associations of two Asian, fully mycoheterotrophic Burmannia species by molecular identification. Sequences of the small subunit ribosomal DNA showed that both Burmannia species are associated with several distinct lineages of Glomus group Ab. Because Glomus group Ab fungi have been confirmed as fungal hosts of various mycoheterotrophic plants in Africa and South America, we suggest they are widely exploited by AM‐forming mycoheterotrophs globally.     

Genetic differentiation between collections of hatchery and wild masu salmon (<Emphasis Type="Italic">Oncorhynchus masou</Emphasis>) inferred from mitochondrial and microsatellite DNA analyses

There has been very little effort to understand genetic divergence between wild and hatchery populations of masu salmon (Oncorhynchus masou). In this study, we used mitochondrial (mt) NADH dehydrogenase subunit 5 gene (ND5) and six polymorphic nuclear microsatellite DNA loci to compare the genetic variability in three hatchery broodstocks of masu salmon with the variability in eight putative wild masu populations sampled in five rivers including one known source river for the hatchery broodstocks. Both ND5 and microsatellites showed no significant genetic divergence (based on F_ST estimates) between four annual collections from the source river population, suggesting no change in genetic diversity over this time period. The F_ST estimates, an analysis of molecular variance (AMOVA), and a neighbor-joining tree using both DNA markers suggested significant differentiation between the three hatchery and all eight putative wild populations. We conclude that genetic diversity of hatchery populations are low relative to putative wild populations of masu salmon, and we discuss the implications for conservation and fisheries management in Hokkaido.     

Genetic structure of Amphioctopus fangsiao (Mollusca,Cephalopoda) in Chinese waters inferred from variation in three mtDNA genes (ATPase 6, ND2, and ND5)

Amphioctopus fangsiao is an economically important resource found in Chinese coastal waters. Three mitochondrial DNA genes were used to assess the genetic structure among nine populations spanning the northern to southern regions of the Chinese coast. Fragments of 575, 639, and 640 bp in length representing three genes (ATPase 6, ND2, and ND5) were amplified from 183, 170, and 167 individuals, respectively. Overall, ATPase 6, ND2, and ND5 showed high haplotype diversity and low nucleotide diversity (HD: 0.683–0.896; −π: 0.021–0.033). All three mtDNA genes revealed high molecular variance among populations and low variance within populations. Φ_ST values obtained for ATPase 6 (Φ_ST = 0.000 to 0.997), ND2 (Φ_ST = 0.000 to 0.997), and ND5 (Φ_ST = 0.125 to 0.983) showed differentiation among the populations. The constructed phylogeographic tree and haplotype network separated the nine populations into two clades representing the northern and southern populations. Low salinity in the Changjiang River estuary may act as a barrier to promote the differentiation between the two clades. These results enhance our understanding of the genetic structure of A. fangsiao and can promote the management of its genetic resources.

     

Ectomycorrhizal Inocybe species associate with the mycoheterotrophic orchid Epipogium aphyllum but not its asexual propagules

Background and Aims

Epipogium aphyllum is a Eurasian achlorophyllous, mycoheterotrophic forest orchid. Due to its rarity, it is often protected, and its biology is poorly known. The identity and pattern of colonization of fungal associates providing carbon to this orchid have not been studied previously.

Methods

Using samples from 34 individuals from 18 populations in Japan, Russia and France, the following were investigated: (a) colonization patterns of fungal associates of E. aphyllum by microscopy; (b) their identity by PCR amplification of nuclear ribosomal ITS carried out on rhizome fragments and hyphal pelotons.

Results and Conclusions

Microscopic investigations revealed that thick rhizomes were densely colonized by fungi bearing clamp-connections and dolipores, i.e. basidiomycetes. Molecular analysis identified Inocybe species as exclusive symbionts of 75 % of the plants investigated and, more rarely, other basidiomycetes (Hebeloma, Xerocomus, Lactarius, Thelephora species). Additionally, ascomycetes, probably endophytes or parasites, were sometimes present. Although E. aphyllum associates with diverse species from Inocybe subgenera Mallocybe and Inocybe sensu stricto, no evidence for cryptic speciation in E. aphyllum was found. Since basidiomycetes colonizing the orchid are ectomycorrhizal, surrounding trees are probably the ultimate carbon source. Accordingly, in one population, ectomycorrhizae sampled around an individual orchid revealed the same fungus on 11·2 % of tree roots investigated. Conversely, long, thin stolons bearing bulbils indicated active asexual multiplication, but these propagules were not colonized by fungi. These findings are discussed in the framework of ecology and evolution of mycoheterotrophy.Key words: Asexual multiplication, ectomycorrhizae, Epipogium, Inocybe, mycoheterotrophy, orchid mycorrhizae, specificity, symbiont transmission     

