Biology subjects

Lasky, J. R.

Publications and source records attributed to Lasky, J. R..

33 records · Page 2Linked to original sources

bioRxiv2022

Natural variation identifies new effectors of water use efficiency in Arabidopsis.

Water use efficiency (WUE) is the ratio of biomass gained per unit of water consumed; thus, it can be altered by genetic factors that affect either side of the ratio. In the present study, we exploited natural variation for WUE as an unbiased approach to discover loci affecting either biomass accumulation or water use as factors affecting WUE. Genome-wide association (GWAS) analysis using integrated WUE measured through carbon isotope discrimination ({delta}13C) of Arabidopsis thaliana accessions identified genomic regions associated with WUE. Reverse genetic analysis of 70 candidate genes selected based on the GWAS results and transcriptome data identified 25 genes affecting WUE as measured by gravimetric and {delta}13C analyses. Mutants of four genes had higher WUE than wild type, while mutants of the other 21 genes had lower WUE. The differences in WUE were caused by either altered biomass or water consumption (or both). Stomatal density was not a primary cause of altered WUE in these mutants. Leaf surface temperatures indicated that transpiration differed for mutants of 16 genes, but generally biomass accumulation had greater effect on WUE. The genes we identified are involved in diverse cellular processes including hormone and calcium signaling, meristematic activity, photosynthesis, flowering time, leaf/vasculature development, and cell wall composition; however, none of them had been previously linked to WUE or traits related to plant water relations. Thus, our study successfully identified new effectors of WUE that can be used to understand the genetic basis of WUE and improve crop productivity.

plant biology↗

bioRxiv2022

Wavelet characterization of spatial pattern in allele frequency

Characterizing spatial patterns in allele frequencies is fundamental to evolutionary biology because these patterns contain evidence of underlying processes. However, the spatial scales at which gene flow, changing selection, and drift act are often unknown. Many of these processes can operate inconsistently across space, causing non-stationary patterns. We present a wavelet approach to characterize spatial pattern in allele frequency that helps solve these problems. We show how our approach can characterize spatial patterns in relatedness at multiple spatial scales, i.e. a multi-locus wavelet genetic dissimilarity. We also develop wavelet tests of spatial differentiation in allele frequency and quantitative trait loci (QTL). With simulation we illustrate these methods under different scenarios. We also apply our approach to natural populations of Arabidopsis thaliana to characterize population structure and identify locally-adapted loci across scales. We find, for example, that Arabidopsis flowering time QTL show significantly elevated genetic differentiation at 300 to 1300 km scales. Wavelet transforms of allele frequencies offer a flexible way to reveal geographic patterns and underlying evolutionary processes.

evolutionary biology↗

bioRxiv2022

Climate biogeography of Arabidopsis thaliana: linking distribution models, individual performance, and life history

AIMPatterns of individual variation are key to testing hypotheses about the mechanisms underlying biogeographic patterns. However, it is challenging to gather data on individual-level variation at large spatial scales. Model organisms are potentially important systems for biogeographical studies, given the available range-wide natural history collections, and the importance of providing biogeographical context to their genetic and phenotypic diversity. LOCATIONGlobal TAXONArabidopsis thaliana ("Arabidopsis") METHODSWe fit occurrence records to climate data, and then projected the distribution of Arabidopsis under last glacial maximum, current, and future climates. We confronted model predictions with individual performance measured on 2,194 herbarium specimens, and we asked whether predicted suitability was associated with life-history and genomic variation measured on [~]900 natural accessions. RESULTSThe most important climate variables constraining the Arabidopsis distribution were winter cold in northern and high elevation regions and summer heat in southern regions. Herbarium specimens from regions with lower habitat suitability in both northern and southern regions were smaller, supporting the hypothesis that the distribution of Arabidopsis is constrained by climate-associated factors. Climate anomalies partly explained interannual variation in herbarium specimen size, but these did not closely correspond to local limiting factors identified in the distribution model. Late-flowering genotypes were absent from the lowest suitability regions, suggesting slower life histories are only viable closer to the center of the realized niche. We identified glacial refugia farther north than previously recognized, as well as refugia concordant with previous population genetic findings. Lower latitude populations, known to be genetically distinct, are most threatened by future climate change. The recently colonized range of Arabidopsis was well-predicted by our native-range model applied to certain regions but not others, suggesting it has colonized novel climates. MAIN CONCLUSIONSIntegration of distribution models with performance data from vast natural history collections is a route forward for testing biogeographical hypotheses about species distributions and their relationship with evolutionary fitness across large scales.

