Biology subjects

Ashman, T.-L.

Publications and source records attributed to Ashman, T.-L..

18 recordsLinked to original sources

bioRxiv2026

Tolerance to herbicide drift in "weedy" species is context-dependent and driven by early vegetative growth

While plant communities that exist at the edges of agricultural fields are typically composed of 'weedy' species, they provide essential resources for insect pollinators and other wildlife. However, little is known about how sublethal exposures to herbicides via drift (off-target chemical movement by air) affects the fitness of weedy plant species across varying agro-ecological environments. If weed species vary in sensitivity to herbicide drift, then this could result in plant community shifts in favor of more tolerant species. Consequently, these changes in species composition could alter resource availability in agroecosystems. Here, we replicated a common garden experiment in three US states where agriculture is a major form of land use (Michigan, Pennsylvania, and Tennessee). We exposed nine weed species to a sublethal, drift-level rate of the herbicide dicamba and examined plant fitness. We found that fitness in the presence of dicamba drift depended on both the weed species and the environmental context. For some species, dicamba drift significantly reduced fitness. For others, it had no effect, indicating greater tolerance to the herbicide. However, more variation in tolerance to dicamba drift among species was observed in Michigan compared to Pennsylvania or Tennessee, a result that was partially explained by the severity of damage from insect herbivory that occurred at each location. In a follow-up study, we explored the relationships between plant developmental traits and fitness to determine the functional pathways that underlie tolerance to dicamba drift using structural equation modeling. This approach revealed that weedy plants that are better able to buffer the effects of dicamba drift on short-term growth are then better equipped to minimize effects on flower production and ultimately fitness (seed set). Overall, our work advances knowledge about how wild plant populations in different contexts are responding to unintentional, yet increasingly common occurrences of anthropogenic stress in the form of off-target herbicide exposures.

ecology↗

bioRxiv2025

The role of plant polyploidy in the structure of plant-pollinator communities

Polyploidization is a major macromutation, bearing notable genomic and ecological consequences. While the impact of polyploidy on plant abiotic niches is well studied, our understanding of its consequences on biotic interactions, and particularly pollination, is lacking and hardly considers its role in shaping community structure. Here, we integrate hundreds of plant-pollinator networks, ploidy inferences, reproductive traits, and climatic attributes to ascertain whether a general pattern characterizes the link between polyploid frequency and community structure. We further examine whether environmental factors and plant traits known to be associated with polyploidy mediate this relationship. Our analysis reveals that an increased frequency of polyploid species is positively associated with network nestedness while being negatively associated modularity. Structural equation modeling reveals that these associations are partially mediated via the frequency of self-compatible plants and to a lesser extent by differences in flower shape. Despite these alterations in community structure, the heightened abundance of polyploids appears to have minimal impact on network connectance and resilience to extinction. Our findings imply that unlike abiotic interactions, the impact of polyploidy on biotic interactions is less predictable, and is affected synergistically by both phenotypic and environmental factors. Collectively, however, polyploidy still exerts an influence on community structure.

evolutionary biology↗

bioRxiv2024

Homoploid Hybridization Resolves the Origin of Octoploid Strawberries

The identity of the diploid progenitors of octoploid cultivated strawberry (Fragaria x ananassa) has been subject to much debate. Past work identified four subgenomes and consistent evidence for F. californica (previously named F. vesca subsp. bracteata) and F. iinumae as donors for subgenomes A and B, respectively, with conflicting results for the origins of subgenomes C and D. Here, reticulate phylogeny and admixture analysis support hybridization between F. viridis and F. vesca in the ancestry of subgenome A, and between F. nipponica and F. iinumae in the ancestry of subgenome B. Using an LTR-age-distribution-based approach, we estimate that the octoploid and its intermediate hexaploid and tetraploid ancestors emerged approximately 0.8, 2, and 3 million years ago, respectively. These results provide an explanation for previous reports of F. viridis and F. nipponica as donors of the C and D subgenomes and unify conflicting hypotheses about the evolutionary origin of octoploid Fragaria.

genetics↗

bioRxiv2024

Off-target drift of the herbicide dicamba disrupts plant-pollinator interactions via novel pathways

