Temperate Eastern North America Research Articles

Complementary roles of EPS, T3SS and Expansin for virulence of Erwinia tracheiphila , the causative agent of cucurbit wilt.

Erwinia tracheiphila (Smith) is a recently emerged plant pathogen that causes severe economic losses in cucurbit crops in temperate Eastern North America. E. tracheiphila is xylem restricted, and virulence is thought to be related to Exopolysaccharides (EPS) and biofilm formation, which occlude the passage of sap in xylem vessels and causes systemic wilt. However, the role of EPS and biofilm formation, and their contribution to disease in relation to other virulence loci are unknown. Here, we use deletion mutants to explore the roles of EPS, Hrp Type III secretion system (Hrp T3SS) and Expansin in plant colonization and virulence. Then, we quantify the expression of the genes encoding these factors during infection. Our results show that Exopolysaccharides are essential for E. tracheiphila survival in host plants, while Hrp T3SS and Expansin are dispensable for survival but needed for systemic wilt symptom development. EPS and Hrp T3SS display contrasting expression patterns in the plant, reflecting their relevance in different stages of the infection. Finally, we show that expression of the eps and hrp T3SS operons is downregulated in mildly increased temperatures, suggesting a link between expression of these virulence factors and geographic restriction of E. tracheiphila to temperate regions. Our work highlights how E. tracheiphila virulence is a complex trait where several loci are coordinated during infection. These results further shed light into the relationship between virulence factors and the ecology of this pathosystem, which will be essential for developing sustainable management strategies for this emerging pathogen.

Bilimbia fuscoviridis (≡ Bacidia fuscoviridis), another overlooked sorediate crustose lichen widely distributed in temperate eastern North America

Bilimbia fuscoviridis (≡ Bacidia fuscoviridis), another overlooked sorediate crustose lichen widely distributed in temperate eastern North America

Width of the temperature range for seed germination of herbaceous plant species in temperate eastern North America: life cycles, seasons and temperature variation and implication for climate warming

AbstractTo persist (without immigration) in habitats with unpredictable environmental conditions, annuals must produce seeds each year or have a seed bank. Thus, we predicted that compared to perennials, annuals have a wider germination temperature range (GTR, the difference in temperature between the week with the highest and the week with the lowest germination during the natural germination season). We determined the GTR via germination phenology data for 350 herbaceous species in 59 families from the eastern USA: summer annuals (SA), 63; winter annuals (WA), 83; monocarpic perennials (MP), 28; and polycarpic perennials (PP), 176. There was no significant phylogenetic signal for the GTR. The width of the GTR during the first spring germination season was 9.6, 8.7 and 8.8°C for MP, PP and SA, respectively, and during the first autumn germination season 12.8, 11.8 and 12.4°C for MP, PP and WA, respectively. Annuals did not have a wider GTR than perennials in either the spring or the autumn germination season. Our data suggest that selection for early germination in either spring or autumn has resulted in only small differences in the GTR. We predict that global warming will have little or no effect on reshaping the germination phenology of herbaceous species of temperate eastern North America.

Glugea weissenbergi . [Descriptions of Fungi and Bacteria

Abstract This article describes the morphology, morphometrics, and geographical distribution of the parasite Glugea weissenbergi infecting largely freshwater fish of the family Gasterosteidae (sticklebacks) in temperate eastern North America. This parasite is only endemic in Maryland, USA.

An Introduced Crop Plant Is Driving Diversification of the Virulent Bacterial Pathogen Erwinia tracheiphila.

Erwinia tracheiphila is the causal agent of bacterial wilt of cucurbits, an economically important phytopathogen affecting an economically important phytopathogen affecting few cultivated Cucurbitaceae few cultivated Cucurbitaceae host plant species in temperate eastern North America. However, essentially nothing is known about E. tracheiphila population structure or genetic diversity. To address this shortcoming, a representative collection of 88 E. tracheiphila isolates was gathered from throughout its geographic range, and their genomes were sequenced. Phylogenomic analysis revealed three genetic clusters with distinct hrpT3SS virulence gene repertoires, host plant association patterns, and geographic distributions. Low genetic heterogeneity within each cluster suggests a recent population bottleneck followed by population expansion. We showed that in the field and greenhouse, cucumber (Cucumis sativus), which was introduced to North America by early Spanish conquistadors, is the most susceptible host plant species and the only species susceptible to isolates from all three lineages. The establishment of large agricultural populations of highly susceptible C. sativus in temperate eastern North America may have facilitated the original emergence of E. tracheiphila into cucurbit agroecosystems, and this introduced plant species may now be acting as a highly susceptible reservoir host. Our findings have broad implications for agricultural sustainability by drawing attention to how worldwide crop plant movement, agricultural intensification, and locally unique environments may affect the emergence, evolution, and epidemic persistence of virulent microbial pathogens.IMPORTANCEErwinia tracheiphila is a virulent phytopathogen that infects two genera of cucurbit crop plants, Cucurbita spp. (pumpkin and squash) and Cucumis spp. (muskmelon and cucumber). One of the unusual ecological traits of this pathogen is that it is limited to temperate eastern North America. Here, we complete the first large-scale sequencing of an E. tracheiphila isolate collection. From phylogenomic, comparative genomic, and empirical analyses, we find that introduced Cucumis spp. crop plants are driving the diversification of E. tracheiphila into multiple lineages. Together, the results from this study show that locally unique biotic (plant population) and abiotic (climate) conditions can drive the evolutionary trajectories of locally endemic pathogens in unexpected ways.