High genetic diversity and significant population structure in Cedrus brevifolia Henry, a narrow endemic Mediterranean tree from Cyprus

Endemic island plant species with a narrow distribution are often, but not always, linked to low genetic variation within populations and a lack of differentiation among populations. Cedrus brevifolia is a narrow endemic island tree species of Cyprus. Its range is restricted to a single forest, divided into five neighbouring sites. This study, using biparentally inherited nuclear microsatellites and paternally inherited plastid (chloroplast) microsatellites, assessed the genetic variation of C. brevifolia within its sole population and the level of genetic differentiation among formed sites. The results from both markers showed high diversity (nuclear H _T?=?0.70; plastid H _T?=?0.93), strongly suggesting that the species did not experience severe bottleneck events or extensive genetic drift. Besides, the maintenance of a high genetic diversity in C. brevifolia may suggest that it originates from a widespread congener species. Significant genetic differentiation at nuclear (G _ST?=?0.052) and plastid (G _ST?=?0.119) markers was found among the formed sites. Remarkably, the relatively high genetic differentiation found at plastid markers was comparable to values observed in two widespread congener cedar species. The genetic differentiation probably occurred due to fragmentation of a previously uniform population. This would lead to the shaping of different genetic groups (Bayesian analysis) and to significant population substructure. Furthermore, significant values observed for both isolation by distance and large-scale spatial genetic structure could indicate ineffective gene flow among sites and the early geographical isolation of the more isolated sites from the core population.     

Do plant populations on distinct inselbergs talk to each other? A case study of genetic connectivity of a bromeliad species in an Ocbil landscape

Here, we explore the historical and contemporaneous patterns of connectivity among Encholirium horridum populations located on granitic inselbergs in an Ocbil landscape within the Brazilian Atlantic Forest, using both nuclear and chloroplast microsatellite markers. Beyond to assess the E. horridum population genetic structure, we built species distribution models across four periods (current conditions, mid‐Holocene, Last Glacial Maximum [LGM], and Last Interglacial) and inferred putative dispersal corridors using a least‐cost path analysis to elucidate biogeographic patterns. Overall, high and significant genetic divergence was estimated among populations for both nuclear and plastid DNA (Φ_ST(n) = 0.463 and Φ_ST(plastid) = 0.961, respectively, p < .001). For nuclear genome, almost total absence of genetic admixture among populations and very low migration rates were evident, corroborating with the very low estimates of immigration and emigration rates observed among E. horridum populations. Based on the cpDNA results, putative dispersal routes in Sugar Loaf Land across cycles of climatic fluctuations in the Quaternary period revealed that the populations’ connectivity changed little during those events. Genetic analyses highlighted the low genetic connectivity and long‐term persistence of populations, and the founder effect and genetic drift seemed to have been very important processes that shaped the current diversity and genetic structure observed in both genomes. The genetic singularity of each population clearly shows the need for in situ conservation of all of them.     

Symbiotic germination and development of fully mycoheterotrophic plants convergently targeting similar Glomeraceae taxa