Assessing the impact of herbicide drift on plant-pollinator interactions is crucial for providing insight into the causes of ongoing pollinator declines. The recent exponential increase in the use of the synthetic auxin herbicide dicamba, which is known to drift long distances following application, renders this concern especially acute. However, experimental data on the consequences of dicamba drift on plant-pollinator interactions are lacking from weed communities in natural settings. We assessed the indirect effects of dicamba drift on pollinator visits for 11 weeds of agricultural crops using a common garden field experiment, focusing on the potential for changes in pollinator abundance and alterations to both plant traits and patterns of pollinator visitation. We found variation among plant species in the extent of damage from dicamba drift exposure, and variation in how growth, flowering time, and flower displays were impacted, with some species showing negative impacts and others showing little effect. Pollinator frequencies were reduced in dicamba-exposed plots, and pollinator approaches and foraging visits were reduced for some weed species yet not others. Structural equation modeling revealed that the relationship between flower display and pollinator visits was disrupted in the presence of dicamba compared to control plots. Our study provides the most comprehensive picture to date of the impacts of dicamba drift on plant-pollinator interactions, with findings that highlight an underappreciated role of services supplied by weedy communities at the agroecological interface.

ecology↗

bioRxiv2024

Learning to handle flowers increases pollen collection benefits for bees but does not affect pollination success for plants

Behavior frequently affects cooperation as well as conflict in plant-pollinator interactions. Pollinators such as bees often modify how they handle flowers with experience and such learning is generally assumed to increase collection of floral food rewards. The complexity of flower morphology also affects how quickly pollinators learn and recall how to access floral rewards from a given flower type. Because learning to handle a flower can increase extraction of food rewards (such as pollen) and often involves the pollinator altering how it interacts with the flowers reproductive organs, pollinator learning could affect pollination success. Yet how pollinator cognition and flower morphology interact to affect pollination success is unknown. We therefore asked how learning and memory of flower handling by pollen-foraging generalist bumble bees (Bombus impatiens) varied among four morphologically distinct flower types (Phacelia campanularia, Exacum affine, Solanum elaeagnifolium, and Erythranthe guttata) and affected pollen collection and pollen deposition on these flowers. We found that bees learned and remembered how to handle some flower types more quickly than others. Learning typically involved development of motor routines unique to each flower type. While bees invariably learned to improve pollen collection, how quickly bees learned and remembered each flower type did not affect pollen collection. Surprisingly, pollen deposition on flowers was not affected by bee foraging experience. Thus, even though learning benefits the bee, it does not alter female (and potentially male) fitness benefits for the plant. We discuss potential reasons for these patterns and consequences for bee behavior and flower evolution.

animal behavior and cognition↗

bioRxiv2023

Neopolyploidy-induced changes in the giant duckweed (Spirodela polyrhiza) alter herbivore preference, performance, and plant population performance

PremisePolyploidy is a widespread mutational process in angiosperms that may alter population performance of not only plants but also their animal associates. Yet, knowledge of whether ploidy affects plant-herbivore dynamics is scarce. Here, we test whether aphid herbivores exhibit preference for diploid or neopolyploid plants, whether ploidy impacts plant and herbivore performance, and whether these interactions depend on plant genetic background. MethodsUsing multiple pairs of independently synthesized neotetraploid greater duckweed (Spirodela polyrhiza) and their diploid progenitors, we evaluated the effect of neopolyploidy on duckweeds interaction with the water-lily aphid (Rhopalosiphum nymphaeae). Using two-way choice experiments, we first evaluated feeding preference by the herbivore. We then evaluated the consequences of ploidy on aphid and plant performance by measuring population growth over multiple generations. Key ResultsAphids preferred neopolyploids over diploids when the plants were provided at equal abundances but not when they were provided at equal surface area, indicating the role of plant size in driving this preference. Additionally, neopolyploidy increased aphid population performance, but this result was highly dependent on the genetic lineage of the plant. Lastly, the impact of herbivory on neopolyploids vs. diploid duckweed varied greatly with genetic lineage, but overall, neopolyploids appeared to be generally less tolerant than diploids. ConclusionsWe conclude that polyploidization can impact the preference and performance of herbivores on their plant hosts, whereas plant performance depends on complex interactions between herbivory, ploidy, and genetic lineage. These results have significant implications for the establishment and persistence of plants and herbivores in nature.

ecology↗

bioRxiv2023

Neopolyploidy increases stress tolerance and reduces fitness plasticity across multiple urban pollutants: support for the 'general purpose' genotype hypothesis.

