Flowering phenology differs among wet and dry sub-alpine meadows in southwestern China

The effect of floral traits, floral rewards and plant water availability on plant-pollinator interactions are well-documented; however, empirical evidence of their impact on flowering phenology in high-elevation meadows remains scarce. In this study, we assessed three levels of flowering phenology, i.e. population-, individual- and flower-level (floral longevity), in two nearby but contrasting (wet versus dry) sub-alpine meadows on Yulong Snow Mountain, southwestern China. We also measured a series of floral traits (pollen number, ovule number, and the ratio of pollen to ovule number per flower, i.e. pollen:ovule ratio [P/O]) and floral rewards (nectar availability and pollen presentation) as plausible additional sources of variation for each phenological level. Floral longevity in the wet meadow was significantly longer than that for the dry meadow, whereas population- and individual-flowering duration were significantly shorter. Our results showed a significant positive relationship between flowering phenology with pollen number and P/O per flower; there was no relationship with ovule number per flower. Further, we found a significant effect of flowering phenology on nectar availability and pollen presentation. Our findings suggest that shorter floral longevity in dry habitats compared to wet might be due to water-dependent maintenance costs of flowers, where the population- and individual-level flowering phenology may be less affected by habitats. Our study shows how different levels of flowering phenology underscore the plausible effects of contrasting habitats on reproductive success.

Plastome phylogenomics and morphological traits analyses provide new insights into the phylogenetic position, species delimitation and speciation of Triplostegia (Caprifoliaceae)

BACKGROUND

The genus Triplostegia contains two recognized species, T. glandulifera and T. grandiflora, but its phylogenetic position and species delimitation remain controversial. In this study, we assembled plastid genomes and nuclear ribosomal DNA (nrDNA) cistrons sampled from 22 wild Triplostegia individuals, each from a separate population, and examined these with 11 recently published Triplostegia plastomes. Morphological traits were measured from herbarium specimens and wild material, and ecological niche models were constructed.

RESULTS

Triplostegia is a monophyletic genus within the subfamily Dipsacoideae comprising three monophyletic species, T. glandulifera, T. grandiflora, and an unrecognized species Triplostegia sp. A, which occupies much higher altitude than the other two. The new species had previously been misidentified as T. glandulifera, but differs in taproot, leaf, and other characters. Triplotegia is an old genus, with stem age 39.96 Ma, and within it T. glandulifera diverged 7.94 Ma. Triplostegia grandiflora and sp. A diverged 1.05 Ma, perhaps in response to Quaternary climate fluctuations. Niche overlap between Triplostegia species was positively correlated with their phylogenetic relatedness.

CONCLUSIONS

Our results provide new insights into the species delimitation of Triplostegia, and indicate that a taxonomic revision of Triplostegia is needed. We also identified that either rpoB-trnC or ycf1 could serve as a DNA barcode for Triplostegia.

Plants, pollinators and their interactions under global ecological change: The role of pollen DNA metabarcoding

Anthropogenic activities are triggering global changes in the environment, causing entire communities of plants, pollinators and their interactions to restructure, and ultimately leading to species declines. To understand the mechanisms behind community shifts and declines, as well as monitoring and managing impacts, a global effort must be made to characterize plant-pollinator communities in detail, across different habitat types, latitudes, elevations, and levels and types of disturbances. Generating data of this scale will only be feasible with rapid, high-throughput methods. Pollen DNA metabarcoding provides advantages in throughput, efficiency and taxonomic resolution over traditional methods, such as microscopic pollen identification and visual observation of plant-pollinator interactions. This makes it ideal for understanding complex ecological networks and their responses to change. Pollen DNA metabarcoding is currently being applied to assess plant-pollinator interactions, survey ecosystem change and model the spatiotemporal distribution of allergenic pollen. Where samples are available from past collections, pollen DNA metabarcoding has been used to compare contemporary and past ecosystems. New avenues of research are possible with the expansion of pollen DNA metabarcoding to intraspecific identification, analysis of DNA in ancient pollen samples, and increased use of museum and herbarium specimens. Ongoing developments in sequencing technologies can accelerate progress towards these goals. Global ecological change is happening rapidly, and we anticipate that high-throughput methods such as pollen DNA metabarcoding are critical for understanding the evolutionary and ecological processes that support biodiversity, and predicting and responding to the impacts of change.

Contrasting range changes of terrestrial orchids under future climate change in China

Climate change has impacted the distribution and abundance of numerous plant and animal species during the last century. Orchidaceae is one of the largest yet most threatened families of flowering plants. However, how the geographical distribution of orchids will respond to climate change is largely unknown. Habenaria and Calanthe are among the largest terrestrial orchid genera in China and around the world. In this paper, we modeled the potential distribution of eight Habenaria species and ten Calanthe species in China under the near-current period (1970-2000) and the future period (2081-2100) to test the following two hypotheses: 1) narrow-ranged species are more vulnerable to climate change than wide-ranged species; 2) niche overlap between species is positively correlated with their phylogenetic relatedness. Our results showed that most Habenaria species will expand their ranges, although the climatic space at the southern edge will be lost for most Habenaria species. In contrast, most Calanthe species will shrink their ranges dramatically. Contrasting range changes between Habenaria and Calanthe species may be explained by their differences in climate-adaptive traits such as underground storage organs and evergreen/deciduous habits. Habenaria species are predicted to generally shift northwards and to higher elevations in the future, while Calanthe species are predicted to shift westwards and to higher elevations. The mean niche overlap among Calanthe species was higher than that of Habenaria species. No significant relationship between niche overlap and phylogenetic distance was detected for both Habenaria and Calanthe species. Species range changes in the future was also not correlated with their near current range sizes for both Habenaria and Calanthe. The results of this study suggest that the current conservation status of both Habenaria and Calanthe species should be adjusted. Our study highlights the importance of considering climate-adaptive traits in understanding the responses of orchid taxa to future climate change.

Community-wide patterns in pollen and ovule production, their ratio (P/O), and other floral traits along an elevation gradient in southwestern China

BACKGROUND

As the male and female gametophytes of flowering plants, pollen and ovules largely determine the upper and lower boundaries of plant reproductive success. It is commonly predicted that pollen and ovule number per flower should increase, and pollen-ovule ratio (P/O) per flower should decrease with increasing elevation in response to a more stochastic pollination environment. Here, we aimed to determine the response of pollen number, ovule number, and P/O to other floral traits and elevation gradients for 84 insect-pollinated herbaceous flowering plant species in five sub-alpine and alpine communities (2709 to 3896 m a.s.l.) on Yulong Snow Mountain, southwestern China.

RESULTS

Six floral traits, including P/O, floral display area, flower number, tube depth, flower shape, and pollen presentation, were highly correlated with pollen and ovule number per flower. With increasing elevation, pollen number and P/O per flower increased marginally and significantly, respectively; ovule number per individual, flower number per individual, stigma stamen separation, and inflorescence height decreased significantly. However, ovule number per flower and other floral traits (i.e., floral display area, tube depth, stigma height, stamen height, and pollen and P/O per individual) did not change with elevation. We detected significant phylogenetic signals for pollen number, ovule number, and P/O, suggesting that these traits may be highly conserved and with limited response to changing environmental conditions.