ecology↗

bioRxiv2022

Genomic signatures of host-specific selection in a parasitic plant

PremiseParasitic plants and their hosts are model systems for studying genetic variation in species interactions across environments. The parasitic plant Striga hermonthica (witchweed) attacks a range of cereal crop hosts in Africa and exhibits substantial variation in performance on different host species. Some of this variation is due to local adaptation, but the genetic basis of specialization on certain hosts is unknown. MethodsTo identify genomic regions that are strongly differentiated between parasites attacking different host species, we present an alignment-free analysis of S. hermonthica population diversity using whole genome sequencing (WGS) data for 68 individuals from western Kenya. We validate our findings with germination experiments and analyses based on a de novo assembled draft genome. ResultsReference-free and reference-based analyses suggest that only a small portion of the S. hermonthica genome is strongly differentiated by host species in populations from western Kenya. Analysis of host-associated k-mers implicated genes involved in development of the parasite haustorium (a specialized structure used to establish vascular connections with host roots) and a potential role of chemocyanins in molecular host-parasitic plant interactions. Conversely, no phenotypic or genomic evidence was observed suggesting host-specific selection on parasite response to strigolactones, hormones exuded by host roots and required for parasite germination. ConclusionsThis study demonstrates the utility of WGS for plant species with large, complex genomes and no available reference. Contrasting with theory emphasizing the role of early recognition loci for host specificity, our findings support host-specific selection on later interaction stages, recurring each generation after homogenizing gene flow.

evolutionary biology↗

bioRxiv2021

Multi-scale phenological niches in diverse Amazonian plant communities

Phenology has long been hypothesized as an avenue for niche partitioning or interspecific facilitation, both promoting species coexistence. Tropical plant communities exhibit striking diversity in reproductive phenology, but many are also noted for large synchronous reproductive events. Here we study whether the phenology of seed fall in such communities is non-random, what are the temporal scales of phenological patterns, and ecological factors that drive reproductive phenology. We applied multivariate wavelet analyses to test for phenological synchrony versus compensatory dynamics (i.e. anti-synchronous patterns where one species decline is compensated by the rise of another) among species and across temporal scales. We used data from long-term seed rain monitoring of hyperdiverse plant communities in the western Amazon. We found significant synchronous whole-community phenology at multiple time scales, consistent with shared environmental responses or positive interactions among species. We also observed both compensatory and synchronous phenology within groups of species likely to share traits (confamilials) and seed dispersal mechanisms. Wind-dispersed species exhibited significant synchrony at ~6 mo scales, suggesting these species share phenological niches to match seasonality of wind. Our results suggest that community phenology is shaped by shared environmental responses but that the diversity of tropical plant phenology may partly result from temporal niche partitioning. The scale-specificity and time-localized nature of community phenology patterns highlights the importance of multiple and shifting drivers of phenology. Open research statementData are provided as private-for-peer review. Code and data can be found at https://github.com/pakdamie/treephenology which is currently public. This submission does not use novel code.

ecology↗

bioRxiv2020

Temporal trait plasticity and neighborhood crowding predict the growth of tropical trees

Functional traits and neighborhood composition have been used to predict tree growth dynamics. Temporal changes in trait values (temporal trait plasticity) is one of the mechanisms for adaptive plastic response to environmental change. However, the consequence of temporal change in trait values and neighborhoods on the growth performance of individuals has rarely been investigated. We, therefore tested the effect of temporal changes in trait values and neighborhood crowding on the growth rate of individuals in a tropical forest using a dataset containing individual level growth and functional trait data for Ficus individuals. We collected trait and size data at two time points (2010 and 2017) for 472 individuals of 15 Ficus species in Xishuangbanna tropical forest dynamics plot, southwest China. We used linear mixed effect model to predict the effect of temporal trait plasticity and neighborhood crowding on the relative growth rate of individuals using these data. We found significant temporal changes in individuals functional traits suggesting a shift in ecological strategies from being functionally acquisitive to conservative. We also found differences in neighborhood crowding between the two census years indicating that the strength of individual interactions might change over time. The temporal changes in trait values and neighborhood crowding were found to predict better the relative growth rate of individuals, compared to static trait or crowding values in the initial and final censuses. We also found major axes of tree functional strategies in a principal component analysis, highlighting potentially adaptive trait differences. Our results in general highlight to consider the temporal dimension of functional traits and biotic interactions, as our result suggest that growth-trait relationships may vary between time points, allowing us to understand the demographic response of species to temporal environmental change.