Whole genome duplication is a common macromutation with extensive impacts from gene expression, to cellular function, and whole organism phenotype. As a result, it has been proposed that polyploids have general purpose genotypes that perform better than their diploid progenitors under stressful conditions. Here we test this hypothesis in the context of stresses presented by anthropogenic pollutants. Specifically, we tested how multiple neotetraploid genetic lineages of the Greater Duckweed (Spirodela polyrhiza) perform across a favorable control environment and five urban pollutants (iron, salt, manganese, copper, and aluminum). By quantifying the population growth rate of duckweed over multiple generations we found that across most pollutants, but not all, polyploidy decreased the growth rate of actively growing propagules but increased that of dormant ones. Yet, when considering total propagule production, polyploidy increased tolerance to most pollutants and polyploids maintained population-level fitness across pollutants better than diploids. Furthermore, broad-sense genetic correlations in growth rate among pollutants were all positive in neopolyploids but not so for diploids. Our results provide a rare test and support for the hypotheses that polyploids are more tolerant of stressful conditions and can maintain fitness better than diploids across heterogenous stresses. These results may help predict the distribution of polyploids across stress gradients such as those caused by urbanization and other human activities.

evolutionary biology↗

bioRxiv2023

Plant neopolyploidy and genetic background differentiates the microbiome of duckweed across a variety of natural freshwater sources

Whole genome duplication has long been appreciated for its role in driving phenotypic novelty in plants, often altering the way organisms interface with the abiotic environment. Only recently, however, have we begun to investigate how polyploidy influences interactions of plants with other species, despite the biotic niche being predicted as one of the main determinants of polyploid establishment. Nevertheless, we lack critical information about how polyploidy affects the diversity and composition of the microbial taxa that colonize plants, and whether this is genotype-dependent and repeatable across natural environments. This information is a critical first step toward understanding whether the microbiome contributes to polyploid establishment. We thus tested the immediate effect of polyploidy on the diversity and composition of the bacterial microbiome of the aquatic plant Spirodela polyrhiza using four pairs of diploids and synthetic autotetraploids. Under controlled conditions, axenic plants were inoculated with pond waters collected from 10 field sites across a broad environmental gradient. Autotetraploids hosted 4-11 % greater bacterial taxonomic and phylogenetic diversity than their diploid progenitors. Polyploidy, along with its interactions with the inoculum source and genetic lineage, collectively explained 7 % of the total variation in microbiome composition. Furthermore, polyploidy broadened the core microbiome, with autotetraploids having 15 unique bacterial taxa in addition to the 55 they shared with diploids. Our results show that whole genome duplication directly leads to novelty in plant microbiome and importantly, that the effect is dependent on the genetic ancestry of the polyploid and generalizable over many environmental contexts.

ecology↗

bioRxiv2022

Polyploidy impacts population growth and competition with diploids: multigenerational experiments reveal key life history tradeoffs

O_LIEcological theory predicts that early generation polyploids ("neopolyploids") should quickly go extinct owing to the disadvantages of rarity and competition with their diploid progenitors. However, polyploids persist in natural habitats globally. This paradox has been addressed theoretically by recognizing that reproductive assurance of neopolyploids and niche differentiation can promote establishment. Despite this, the direct effects of polyploidy at the population level remain largely untested even though establishment is an intrinsically population-level process. C_LIO_LIWe conducted population-level experiments where investment in current and future growth was tracked in four lineage pairs of diploids and synthetic neopolyploids of the aquatic plant Spirodela polyrhiza. Population growth was evaluated with and without competition between diploids and neopolyploids across a range of nutrient treatments. C_LIO_LIAlthough neopolyploid populations produce more biomass, they reach lower population sizes, and have reduced carrying capacities when growing alone or in competition across all nutrient treatments. Thus, contrary to individual-level studies, our population-level data suggest that neopolyploids are competitively inferior to diploids. Conversely, neopolyploid populations have greater investment in dormant propagule production than diploids. C_LIO_LIOur results show that neopolyploid populations should not persist based on current growth dynamics, but high potential future growth may allow polyploids to establish in subsequent growing seasons. C_LI

ecology↗

bioRxiv2020

Pollinators mediate floral microbial diversity and network under agrochemical disturbance