CONCLUSIONS

Results revealed patterns of plant reproductive character evolution along elevation gradients and the potential factors governing their spatial variation in high-elevation environments. Plant species at high elevations are more likely adapted to cross-pollination, indicated by increased P/O per flower at high elevations on Yulong Mountain. Combined effects of phylogenetic history and plant-pollinator interactions should determine plant trait evolution.

Plant DNA-barcode library for native flowering plants in the arid region of northwestern China

DNA barcoding is a well-established tool for rapid species identification and biodiversity monitoring. A reliable and traceable DNA barcode reference library with extensive coverage is necessary but unavailable for many geographic regions. The arid region in northwestern China, a vast area of about 2.5 million km² , is ecologically fragile and often overlooked in biodiversity studies. In particular, DNA barcode data from the arid region in China are lacking. We develop and evaluate the efficacy of an extensive DNA-barcode library for native flowering plants in the arid region of northwestern China. Plant specimens were collected, identified, and vouchered for this purpose. The database utilized four DNA barcode markers, namely rbcL, matK, ITS, and ITS2, for 1,816 accessions (representing 890 species from 386 genera and 72 families) and consisted of 5,196 barcode sequences. Individual barcodes varied in resolution rates; species- and genus-level rates for rbcL, matK, ITS, and ITS2 were 79.9-51.1%/76.1%, 79.9-67.2%/88.9%, 85.0-72.0%/88.2%, and 81.0-67.4%/84.9%, respectively. The three-barcode combination of rbcL + matK + ITS (RMI) revealed a higher species- and genus-level resolution (75.5%/92.1%, respectively). A total of 110 plastomes were newly generated as super-barcodes to increase species resolution for seven species-rich genera, namely Astragalus, Caragana, Lactuca, Lappula, Lepidium, Silene, and Zygophyllum. Plastomes revealed higher species resolution compared to standard DNA barcodes and their combination. We suggest future databases include super-barcodes, especially for species-rich and complex genera. The plant DNA barcode library in the current study provides a valuable resource for future biological investigations in the arid regions of China.

Contributions to Ecuadorian butterworts (Lentibulariaceae, Pinguicula): two new species and a re-evaluation of Pinguiculacalyptrata

Comparatively few species of the insectivorous genus Pinguicula L. have been recognized in South America so far. In recent years, a number of narrowly endemic taxa from the Andes have been described that simultaneously refined the broad taxonomic concepts of the "historical" species. Here, we describe two striking new species from Southern Ecuador that further condense the circumscription of Pinguiculacalyptrata Kunth. Pinguiculajimburensissp. nov. and P.ombrophilasp. nov. are clearly beyond the taxonomic scope of the known species and consequently described as new to science. The deviating morphological features of the two new taxa are described and illustrated and the remaining morphological spectrum of P.calyptrata in Ecuador is outlined. The two new species add to the exceptional biodiversity in the Amotape-Huancabamba Zone and underline its importance as a biodiversity hotspot in urgent need of protection.

Primula luquanensis sp. nov. (Primulaceae), a New Species from Southwestern China, Reveals a Novel Floral Form in the Heterostyly-Prevailing Genus

A new species, Primula luquanensis Z.K.Wu and Wei Zhou sp. nov. (Primulaceae) is described and illustrated from Yunnan Province, China. It is morphologically assigned to P. sect Aleuritia based on its dwarf and hairless habit and coverage by farina on both sides of the leaf blade and scape. This new species is similar to P. nutantiflora and P. yunnanensis, but it is easily distinguished by its stolons, solitary bract, bell-shaped corolla and monomorphic floral form. The new species also has a substantially reduced corolla tube, presenting a unique floral form in a genus where heterostyly typically prevails.

Variation in plant traits and phylogenetic structure associated with native and nonnative species in an industrialized flora

Industrialized sites are hotspots for nonnative species because of continuous anthropogenic disturbance and nonnative propagule rain resulting from hitchhikers exchanged through global trade. Investigating plant traits and the phylogenetic structure of species at initial ports of entry can contribute to our understanding of how species are introduced to, assembled into, and survive at industrialized sites, which can also inform how susceptible these sites are to nonnative plant invasions. To compare native and nonnative species, we asked three questions: 1) Are plant traits differentially associated with species nativity (native versus nonnative)? (2) Do these traits have phylogenetic signals? and (3) What is the phylogenetic structure of each trait for native and nonnative species? We collected, identified, and vouchered 170 angiosperm species within the Garden City Terminal at the Port of Savannah, Georgia, USA, the largest container terminal in North America. Species nativity was derived from the literature, as were traits of pollination syndrome, dispersal syndrome, duration, and growth habit. Pearson’s Chi-squared tests were used to determine if traits were differentially associated with species nativity. Phylogenetic signal, along with mean pairwise distance (MPD) and mean nearest taxon distance (MNTD), were used to assess the degree of phylogenetic relatedness of native and nonnative species with each trait. Nonnative species showed a significant association with multiple pollination syndromes. Native species were significantly associated with perennial duration and zoophily pollination syndrome. All traits possessed a phylogenetic signal, and the anemophily pollination syndrome was significantly clustered for both native and nonnative species. Still, most other traits differed in their phylogenetic structure pattern based on the nativity. Overall, findings suggest that the environment is filtering for native and nonnative species that possess traits promoting introduction and survival at this industrialized point-of-entry. They also suggest that nonnative species trait differences partition available niches that promote their introduction to the site. More research is needed at industrialized sites to inventory and monitor the floristic community, investigate the establishment and spread probabilities of nonnative species, and prevent and mitigate nonnative species risks and impacts.

Genetic markers in Andean Puya species (Bromeliaceae) with implications on plastome evolution and phylogeny

The Andean plant endemic Puya is a striking example of recent and rapid diversification from central Chile to the northern Andes, tracking mountain uplift. This study generated 12 complete plastomes representing nine Puya species and compared them to five published plastomes for their features, genomic evolution, and phylogeny. The total size of the Puya plastomes ranged from 159,542 to 159,839 bp with 37.3%–37.4% GC content. The Puya plastomes were highly conserved in organization and structure with a typical quadripartite genome structure. Each of the 17 consensus plastomes harbored 133 genes, including 87 protein‐coding genes, 38 tRNA (transfer RNA) genes, and eight rRNA (ribosomal RNA) genes; we found 69–78 tandem repeats, 45–60 SSRs (simple sequence repeats), and 8–22 repeat structures among 13 species. Four protein‐coding genes were identified under positive site‐specific selection in Puya. The complete plastomes and hypervariable regions collectively provided pronounced species discrimination in Puya and a practical tool for future phylogenetic studies. The reconstructed phylogeny and estimated divergence time for the lineage suggest that the diversification of Puya is related to Andean orogeny and Pleistocene climatic oscillations. This study provides plastome resources for species delimitation and novel phylogenetic and biogeographic studies.