ecology↗

bioRxiv2020

Effects of genomic and functional diversity on stand-level productivity and performance of non-native Arabidopsis

Biodiversity can affect the properties of groups of organisms, such as ecosystem function and the persistence of colonizing populations. Genomic data offer a newly available window to diversity, complementary to other measures like taxonomic or phenotypic diversity. We tested whether native genetic diversity in field experimental stands of Arabidopsis thaliana affected their aboveground biomass and fecundity in their colonized range. We constructed some stands of genotypes that we a priori predicted would differ in performance or show overyielding. We found no relationship between genetic diversity and stand total biomass. However, increasing stand genetic diversity increased fecundity in high resource conditions. Polyculture (multiple genotype) stands consistently yielded less biomass than expected based on the yields of component genotypes in monoculture. This under-yielding was strongest in stands with late-flowering and high biomass genotypes, potentially due to interference competition by these genotypes. Using a new implementation of association mapping, we identified genetic loci whose diversity was associated with stand-level yield, revealing a major flowering time locus associated with under-yielding of polycultures. Our field experiment supports community ecology studies that find a range of diversity-function relationships. Nevertheless, our results suggest diversity in colonizing propagule pools can enhance population fitness. Furthermore, interference competition among genotypes differing in flowering time might limit the advantages of polyculture.

ecology↗

bioRxiv2019

Competition-by-drought interactions change phenotypic plasticity and the direction of selection on Arabidopsis traits

O_LIPopulations often exhibit genetic diversity in traits involved in responses to abiotic stressors, but what maintains this diversity is unclear. Arabidopsis thaliana exhibits high within-population variation in drought response. One hypothesis is that competition, varying at small scales, promotes diversity in resource use strategies. However, little is known about natural variation in competition effects on Arabidopsis physiology. C_LIO_LIWe imposed drought and competition treatments on diverse genotypes. We measured resource economics traits, physiology, and fitness to characterize plasticity and selection in response to treatments. C_LIO_LIPlastic responses to competition differed depending on moisture availability. We observed genotype-drought-competition interactions for relative fitness: competition had little effect on relative fitness under well-watered conditions, while under drought competition caused rank changes in fitness. Early flowering was always selected. Higher {delta}13C was selected only in the harshest treatment (drought and competition). Competitive context significantly changed the direction of selection on aboveground biomass and inflorescence height in well-watered environments. C_LIO_LIOur results highlight how local biotic conditions modify abiotic selection, in some cases promoting diversity in abiotic stress response. The ability of populations to adapt to environmental change may thus depend on small-scale biotic heterogeneity. C_LI

evolutionary biology↗

bioRxiv2019

Genomic history and ecology of the geographic spread of rice

Rice (Oryza sativa) is one of the worlds most important food crops. We reconstruct the history of rice dispersal in Asia using whole-genome sequences of >1,400 landraces, coupled with geographic, environmental, archaeobotanical and paleoclimate data. We also identify extrinsic factors that impact genome diversity, with temperature a leading abiotic factor. Originating [~]9,000 years ago in the Yangtze Valley, rice diversified into temperate and tropical japonica during a global cooling event [~]4,200 years ago. Soon after, tropical rice reached Southeast Asia, where it rapidly diversified starting [~]2,500 yBP. The history of indica rice dispersal appears more complicated, moving into China [~]2,000 yBP. Reconstructing the dispersal history of rice and its climatic correlates may help identify genetic adaptation associated with the spread of a key domesticated species.\n\nOne sentence summaryWe reconstructed the ancient dispersal of rice in Asia and identified extrinsic factors that impact its genomic diversity.

evolutionary biology↗

bioRxiv2019

In the presence of population structure: From genomics to candidate genes underlying local adaptation

