Genome-material costs and functional trade-offs in the autopolyploid Solidago gigantea (giant goldenrod) series.

PREMISE: Increased genome-material costs of N and P atoms inherent to organisms with larger genomes have been proposed to limit growth under nutrient scarcities and to promote growth under nutrient enrichments. Such responsiveness may reflect a nutrient-dependent diploid versus polyploid advantage that could have vast ecological and evolutionary implications, but direct evidence that material costs increase with ploidy level and/or influence cytotype-dependent growth, metabolic, and/or resource-use trade-offs is limited. METHODS: We grew diploid, autotetraploid, and autohexaploid Solidago gigantea plants with one of four ambient or enriched N:P ratios and measured traits related to material costs, primary and secondary metabolism, and resource-use. RESULTS: Relative to diploids, polyploids invested more N and P into cells, and tetraploids grew more with N enrichments, suggesting that material costs increase with ploidy level. Polyploids also generally exhibited strategies that could minimize material-cost constraints over both long (reduced monoploid genome size) and short (more extreme transcriptome downsizing, reduced photosynthesis rates and terpene concentrations, enhanced N-use efficiencies) evolutionary time periods. Furthermore, polyploids had lower transpiration rates but higher water-use efficiencies than diploids, both of which were more pronounced under nutrient-limiting conditions. CONCLUSIONS: N and P material costs increase with ploidy level, but material-cost constraints might be lessened by resource allocation/investment mechanisms that can also alter ecological dynamics and selection. Our results enhance mechanistic understanding of how global increases in nutrients might provide a release from material-cost constraints in polyploids that could impact ploidy (or genome-size)-specific performances, cytogeographic patterning, and multispecies community structuring.

Goldenrod herbariomics: Hybrid-sequence capture reveals the phylogeny of Solidago.

PREMISE: The phylogenetic relationships among the ca. 138 species of goldenrods (Solidago; Asteraceae) have been difficult to infer due to species richness, and shallow interspecific genetic divergences. This study aims to overcome these obstacles by combining extensive sampling of goldenrod herbarium specimens with the use of a custom Solidago hybrid-sequence capture probe set. METHODS: A set of tissues from herbarium samples comprising ca. 90% of Solidago species was assembled and DNA was extracted. A custom hybrid-sequence capture probe set was designed, and data from 854 nuclear regions were obtained and analyzed from 209 specimens. Maximum likelihood and coalescent approaches were used to estimate the genus phylogeny for 157 diploid samples. RESULTS: Although DNAs from older specimens were both more fragmented and produced fewer sequencing reads, there was no relationship between specimen age and our ability to obtain sufficient data at the target loci. The Solidago phylogeny was generally well-supported, with 88/155 (57%) nodes receiving ≥95% bootstrap support. Solidago was supported as monophyletic, with Chrysoma pauciflosculosa identified as sister. A clade comprising Solidago ericameriodes, Solidago odora, and Solidago chapmanii was identified as the earliest diverging Solidago lineage. The previously segregated genera Brintonia and Oligoneuron were identified as placed well within Solidago. These and other phylogenetic results were used to establish four subgenera and fifteen sections within the genus. CONCLUSIONS: The combination of expansive herbarium sampling and hybrid-sequence capture data allowed us to quickly and rigorously establish the evolutionary relationships within this difficult, species-rich group.

Do water and soil nutrient scarcities differentially impact the performance of diploid and tetraploid Solidago gigantea (Giant Goldenrod, Asteraceae)?