How pollinators mediate microbiome assembly in the anthosphere is a major unresolved question of theoretical and applied importance in the face of anthropogenic disturbance. We addressed this question by linking visitation of diverse pollinator functional groups (bees, wasps, flies, butterflies, beetles, true bugs and other taxa) to the key properties of floral microbiome (microbial - and {beta}-diversity and microbial network) under agrochemical disturbance, using a field experiment of bactericide and fungicide treatments on cultivated strawberries that differ in flower abundance. Structural equation modeling was used to link agrochemical disturbance and flower abundance to pollinator visitation to floral microbiome properties. Our results revealed that (1) pollinator visitation influenced the - and {beta}-diversity and network centrality of floral microbiome, with different pollinator functional groups affecting different microbiome properties; (2) flower abundance influenced floral microbiome both directly by governing the source pool of microbes and indirectly by enhancing pollinator visitation; and (3) agrochemical disturbance affected floral microbiome primarily directly by fungicide, and less so indirectly via pollinator visitation. These findings improve the mechanistic understanding of floral microbiome assembly, and may be generalizable to many other plants that are visited by diverse insect pollinators in natural and managed ecosystems.

ecology↗

bioRxiv2020

Pollinator niche partitioning and asymmetric facilitation contribute to the maintenance of diversity

AbstractMechanisms that favor rare species are key to the maintenance of diversity. One of the most critical tasks for biodiversity conservation is understanding how plant-pollinator mutualisms contribute to the persistence of rare species, yet this remains poorly understood. Using a process-based model that integrates plant-pollinator and interspecific pollen transfer networks with floral functional traits, we show that niche partitioning in pollinator use and asymmetric facilitation confer fitness advantage of rare species in a biodiversity hotspot. While co-flowering species filtered pollinators via floral traits, rare species showed greater pollinator specialization leading to higher pollination-mediated male and female fitness than abundant species. When plants shared pollinator resources, asymmetric facilitation via pollen transport dynamics benefited the rare species at the cost of the abundant ones, serving as an alternative diversity-promoting mechanism. Our results emphasize the importance of community-wide plant-pollinator interactions that affect reproduction for biodiversity maintenance.

ecology↗

bioRxiv2020

Recipient and donor characteristics govern the hierarchical structure of heterospecific pollen competition networks

O_LIPollinator sharing can have negative consequences for plant fitness with the arrival of foreign pollen, yet responses are often variable among species. Plant traits and relatedness of donor and recipient species have been suggested to drive the variations in plant fitness, but how they shape the structure of pollen competition networks has been overlooked at the community level. C_LIO_LITo understand the importance of traits and relatedness we conducted a controlled glasshouse experiment with an artificial co-flowering community. We performed 900 reciprocal crosses by experimentally transferring pollen among 10 species belonging to three different plant families. C_LIO_LIWe found a significant reduction in seed set for 67% of the crosses, driven largely by recipient traits and the interaction between recipient-donor traits under specific circumstances of trait-matching. These traits and their asymmetries among species led to a hierarchical (or transitive) structure of pollen competition with clear winners and losers depending on specific combination of traits. C_LIO_LIA greater understanding of the importance of trait matching and asymmetries among donor and recipient plant species will facilitate knowledge of the mechanisms underlying foreign pollen impacts upon plant reproductive fitness. This will require a shift from pairwise to community level interactions. C_LI

ecology↗

bioRxiv2019

Floral organs act as environmental filters and interact with pollinators to structure the yellow monkeyflower (Mimulus guttatus) floral microbiome.

