Steve Tonsor | University of Pittsburgh (original) (raw)

Papers by Steve Tonsor

Oecologia, Dec 1, 1983

ABSTRACT Clonal replicates of six genotypes of Solanum dulcamara L. grown in eight different envi... more ABSTRACT Clonal replicates of six genotypes of Solanum dulcamara L. grown in eight different environments were compared for photosynthesis and growth. Four of the genotypes were native to shaded habitats, two to sun habitats. The experimental growth environments differed in light level, daily temperature amplitude and substrate moisture availability. Treatments elicited large differences in lightsaturated photosynthetic rates and growth. Genotypic differences in response to the treatments were identified. However, when genotypes native to sun and shade habitats were compared, there were no consistent differences in photosynthesis or total plant dry weight. It was concluded that previously reported differences in the photosynthetic response of genotypes native to sun and shade habitats to treatment light level may have been the result of the persistent after-effects to changes in leaf water potential and not an adaptive response to growth light level.

Hydrobiologia, Jul 3, 2015

Understanding landscape influences on stream ecosystems is a challenging task due to the spatial ... more Understanding landscape influences on stream ecosystems is a challenging task due to the spatial complexity and connectedness of stream networks. Here, we control for longitudinal connectivity to provide a robust test of the relative importance of reach-and catchment-scale factors in determining macroinvertebrate community structure in southwestern Pennsylvania streams. We determined that sites separated by B510 m along the stream network had significantly correlated macroinvertebrate community scores. After controlling for this spatial autocorrelation, a partial least squares regression identified two factors that together accounted for 32% of the variation in community scores. In this model, two reach-scale factors-habitat assessment score and stream pHwere the most important factors for predicting a stream's macroinvertebrate community score. However, landscape diversity was also important. Landscape diversity is a catchment-scale factor that was highly correlated with percent pasture/hay and measures of habitat fragmentation. Our results provide support for the idea that stream communities in undisturbed areas are heavily influenced by reachscale characteristics. Furthermore, our results indicate that Pennsylvania natural resource managers should consider habitat score and stream pH after accounting for spatial autocorrelation when identifying restoration targets for impacted streams.

These data were collected in controlled environment chambers at the University of Pittsburgh, Dep... more These data were collected in controlled environment chambers at the University of Pittsburgh, Department of Biological Sciences. Plants were grown in a robotic ebb-and-flood watering system under controlled CO2 content atmosphere at 4 nitrogen supply levels, supplied with Dosatron apportioners and calibrated with an ion-specific probe. All 4 N treatments were included in each of the 4 chambers. The plants were 160 lines from the Landberg-Cape Verdi Islands recombinant inbred line (RIL) population of Alonso-Blanco and Koornneef. RIL means were calculated using proc means in SAS after removing the chamber mean residuals

Oecologia, 1980

BioScience, 2019

Widespread specimen digitization has greatly enhanced the use of herbarium data in scientific res... more Widespread specimen digitization has greatly enhanced the use of herbarium data in scientific research. Publications using herbarium data have increased exponentially over the last century. Here, we review changing uses of herbaria through time with a computational text analysis of 13,702 articles from 1923 to 2017 that quantitatively complements traditional review approaches. Although maintaining its core contribution to taxonomic knowledge, herbarium use has diversified from a few dominant research topics a century ago (e.g., taxonomic notes, botanical history, local observations), with many topics only recently emerging (e.g., biodiversity informatics, global change biology, DNA analyses). Specimens are now appreciated as temporally and spatially extensive sources of genotypic, phenotypic, and biogeographic data. Specimens are increasingly used in ways that influence our ability to steward future biodiversity. As we enter the Anthropocene, herbaria have likewise entered a new era...