Plants require water and nutrients for survival, although the effects of their availabilities on plant fitness differ amongst species. Genome size variation, within and across species, is suspected to influence plant water and nutrient requirements, but little is known about how variations in these resources concurrently affect plant fitness based on genome size. We examined how genome size variation between autopolyploid cytotypes influences plant morphological and physiological traits, and whether cytotype-specific trait responses differ based on water and/or nutrient availability. Diploid and autotetraploid Solidago gigantea (Giant Goldenrod) were grown in a greenhouse under four soil water:N+P treatments (L:L, L:H, H:L, H:H), and stomata characteristics (size, density), growth (above- and belowground biomass, R/S), and physiological (Anet , E, WUE) responses were measured. Resource availabilities and cytotype identity influenced some plant responses but their effects were independent of each other. Plants grown in high-water and nutrient treatments were larger, plants grown in low-water or high-nutrient treatments had higher WUE but lower E, and Anet and E rates decreased as plants aged. Autotetraploids also had larger and fewer stomata, higher biomass and larger Anet than diploids. Nutrient and water availability could influence intra- and interspecific competitive outcomes. Although S. gigantea cytotypes were not differentially affected by resource treatments, genome size may influence cytogeographic range patterning and population establishment likelihood. For instance, the larger size of autotetraploid S. gigantea might render them more competitive for resources and niche space than diploids.

A geographic mosaic of coevolution between Eurosta solidaginis (Fitch) and its host plant tall goldenrod Solidago altissima (L.).

A geographic mosaic of coevolution has produced local reciprocal adaptation in tall goldenrod, Solidago altissima (L.), and the goldenrod ball-gall fly, Eurosta solidaginis (Fitch 1855). The fly is selected to induce gall diameters that minimize mortality from natural enemies, and the plant is selected to limit gall growth that reduces plant fitness. We conducted a double reciprocal transplant experiment where S. altissima and E. solidaginis from three sites were grown in gardens at each site to partition the gall morphology variation into fly genotype, plant genotype, and the environment components. The host plant gall diameter induced by each E. solidaginis population was adapted to inhibit local natural enemies from ovipositing on or consuming enclosed larvae. Reciprocally, increasing the gall size induced by the local fly population increased the resistance of the local plant host population to gall growth. Differences among sites in natural enemies produced a mosaic of hotspots of coevolutionary arms races between flies selecting for greater gall diameter and plants for smaller diameters, and coldspots where there is no selection on plant or fly for a change in gall diameter. In contrast, the geographic variations of gall length and gall shape were not due to coevolutionary interactions.

Integrated analysis of mRNA-seq and miRNA-seq reveals the advantage of polyploid Solidago canadensis in sexual reproduction.

BACKGROUND: The invasion of Solidago canadensis probably related to polyploidy, which may promotes its potential of sexual reproductive. S. canadensis as an invasive species which rapidly widespread through yield huge numbers of seed, but the mechanism remains unknown. To better understand the advantages of sexual reproduction in hexaploid S. canadensis, transcriptome and small RNA sequencing of diploid and hexaploid cytotypes in flower bud and fruit development stages were performed in this study. RESULTS: The transcriptome analysis showed that in the flower bud stage, 29 DEGs were MADS-box related genes with 14 up-regulated and 15 down-regulated in hexaploid S. canadensis; 12 SPL genes were detected differentially expressed with 5 up-regulated and 7 down-regulated. In the fruit development stage, 26 MADS-box related genes with 20 up-regulated and 6 down-regulated in hexaploid S. canadensis; 5 SPL genes were all up-regulated; 28 seed storage protein related genes with 18 were up-regulated and 10 down-regulated. The weighted gene co-expression network analysis (WGCNA) identified 19 modules which consisted of co-expressed DEGs with functions such as sexual reproduction, secondary metabolism and transcription factors. Furthermore, we discovered 326 miRNAs with 67 known miRNAs and 259 novel miRNAs. Some of miRNAs, such as miR156, miR156a and miR156f, which target the sexual reproduction related genes. CONCLUSION: Our study provides a global view of the advantages of sexual reproduction in hexaploid S. canadensis based on the molecular mechanisms, which may promote hexaploid S. canadensis owing higher yield and fruit quality in the process of sexual reproduction and higher germination rate of seeds, and finally conductive to diffusion, faster propagation process and enhanced invasiveness.

Plant community and the influence of plant taxonomic diversity on community stability and invasibility: A case study based on Solidago canadensis L.