Lecanora caperatica (Lecanoraceae, lichenized ascomycetes) a new sorediate species widespread in eastern North America

Lecanora caperatica is described based on collections from throughout temperate eastern North America. It is a crustose sorediate species in the L. subfusca group which has pulcaris-type apothecia, and produces atranorin and caperatic acid often with accessory roccellic/angardianic acid. The species is chemically similar to the European L. mughosphagneti, which differs in ecology, thallus morphology and in having albella-type apothecia. The generic placement of L. caperatica, and its affinity to the L. subfusca group, are confirmed by molecular phylogenetic analysis.

Comment on Cook and Comstock's “Evaluating the Old Wood Problem in a Temperate Climate: A Fort Ancient Case Study“

In their recent report, Cook and Comstock (2014) purport to address the "old wood" problem in temperate eastern North America. Here we point out several interpretive and analytical errors in their work. We conclude that careful selection of wood charcoal for radiocarbon assay can result in accurate chronology for events of interest. However, this does not obviate the need to critically assess the extant database of wood charcoal dates in any chronology building effort.

Lecanora layana(Lecanoraceae), a new sorediate species widespread in temperate eastern North America

Abstract Lecanora layana is described as new to science based on collections from throughout temperate eastern North America. The species is sorediate and both morphologically and chemically similar to L. nothocaesiella, differing in the production of stictic acid in addition to atranorin and zeorin. As apothecia are unknown in L. layana, the hypothesized generic placement and relationship with L. nothocaesiella were confirmed with molecular phylogenetic analyses of mtSSU sequence data.

Hemlock Legacy Project (HeLP)

Eastern North American forests have effectively lost two major tree species (American chestnut and American elm) in the last 100 years and two more, eastern and Carolina hemlock, will be functionally extinct over much of their ranges within a couple of decades. The loss of eastern hemlock is of particular concern because hemlock is: (1) a foundation species; (2) one of the longest-lived tree species over much of temperate eastern North America; and (3) sensitive to climatic variation and ecosystem disturbance, making it an ideal species for the reconstruction of environmental history. Unlike American chestnut, we have a small window of opportunity to salvage environmental histories from hemlock before they are lost. In this progress report, we review the extensive body of science derived from this paleoenvironmental archive and urge scientists from eastern North America to sample and archive old-growth hemlock while living and dead material remain. Here we describe a community-based approach to salvaging paleoenvironmental archives that could serve as a model for collections from other foundation species currently threatened by exotic forests pests and pathogens (e.g. whitebark pine, ash). The approach supports Schlesinger’s (2010) call for ‘translational ecology’ by building connections between scientists, students, environmental NGOs, and land managers focused on old-growth forests.

Taxonomy of mayapple rust: the genus Allodus resurrected

Mayapple rust is a common, disfiguring disease that is widespread in temperate eastern North America wherever the host, Podophyllum peltatum, occurs. Puccinia podophylli, the etiological agent of this rust, has been shown to be distantly related to both Puccinia and Uromyces as exemplified by their types. A systematic study was made to determine the generic classification of P. podophylli. Phylogenetic analyses of two rDNA loci from multiple specimens support the recognition of this taxon as a separate genus of Pucciniaceae. Based on historical literature and type material, P. podophylli was found to represent the type of the forgotten genus Allodus and it is correctly named Allodus podophylli. A neotype is designated for Puccinia podophylli Schwein. (≡ Allodus podophylli) and a lectotype is designated for Aecidium podophylli.