Plants ameliorate heat stress by avoiding heat loading, reducing tissue temperature through evapo... more Plants ameliorate heat stress by avoiding heat loading, reducing tissue temperature through evaporative cooling, and/or through tolerance, i.e. maintaining function at high temperature. Here Arabidopsis thaliana natural populations from two ends of an elevation gradient in NE Spain were used to ask: do plants from contrasting climates 1) show genetically based differences in heat stress damage and 2) adopt different avoidance-tolerance patterns? Four low-and four high-elevation populations were repeatedly exposed to high temperature (45 o C) in a growth chamber at bolting stage. High temperature induced 23% more inflorescence branches, 25% longer total reproductive branch length, and 12% less root dry mass, compared with control. However summed fruit length, hence fitness, decreased by 15%, populations did not differ significantly in fitness reduction. High elevation populations showed more avoidance, i.e. lower rosette temperature at 45 o C. Low elevation populations showed more tolerance, maintaining relatively higher photosynthetic rate at 45 o C. Avoidance was associated with high transpiration rate and flat rosette leaf angle. Tolerance was negatively associated with heat shock protein 101 (Hsp101) and salicylic acid (SA) accumulation. The divergent avoidance-tolerance patterns for populations from thermally contrasting climates may indicate both constraints on the evolution and contrasting adaptive divergence regulated by local climates.

Although adaptive plasticity would seem always to be favored by selection, it occurs less often t... more Although adaptive plasticity would seem always to be favored by selection, it occurs less often than expected. This lack of ubiquity suggests that there must be trade-offs, costs, or limitations associated with plasticity. Yet, few costs have been found. We explore one type of limitation, a correlation between plasticity and developmental instability, and use quantitative genetic theory to show why one should expect a genetic correlation. We test that hypothesis using the Landsberg erecta × Cape Verde Islands recombinant inbred lines (RILs) of Arabidopsis thaliana. RILs were grown at four different nitrogen (N) supply levels that span the range of N availabilities previously documented in North American field populations. We found a significant multivariate relationship between the cross-environment trait plasticity and the within-environment, within-RIL developmental instability across 13 traits. This genetic covariation between plasticity and developmental instability has two costs. First, theory predicts diminished fitness for highly plastic lines under stabilizing selection, because their developmental instability and variance around the optimum phenotype will be greater compared to nonplastic genotypes. Second, empirically the most plastic traits exhibited heritabilities reduced by 57% on average compared to nonplastic traits. This demonstration of potential costs in inclusive fitness and heritability provoke a rethinking of the evolutionary role of plasticity

Phenotypic variation in stress response has been widely observed within species. This variation i... more Phenotypic variation in stress response has been widely observed within species. This variation is an adaptive response to local climates and is controlled by gene sequence variation and especially by variation in expression at the transcriptome level. Plants from contrasting climates are thus expected to have different patterns in gene expression. Acclimation, a pre-exposure to sub-lethal temperature before exposing to extreme high temperature, is an important adaptive mechanism of plant survival. We are interested to evaluate the gene expression difference to heat stress for plants from contrasting climates and the role of acclimation in altering their gene expression pattern. Natural Arabidopsis thaliana plants from low elevation mediterranean and high elevation montane climates were exposed to two heat treatments at the bolting stage: a) 45 oC: a direct exposure to 45oC heat; b) 38/45 oC: an exposure to 45oC heat after a 38oC acclimation treatment. Variation in overall gene expr...

Background/Question/Methods Mutualisms are widespread in nature but the strength of these interac... more Background/Question/Methods Mutualisms are widespread in nature but the strength of these interactions can vary with environmental conditions. Under certain circumstances, mutualisms can erode into parasitism as conflict arises between the two species. In the plant-arbuscular mycorrhizal fungi (AMF) mutualism, AMF external hyphae provide plants with nutrients/water, and plants supply AMF with carbon. This mutualism is critical for many plants; ~70% of forest understory species are obligately dependent on AMF. Garlic mustard (Alliaria petiolata) produces allelochemicals that are toxic to the nutrient-providing AMF external hyphae, yet can leave the carbon-absorbing AMF arbuscules intact, potentially setting up a conflict. Thus, the recent invasion of forests by garlic mustard may be altering conditions that favor this widespread mutualism. Because AMF external hyphae of forest plants should die upon exposure to garlic mustard allelochemicals, we hypothesized that reduced soil respira...