Plants producing dust seeds often meet their carbon demands by exploiting fungi at the seedling stage. This germination strategy (i.e. mycoheterotrophic germination) has been investigated among orchidaceous and ericaceous plants exploiting Ascomycota or Basidiomycota. Although several other angiosperm lineages have evolved fully mycoheterotrophic relationships with Glomeromycota, the fungal identities involved in mycoheterotrophic germination remain largely unknown. Here, we conducted in situ seed baiting and high-throughput DNA barcoding to identify mycobionts associated with seedlings of Burmannia championii (Burmanniaceae: Dioscoreales) and Sciaphila megastyla (Triuridaceae: Pandanales), which have independently evolved full mycoheterotrophy. Subsequently, we revealed that both seedlings and adults in B. championii and S. megastyla predominantly associate with Glomeraceae. However, mycorrhizal communities are somewhat distinct between seedling and adult stages, particularly in S. megastyla. Notably, the dissimilarity of mycorrhizal communities between S. megastyla adult samples and S. megastyla seedling samples is significantly higher than that between B. championi adult samples and S. megastyla adult samples, based on some indices. This pattern is possibly due to both mycorrhizal shifts during ontogenetic development and convergent recruitment of cheating-susceptible fungi. The extensive fungal overlap in two unrelated mycoheterotrophic plants indicates that both species convergently exploit specific AM fungal phylotypes.     

Phylogenetic affinity of arbuscular mycorrhizal symbionts in <Emphasis Type="Italic">Psilotum nudum</Emphasis>

Many lineages of land plants (from lycopsids to angiosperms) have non-photosynthetic life cycle phases that involve obligate mycoheterotrophic arbuscular mycorrhizal (AM) associations where the plant host gains organic carbon through glomalean symbionts. Our goal was to isolate and phylogenetically identify the AM fungi associated with both the autotrophic and underground mycoheterotrophic life cycle phases of Psilotum nudum. Phylogenetic analyses recovered 11 fungal phylotypes in four diverse clades of Glomus A that form AM associations with P. nudum mycoheterotrophic gametophytes and autotrophic sporophytes, and angiosperm roots found in the same greenhouse pots. The correspondence of identities of AM symbionts in P. nudum sporophytes, gametophytes and neighboring angiosperms provides compelling evidence that photosynthetic heterospecific and conspecific plants can serve as the ultimate sources of fixed carbon for mycoheterotrophic gametophytes of P. nudum, and that the transfer of carbon occurs via shared fungal networks. Moreover, broader phylogenetic analyses suggest greenhouse Psilotum populations, like field-surveyed populations of mycoheterotrophic plants, form AM associations with restricted clades of Glomus A. The phylogenetic affinities and distribution of Glomus A symbionts indicate that P. nudum greenhouse populations have the potential to be exploited as an experimental system to further study the physiology, ecology and evolution of mycoheterotrophic AM associations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

High mycorrhizal specificity in a widespread mycoheterotrophic plant, Eulophia zollingeri (Orchidaceae)

Because mycoheterotrophic plants fully depend on their mycorrhizal partner for their carbon supply, the major limiting factor for the geographic distribution of these plants may be the presence of their mycorrhizal partner. Although this factor may seem to be a disadvantage for increasing geographic distribution, widespread mycoheterotrophic species nonetheless exist. The mechanism causing the wide distribution of some mycoheterotrophic species is, however, seldom discussed. We identified the mycorrhizal partner of a widespread mycoheterotrophic orchid, Eulophia zollingeri, using 12 individuals from seven populations in Japan, Myanmar, and Taiwan by DNA-based methods. All fungal ITS sequences from the roots closely related to those of Psathyrella candolleana (Coprinaceae) from GenBank accessions and herbarium specimens. These results indicate that E. zollingeri is exclusively associated with the P. candolleana species group. Further, the molecular data support the wide distribution and wide-ranging habitat of this fungal partner. Our data provide evidence that a mycoheterotrophic plant can achieve a wide distribution, even though it has a high mycorrhizal specificity, if its fungal partner is widely distributed.     

Extensive sampling of polar bears (Ursus maritimus) in the Northwest Passage (Canadian Arctic Archipelago) reveals population differentiation across multiple spatial and temporal scales