Invasive alien plants (IAPs) can negatively affect plant taxonomic diversity, community stability, and invasibility in the invaded habitats. This study aimed to assess the degree of influence of the IAP Solidago canadensis L. under various levels of invasion (i.e., light, moderate, and heavy invasion based on its relative abundance in the invaded communities) on plant taxonomic diversity, community stability, and invasibility. In addition, we determined the contribution of plant taxonomic diversity to community stability and invasibility under various levels of S. canadensis invasion. The degree of influence of S. canadensis on plant taxonomic diversity and community stability increases as the level of S. canadensis invasion increases. Community invasibility increases as the level of S. canadensis invasion increases. The competitive advantage of S. canadensis is negatively associated with all indexes of plant taxonomic diversity and community stability but positively connected with community invasibility. Community stability is positively related to Shannon's diversity and Simpson's dominance indexes but negatively associated with community invasibility. Inversely, communities were more likely to be invaded when they had less plant taxonomic diversity. Thus, plant communities with lower values of plant taxonomic diversity and community stability are more vulnerable to S. canadensis invasion. Plant diversity causes a greater pressure on community stability than the other indexes of plant taxonomic diversity under various levels of S. canadensis invasion. However, the contribution intensity of the number of plant species to community invasibility is higher than the other indexes of plant taxonomic diversity under various levels of S. canadensis invasion.

Phylogeographic and demographic modeling analyses of the multiple origins of the rheophytic goldenrod Solidago yokusaiana Makino.

Understanding adaptation mechanisms is important in evolutionary biology. Parallel adaptation provides good opportunities to investigate adaptive evolution. To confirm parallel adaptation, it is effective to examine whether the phenotypic similarity has one or multiple origins and to use demographic modeling to consider the gene flow between ecotypes. Solidago yokusaiana is a rheophyte endemic to the Japanese Archipelago that diverged from Solidago virgaurea. This study examined the parallel origins of S. yokusaiana by distinguishing between multiple and single origins and subsequent gene flow. The haplotypes of noncoding chloroplast DNA and genotypes at 14 nuclear simple sequence repeat (nSSR) loci and single-nucleotide polymorphisms (SNPs) revealed by double-digest restriction-associated DNA sequencing (ddRADseq) were used for phylogeographic analysis; the SNPs were also used to model population demographics. Some chloroplast haplotypes were common to S. yokusaiana and its ancestor S. virgaurea. Also, the population genetic structures revealed by nSSR and SNPs did not correspond to the taxonomic species. The demographic modeling supported the multiple origins of S. yokusaiana in at least four districts and rejected a single origin with ongoing gene flow between the two species, implying that S. yokusaiana independently and repeatedly adapted to frequently flooding riversides.

Two cytotype niche shifts are of different magnitude in Solidago gigantea.

PREMISE: Polyploidy may serve to contribute to range size if autopolyploid cytotypes are adapted to differing ecological conditions. This study aims to establish the geographic distribution of cytotypes within the giant goldenrod (Solidago gigantea), and to assess whether cytotypes exhibit differing ecological tolerances and morphology. METHODS: A range-wide set of 629 Solidago gigantea individuals was obtained through field collecting, sampling from herbarium specimens, and incorporating existing chromosome counts. Cytotype of each unknown sample was estimated by observing allele numbers at twelve microsatellite loci, a strategy that was assessed by comparing estimated to known cytotype in 20 chromosome-counted samples. Abiotic ecological differentiation was assessed for two transitions: diploid-tetraploid and tetraploid-hexaploid. Morphological differentiation among cytotypes was assessed. RESULTS: Microsatellite repeat variation accurately estimated cytotype in 85% of samples for which ploidy was known. Applying this approach to samples of unknown ploidy established that the three cytotypes are non-randomly distributed. Although niche modeling and MANOVA approaches identified significant differences in macro-climatic conditions for both cytotype transitions, the tetraploid to hexaploid transition was more substantial. Leaf length and width did not differ among cytotypes. Although leaf vestiture exhibited strong trends, no absolute differences were observed among cytotypes. CONCLUSIONS: With the largest such study to date, we established niche transitions among giant goldenrod cytotypes of differing magnitudes. Collectively, this suggests that whole-genome duplication has contributed to Solidago gigantea's large range.