Multitrophic diversity and biotic associations influence subalpine forest ecosystem multifunctionality

Biodiversity across multiple trophic levels is required to maintain multiple ecosystem functions. Yet, it remains unclear how multitrophic diversity and species interactions regulate ecosystem multifunctionality. Here, combining data from nine different trophic groups (including trees, shrubs, herbs, leaf mites, small mammals, bacteria, pathogenic fungi, saprophytic fungi and symbiotic fungi) and 13 ecosystem functions related to supporting, provisioning and regulating services, we used a multitrophic perspective to evaluate the effects of elevation, diversity and network complexity on scale-dependent subalpine forest multifunctionality. Our results demonstrate that elevation and soil pH significantly modified species composition and richness across multitrophic groups and influenced multiple functions simultaneously. We provide evidence that species richness across multiple trophic groups had stronger effects on multifunctionality than species richness at any single trophic level. Moreover, biotic associations, indicating the complexity of trophic networks, were positively associated with multifunctionality. The relative effects of diversity on multifunctionality increased at the scale of the larger community compared to a scale accounting for neighbouring interactions. Our results highlight the paramount importance of scale- and context- dependent multitrophic diversity and interactions for a better understanding of mountain ecosystem multifunctionality in a changing world. This article is protected by copyright. All rights reserved.

Species pool size and rainfall account for the relationship between biodiversity and biomass production in natural forests of China

The strength of biodiversity–biomass production relationships increases with increasing environmental stress and time. However, we know little about the effects of abiotic (e.g., climate) and biotic (e.g., species pool and community composition) factors on this trend. Whether variation in biomass production is best explained by phylogenetic diversity metrics or traditional measures of species richness also remains elusive. We compiled estimates of community composition and biomass production for tree species in 111 permanent quadrats spanning three natural forests (tropical, subtropical, and temperate) in China. Based on ~10 years of data, we compared temperature, rainfall, species pool size, and community composition in each forest each year. We estimated species richness and phylogenetic diversity in each quadrat each year; the latter metric was based on the sum of branch lengths of a phylogeny that connects species in each quadrat each year. Using generalized linear mixed‐effect models, we found that top‐ranked models included the interaction between forest and biodiversity and the interaction between forest and year for both biodiversity metrics. Variation in biomass production was best explained by phylogenetic diversity; biomass production generally increased with phylogenetic diversity, and the relationship was stronger in subtropical and temperate forests. Increasing species pool size, temperature, and rainfall and decreasing inter‐quadrat dissimilarity range shifted the relationship between biomass production and phylogenetic diversity from positive to neutral. When considered alone, species pool size had the strongest influence on biomass production, while species pool size, rainfall, and their interaction with phylogenetic diversity constituted the top‐ranked model. Our study highlights the importance of species pool size and rainfall on the relationship between phylogenetic diversity and biomass production in natural forest ecosystems.

Natural hybridization among three Rhododendron species (Ericaceae) revealed by morphological and genomic evidence

BACKGROUND

Natural hybridization can influence the adaptive response to selection and accelerate species diversification. Understanding the composition and structure of hybrid zones may elucidate patterns of hybridization processes that are important to the formation and maintenance of species, especially for taxa that have experienced rapidly adaptive radiation. Here, we used morphological traits, ddRAD-seq and plastid DNA sequence data to investigate the structure of a Rhododendron hybrid zone and uncover the hybridization patterns among three sympatric and closely related species.

RESULTS

Our results show that the hybrid zone is complex, where bi-directional hybridization takes place among the three sympatric parental species: R. spinuliferum, R. scabrifolium, and R. spiciferum. Hybrids between R. spinuliferum and R. spiciferum (R. ×duclouxii) comprise multiple hybrid classes and a high proportion of F₁ generation hybrids, while a novel hybrid taxon between R. spinuliferum and R. scabrifolium dominated the F₂ generation, but no backcross individuals were detected. The hybrid zone showed basically coincident patterns of population structure between genomic and morphological data.

CONCLUSIONS

Natural hybridization exists among the three Rhododendron species in the hybrid zone, although patterns of hybrid formation vary between hybrid taxa, which may result in different evolutionary outcomes. This study represents a unique opportunity to dissect the ecological and evolutionary mechanisms associated with adaptive radiation of Rhododendron species in a biodiversity hotspot.

Comparing whole-genome shotgun sequencing and DNA metabarcoding approaches for species identification and quantification of pollen species mixtures

Molecular identification of mixed-species pollen samples has a range of applications in various fields of research. To date, such molecular identification has primarily been carried out via amplicon sequencing, but whole-genome shotgun (WGS) sequencing of pollen DNA has potential advantages, including (1) more genetic information per sample and (2) the potential for better quantitative matching. In this study, we tested the performance of WGS sequencing methodology and publicly available reference sequences in identifying species and quantifying their relative abundance in pollen mock communities. Using mock communities previously analyzed with DNA metabarcoding, we sequenced approximately 200Mbp for each sample using Illumina HiSeq and MiSeq. Taxonomic identifications were based on the Kraken k-mer identification method with reference libraries constructed from full-genome and short read archive data from the NCBI database. We found WGS to be a reliable method for taxonomic identification of pollen with near 100% identification of species in mixtures but generating higher rates of false positives (reads not identified to the correct taxon at the required taxonomic level) relative to rbcL and ITS2 amplicon sequencing. For quantification of relative species abundance, WGS data provided a stronger correlation between pollen grain proportion and sequence read proportion, but diverged more from a 1:1 relationship, likely due to the higher rate of false positives. Currently, a limitation of WGS-based pollen identification is the lack of representation of plant diversity in publicly available genome databases. As databases improve and costs drop, we expect that eventually genomics methods will become the methods of choice for species identification and quantification of mixed-species pollen samples.

Seeds attached to refrigerated shipping containers represent a substantial risk of nonnative plant species introduction and establishment

The initial processes for successful biological invasions are transport, introduction, and establishment. These can be directly influenced or completely avoided through activities that reduce the number and frequency of entering nonnative propagules. Economic and environmental benefits through preventative monitoring programs at early stages of invasion far outweigh the long-term costs associated with mitigating ecological and economic impacts once nonnative species establish and spread. In this study, we identified 30 taxa of hitchhiking plant propagules on the air-intake grilles of refrigerated shipping containers arriving into a United States seaport from a port on the Pacific coast of South America. The four monocotyledonous taxa with the highest number of seeds collected were analyzed; we estimated propagule pressure, germination, and survivorship of these taxa, and we used the estimates to determine likelihood of establishment. At the levels of propagule pressure estimated here, non-zero germination and survival rates resulted in high establishment probabilities even when escape rates from shipping containers were modelled to be exceedingly low. Our results suggest high invasion risk for nonnative taxa including Saccharum spontaneum L., a listed Federal Noxious Weed. Currently, not all shipping containers arriving at USA ports are thoroughly inspected due to limited personnel and funding for biological invasion prevention. Our results indicate that there is a significant risk from only a few propagules escaping into the environment from this source, and we propose possible solutions for reducing this risk.