Epiphyllous bryophytes in the Appalachian Plateau of Kentucky and Tennessee, U.S.A

Epiphyllous bryophytes are poorly documented for temperate eastern North America. Ten liverwort taxa and one moss species are reported as epiphylls on Rhododendron maximum from the Appalachian Plateau (Fentress County, Tennessee, and Menifee County, Kentucky). The Kentucky localities represent the northernmost documented sites for bryophyte epiphylls in eastern North America. Three North American liverwort endemics, Lejeunea ruthii, Leucolejeunea clypeata, and Radula obconica, and the moss, Platygyrium repens, are newly reported as epiphylls. Colony size ranged from <0.1 mm to 20 mm in diameter. Host plant leaf coverage of epiphylls was as high as 15%. A quantitative study at one locality showed 0% of one-year-old host leaves supported bryoepiphylls with 8.9% of two and 13.3% of three-year-old leaves supporting epiphylls. The frequency and northern limits of bryoepiphylly in eastern North America are likely well underestimated.

Comparison of the seed germination of native and non‐native winter annual Apiaceae in North America, with particular focus onCyclospermum leptophyllumnaturalized from South America

AbstractTo increase our knowledge of the seed dormancy breaking and germination requirements of native and non‐native winter annual Apiaceae in temperate eastern North America, a study was conducted on seeds ofCyclospermum (Apium) leptophyllum, which is native to South America, but naturalized in North America and elsewhere. A high percentage of fresh seeds germinated over a narrow range of temperatures, but the range increased when seeds were incubated continuously in light or buried in soil at high summer temperatures, indicating the presence of conditional physiological dormancy (PD). Embryos grew from approximately 0.3 to 1.25 mm (316% increase in length) inside the seeds before the radicle emerged; thus, seeds had morphological dormancy (MD) as well as PD, that is, morphophysiological dormancy (MPD). Embryo growth did not occur during summer in seeds exposed to natural temperatures, but embryos did grow in autumn. For seeds sown in the field in June, both embryo growth and germination occurred in autumn. Thus, seeds have non‐deep simple MPD, with PD being broken in summer and MD in autumn. A comparison ofC. leptophyllumwith native and non‐native winter annual Apiaceae in the region reveals that all species have MD, but the proportion of fresh seeds that also has PD (thus, MPD) varies between species. A combination of factors, including PD, an inability to germinate at high summer temperatures, a relatively low temperature requirement for embryo growth and a lack of dispersal until autumn (in two non‐natives), delays germination of both natives and non‐natives until autumn, when conditions are favorable for both germination and seedling establishment.

DOES NICHE CONSERVATISM PROMOTE SPECIATION? A CASE STUDY IN NORTH AMERICAN SALAMANDERS

Abstract Recent speciation research has generally focused on how lineages that originate in allopatry evolve intrinsic reproductive isolation, or how ecological divergence promotes nonallopatric speciation. However, the ecological basis of allopatric isolation, which underlies the most common geographic mode of speciation, remains poorly understood and largely unstudied. Here, we explore the ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America. Based on published molecular phylogenetic estimates and the degree of geographic range overlap among extant species, we find strong evidence for a role for geographic isolation in speciation. We then examine the relationship between climatic variation and speciation in 16 sister-taxon pairs using geographic information system maps of climatic variables, new methods for modeling species' potential geographic distributions, and data on geographic patterns of genetic variation. In contrast to recent studies in tropical montane regions, we found no evidence for parapatric speciation along climatic gradients. Instead, many montane sister taxa in the Appalachian Highlands inhabit similar climatic niches and seemingly are allopatric because they are unable to tolerate the climatic conditions in the intervening lowlands. This temporal and spatial-ecological pattern suggests that niche conservatism, rather than niche divergence, plays the primary role in promoting allopatric speciation and montane endemism in this species-rich group of vertebrates. Our results demonstrate that even the relatively subtle climatic differences between montane and lowland habitats in eastern North America may play a key role in the origin of new species.

DOES NICHE CONSERVATISM PROMOTE SPECIATION? A CASE STUDY IN NORTH AMERICAN SALAMANDERS

Recent speciation research has generally focused on how lineages that originate in allopatry evolve intrinsic reproductive isolation, or how ecological divergence promotes nonallopatric speciation. However, the ecological basis of allopatric isolation, which underlies the most common geographic mode of speciation, remains poorly understood and largely unstudied. Here, we explore the ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America. Based on published molecular phylogenetic estimates and the degree of geographic range overlap among extant species, we find strong evidence for a role for geographic isolation in speciation. We then examine the relationship between climatic variation and speciation in 16 sister-taxon pairs using geographic information system maps of climatic variables, new methods for modeling species' potential geographic distributions, and data on geographic patterns of genetic variation. In contrast to recent studies in tropical montane regions, we found no evidence for parapatric speciation along climatic gradients. Instead, many montane sister taxa in the Appalachian Highlands inhabit similar climatic niches and seemingly are allopatric because they are unable to tolerate the climatic conditions in the intervening lowlands. This temporal and spatial-ecological pattern suggests that niche conservatism, rather than niche divergence, plays the primary role in promoting allopatric speciation and montane endemism in this species-rich group of vertebrates. Our results demonstrate that even the relatively subtle climatic differences between montane and lowland habitats in eastern North America may play a key role in the origin of new species.