The American Naturalist, 2009

Explaining the diversity in geographic range sizes among species is a central goal of ecological ... more Explaining the diversity in geographic range sizes among species is a central goal of ecological and evolutionary studies. We tested species age as an explanation of range size variation within a group of understory shrubs in the Neotropics (Psychotria subgenus Psychotria, Rubiaceae). We distinguish between range occupancy (filling an occupied area) and range extent (maximum distances dispersed). We used Bayesian relaxed-clock dating of molecular sequence data to estimate the relative age of species, and we used species distribution modeling to predict species' potential ranges. If the range sizes of species are limited by time for dispersal, we hypothesize that older species should have (1) larger realized range occupancies and realized range extents than younger species, (2) filled a greater proportion of their potential range occupancies, and (3) colonized a greater proportion of their potential range extents. We found (1) a significant but weak positive relationship between species age versus both realized range occupancy and realized range extent, (2) no relationship between species age and filling of potential range occupancies, but (3) that older species had colonized a significantly greater proportion of their potential range extents than younger species. Our results indicate that a time-for-dispersal effect can limit the extent of ranges of species but not necessarily their occupancies.

Ecosphere, 2011

Soil resources derived from mutualistic arbuscular mycorrhizal fungi (AMF) play a critical role i... more Soil resources derived from mutualistic arbuscular mycorrhizal fungi (AMF) play a critical role in the physiological function of many native plant species. Allelopathic plant invasion studies have revealed declines in AMF inoculation potential of invaded soils, and lost opportunities for plants to form new AMF associations. Yet, if allelochemicals also kill AMF external hyphae already associated with plant roots, this mutualism disruption should result in physiological stress for native plants. We previously demonstrated that forest soils infested with garlic mustard (Alliaria petiolata), an allelopathic invader, exhibit reduced fungal hyphal abundance. Here, we demonstrate for the first time that treatment with garlic mustard tissue reduces soil respiration rates and diminishes physiological function of false Solomon's seal (Maianthemum racemosum), an AMF-dependant forest understory native. Treated plants exhibited reduced stomatal conductance and photosynthesis relative to controls, consistent with the proposed loss of AMF function. Such physiological declines, if sustained over several growing seasons, could decrease native understory perennials' growth rates and increase their susceptibility to environmental stresses. These data provide an explicit mechanism that can help explain the loss of established native perennials from invaded mature forests. We propose that the physiological costs of mutualism disruption may be a widespread but previously untested mechanism enhancing the invasion of undisturbed ecosystems by allelopathic species.

Ecology, 1999

Seed dispersal creates the initial spatial distribution of individuals in a population and in con... more Seed dispersal creates the initial spatial distribution of individuals in a population and in conjunction with the mating system influences spatial patterns of relatedness. This spatial template of related individuals sets the stage for all subsequent density-dependent and frequency-dependent interactions. In this study we document how ant-mediated seed dispersal affects the number and relatedness of seeds in both dispersed and undispersed aggregations and how these patterns influence seedling emergence in the long-lived perennial, Trillium grandiflorum. Experimental hand-pollinations in two years demonstrated that selfing is extremely rare and suggested that self-incompatibility (SI) is a likely explanation. Our multi-locus outcrossing estimate (t m ϭ 1.05 Ϯ 0.056) confirms this result and also suggests that seeds within a fruit are likely to have the same pollen parent. Thus a highly outcrossing mating system is the initial determinant of relatedness among seeds within a fruit. We tracked uniquely coded, radiolabeled seeds from 30 and 40 fruits in 1991 and 1992, respectively, to determine how dispersal alters this initial relatedness of seeds. Of the 335 and 876 seeds labeled in these two years, we recovered 63% and 76% of the seeds postdispersal and found that 19% and 23% of the recovered seeds were dispersed Ͼ10 cm from the maternal parent in the first and second years, respectively. In both years, ant-mediated dispersal reduced the number of seeds near the maternal parent. However, the effect of seed dispersal on the number of seeds in aggregations varied among years. Antmediated dispersal increased the number of seeds in dispersed aggregations in the first year and decreased the number in the second year. The average seed dispersal distance also differed between years: 2.41 m (Ϯ0.33) vs. 0.53 m (Ϯ0.06) in years 1 and 2, respectively. Ant-mediated seed dispersal decreased the probability of a seed having a sibling as its nearest neighbor postdispersal by between one-third and one-half. In contrast, seedling emergence was related to neither dispersal nor seed aggregation size in our study. However, the fitness effects of dispersal may be important later in the life cycle of this long-lived species and as such were undetected. One scenario is that plants derived from seeds dispersed out of their sibling relatedness group may gain minority advantage both in terms of mating success (if the population is SI) and other frequency-dependent processes like disease resistance.