The utility of DNA barcodes to confirm the identification of palm collections in botanical gardens

The palm family (Arecaceae) is of high ecological and economic value, yet identification in the family remains a challenge for both taxonomists and horticulturalists. The family consists of approximately 2600 species across 181 genera and DNA barcoding may be a useful tool for species identification within the group. However, there have been few systematic evaluations of DNA barcodes for the palm family. In the present study, five DNA barcodes (rbcL, matK, trnH-psbA, ITS, ITS2) were evaluated for species identification ability across 669 samples representing 314 species and 100 genera in the Arecaceae, employing four analytical methods. The ITS gene region was found to not be a suitable barcode for the palm family, due in part, to low recovery rates and paralogous gene copies. Among the four analyses used, species resolution for ITS2 was much higher than that achieved with the plastid barcodes alone (rbcL, matK, trnH-psbA), and the barcode combination ITS2 + matK + rbcL gave the highest resolution among all single barcodes and their combinations, followed by ITS2 + matK. Among 669 palm samples analyzed, 110 samples (16.3%) were found to be misidentified. The 2992 DNA barcode sequences generated in this study greatly enriches the existing identification toolbox available to plant taxonomists that are interested in researching genetic relationships among palm taxa as well as for horticulturalists that need to confirm palm collections for botanical garden curation and horticultural applications. Our results indicate that the use of the ITS2 DNA barcode gene region provides a useful and cost-effective tool to confirm the identity of taxa in the Palm family.

Complete plastome sequencing resolves taxonomic relationships among species of Calligonum L. (Polygonaceae) in China

BACKGROUND

Calligonum (Polygonaceae) is distributed from southern Europe through northern Africa to central Asia, and is typically found in arid, desert regions. Previous studies have revealed that standard DNA barcodes fail to discriminate Calligonum species. In this study, the complete plastid genomes (plastome) for 32 accessions of 21 Calligonum species is sequenced to not only generate the first complete plastome sequence for the genus Calligonum but to also 1) Assess the ability of the complete plastome sequence to discern species within the group, and 2) screen the plastome sequence for a cost-effective DNA barcode that can be used in future studies to resolve taxonomic relationships within the group.

RESULTS

The whole plastomes of Calligonum species possess a typical quadripartite structure. The size of the Calligonum plastome is approximately 161 kilobase pairs (kbp), and encodes 113 genes, including 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. Based on ML phylogenetic tree analyses, the complete plastome has higher species identification (78%) than combinations of standard DNA barcodes (rbcL + matK + nrITS, 56%). Five newly screened gene regions (ndhF, trnS-G, trnC-petN, ndhF-rpl32, rpl32-trnL) had high species resolution, where ndhF and trnS-G were able to distinguish the highest proportion of Calligonum species (56%).

CONCLUSIONS

The entire plastid genome was the most effective barcode for the genus Calligonum, although other gene regions showed great potential as taxon-specific barcodes for species identification in Calligonum.

An initial industrial flora: A framework for botanical research in cooperation with industry for biodiversity conservation

Humans have created an accelerating, increasingly connected, globalized economy, resulting in a more globalized, shared flora. The prevention of new, establishing species is less costly, both economically and ecologically, and is more manageable than eradicating nonnative invasive species once they are widespread and negatively impactful. We ask if international trade hubs and points-of-entry with high-volume trade, constant disturbance, and propagule rain have a higher number of nonnative species compared to surrounding areas and if they may serve as initial establishment sites and refugia of nonnative, invasive populations. Therefore, we partnered with various federal, state, and private interests to evaluate the floristic composition at the Garden City Terminal of the Port of Savannah, Georgia, USA. We conducted the following study to demonstrate the collaborative relationship-building between researchers and industry and to develop a framework for biodiversity conservation. In our study, we collected all reproductive vascular plants in the secured areas of the Garden City Terminal during four major seasonal time points over two years. The percent of nonnative species and number of nonnative plant species per hectare at this industrial location exceeded all other comparison floras. The mean coefficient of conservatism was lowest among the comparison floras, indicating a highly disturbed habitat with nonnative, weedy native, and other native species tolerant of disturbance. Our study represents one of the first inventories of an Industrialized Flora and indicates that such areas are hot-spots of nonnative plant diversity and possible sources of emergent plant invasions. We posit that industrial sites and international points-of-entry should be considered laboratories for research on species transport and introduction, adaptability, and taxonomic delineation to better understand the mechanisms and consequences of biotic homogenization due to the volume and frequency of anthropogenic activities.

Microsatellite markers for the endangered Puya raimondii in Peru

PREMISE

Microsatellite primers were developed for Puya raimondii (Bromeliaceae), an endangered species distributed in the Andean Mountains of Bolivia and Peru.

METHODS AND RESULTS

Genome skimming of P. raimondii, P. macrura, and P. hutchisonii resulted in the selection of 46 pairs of cross-species microsatellite markers. Of these, 12 microsatellite primer pairs produced clear and polymorphic bands in P. raimondii. These primer sets were then used for the detection of potential polymorphisms in 84 P. raimondii individuals collected from four populations in Peru. The number of alleles per locus ranged from one to six, and the observed and expected levels of heterozygosity ranged from 0.000 to 0.8929 and from 0.000 to 0.7662, respectively.

CONCLUSIONS

The microsatellite markers developed in this study will be useful for future population genetic analyses and breeding system studies in P. raimondii.

Distribution and Community Assembly of Trees Along an Andean Elevational Gradient

Highlighting patterns of distribution and assembly of plants involves the use of community phylogenetic analyses and complementary traditional taxonomic metrics. However, these patterns are often unknown or in dispute, particularly along elevational gradients, with studies finding different patterns based on elevation. We investigated how patterns of tree diversity and structure change along an elevation gradient using taxonomic and phylogenetic diversity metrics. We sampled 595 individuals (36 families; 53 genera; 88 species) across 15 plots along an elevational gradient (2440-3330 m) in Ecuador. Seventy species were sequenced for the rbcL and matK gene regions to generate a phylogeny. Species richness, Shannon-Weaver diversity, Simpson's Dominance, Simpson's Evenness, phylogenetic diversity (PD), mean pairwise distance (MPD), and mean nearest taxon distance (MNTD) were evaluated for each plot. Values were correlated with elevation and standardized effect sizes (SES) of MPD and MNTD were generated, including and excluding tree fern species, for comparisons across elevation. Taxonomic and phylogenetic metrics found that species diversity decreases with elevation. We also found that overall the community has a non-random phylogenetic structure, dependent on the presence of tree ferns, with stronger phylogenetic clustering at high elevations. Combined, this evidence supports the ideas that tree ferns have converged with angiosperms to occupy the same habitat and that an increased filtering of clades has led to more closely related angiosperm species at higher elevations.