Evidence that ERF transcriptional regulators serve as possible key molecules for natural variation in defense against herbivores in tall goldenrod.

We collected Solidago altissima clones to explore their leaf damage resistance, and as a result identified five accessions that exhibited variable defense abilities against the generalist herbivore Spodoptera litura. In order to characterize molecules involved in such natural variation, we focused on ethylene response factors (ERFs) that exhibited distinct transcription patterns in the leaves of the five accessions (e.g., S1 and S2) after wounding: the transcript of SaERF1 and SaERF2 was induced in wounded S1 and S2 leaves, respectively. Although transcription levels of SaERFs in leaves of the five accessions did not correlate with the accessions' phytohormone levels, these transcription levels accorded with the possibility that ethylene and jasmonate signaling play crucial roles in wound-induced transcription of SaERF1 in S1 leaves, and SaERF2 in S2 leaves, respectively. SaERF1 was found to be a positive regulator of the GCC box and DRE element in the upstream regions of promoters of defense genes, whereas SaERF2 served as a negative regulator of genes controlled through the GCC box. Transgenic Arabidopsis plants expressing SaERF1 or SaERF2 showed enhanced and suppressed transcript levels, respectively, of a defensin gene, indicating that ERFs may be partly responsible for herbivore resistance properties of S. altissima accessions.

Ecological rigidity and the hardness of selection in the wild.

Hutchinson's ecological theater and evolutionary play is a classical view of evolutionary ecology-ecology provides a template in which evolution occurs. An opposing view is that ecological and evolutionary changes are like two actors on a stage, intertwined by density and frequency dependence. These opposing views correspond to hard and soft selection, respectively. Although often presented as diametrically opposed, both types of selection can occur simultaneously, yet we largely lack knowledge of the relative importance of hard versus soft selection in the wild. I use a dataset of 3000 individual gall makers from 15 wild local populations over 5 years to investigate the hardness of selection. I show that enemy attack consistently favors some gall sizes over others (hard selection) but that these biases can be fine-tuned by density and frequency dependence (soft selection). As a result, selection is hard and soft in roughly equal measures, but the importance of each type varies as species interactions shift. I conclude that eco-evolutionary dynamics should occur when a mix of hard and soft selection acts on a population. This work contributes to the rapprochement of disparate views of evolutionary ecology-ecology is neither a rigid theater nor a flexible actor, but instead embodies components of both.

Polyploidization-driven differentiation of freezing tolerance in Solidago canadensis.

Solidago canadensis, originating from the temperate region of North America, has expanded southward to subtropical regions through polyploidization. Here we investigated whether freezing tolerance of S. canadensis was weakened during expansion. Measurement of the temperature causing 50% ruptured cells (LT50 ) in 35 S. canadensis populations revealed ploidy-related differentiation in freezing tolerance. Freezing tolerance was found to decrease with increasing ploidy. The polyploid populations of S. canadensis had lower ScICE1 gene expression levels but more ScICE1 gene copies than the diploids. Furthermore, more DNA methylation sites in the ScICE1 gene promoter were detected in the polyploids than in the diploids. The results suggest that promoter methylation represses the expression of multi-copy ScICE1 genes, leading to weaker freezing tolerance in polyploid S. canadensis compared to the diploids. The study provides empirical evidence that DNA methylation regulates expression of the gene copies and supports polyploidization-driven adaptation to new environments.

Metabolome and Transcriptome Analysis of Hexaploid Solidago canadensis Roots Reveals its Invasive Capacity Related to Polyploidy.