Understanding the genomic signatures, genes, and traits underlying local adaptation of organisms to heterogeneous environments is of central importance to the field evolutionary biology. Mixed linear mrsodels that identify allele associations to environment, while controlling for genome-wide variation at other loci, have emerged as the method of choice when studying local adaptation. Despite their importance, it is unclear whether this approach performs better than identifying environmentally-associated SNPs without accounting for population structure. To examine this, we first use the mixed linear model GEMMA, and simple Spearman correlations, to identify SNPs showing significant associations to climate with and without accounting for population structure. Subsequently, using Italy and Sweden populations, we compare evidence of allele frequency differentiation (FST), linkage disequilibrium (LD), fitness variation, and functional constraint, underlying these SNPs. Using a lenient cut-off for significance, we find that SNPs identified by both approaches, and SNPs uniquely identified by Spearman correlations, were enriched at sites showing genomic evidence of local adaptation and function but were limited across Quantitative Trait Loci (QTL) explaining fitness variation. SNPs uniquely identified by GEMMA, showed no direct or indirect evidence of local adaptation, and no enrichment along putative functional sites. Finally, SNPs that showed significantly high FST and LD, were enriched along fitness QTL peaks and cis-regulatory/nonsynonymous sites showing significant functional constraint. Using these SNPs, we identify genes underlying fitness QTL, and genes linking flowering time to local adaptation. These include a regulator of abscisic-acid (FLDH) and flowering time genes PIF3, FIO1, and COL5.

evolutionary biology↗

bioRxiv2019

The Chinese chestnut genome: a reference for species restoration

Forest tree species are increasingly subject to severe mortalities from exotic pests, diseases, and invasive organisms, accelerated by climate change. Forest health issues are threatening multiple species and ecosystem sustainability globally. While sources of resistance may be available in related species, or among surviving trees, introgression of resistance genes into threatened tree species in reasonable time frames requires genome-wide breeding tools. Asian species of chestnut (Castanea spp.) are being employed as donors of disease resistance genes to restore native chestnut species in North America and Europe. To aid in the restoration of threatened chestnut species, we present the assembly of a reference genome with chromosome-scale sequences for Chinese chestnut (C. mollissima), the disease-resistance donor for American chestnut restoration. We also demonstrate the value of the genome as a platform for research and species restoration, including new insights into the evolution of blight resistance in Asian chestnut species, the locations in the genome of ecologically important signatures of selection differentiating American chestnut from Chinese chestnut, the identification of candidate genes for disease resistance, and preliminary comparisons of genome organization with related species.

genomics↗

bioRxiv2018

Effects of two centuries of global environmental variation on phenology and physiology of Arabidopsis thaliana

Intraspecific trait variation is caused by genetic and plastic responses to environment. This intraspecific diversity is captured in immense natural history collections, giving us a window into trait variation across continents and through centuries of environmental shifts. Here we tested if hypotheses based on life history and the leaf economics spectrum explain intraspecific trait changes across global spatiotemporal environmental gradients. We measured phenotypes on a 216-year time series of Arabidopsis thaliana accessions from across the native range and applied spatially varying coefficient models to quantify region-specific trends in trait coordination and trait responses to climate gradients. All traits exhibited significant change across space and/or through time. For example, {delta}15N decreased over time across much of the range and leaf C:N increased, consistent with predictions based on anthropogenic changes in land use and atmosphere. Plants were collected later in the growing season in more recent years in many regions, possibly because populations shifted toward more spring germination and summer flowering as opposed to fall germination and spring flowering. When climate variables were considered, collection dates were earlier in warmer years, while summer rainfall had opposing associations with collection date depending on regions. There was only a modest correlation among traits, indicating a lack of a single life history/physiology axis. Nevertheless, leaf C:N was low for summer- versus spring-collected plants, consistent with a life history-physiology axis from slow-growing winter annuals to fast-growing spring/summer annuals. Regional heterogeneity in phenotype trends indicates complex responses to spatiotemporal environmental gradients potentially due to geographic genetic variation and climate interactions with other aspects of environment. Our study demonstrates how natural history collections can be used to broadly characterize trait responses to environment, revealing heterogeneity in response to anthropogenic change.