American Journal of Botany, 2001

To ascertain the inheritance of responses to changing atmospheric CO 2 content, we partitioned re... more To ascertain the inheritance of responses to changing atmospheric CO 2 content, we partitioned response to elevated CO 2 in Plantago lanceolata between families and populations in 18 families in two populations. Plants were grown in 35 Pa and 71 Pa partial pressure of CO 2 (pCO 2) in open-top chambers. We measured above-and belowground mass, carbon (C), nitrogen (N), hexose sugar, and gas exchange properties in both CO 2 treatments. Families within populations differed in mass, mass allocation, root : shoot ratios, aboveground percentage N, C : N ratio, and gas exchange properties. The CO 2 ϫ family interaction is the main indicator of potential evolutionary responses to changing CO 2. Significant CO 2 ϫ family interactions were observed for N content, C : N ratio, and photosynthetic rate (A: instantaneous light-saturated carbon assimilation capacity), intercellular CO 2 concentration, transpiration rate (E), and water use efficiency (WUE ϭ A/E), but not for stomatal conductance. Families differed significantly in acclimation across time. The ratio of A in elevated vs. ambient growth CO 2 , when measured at a common internal CO 2 partial pressure was 0.79, indicating downregulation of A under CO 2 enrichment. Mass, C : N ratio, percentage, C (%C), and soluble sugar all increased significantly but overall %N did not change. Increases in %C and sugar were significant and were coincident with redistribution of N aboveground. The observed variation among populations and families in response to CO 2 is evidence of genetic variation in response and therefore of the potential for novel evolutionary trajectories with rising atmospheric CO 2 .

American Journal of Botany, 2009

A metamorphosis from rosette to infl orescence in many annuals shifts photosynthetic tissue from ... more A metamorphosis from rosette to infl orescence in many annuals shifts photosynthetic tissue from a two-dimensional array in the soil boundary layer during cool months to a three-dimensional structure in the troposphere as spring progresses. We propose that this shift allows escape from both self-shading and an increasingly stressful boundary layer microclimate, permitting continued increases in growth. As a fi rst step in exploring this hypothesis, we compared the lifetime C gain, water loss, and instantaneous water use effi ciency (WUE) of fi ve Arabidopsis thaliana genotypes by measuring gas exchange across the life cycle. On average, the infl orescence contributed 55% (± 5% SE) of lifetime C gain, but only 25% of lifetime water loss. Mean infl orescence WUE was nearly fourfold that of the rosette. The infl orescence continued to fi x C after rosette senescence. The percentage infl orescence: total C gain varied among genotypes, from 36% to 93%. Genotypes differed in WUE for both structures. We suggest that local climates may have selected for divergence in these traits. For many annuals and winter annuals, understanding C and water budgets and their evolution must include measures of both rosette and infl orescence gas exchange.

PLoS ONE, 2009

Background: Understanding the relationship between environment and genetics requires the integrat... more Background: Understanding the relationship between environment and genetics requires the integration of knowledge on the demographic behavior of natural populations. However, the demographic performance and genetic composition of Arabidopsis thaliana populations in the species' native environments remain largely uncharacterized. This information, in combination with the advances on the study of gene function, will improve our understanding on the genetic mechanisms underlying adaptive evolution in A. thaliana. Methodology/Principal Findings: We report the extent of environmental, demographic, and genetic variation among 10 A. thaliana populations from Mediterranean (coastal) and Pyrenean (montane) native environments in northeast Spain. Geographic, climatic, landscape, and soil data were compared. Demographic traits, including the dynamics of the soil seed bank and the attributes of aboveground individuals followed over a complete season, were also analyzed. Genetic data based on genome-wide SNP markers were used to describe genetic diversity, differentiation, and structure. Coastal and montane populations significantly differed in terms of environmental, demographic, and genetic characteristics. Montane populations, at higher altitude and farther from the sea, are exposed to colder winters and prolonged spring moisture compared to coastal populations. Montane populations showed stronger secondary seed dormancy, higher seedling/ juvenile mortality in winter, and initiated flowering later than coastal populations. Montane and coastal regions were genetically differentiated, montane populations bearing lower genetic diversity than coastal ones. No significant isolationby-distance pattern and no shared multilocus genotypes among populations were detected. Conclusions/Significance: Between-region variation in climatic patterns can account for differences in demographic traits, such as secondary seed dormancy, plant mortality, and recruitment, between coastal and montane A. thaliana populations. In addition, differences in plant mortality can partly account for differences in the genetic composition of coastal and montane populations. This study shows how the interplay between variation in environmental, demographic, and genetic parameters may operate in natural A. thaliana populations.