Assembly of microbial communities is the result of neutral and selective processes. However, the relative importance of these processes is still debated. Microbial communities of flowers, in particular, have gained recent attention because of their potential impact to plant fitness and plant-pollinator interactions. However, the role of selection and dispersal in the assembly of these communities remains poorly understood. We evaluated the role of pollinator-mediated dispersal on the contribution of neutral and selective processes in the assembly of floral microbiomes of the yellow monkeyflower (Mimulus guttatus). We sampled floral organs from flowers in the presence and absence of pollinators within five different serpentine seeps in CA and obtained 16S amplicon data on the epiphytic bacterial communities. Consistent with strong micro-environment selection within flowers we observed significant differences in community composition across floral organs and only a small effect of geographic distance. Pollinator exposure affected the contribution of environmental selection and depended on the rate and \"intimacy\" of interactions with flower visitors. This study provides evidence of the importance of dispersal and within-flower heterogeneity in shaping epiphytic bacterial communities of flowers, and highlights the complex interplay between pollinator behavior, environmental selection and additional abiotic factors in shaping the epiphytic bacterial communities of flowers.

ecology↗

bioRxiv2019

Revisiting the Origin of the Octoploid Strawberry

The cultivated strawberry, Fragaria xananassa, originated in France approximately 270 years ago via hybridization between two wild species introduced from North and South America. Both the cultivated strawberry and its parental species are octoploids with 2n=8x=56 chromosomes. In the recent publication of the genome of the cultivated strawberry, the authors present a novel phylogenetic hypothesis, proposing that each of the four subgenomes originated from a different 2n=2x=14 diploid progenitor. They further suggest that the hexaploid species Fragaria moschata was a direct ancestor of the strawberries. We reanalyzed the four octoploid subgenomes in a phylogenomic context, and found that only two extant diploids were progenitors, a result that is consistent with several previous studies. We also conducted a phylogenetic analysis of genetic linkage-mapped loci in the hexaploid F. moschata, and resolved its origin as independent of the octoploids. We identified assumptions in their tree-searching algorithm that prevented it from accepting extinct or unsampled progenitors, and we argue that this is a critical weakness of their approach. Correctly identifying their diploid progenitors is important for understanding and predicting the responses of polyploid plants to climate change and associated environmental stress.

plant biology↗

bioRxiv2019

The effect of alien species on plant-pollinator network structure across a gradient of plant species invasion

The interactions between pairs of native and alien plants via shared use of pollinators have been widely studied. Studies of invasive species effects at the community level on the other hand are still scarce. Few community level studies, however, have considered how differences in the intensity of invasion, and degree of floral trait similarity between native and invasive species, can mediated effects on native plant-pollinator communities. Here, we evaluated the effect of alien species on overall plant-pollinator network structure, and species-level network parameters, across nine coastal communities distributed along 205 km at Yucatan, Mexico that vary in alien species richness and flower abundance. We further assessed the effect of alien plant species on plant-pollinator network structure and robustness via computational simulation of native and invasive plant extinction scenarios. We did not find significant differences between native and alien species in functional floral phenotypes, the visitation rate and species composition of the pollinator community. Variation in the proportion of alien plant species and flower abundance across sites did not affect plant-pollinator networks structure. Species-level network parameters (i.e., normalized degree and nestedness contribution) did not differ between native and alien species. Furthermore, our simulation analyses revealed that alien species are functionally equivalent to native species and contribute equally to network structure and robustness. Overall, our results suggest that alien species are well integrated into native coastal plant-pollinator networks which may be facilitated by high levels of floral trait similarity and pollinator use overlap. As a result, alien species may play a similar role than that of natives in the structure and stability of native plant and pollinator communities in the studied coastal sand dune ecosystem.

ecology↗

bioRxiv2018

Both functional trait divergence and trait plasticity confer polyploid advantage in changing environments

Polyploidy, or whole genome duplication, exists in all eukaryotes and is thought to drive ecological and evolutionary success especially in plants. The mechanisms of polyploid success in ecologically relevant contexts, however, remain largely unknown. Here we conducted an extensive test of functional trait divergence and trait plasticity in conferring polyploid fitness advantage in changing environments by growing clonal replicates of a worldwide genotype collection of six polyploid and five diploid wild strawberry (Fragaria) species in three climatically different common gardens. Among leaf functional traits, we detected divergence in means but not plasticities between polyploids and diploids, suggesting that increased genomic redundancy does not necessarily translate into broader phenotypic amplitude in polyploids. Across the heterogeneous garden environments, however, polyploids exhibited fitness advantage, which was conferred by both trait means and adaptive trait plasticities, supporting a jack-and-master hypothesis for polyploids. Our findings provide unparalleled insight into the prevalence and persistence of polyploidization.