The use of DNA barcodes to estimate phylogenetic diversity in forest communities of southern China

To elucidate potential ecological and evolutionary processes associated with the assembly of plant communities, there is now widespread use of estimates of phylogenetic diversity that are based on a variety of DNA barcode regions and phylogenetic construction methods. However, relatively few studies consider how estimates of phylogenetic diversity may be influenced by single DNA barcodes incorporated into a sequence matrix (conservative regions vs. hypervariable regions) and the use of a backbone family-level phylogeny. Here, we use general linear mixed-effects models to examine the influence of different combinations of core DNA barcodes (rbcL, matK, ITS, and ITS2) and phylogeny construction methods on a series of estimates of community phylogenetic diversity for two subtropical forest plots in Guangdong, southern China. We ask: (a) What are the relative influences of single DNA barcodes on estimates phylogenetic diversity metrics? and (b) What is the effect of using a backbone family-level phylogeny to estimate topology-based phylogenetic diversity metrics? The combination of more than one barcode (i.e., rbcL + matK + ITS) and the use of a backbone family-level phylogeny provided the most parsimonious explanation of variation in estimates of phylogenetic diversity. The use of a backbone family-level phylogeny showed a stronger effect on phylogenetic diversity metrics that are based on tree topology compared to those that are based on branch lengths. In addition, the variation in the estimates of phylogenetic diversity that was explained by the top-rank models ranged from 0.1% to 31% and was dependent on the type of phylogenetic community structure metric. Our study underscores the importance of incorporating a multilocus DNA barcode and the use of a backbone family-level phylogeny to infer phylogenetic diversity, where the type of DNA barcode employed and the phylogenetic construction method used can serve as a significant source of variation in estimates of phylogenetic community structure.

Incomplete reproductive isolation between Rhododendron taxa enables hybrid formation and persistence

The evolutionary consequences of hybridization ultimately depend on the magnitude of reproductive isolation between hybrids and their parents. We evaluated the relative contributions of pre- and post-zygotic barriers to reproduction for hybrid formation, hybrid persistence and potential for reproductive isolation of hybrids formed between two Rhododendron species, R. spiciferum and R. spinuliferum. Our study established that incomplete reproductive isolation promotes hybrid formation and persistence and delays hybrid speciation. All pre-zygotic barriers to reproduction leading to hybrid formation are incomplete: parental species have overlapping flowering; they share the same pollinators; reciprocal assessments of pollen tube germination and growth do not differ among parents. The absence of post-zygotic barriers between parental taxa indicates that the persistence of hybrids is likely. Reproductive isolation was incomplete between hybrids and parents in all cases studied, although asymmetric differences in reproductive fitness were prevalent and possibly explain the genetic structure of natural hybrid swarms where hybridization is known to be bidirectional but asymmetric. Introgression, rather than speciation, is a probable evolutionary outcome of hybridization between the two Rhododendron taxa. Our study provides insights into understanding the evolutionary implications of natural hybridization in woody plants.

Upward elevation and northwest range shifts for alpine Meconopsis species in the Himalaya-Hengduan Mountains region

Climate change may impact the distribution of species by shifting their ranges to higher elevations or higher latitudes. The impacts on alpine plant species may be particularly profound due to a potential lack of availability of future suitable habitat. To identify how alpine species have responded to climate change during the past century as well as to predict how they may react to possible global climate change scenarios in the future, we investigate the climatic responses of seven species of Meconopsis, a representative genus endemic in the alpine meadow and subnival region of the Himalaya-Hengduan Mountains. We analyzed past elevational shifts, as well as projected shifts in longitude, latitude, elevation, and range size using historical specimen records and species distribution modeling under optimistic (RCP 4.5) and pessimistic (RCP 8.5) scenarios across three general circulation models for 2070. Our results indicate that across all seven species, there has been an upward shift in mean elevation of 302.3 m between the pre-1970s (1922-1969) and the post-1970s (1970-2016). The model predictions suggest that the future suitable climate space will continue to shift upwards in elevation (as well as northwards and westwards) by 2070. While for most of the analyzed species, the area of suitable climate space is predicted to expand under the optimistic emission scenario, the area contracts, or, at best, shows little change under the pessimistic scenario. Species such as M. punicea, which already occupy high latitudes, are consistently predicted to experience a contraction of suitable climate space across all the models by 2070 and may consequently deserve particular attention by conservation strategies. Collectively, our results suggest that the alpine high-latitude species analyzed here have already been significantly impacted by climate change and that these trends may continue over the coming decades.

Distributional responses to climate change for alpine species of Cyananthus and Primula endemic to the Himalaya-Hengduan Mountains

Global warming increases the vulnerability of plants, especially alpine herbaceous species, to local extinction. In this study, we collected species distribution information from herbarium specimens for ten selected Cyananthus and Primula alpine species endemic to the Himalaya-Hengduan Mountains (HHM). Combined with climate data from WorldClim, we used Maximum Entropy Modeling (MaxEnt) to project distributional changes from the current time period to 2070. Our predictions indicate that, under a wide range of climate change scenarios, the distributions of all species will shift upward in elevation and northward in latitude; furthermore, under these scenarios, species will expand the size of their range. For the majority of the species in this study, habitats are available to mitigate upward and northward shifts that are projected to be induced by changing climate. If current climate projections, however, increase in magnitude or continue to increase past our projection dates, suitable habitat for future occupation by alpine species will be limited as we predict range contraction or less range expansion for some of the species under more intensified climate scenarios. Our study not only underscores the value of herbarium source information for future climate model projections but also suggests that future studies on the effects of climate change on alpine species should include additional biotic and abiotic factors to provide greater resolution of the local dynamics associated with species persistence under a warming climate.

Biodiversity explains maximum variation in productivity under experimental warming, nitrogen addition, and grazing in mountain grasslands

Anthropogenic global warming, nitrogen addition, and overgrazing alter plant communities and threaten plant biodiversity, potentially impacting community productivity, especially in sensitive mountain grassland ecosystems. However, it still remains unknown whether the relationship between plant biodiversity and community productivity varies across different anthropogenic influences, and especially how changes in multiple biodiversity facets drive these impacts on productivity. Here, we measured different facets of biodiversity including functional and phylogenetic richness and evenness in mountain grasslands along an environmental gradient of elevation in Yulong Mountain, Yunnan, China. We combined biodiversity metrics in a series of linear mixed-effect models to determine the most parsimonious predictors for productivity, which was estimated by aboveground biomass in community. We examined how biodiversity-productivity relationships were affected by experimental warming, nitrogen addition, and livestock-grazing. Species richness, phylogenetic diversity, and single functional traits (leaf nitrogen content, mg/g) represented the most parsimonious combination in these scenarios, supporting a consensus that single-biodiversity metrics alone cannot fully explain ecosystem function. The biodiversity-productivity relationships were positive and strong, but the effects of treatment on biodiversity-productivity relationship were negligible. Our findings indicate that the strong biodiversity-productivity relationships are consistent in various anthropogenic drivers of environmental change.