Evolution, 2012

Early life-history transitions are crucial determinants of lifetime survival and fecundity. Adapt... more Early life-history transitions are crucial determinants of lifetime survival and fecundity. Adaptive evolution in early life-history traits involves a complex interplay between the developing plant and its current and future environments. We examined the plant's earliest life-history traits, dissecting an integrated suite of pregermination processes: primary dormancy, thermal induction of secondary dormancy, and seasonal germination response. We examined genetic variation in the three processes, genetic correlations among the processes, and the scaling of germination phenology with the source populations' climates. A spring annual life history was associated with genetic propensities toward both strong primary dormancy and heat-induced secondary dormancy, alone or in combination. Lineages with similar proportions of winter and spring annual life history have both weak primary dormancy and weak thermal dormancy induction. A genetic bias to adopt a spring annual strategy, mediated by rapid loss of primary dormancy and high thermal dormancy induction, is associated with a climatic gradient characterized by increasing temperature in summer and rainfall in winter. This study highlights the importance of considering combinations of multiple genetically based traits along a climatic gradient as adaptive strategies differentiating annual plant life-history strategies. Despite the genetic-climatic cline, there is polymorphism for life-history strategies within populations, classically interpreted as bet hedging in an unpredictable world.

Total Biological Score: 58.9 3 Dominant Taxa Present: 1. Chironomidae (40.5-pct) 2. Isoperla (26-... more Total Biological Score: 58.9 3 Dominant Taxa Present: 1. Chironomidae (40.5-pct) 2. Isoperla (26-pct) 3. Oligochaeta (6-pct) D1.B.8-Stream Habitat Assessment Sediment Deposition: Some new increase in bar formation, mostly from gravel, sand or fine sediment; 20 to 50-pct of the bottom affected; slight deposition in pools (larger amounts of sediment found in 32511 over panels 14C and 15C). Channel Flow Status: Water reaches base of both lower banks, and minimal amount of channel substrate is exposed. Velocity/Depth Regime: No data. Frequency of Riffles (or Bends): No data. D1.B.9-Status of Reported Effects The PA DEP determined on May 17, 2006 that reported flow loss effects over panels 14C and 15C were resolved; flow had been sufficiently restored. As of August 20, 2008, land access issues prevented resolution of reported effects over panel 16C.

Molecular Ecology, 2008

The Hsp100/ClpB heat shock protein family is ancient and required for high temperature survival, ... more The Hsp100/ClpB heat shock protein family is ancient and required for high temperature survival, but natural variation in expression and its phenotypic effects is unexplored in plants. In controlled environment experiments, we examined the effects of variation in the Arabidopsis cytosolic AtHsp101 (hereafter Hsp101). Ten wild-collected ecotypes differed in Hsp101 expression responses across a 22 to 40 °C gradient. Genotypes from low latitudes expressed the least Hsp101. We tested fitness and pleiotropic consequences of varying Hsp101 expression in 'control' vs. mild thermal stress treatments (15/25 °C D/N vs. 15/25° D/N plus 3 h at 35 °C 3 days/week). Comparing wild type and null mutants, wt Columbia (Col) produced ~33% more fruits compared to its Hsp101 homozygous null mutant. There was no difference between Landsberg erecta null mutant NIL (Ler) and wt Ler; wt Ler showed very low Hsp101 expression. In an assay of six genotypes, fecundity was a saturating function of Hsp101 content, in both experimental treatments. Thus, in addition to its essential role in acquired thermal tolerance, Hsp101 provides a substantial fitness benefit under normal growth conditions. Knocking out Hsp101 decreased fruit production, days to germination and days to bolting, total dry mass, and number of inflorescences; it increased transpiration rate and allocation to root mass. Root : total mass ratio decayed exponentially with Hsp101 content. This study shows that Hsp101 expression is evolvable in natural populations. Our results further suggest that Hsp101 is primarily an emergency high-temperature tolerance mechanism, since expression levels are lower in low-latitude populations from warmer climates. Hsp101 expression appears to carry an important trade-off in reduced root growth. This trade-off may select for suppressed expression under chronically high temperatures.