ecology↗

bioRxiv2018

Eco-evolutionary community turnover following environmental change

Co-occurring species often differ in intraspecific genetic diversity, which in turn can affect adaptation in response to environmental change. Specifically, the simultaneous evolutionary responses of co-occurring species to temporal environmental change may influence community dynamics. Local adaptation along environmental gradients combined with gene flow can promote genetic diversity of traits under selection within populations. Here I build off existing quantitative genetic theory to study community dynamics of locally adapted species in response to temporal environmental change. I show that species with greater gene flow have lower equilibrium population size due to maladaptive immigrant genotypes (migration load). However, following abrupt environmental change that leaves all species initially maladapted, high gene flow species adapt faster due to greater standing genetic diversity. As a result, communities may undergo a transient reversal in relative abundance, sometimes only after substantial lag periods. If constant temporal environmental change is applied, the community exhibits a shift toward stable dominance by species with intermediate gene flow. High gene flow species can sometimes increase abundance under environmental change if environmental change supresses superior competitor but lower gene flow species. The community dynamics observed here parallel the purely ecological successional dynamics following disturbances and are analogous to the transient benefit of hypermutator alleles under changing environments. My results demonstrate how interspecific variation in life history can have far-reaching impacts on eco-evolutionary community response to environmental change.

evolutionary biology↗

bioRxiv2017

Using genotype-environment associations to identify multilocus local adaptation

Identifying adaptive loci can provide insight into the mechanisms underlying local adaptation. Genotype-environment association (GEA) methods, which identify these loci based on correlations between genetic and environmental data, are particularly promising. Univariate methods have dominated GEA, despite the high dimensional nature of genotype and environment. Multivariate methods, which analyze many loci simultaneously, may be better suited to these data since they consider how sets of markers covary in response to environment. These methods may also be more effective at detecting adaptive processes that result in weak, multilocus signatures. Here, we evaluate four multivariate methods, and five univariate and differentiation-based approaches, using published simulations of multilocus selection. We found that Random Forest performed poorly for GEA. Univariate GEAs performed better, but had low detection rates for loci under weak selection. Constrained ordinations showed a superior combination of low false positive and high true positive rates across all levels of selection. These results were robust across the demographic histories, sampling designs, sample sizes, and levels of population structure tested. The value of combining detections from different methods was variable, and depended on study goals and knowledge of the drivers of selection. Reanalysis of genomic data from gray wolves highlighted the unique, covarying sets of adaptive loci that could be identified using redundancy analysis, a constrained ordination. Although additional testing is needed, this study indicates that constrained ordinations are an effective means of detecting adaptation, including signatures of weak, multilocus selection, providing a powerful tool for investigating the genetic basis of local adaptation.

genomics↗

bioRxiv2016

Topological features of gene regulatory networks predict patterns of natural diversity in environmental response

Molecular interactions affect the evolution of complex traits. For instance, adaptation may be constrained by pleiotropic or epistatic effects, both of which will be reflected in the structure of molecular interaction networks. To date, empirical studies investigating the role of molecular interactions in phenotypic evolution have been idiosyncratic, offering no clear patterns. Here, we investigated the network topology of genes putatively involved in local adaptation to two abiotic stressors--drought and cold--in Arabidopsis thaliana. Our findings suggest that the gene-interaction topologies for both cold and drought stress response are non-random, with genes that show genetic variation in drought response (GxE) being significantly more peripheral and cold response genes being significantly more central than genes not involved in either response. We suggest that the observed topologies reflect different constraints on the genetic pathways involved in the assayed phenotypes. The approach presented here may inform predictive models linking genetic variation in molecular signaling networks with phenotypic variation, specifically traits involved in environmental response.\n\nSignificance StatementOur study focuses on genes whose transcriptional activity exhibits genetic variation in response to the environment, or \"GxE.\" GxE is a widely observed phenomenon of critical importance to understanding the genotype-to-phenotype map, the evolution of natural populations, medical genetics, population response to climate change, and agricultural improvement. We investigated expression GxE in plant responses to two abiotic cues: cold and drought. We found that genes showing genetically variable response to cold stress are centrally located in regulatory networks whereas genes showing genetically variable response to drought stress are peripherally located in regulatory networks. This result suggests that selection is presented with vastly different mutational landscapes for shaping evolutionary or breeding response to these two important climatic factors

evolutionary biology↗