DNA barcoding herbaceous and woody plant species at a subalpine forest dynamics plot in Southwest China

Although DNA barcoding has been widely used to identify plant species composition in temperate and tropical ecosystems, relatively few studies have used DNA barcodes to document both herbaceous and woody components of forest plot. A total of 201 species (72 woody species and 129 herbaceous species) representing 135 genera distributed across 64 families of seed plants were collected in a 25 ha CForBio subalpine forest dynamics plot. In total, 491 specimens were screened for three DNA regions of the chloroplast genome (rbcL, matK, and trnH-psbA) as well as the internal transcribed spacers (ITS) of nuclear ribosomal DNA. We quantified species resolution for each barcode separately or in combination using a ML tree-based method. Amplification and sequencing success were highest for rbcL, followed by trnH-psbA, which performed better than ITS and matK. The rbcL + ITS barcode had slightly higher species resolution rates (88.60%) compared with rbcL + matK (86.60%) and rbcL + trnH-psbA (86.01%). The addition of trnH-psbA or ITS to the rbcL + matK barcode only marginally increased species resolution rates, although in combination the four barcodes had the highest discriminatory power (90.21%). The situations where DNA barcodes did not discriminate among species were typically associated with higher numbers of co-occurring con-generic species. In addition, herbaceous species were much better resolved than woody species. Our study represents one of the first applications of DNA barcodes in a subalpine forest dynamics plot and contributes to our understanding of patterns of genetic divergence among woody and herbaceous plant species.

Functional trade-offs and the phylogenetic dispersion of seed traits in a biodiversity hotspot of the Mountains of Southwest China

The diversity of traits associated with plant regeneration is often shaped by functional trade-offs where plants typically do not excel at every function because resources allocated to one function cannot be allocated to another. By analyzing correlations among seed traits, empirical studies have shown that there is a trade-off between seedling development and the occupation of new habitats, although only a small range of taxa have been tested; whether such trade-off exists in a biodiverse and complex landscape remains unclear. Here, we amassed seed trait data of 1,119 species from a biodiversity hotspot of the Mountains of Southwest China and analyzed the relationship between seed mass and the number of seeds and between seed mass and time to germination. Our results showed that seed mass was negatively correlated with seed number but positively correlated with time to germination. The same trend was found regardless of variation in life-form and phylogenetic conservatism. Furthermore, the relation between seed mass and other seed traits was randomly dispersed across the phylogeny at both the order and family levels. Collectively, results suggest that there is a functional trade-off between seedling development and new habitat occupation for seed plants in this region. Larger seeds tend to produce fewer seedlings but with greater fitness compared to those produced by smaller seeds, whereas smaller seeds tend to have a larger number of seeds that germinate faster compared to large-seeded species. Apart from genetic constraints, species that produce large seeds will succeed in sites where resource availability is low, whereas species with high colonization ability (those that produce a high number of seeds per fruit) will succeed in new niches. This study provides a mechanistic explanation for the relatively high levels of plant diversity currently found in a heterogeneous region of the Mountains of Southwest China.

Green synthesis of new pyrrolidine-fused spirooxindoles via three-component domino reaction in EtOH/H2O

An efficient, green and sustainable approach for the synthesis of novel polycyclic pyrrolidine-fused spirooxindole compounds was developed. The synthesis included a one-pot, three-component, domino reaction of (E)-3-(2-nitrovinyl)-indoles, isatins and chiral polycyclic α-amino acids under catalyst-free conditions at room temperature in EtOH–H₂O. The salient features of this methodology are eco-friendliness, high yields and the ease of obtaining target compounds without the involvement of toxic solvents and column chromatography. These novel polycyclic pyrrolidine-fused spirooxindoles provide a collection of structurally diverse compounds that show promise for future bioassays and medical treatments.

An efficient, green and sustainable approach was developed for the synthesis of novel polycyclic pyrrolidine-fused spirooxindole compounds.

Pollen sleuthing for terrestrial plant surveys: Locating plant populations by exploiting pollen movement

PREMISE OF THE STUDY

We present an innovative technique for sampling, identifying, and locating plant populations that release pollen, without extensive ground surveys. This method (1) samples pollen at random locations within the target species' habitat, (2) detects species' presence using morphological pollen analysis, and (3) uses kriging to predict likely locations of populations to focus future search efforts.

METHODS

To demonstrate, we applied the pollen sleuthing system to search for artificially constructed populations of Brassica rapa in an old field. Population size varied from 0-100 flowers labeled with artificial pollen (paint pellets). After characterizing the landscape, we pan-trapped 2762 potential insect vectors from random locations across the field and washed particulate matter from their bodies to assess artificial pollen abundance with a microscope.

RESULTS

Population size greatly influenced artificial pollen detection success; following random pollen trap sampling and interpolation, ground surveys would be best focused on identified areas with high pollen density and low variation in pollen density. Sampling sites most successfully detected artificial pollen when they were located at higher elevations, near showy flowering plants that were not grasses.

DISCUSSION

Detection of nascent populations using the proposed system is possible but accuracy will depend on local environmental factors (e.g., wind, elevation). Conservation and invasive species control programs may be improved by using this approach.

Asymmetrical natural hybridization varies among hybrid swarms between two diploid Rhododendron species

Background and Aims

The extent to which hybridization leads to gene flow between plant species depends on the structure of hybrid populations. However, if this varies between locations, species barriers might prove permeable in some locations but not in others. To assess possible variation in hybrid population structure, the magnitude and direction of natural hybridization between two Chinese endemic species, Rhododendron spiciferum and Rhododendron spinuliferum , were evaluated.

Methods

Thirteen nuclear microsatellite markers were employed to characterize 566 individuals collected from 15 non-allopatric populations and nine allopatric parental populations. Chloroplast DNA (cpDNA) sequences were obtained from a subset of samples. Genetic structure and direction of gene flow was determined using a combination of STRUCTURE and NEWHYBRIDS analysis.

Key Results

Nuclear analysis revealed that parental taxa formed two genetically distinct clusters and hybrids shared the genetic background of both parents and did not form a separate genetic lineage. Overall, hybrid swarms were dominated by early- and later-generation hybrids, with a significantly higher proportion of hybrids (59·6 %) possessing >50 % R. spiciferum-like nuclear germplasm. The cpDNA analysis further indicated that a significantly greater proportion of hybrids (61·1 %) possessed the R. spiciferum cpDNA haplotype.

Conclusions

Gene flow between R. spiciferum and R. spinuliferum was found to be bidirectional in 14 of the 15 hybrid swarms and asymmetrical in six hybrid swarms. Asymmetrical gene flow was evident for only nuclear DNA (nDNA) in two populations, for only cpDNA in three populations, and for both nDNA and cpDNA in one population. Collectively, the variation in genetic structure found among the 15 hybrid swarms suggests that introgression rather than hybrid speciation is a more likely outcome of hybridization between these hybridizing taxa.