Monongahela Subsistence-settlement Change?

The Late Prehistoric (c. A.D. 1050/1100-1635) Monongahela tradi- tion of southwestern Pennsylvania and portions of adjoining states has come to be associated with specific subsistence-settlement traits. These include a heavy dependence on maize-based agriculture, large percentages of villages in upland locales, and use of semisubterranean storage facilities. In the traditional approach, that entails the con- struction of a series of sequential time periods, changes in subsistence and settlement traits are most often interpreted to have occurred at the boundaries of the time periods. These periods are defined on the basis of pottery style changes and the addition of European artifacts. An accumulation of data now allows for statistical analysis of posited changes in Monongahela tradition settlement and subsistence traits. Results of this study do not support the proposed subsistence and settlement pattern shifts at time period boundaries. Rather, the results support the position of continuous variation in the settlement and subsistence traits through the entire sequence with no evidence of regional uniformity. Throughout much of the northern portions of temperate eastern North America, late prehistoric (c. A.D. 1000-1600) societies were small-scale and sedentary, with subsistence focused to varying degrees on agricultural production (Hart and Means 2002; Hart and Rieth 2002). Our knowledge of such societies suggests that there should be considerable variation in the expression of socio-economic traits in the archaeological record at all scales of analysis. Archaeologists interested in such societies generally rely on culture-historic taxa and their temporal subdivisions as units of study, often without considering the appropriateness of their scale or definition

Steatite Vessel Age and Occurrence in Temperate Eastern North America

Despite a general interest in studying technological change, archaeologists have only rarely attempted to explain the rise and fall of steatite vessel manufacture. Explaining steatite vessel manufacture requires that all information on age and spatial distribution be extensively sampled and accounted for. Documenting spatial distribution shows that steatite vessels are not restricted to a single environmental or depositional context, nor were they manufactured at all steatite outcrops. A correlation between vessel distribution and mast forest, however, was identified. Analyzing steatite vessel age reveals that the technology was present at low levels for lengthy periods of time, but the absence of a trend in age across space fails to support migration/diffusion models of spread. As a durable and portable boiling technology, steatite vessels would have offset the relatively high processing costs of mast by reducing processing time and replacement costs among mobile populations.

Progress in Northern Hemisphere Phytogeography: An Introduction

The problem of Northern Hemisphere plant geography was framed long ago by the observation of striking floristic similarities between eastern North America and eastern Asia. Of primary importance was the work of Asa Gray, who produced a series of detailed comparisons of these floras (see Li 1952; Boufford and Spongberg 1983; Wen 1999). During the past several decades, two major symposia, “Floristics and Paleofloristics of Asia and Eastern North America” (Graham 1972) and “Biogeographical Relationships between Temperate Eastern Asia and Temperate Eastern North America” (Davidse 1983), served to highlight both the nature of the problem and the variety of approaches used to examine intercontinental discontinuities in plants. Not long afterward, two landmark papers by Tiffney (1985a, 1985b) provided a synthesis of paleobotanical and neobotanical data in the context of a dynamic view of Earth history and emphasized floristic exchange via both the North Atlantic and the Bering Land Bridges. In this context, Tiffney (1985b, p. 73) noted that “three-area tests of the variety suggested by cladistic biogeographers need to be made and analyzed to determine whether the eastern Asia–eastern North American similarity is a unique pattern or simply a distinctive subset of a larger pattern.” Over the last two decades we have witnessed remarkable progress in elucidating phylogenetic relationships at all levels, and the number of phylogenies of Northern Hemisphere plant clades has grown to the point that meaningful comparisons are now feasible. Furthermore, there have been major developments in the theory of biogeography as well as in our knowledge of relevant fossils and Earth-history events. The symposium from which the articles in this volume emerged was part of the Botany 2000 meetings in Portland, Oregon. It was designed to create a forum for new analyses of the Northern Hemisphere problem, bringing together a set of paleobotanists and phylogeneticists who have concentrated on relevant areas and plant groups. The goal was to provide a focal point for investigators working from various perspectives on reconstructing relationships among the major areas of endemism and to identify key events that might be responsible for observed patterns of diversity and disjunction. The analyses presented here represent the initial steps toward assembling a modern synthesis based on phylogenetic knowledge, fossil distributions, estimates of sequence diver