ecology↗

bioRxiv2017

The effects of host species and sexual dimorphism differ among root, leaf and flower microbiomes of wild strawberries in situ

Plant-associated microbiomes profoundly influence host interactions with below- and aboveground environments. Characterizing plant-associated microbiomes in experimental settings have revealed important drivers of microbiota assemblies within host species. However, it remains unclear how important these individual drivers (e.g., organ type, host species, host sexual phenotype) are in structuring the patterns of plant-microbiota association in the wild.\n\nUsing 16s rRNA sequencing, we characterized root, leaf and flower microbiomes in three closely related, sexually polymorphic Fragaria species, in the broadly sympatric portion of their native ranges in Oregon, USA. Taking into account the potential influence of broad-scale abiotic environments, we quantified the relative effects of organ type, host species and sex on the - and {beta}-diversity of bacterial communities in these wild populations. Our statistical models showed that organ type explained the largest variation of compositional and phylogenetic - and {beta}-diversity of plant microbiomes, and its overall effect exceeded that of host plant species. Yet, the influence of host species increased from root to leaf to flower microbiomes. We found strong sexual dimorphism in flower and leaf microbiomes, especially in host species with the most complete separation of sexes. Our results provide the first demonstration of enhanced effects of host species and sexual dimorphism from root to flower microbiomes. While these findings await manipulative experiments to disentangle contributions of micro-environment and the residing microbiota from host genetic effects, we anticipate that such phenotypic patterns of host species-microbiota association may be broadly applicable to other plants in the wild.

microbiology↗

bioRxiv2017

Repeated translocation of a gene cassette drives sex chromosome turnover in strawberries

Turnovers of sex-determining systems represent important diversifying forces across eukaryotes. Shifts in sex chromosomes, but conservation of the master sex-determining genes, characterize distantly-related animal lineages. Yet in plants, where separate sexes have evolved repeatedly and sex chromosomes are typically homomorphic, we do not know whether such translocations drive turnovers within closely related groups. This phenomenon can only be demonstrated by identifying sex-associated nucleotide sequences, still largely unknown in plants. The wild North American octoploid strawberries (Fragaria) exhibit separate sexes (dioecy) with homomorphic, female heterogametic (ZW) inheritance, yet sex maps to at least three different chromosomes. To characterize these turnovers, we sequenced the complete genomes of 60 plants of known sex from five Fragaria taxa. We identified 31-mers unique to females and assembled their reads into contigs. Remarkably, a short (13 kb) sequence is observed in nearly all females and never in male-fertile individuals, implicating it as the sex-determining region (SDR). This female-specific \"SDR cassette\" contains both a gene with a known role in fruit and pollen production and a novel retrogene absent on Z and autosomal chromosomes. Comparing SDR cassettes across taxa reveals a history of repeated translocation, which can be ordered temporally due to the capture of adjacent sequence with each successive move. The accumulation of these \"souvenirs\" suggests an adaptive basis for the expanding (up to at least 23 kb) hemizygous region. This is the first plant SDR known to be translocated, and it suggests a new mechanism (\"move-lock-grow\") for expansion and diversification of incipient sex chromosomes.\n\nSignificance StatementSex chromosomes frequently restructure themselves during organismal evolution, often becoming highly differentiated. This dynamic process is poorly understood for most taxa, especially during the early stages typical of many dioecious plants. In wild strawberries, a sex-determining region of DNA has repeatedly changed its genomic location, each time increasing the size of the hemizygous female-specific sequence. This observation shows for the first time that plant sex regions can \"jump\", and suggests that this phenomenon may be adaptive by gathering and locking new genes into linkage with sex. This conserved and presumed causal sequence with a variable genomic location presents a unique opportunity to understand how sex chromosomes first begin to differentiate.

evolutionary biology↗