As global warming accelerates the melting of Arctic sea ice, polar bears (Ursus maritimus) must adapt to a rapidly changing landscape. This process will necessarily alter the species distribution together with population dynamics and structure. Detailed knowledge of these changes is crucial to delineating conservation priorities. Here, we sampled 361 polar bears from across the center of the Canadian Arctic Archipelago spanning the Gulf of Boothia (GB) and M'Clintock Channel (MC). We use DNA microsatellites and mitochondrial control region sequences to quantify genetic differentiation, estimate gene flow, and infer population history. Two populations, roughly coincident with GB and MC, are significantly differentiated at both nuclear (F_ST = 0.01) and mitochondrial (Φ_ST = 0.47; F_ST = 0.29) loci, allowing Bayesian clustering analyses to assign individuals to either group. Our data imply that the causes of the mitochondrial and nuclear genetic patterns differ. Analysis of mtDNA reveals the matrilineal structure dates at least to the Holocene, and is common to individuals throughout the species’ range. These mtDNA differences probably reflect both genetic drift and historical colonization dynamics. In contrast, the differentiation inferred from microsatellites is only on the scale of hundreds of years, possibly reflecting contemporary impediments to gene flow. Taken together, our data suggest that gene flow is insufficient to homogenize the GB and MC populations and support the designation of GB and MC as separate polar bear conservation units. Our study also provide a striking example of how nuclear DNA and mtDNA capture different aspects of a species demographic history.     

GENETIC STRUCTURE AND MALE-MEDIATED GENE FLOW IN THE GHOST BAT (MACRODERMA GIGAS)

The Australian ghost bat is a large, opportunistic carnivorous species that has undergone a marked range contraction toward more mesic, tropical sites over the past century. Comparison of mitochondrial DNA (mtDNA) control region sequences and six nuclear microsatellite loci in 217 ghost bats from nine populations across subtropical and tropical Australia revealed strong population subdivision (mtDNA φ_ST = 0.80; microsatellites UR_ST = 0.337). Low-latitude (tropical) populations had higher heterozygosity and less marked phylogeographic structure and lower subdivision among sites within regions (within Northern Territory [NT] and within North Queensland [NQ]) than did populations at higher latitudes (subtropical sites; central Queensland [CQ]), although sampling of geographically proximal breeding sites is unavoidably restricted for the latter. Gene flow among populations within each of the northern regions appears to be male biased in that the difference in population subdivision for mtDNA and microsatellites (NT φ_ST = 0.39, UR_ST = 0.02; NQ φ_ST = 0.60, UR_ST = ?0.03) is greater than expected from differences in the effective population size of haploid versus diploid loci. The high level of population subdivision across the range of the ghost bat contrasts with evidence for high gene flow in other chiropteran species and may be due to narrow physiological tolerances and consequent limited availability of roosts for ghost bats, particularly across the subtropical and relatively arid regions. This observation is consistent with the hypothesis that the contraction of the species' range is associated with late Holocene climate change. The extreme isolation among higher-latitude populations may predispose them to additional local extinctions if the processes responsible for the range contraction continue to operate.     

Isotopic evidence of partial mycoheterotrophy in Burmannia coelestis (Burmanniaceae)

The Burmanniaceae contain several lineages of achlorophyllous mycoheterotrophic plants that associate with arbuscular mycorrhizal fungi (AMF). Here we investigate the isotopic profile of a green and potentially mycoheterotrophic plant in situ, Burmannia coelestis, and associated reference plants. We generated δ ¹³C and δ ¹⁵N stable isotope profiles for five populations of B. coelestis. Burmannia coelestis was significantly enriched in ¹³C relative to surrounding C₃ reference plants and significantly depleted in ¹³C relative to C₄ reference plants. No significant differences were detected in ¹⁵N enrichment between B. coelestis and reference plants. The isotopic profiles measured are suggestive of partial mycoheterotrophy in B. coelestis. Within the genus Burmannia transitions to full mycoheterotrophy have occurred numerous times, suggesting that some green Burmannia species are likely to be partially mycoheterotrophic but in many conditions this mode of nutrition may only be detectable using natural abundance stable isotopic methods, such as when associated with C₄ mycorrhizal plants.     