Polyploid plants are more often invasive species than their diploid counterparts. As the invasiveness of a species is often linked to its production of allelopathic compounds, we hypothesize that differences in invasive ability between cytotypes may be due to their different ability to synthesize allelopathic metabolites. We test this using two cytotypes of Solidago canadensis as the model and use integrated metabolome and transcriptome data to resolve the question. Metabolome analysis identified 122 metabolites about flavonoids, phenylpropanoids and terpenoids, of which 57 were differentially accumulated between the two cytotypes. Transcriptome analysis showed that many differentially expressed genes (DEGs) were enriched in 'biosynthesis of secondary metabolites', 'plant hormone signal transduction', and 'MAPK signaling', covering most steps of plant allelopathic metabolite synthesis. Importantly, the differentially accumulated flavonoids, phenylpropanoids and terpenoids were closely correlated with related DEGs. Furthermore, 30 miRNAs were found to be negatively associated with putative targets, and they were thought to be involved in target gene expression regulation. These miRNAs probably play a vital role in the regulation of metabolite synthesis in hexaploid S. canadensis. The two cytotypes of S. canadensis differ in the allelopathic metabolite synthesis and this difference is associated with regulation of expression of a range of genes. These results suggest that changes in gene expression may underlying the increased invasive potential of the polyploidy.

Constituents of a mixed-ploidy population of Solidago altissima differ in plasticity and predicted response to selection under simulated climate change.

PREMISE OF THE STUDY: Polyploids possess unique attributes that influence their environmental tolerance and geographic distribution. It is often unknown, however, whether cytotypes within mixed-ploidy populations are also uniquely adapted and differ in their responses to environmental change. Here, we examine whether diploids and hexaploids from a single mixed-ploidy population of Solidago altissima differ in plasticity and potential response to natural selection under conditions simulating climate change. METHODS: Clonal replicates of diploid and hexaploid genotypes were grown in a randomized split-plot design under two temperature (+1.9°C) and two watering treatments (-13% soil moisture) implemented with open-top passive chambers placed under rainout shelters. Physiological, phenological, morphological traits, and a fitness correlate, reproductive biomass, were measured and compared among treatments. KEY RESULTS: Differences in traits suggest that diploids are currently better adapted to low- water availability than hexaploids. Both ploidy levels had adaptive plastic responses to treatments and are predicted to respond to selection, but often for different traits. Water availability generally had a stronger effect than temperature, but for some traits the effect of water depended on temperature. CONCLUSIONS: Diploid and hexaploid S. altissima may maintain fitness in the short term through adaptive plasticity and evolution depending on which traits are important in a warmer, drier environment. Hexaploids may be at a disadvantage compared to diploids because fewer traits were heritable. Our results underscore the importance of studying combinations of climate variables that are predicted to change simultaneously.

Adaptive Divergence in a Defense Symbiosis Driven from the Top Down.

Most studies of adaptive radiation in animals focus on resource competition as the primary driver of trait divergence. The roles of other ecological interactions in shaping divergent phenotypes during such radiations have received less attention. We evaluate natural enemies as primary agents of diversifying selection on the phenotypes of an actively diverging lineage of gall midges on tall goldenrod. In this system, the gall of the midge consists of a biotrophic fungal symbiont that develops on host-plant leaves and forms distinctly variable protective carapaces over midge larvae. Through field studies, we show that fungal gall morphology, which is induced by midges (i.e., it is an extended phenotype), is under directional and diversifying selection by parasitoid enemies. Overall, natural enemies disruptively select for either small or large galls, mainly along the axis of gall thickness. These results imply that predators are driving the evolution of phenotypic diversity in symbiotic defense traits in this system and that divergence in defensive morphology may provide ecological opportunities that help to fuel the adaptive radiation of this genus of midges on goldenrods. This enemy-driven phenotypic divergence in a diversifying lineage illustrates the potential importance of consumer-resource and symbiotic species interactions in adaptive radiation.