Species richness in plant genera disjunct between temperate eastern Asia and North America

Abstract The species richness of 109 amphi-Pacific disjunct genera was examined in eastern Asia and North America. Although the entire flora of eastern Asia contains approximately one-third more species than that of North America, the difference in species richness among disjunct taxa is less. When woody and herbaceous genera are considered separately, the former exhibit a strong diversity bias favouring eastern Asia whereas there is no significant difference in diversity between continents among herbaceous genera. This result is not due to habitat differences between woody and herbaceous genera, because the disjunct herbs inhabit primarily moist forests and woodlands. This result is also not related to relative phylogenetic advancement, even though older major lineages of plants tend to have a predominance of woody taxa. Woody genera are distributed in lower latitudes than herbaceous genera on both continents, and both woody and herbaceous genera are distributed in lower latitudes in eastern Asia than in North America. The North American temperate flora is primarily a relict of a flora formerly more widespread throughout the Northern Hemisphere. Contemporary patterns of diversity suggest that the effects of climate changes in the late Tertiary were less severe in eastern Asia and promoted diversification, but were more severe in North America and may have caused widespread extinction. The difference in the effect of climate change on diversity in herbaceous and woody lineages reflects the different ecological relationships of species having these contrasting life forms. Clearly, the contemporary floras of eastern Asia and North America bear the imprint of history and emphasize the important interface between ecological relationships and evolutionary responses.

Species richness in plant genera disjunct between temperate eastern Asia and North America

The species richness of 109 amphi-Pacific disjunct genera was examined in eastern Asia and North America. Although the entire flora of eastern Asia contains approximately one-third more species than that of North America, the difference in species richness among disjunct taxa is less. When woody and herbaceous genera are considered separately, the former exhibit a strong diversity bias favouring eastern Asia whereas there is no significant difference in diversity between continents among herbaceous genera. This result is not due to habitat differences between woody and herbaceous genera, because the disjunct herbs inhabit primarily moist forests and woodlands. This result is also not related to relative phylogenetic advancement, even though older major lineages of plants tend to have a predominance of woody taxa. Woody genera are distributed in lower latitudes than herbaceous genera on both continents, and both woody and herbaceous genera are distributed in lower latitudes in eastern Asia than in North America. The North American temperate flora is primarily a relict of a flora formerly more widespread throughout the Northern Hemisphere. Contemporary patterns of diversity suggest that the effects of climate changes in the late Tertiary were less severe in eastern Asia and promoted diversification, but were more severe in North America and may have caused widespread extinction. The difference in the effect of climate change on diversity in herbaceous and woody lineages reflects the different ecological relationships of species having these contrasting life forms. Clearly, the contemporary floras of eastern Asia and North America bear the imprint of history and emphasize the important interface between ecological relationships and evolutionary responses.

Seed dormancy and germination in Rhexia mariana var. interior (Melastomataceae) and eco-evolutionary implications

Ninety-seven percent of the Rhexia mariana L. seeds collected in Tennessee were physiologically dormant at maturity in autumn, and they became nondormant during stratification. Light was required for germination, and seeds germinated to higher percentages on filter paper than on sand. Seeds buried in soil in October 1992 and 1994 and exposed to natural seasonal temperatures were exhumed and tested for germination at monthly or bimonthly intervals for 30 and 32 months, respectively. Seeds gained the ability to germinate to 80% or more at 30:15 and 35:20°C during the first winter of burial and also at 25:15°C during the second winter, but they did not re-enter dormancy. In contrast, seeds incubated at 20:10°C exhibited an annual cycle of moderate to high germination percentages in winter-spring and low germination percentages in summer-autumn. Thus, germination can occur at habitat temperatures in Tennessee from April to September. This is the first report of physiological dormancy in seeds of the Melastomataceae in the temperate region. Like members of many plant families in temperate eastern North America, seeds of R. mariana (i) show a decrease in the minimum temperature for germination as they come out of dormancy and (ii) exhibit some seasonal variation in the temperature range for germination. Thus, these dormancy or germination characteristics appear to be adaptations of species to the climatic conditions in temperate eastern North America.Key words: seed dormancy, seed germination, dormancy cycles, buried seeds, Melastomataceae, Rhexia.