Chloroplast phylogeographic patterns of Calligonum sect. Pterococcus (Polygonaceae) in arid Northwest China

To understand the impacts of past climatic change and geological events on the evolutionary history of Calligonum sect. Pterococcus, including C. aphyllum, C. rubicundum and C. leucocladum, a total of 128 individuals from 14 populations, mainly from arid Northwest China, were sampled. Two cpDNA intergenic spacer regions (rpl32‐trnL and ycf6‐psbM) were sequenced and 11 haplotypes were identified. Levels of genetic differentiation between populations was low in C. rubicundum (F_ST = 0.54317, p < 0.001) and C. aphyllum (F_ST = 0.55795), while much higher in C. leucocladum (F_ST = 0.95800, p < 0.001), possibly as an effct of differences in geographic distributions and habitats. Analysis of molecular variance (AMOVA) revealed that most of the total genetic variations occurred among species (72.97%). Among eleven identified haplotypes, only H1 and H2 were shared between C. aphyllum and C. rubicundum, while nine were private for one of the three species. The eleven identified haplotypes were divided into two major clades, but they did not yield three species‐specific lineages. Calligonum sect. Pterococcus therefore not appeared reciprocally monophyletic, more likely due to incomplete lineage sorting than hybridization. Mismatch distribution analysis suggested that only C. aphyllum has experienced recent demographic expansion. Divergence time among the 11 haplotypes was estimated at between 2.84 Ma and 0.06 Ma. Within the two clades, haplotype divergence began in early Pleistocene and mainly occurred during the middle to late Pleistocene and was most likely triggered by Quaternary climatic oscillations and increasing aridity of the region.     

Fungal‐host diversity among mycoheterotrophic plants increases proportionally to their fungal‐host overlap

The vast majority of plants obtain an important proportion of vital resources from soil through mycorrhizal fungi. Generally, this happens in exchange of photosynthetically fixed carbon, but occasionally the interaction is mycoheterotrophic, and plants obtain carbon from mycorrhizal fungi. This process results in an antagonistic interaction between mycoheterotrophic plants and their fungal hosts. Importantly, the fungal‐host diversity available for plants is restricted as mycoheterotrophic interactions often involve narrow lineages of fungal hosts. Unfortunately, little is known whether fungal‐host diversity may be additionally modulated by plant–plant interactions through shared hosts. Yet, this may have important implications for plant competition and coexistence. Here, we use DNA sequencing data to investigate the interaction patterns between mycoheterotrophic plants and arbuscular mycorrhizal fungi. We find no phylogenetic signal on the number of fungal hosts nor on the fungal hosts shared among mycoheterotrophic plants. However, we observe a potential trend toward increased phylogenetic diversity of fungal hosts among mycoheterotrophic plants with increasing overlap in their fungal hosts. While these patterns remain for groups of plants regardless of location, we do find higher levels of overlap and diversity among plants from the same location. These findings suggest that species coexistence cannot be fully understood without attention to the two sides of ecological interactions.     

Population genetics of the endangered Wattled Curassow (Crax globulosa,Cracidae, Aves) of the Colombian–Peruvian Amazon using DNA microsatellites and ND2 mitochondrial sequences

The Wattled Curassow (Crax globulosa, Cracidae, Aves) is a large bird living in the Western Amazon basin and a critically endangered species in the Colombian and in the Peruvian Amazon. We carried out the first population genetics analysis of this species employing six nuclear microsatellite markers and sequences of the mtND2 gene. The main results are as follows. (1) The levels of gene diversity were high for the overall population as well as for each of the three islands for both microsatellites and mtDNA. (2) A small amount of genetic differentiation among populations was found with both types of markers (F_ST = 0.027 for microsatellites and N_ST = 0.17 for mitochondrial sequences). (3) Using microsatellites, the Geneclass 2.0 software detected a low correct assignment of individuals to their respective populations. The Structure software only detected one gene pool for the entire area studied. These results are relevant for conservation efforts of this critically endangered species.     

Genetic variation in two populations of the rough‐skinned newt (Taricha granulosa) assessed using novel tetranucleotide microsatellite loci

Seven novel tetranucleotide microsatellite loci were identified from a partial genomic DNA library, enriched for GATA‐motif microsatellites, from the rough‐skinned newt (Taricha granulosa). All loci were polymorphic, and one displayed a high frequency null allele. A related species, T. rivularis, displays strong site fidelity and detectable population structure over small spatial scales, so we assessed genetic variation in two samples of T. granulosa separated by 16 km. Distributions of allele frequencies differ significantly between our two sites, but small values of F_ST and Rho_ST suggest that the populations are linked by a large amount of gene flow.     