Effects of Intraspecific Genetic Variation and Prior Herbivory in an Old-Field Plant on the Abundance of the Specialist Aphid Uroleucon nigrotuberculatum (Hemiptera: Aphididae).

Intraspecific genetic variation in plants can contribute to the diversity and abundance of associated insects, though many questions remain about why some genotypes support more insects than others. Since plant secondary metabolites, which may be induced after insect attack, may potentially vary among genotypes, these compounds provide a possible explanation for insect abundance variation in plants with substantial genetic variation. In this study, we examined four genotypes of the old-field plant species Solidago altissima (L.; Asterales: Asteraceae) and asked if the abundance of the specialist aphid Uroleucon nigrotuberculatum (Olive; Hemiptera: Aphididae) was affected by genotype and previous foliage damage by a specialist beetle. We hypothesized that different genotypes and prior herbivory would result in different quantities of terpenes produced by S. altissima, and that terpenes would affect aphid abundance. We found evidence of foliar terpene induction in a greenhouse environment, and significant differences in terpene production among genotypes in a field setting, though prior damage had little effect on aphid abundance in the field. There were significant effects of genotypes on aphid abundance, as well as genotype effects on terpenes and foliar nutrients (leaf N and C:N). Noteworthy was a change in the allocation of particular terpenes among genotypes that related to aphid abundance. Our analyses demonstrated that phytochemicals, and especially terpenes, related to aphid abundance. This study adds to a previous finding that variation in leaf terpenes in S. altissima provides a partial explanation for variable abundance among genotypes of a specialist aphid, and suggests that differences in the allocation of compounds is important.

Phylogeographic analysis of the East Asian goldenrod (Solidago virgaurea complex, Asteraceae) reveals hidden ecological diversification with recurrent formation of ecotypes.

Background and Aims: The processes and mechanisms underlying lineage diversification are major topics in evolutionary biology. Eurasian goldenrod species of the Solidago virgaurea complex show remarkable morphological and ecological diversity in the Japanese Archipelago, with ecotypic taxa well adapted to specific environments (climate, edaphic conditions and disturbance regimes). The species complex is a suitable model to investigate the evolutionary processes of actively speciating plant groups, due to its ability to evolve in relation to environmental adaptation and its historical population dynamics. Methods: Two chloroplast markers, 18 nuclear microsatellite markers and ddRAD-sequencing were used to infer population genetic demography of S. virgaurea complex with its related species/genera. Key Results: Our analysis showed that populations in Japan form an evolutionary unit, which was genetically diverged from adjacent continental populations. The phylogenetic structure within the archipelago strongly corresponds to the geography, but interestingly there is no concordance between genetic structure and ecotypic boundaries; neighbouring populations of distinct ecotypes share a genetic background. Conclusions: We propose that the traits specific to the ecotypic entities are maintained by natural selection or are very recently generated and have little effect on the genomes, making genome-wide genetic markers unsuitable for detecting ecotypic differentiation. Furthermore, some sporadically distributed taxa (found as rheophytes and alpine plants) were repeatedly generated from a more widespread taxon in geographically distant areas by means of selection. Overall, this study showed that the goldenrod complex has a high ability to evolve, enabling rapid ecological diversification over a recent timeframe.

Population genetics and adaptation to climate along elevation gradients in invasive Solidago canadensis.

Gene flow between populations may either support local adaptation by supplying genetic variation on which selection may act, or counteract it if maladapted alleles arrive faster than can be purged by selection. Although both such effects have been documented within plant species' native ranges, how the balance of these forces influences local adaptation in invasive plant populations is less clear, in part because introduced species often have lower genetic variation initially but also tend to have good dispersal abilities. To evaluate the extent of gene flow and adaptation to local climate in invasive populations of Solidago canadensis, and the implications of this for range expansion, we compared population differentiation at microsatellite and chloroplast loci for populations across Switzerland and assessed the effect of environmental transfer distance using common gardens. We found that while patterns of differentiation at neutral genetic markers suggested that populations are connected through extensive pollen and seed movement, common-garden plants nonetheless exhibited modest adaptation to local climate conditions. Growth rate and flower production declined with climatic distance from a plant's home site, with clones from colder home sites performing better at or above the range limit. Such adaptation in invasive species is likely to promote further spread, particularly under climate change, as the genotypes positioned near the range edge may be best able to take advantage of lengthening growing seasons to expand the range.