Applying pollen DNA metabarcoding to the study of plant-pollinator interactions

PREMISE OF THE STUDY

To study pollination networks in a changing environment, we need accurate, high-throughput methods. Previous studies have shown that more highly resolved networks can be constructed by studying pollen loads taken from bees, relative to field observations. DNA metabarcoding potentially allows for faster and finer-scale taxonomic resolution of pollen compared to traditional approaches (e.g., light microscopy), but has not been applied to pollination networks.

METHODS

We sampled pollen from 38 bee species collected in Florida from sites differing in forest management. We isolated DNA from pollen mixtures and sequenced rbcL and ITS2 gene regions from all mixtures in a single run on the Illumina MiSeq platform. We identified species from sequence data using comprehensive rbcL and ITS2 databases.

RESULTS

We successfully built a proof-of-concept quantitative pollination network using pollen metabarcoding.

DISCUSSION

Our work underscores that pollen metabarcoding is not quantitative but that quantitative networks can be constructed based on the number of interacting individuals. Due to the frequency of contamination and false positive reads, isolation and PCR negative controls should be used in every reaction. DNA metabarcoding has advantages in efficiency and resolution over microscopic identification of pollen, and we expect that it will have broad utility for future studies of plant-pollinator interactions.

Using In Situ Symbiotic Seed Germination to Restore Over-collected Medicinal Orchids in Southwest China

Due to increasing demand for medicinal and horticultural uses, the Orchidaceae is in urgent need of innovative and novel propagation techniques that address both market demand and conservation. Traditionally, restoration techniques have been centered on ex situ asymbiotic or symbiotic seed germination techniques that are not cost-effective, have limited genetic potential and often result in low survival rates in the field. Here, we propose a novel in situ advanced restoration-friendly program for the endangered epiphytic orchid species Dendrobium devonianum, in which a series of in situ symbiotic seed germination trials base on conspecific fungal isolates were conducted at two sites in Yunnan Province, China. We found that percentage germination varied among treatments and locations; control treatments (no inoculum) did not germinate at both sites. We found that the optimal treatment, having the highest in situ seed germination rate (0.94-1.44%) with no significant variation among sites, supported a warm, moist and fixed site that allowed for light penetration. When accounting for seed density, percentage germination was highest (2.78-2.35%) at low densities and did not vary among locations for the treatment that supported optimal conditions. Similarly for the same treatment, seed germination ranged from 0.24 to 5.87% among seasons but also did vary among sites. This study reports on the cultivation and restoration of an endangered epiphytic orchid species by in situ symbiotic seed germination and is likely to have broad application to the horticulture and conservation of the Orchidaceae.

Pollen DNA barcoding: current applications and future prospects

Identification of the species origin of pollen has many applications, including assessment of plant–pollinator networks, reconstruction of ancient plant communities, product authentication, allergen monitoring, and forensics. Such applications, however, have previously been limited by microscopy-based identification of pollen, which is slow, has low taxonomic resolution, and has few expert practitioners. One alternative is pollen DNA barcoding, which could overcome these issues. Recent studies demonstrate that both chloroplast and nuclear barcoding markers can be amplified from pollen. These recent validations of pollen metabarcoding indicate that now is the time for researchers in various fields to consider applying these methods to their research programs. In this paper, we review the nascent field of pollen DNA barcoding and discuss potential new applications of this technology, highlighting existing limitations and future research developments that will improve its utility in a wide range of applications.

Age-Related Changes in MicroRNA Expression and Pharmacogenes in Human Liver

Developmental changes in the liver can significantly impact drug disposition. Due to the emergence of microRNAs (miRNAs) as important regulators of drug disposition gene expression, we studied age-dependent changes in miRNA expression. Expression of 533 miRNAs was measured in 90 human liver tissues (fetal, pediatric [1-17 years], and adult [28-80 years]; n = 30 each). In all, 114 miRNAs were upregulated and 72 were downregulated from fetal to pediatric, and 2 and 3, respectively, from pediatric to adult. Among the developmentally changing miRNAs, 99 miRNA-mRNA interactions were predicted or experimentally validated (e.g., hsa-miR-125b-5p-CYP1A1; hsa-miR-34a-5p-HNF4A). In human liver samples (n = 10 each), analyzed by RNA-sequencing, significant negative correlations were observed between the expression of >1,000 miRNAs and mRNAs of drug disposition and regulatory genes. Our data suggest a mechanism for the marked changes in hepatic gene expression between the fetal and pediatric developmental periods, and support a role for these age-dependent miRNAs in regulating drug disposition.

Spatial patterns of plant diversity below-ground as revealed by DNA barcoding

Our understanding of the spatial organization of root diversity in plant communities and of the mechanisms of community assembly has been limited by our ability to identify plants based on root tissue, especially in diverse communities. Here, we test the effectiveness of the plastid gene rbcL, a core plant DNA barcoding marker, for investigating spatial patterns of root diversity, and relate observed patterns to above-ground community structure. We collected 3800 root fragments from four randomly positioned, 1-m-deep soil profiles (two vertical transects per plot), located in an old-field community in southern Ontario, Canada, and extracted and sequenced DNA from 1531 subsampled fragments. We identified species by comparing sequences with a DNA barcode reference library developed previously for the local flora. Nearly 85% of sampled root fragments were successfully sequenced and identified as belonging to 29 plant species or species groups. Root abundance and species richness varied in horizontal space and were negatively correlated with soil depth. The relative abundance of taxa below-ground was correlated with their frequency above-ground (r = 0.73, P = 0.0001), but several species detected in root tissue were not observed in above-ground quadrats. Multivariate analyses indicated that diversity was highly structured below-ground, and associated with depth, root morphology, soil chemistry and soil texture, whereas little structure was evident above-ground. Furthermore, analyses of species co-occurrence indicates strong species segregation overall but random co-occurrence among confamilials. Our results provide insights into the role of environmental filtering and competitive interactions in the organization of plant diversity below-ground, and also demonstrate the utility of barcoding for the identification of plant roots.

Manipulation of flowering time: phenological integration and maternal effects

Timing of flowering is central to reproductive success and is currently advancing in many natural populations due to a warmer climate. However, we have little understanding of how earlier initiation of flowering influences subsequent reproductive phenology or the expression of traits in the offspring. To evaluate the consequences of an altered flowering phenology we manipulated cohorts of Campanulastrum americanum, an herb with annual and biennial growth forms, to flower and disperse seeds up to a month earlier, at the same time, and up to a month later than a natural population in two separate years. Relative to the date of first flower, the temporal patterns of flower production and the timing of fruit maturation and seed dispersal were similar among individuals that initiated flowering over the expanded reproductive season, indicating strong phenological integration of reproductive traits. However, plants that initiated flowering substantially outside the natural window showed a change in the rate of reproduction, with a compressed reproductive schedule for early-flowering individuals and an expanded one for late-flowering plants. Changes in flowering time had more dramatic effects on the offspring generation. Initiation of flowering two weeks earlier would result in a fourfold increase in the frequency of annual offspring, and four weeks earlier would result in a tenfold increase. The frequency of annuals was less sensitive to modest delays in flowering time but decreased with greater delays in flowering time. Collectively, these results reveal a tightly integrated reproductive phenology that shifts with timing of flowering within generations but may lead to more dramatic responses to climate change between generations.