Analyses of genetic population structure of two ecologically important mangrove tree species, Bruguiera gymnorrhiza and Kandelia obovata from different river basins of Iriomote Island of the Ryukyu Archipelago, Japan

We analyzed nuclear and chloroplast microsatellite makers to assess genetic diversity and examine genetic structure of two mangrove tree species, Bruguiera gymnorrhiza and Kandelia obovata recovered from nine major river basins of Iriomote Island of the Ryukyu Archipelago, Japan. The average number of alleles per nuclear locus per population was 2.6 in B. gymnorrhiza and 1.7 in K. obovata. Bayesian clustering analysis using InStruct identified two genetic clusters in B. gymnorrhiza and three clusters in K. obovata. Chloroplast microsatellites revealed two dominant haplotypes from B. gymnorrhiza and three haplotypes from K. obovata. The overall result suggests low genetic diversity for both species. AMOVA for nuclear microsatellites showed 9.3?% of population variation in B. gymnorrhiza. Although genetic differentiation between several populations was significant in this species, F _ST suggested low to moderate level of differentiations between most of the populations. Distribution of genetic clusters and chloroplast haplotypes also suggested weak differentiations among B. gymnorrhiza populations. In K. obovata, population variation was, however, relatively high (27.8?%). The high differentiation between K. obovata populations was also suggested from the F _ST and genetic clusters from nuclear microsatellites, and chloroplast haplotypes. A significant correlation between chloroplast genetic distances and coastline distances as well as haplotype distributions for both species suggest that propagules from each species mostly disperse to the neighboring river basins. While significant F _IS and higher percentage of admixed clusters from nuclear microsatellites suggested inbreeding, continual gene exchange by propagule dispersal among populations especially among neighboring populations was suggested for both species from maternally inherited chloroplast microsatellites analyses.     

Specificity of assemblage,not fungal partner species,explains mycorrhizal partnerships of mycoheterotrophic Burmannia plants

Mycoheterotrophic plants (MHPs) growing on arbuscular mycorrhizal fungi (AMF) usually maintain specialized mycorrhizal associations. The level of specificity varies between MHPs, although it remains largely unknown whether interactions with mycorrhizal fungi differ by plant lineage, species, and/or by population. Here, we investigate the mycorrhizal interactions among Burmannia species (Burmanniaceae) with different trophic modes using high-throughput DNA sequencing. We characterized the inter- and intraspecific dynamics of the fungal communities by assessing the composition and diversity of fungi among sites. We found that fully mycoheterotrophic species are more specialized in their fungal associations than chlorophyllous species, and that this specialization possibly results from the gradual loss of some fungal groups. In particular, although many fungal species were shared by different Burmannia species, fully MHP species typically host species-specific fungal assemblages, suggesting that they have a preference for the selected fungi. Although no apparent cophylogenetic relationship was detected between fungi and plants, we observe that evolutionarily closely related plants tend to have a greater proportion of shared or closely related fungal partners. Our findings suggest a host preference and specialization toward fungal assemblages in Burmannia, improving understanding of interactions between MHPs and fungi.Subject terms: Fungi, Plant sciences, Evolution     

Natural selection and neutral evolutionary processes contribute to genetic divergence in leaf traits across a precipitation gradient in the tropical oak Quercus oleoides

The impacts of drought are expanding worldwide as a consequence of climate change. However, there is still little knowledge of how species respond to long‐term selection in seasonally dry ecosystems. In this study, we used Q_ST‐F_ST comparisons to investigate (i) the role of natural selection on population genetic differentiation for a set of functional traits related to drought resistance in the seasonally dry tropical oak Quercus oleoides and (ii) the influence of water availability at the site of population origin and in experimental treatments on patterns of trait divergence. We conducted a thorough phenotypic characterization of 1912 seedlings from ten populations growing in field and greenhouse common gardens under replicated watering treatments. We also genotyped 218 individuals from the same set of populations using eleven nuclear microsatellites. Q_ST distributions for leaf lamina area, specific leaf area, leaf thickness and stomatal pore index were higher than F_ST distribution. Results were consistent across growth environments. Genetic differentiation among populations for these functional traits was associated with the index of moisture at the origin of the populations. Together, our results suggest that drought is an important selective agent for Q. oleoides and that differences in length and severity of the dry season have driven the evolution of genetic differences in functional traits.