Simultaneous evaluation of the effects of geographic, environmental and temporal isolation in ecotypic populations of Solidago virgaurea.

Early stages of ecological speciation can create populations with an ecology and reproduction timing distinct from those of related populations. Landscape genetic models incorporating environmental heterogeneity and population-specific reproductive traits enable the processes of population genetic differentiation to be inferred. We investigated genome-wide genetic variation in ecotypic populations of Solidago virgaurea sensu lato, a herbaceous plant inhabiting a wide range of habitats (woodlands, serpentine barrens and alpine grasslands) and displaying remarkable variation in flowering time. Simultaneous evaluation of environmental factors revealed an overwhelming effect of soil type differences on neutral genetic differentiation, compared with elevational differences. This result probably reflects the abrupt environmental changes generated by geological boundaries, whereas mountain slopes exhibit clinal changes, facilitating gene exchange between neighbouring populations. Temporal isolation was positively associated with genetic differentiation, with some early-flowering serpentine populations having allele frequencies distinct from adjacent nonserpentine populations. Overall, this study highlights the importance of ecological processes and of evolution of flowering time to promote genetic differentiation of S. virgaurea populations in a complex landscape.

Characterization of cold-associated microRNAs in the freeze-tolerant gall fly Eurosta solidaginis using high-throughput sequencing.

Significant physiological and biochemical changes are observed in freeze-tolerant insects when confronted with cold temperatures. These insects have adapted to winter by retreating into a hypometabolic state of diapause and implementing cryoprotective mechanisms that allow them to survive whole body freezing. MicroRNAs (miRNAs), a family of short ribonucleic acids, are emerging as likely molecular players underlying the process of cold adaptation. Unfortunately, the data is sparse concerning the signature of miRNAs that are modulated following cold exposure in the freeze-tolerant goldenrod gall fly Eurosta solidaginis. Leveraging for the first time a next-generation sequencing approach, differentially expressed miRNAs were evaluated in 5°C and -15°C-exposed E. solidaginis larvae. Next-generation sequencing expression data was subsequently validated by qRT-PCR for selected miRNA targets. Results demonstrate 24 differentially expressed freeze-responsive miRNAs. Notable, miR-1-3p, a miRNA modulated at low temperature in another cold-hardy insect, and miR-14-3p, a miRNA associated with stress response in the fruit fly, were shown to be significantly up-regulated in -15°C-exposed larvae. Overall, this work identifies, for the first time in a high-throughput manner, differentially expressed miRNAs in cold-exposed E. solidaginis larvae and further clarifies an emerging signature of miRNAs modulated at low temperatures in cold-hardy insects.

Seed Predators, not Herbivores, Exert Natural Selection on Solidago spp. in an Urban Archipelago.

The effects of urbanization on biodiversity are well established, as a growing city will reduce the size and diversity of patches of native plants. Recolonization of old patches and discovery of new ones by arthropod herbivores should occur as predicted by island biogeography theory. Although colonization represents an increase in biodiversity, such arrivals may exert new forms of natural selection on plants through herbivory and seed predation. Using a single species of old-field aster (Solidago altissima L.), we found that the level of natural selection by seed predators and herbivores follows patterns of island biogeography, with lower amounts of damage on smaller islands, where there are fewer species, and hypothetically smaller populations of arthropods. We also found that in an urban system, levels of herbivory are far below the tolerance levels of Solidago, and that seed predators are likely to be the only arthropod to cause reduced fitness. The pattern seen also implies that as a patch of Solidago grows through clonal expansion, it will come under higher selective pressure.