Multiple multilocus DNA barcodes from the plastid genome discriminate plant species equally well

A universal barcode system for land plants would be a valuable resource, with potential utility in fields as diverse as ecology, floristics, law enforcement and industry. However, the application of plant barcoding has been constrained by a lack of consensus regarding the most variable and technically practical DNA region(s). We compared eight candidate plant barcoding regions from the plastome and one from the mitochondrial genome for how well they discriminated the monophyly of 92 species in 32 diverse genera of land plants (N = 251 samples). The plastid markers comprise portions of five coding (rpoB, rpoC1, rbcL, matK and 23S rDNA) and three non-coding (trnH-psbA, atpF-atpH, and psbK-psbI) loci. Our survey included several taxonomically complex groups, and in all cases we examined multiple populations and species. The regions differed in their ability to discriminate species, and in ease of retrieval, in terms of amplification and sequencing success. Single locus resolution ranged from 7% (23S rDNA) to 59% (trnH-psbA) of species with well-supported monophyly. Sequence recovery rates were related primarily to amplification success (85-100% for plastid loci), with matK requiring the greatest effort to achieve reasonable recovery (88% using 10 primer pairs). Several loci (matK, psbK-psbI, trnH-psbA) were problematic for generating fully bidirectional sequences. Setting aside technical issues related to amplification and sequencing, combining the more variable plastid markers provided clear benefits for resolving species, although with diminishing returns, as all combinations assessed using four to seven regions had only marginally different success rates (69-71%; values that were approached by several two- and three-region combinations). This performance plateau may indicate fundamental upper limits on the precision of species discrimination that is possible with DNA barcoding systems that include moderate numbers of plastid markers. Resolution to the contentious debate on plant barcoding should therefore involve increased attention to practical issues related to the ease of sequence recovery, global alignability, and marker redundancy in multilocus plant DNA barcoding systems.

Interspecific seed discounting and the fertility cost of hybridization in an endangered species

Hybrid fertilizations can have negative demographic effects on taxa by usurping ovules that would otherwise give rise to nonhybrid offspring. The consequent reduction in conspecific matings may be exaggerated in rare taxa and constitutes a fertility cost that has rarely been quantified. Here, the effect of interspecific mating was estimated on the fecundity of locally rare red mulberry (Morus rubra), which hybridizes with introduced white mulberry (Morus alba) and red yen white hybrids. First, the asymmetry in pollen production among red, white and hybrid mulberry in two sympatric populations was quantified. The fertility cost of hybridization was then assessed experimentally by estimating seed production and rates of interspecific mating in red mulberry trees from plots where white and hybrid mulberry trees were selectively removed. On average, the percentage of mulberry pollen per plot produced by red mulberry (8%) was significantly lower than the mean for white and hybrid mulberry combined (92%). Experimentally removing white and hybrid mulberry increased the siring fertility of red mulberry by 14% but produced no change in seed set. Results indicate that seeds of red mulberry, ordinarily sired by conspecific pollen, are being discounted through fertilization of ovules by heterospecific pollen, which may contribute to local decline of red mulberry.

Artificial selection shifts flowering phenology and other correlated traits in an autotetraploid herb

There is mounting evidence that plants are responding to anthropogenic climate change with shifts in flowering phenologies. We conducted a three-generation artificial selection experiment on flowering time in Campanulastrum americanum, an autotetraploid herb, to determine the potential for adaptive evolution of this trait as well as possible costs associated with enhanced or delayed flowering. Divergent selection for earlier and later flowering resulted in a 25-day difference in flowering time. Experiment-wide heritability was 0.31 and 0.23 for the initiation of flowering in early and late lines, respectively. Selection for earlier flowering resulted in significant correlated responses in other traits including smaller size, fewer branches, smaller floral displays, longer fruit maturation times, fewer seeds per fruit and slower seed germination. Results suggest that although flowering time shows the potential to adapt to a changing climate, phenological shifts may be associated with reduced plant fitness possibly hindering evolutionary change.

Asymmetrical introgression between two Morus species (M. alba, M. rubra) that differ in abundance

Asymmetrical introgression is an expected genetic consequence of hybridization when parental taxa differ in abundance; however, evidence for such effects in small populations is scarce. To test this prediction, we estimated the magnitude and direction of hybridization between red mulberry (Morus rubra L.), an endangered species in Canada, and the introduced and more abundant white mulberry (Morus alba L.) using nuclear (randomly amplified polymorphic DNA) and cytoplasmic (chloroplast DNA sequence) markers. Parentage of 184 trees (n = 42 using cpDNA) from four sympatric populations was estimated using a hybrid index and related to six morphological characters and population frequencies of the parental classes. Overall, the frequency of nuclear hybrids was 53.7% (n = 99) and ranged from 43% to 67% among populations. The parental and hybrid taxa differed with respect to all of the morphological traits. Sixty-seven percent of all hybrids contained more nuclear markers from M. alba than M. rubra (hybrid index x = 0.46); among populations, the degree of M. alba bias was correlated with the frequency of M. alba. In addition, the majority of hybrids (68%) contained the chloroplast genome of white mulberry. These results suggest that introgression is bidirectional but asymmetrical and is related, in part, to the relative frequency of parental taxa.

Maternal and paternal contributions to the fitness of hybrids between red and white mulberry (Morus, Moraceae)

The fitness of hybrids depends on the genetic disparity between parental taxa and the magnitude of their nuclear and non-nuclear contributions. To estimate the role of non-nuclear effects, we crossed red (R), white (W) and hybrid (H) mulberry in all combinations and compared the magnitude of maternal and paternal effects on offspring fitness (seed set, germination, survival and aboveground biomass) in a greenhouse environment. Variation in offspring fitness was determined largely by the identity of the maternal parent; specifically, progeny with white mothers had the highest cumulative fitness. As fathers, red, white, and hybrid mulberry had no effect on fitness, and maternal × paternal interactions were significant only for survival. Individual cross-types differed significantly for all fitness components except seed set. Offspring from hybrid crosses (W × R, H × R, H × W) often differed from at least one of the within-parent crosses (W × W, R × R) as well as from other hybrid crosses, although their fitness values never exceeded the most fit parent. Reciprocal crosses differed in only two of 15 possible parental combinations: W × H (cumulative fitness) and W × R (aboveground biomass). Overall, the strong asymmetry in magnitude of maternal and paternal effects suggests that fitness of hybrid mulberry is governed largely by non-nuclear, parental effects.