Research Overview and Statement
The overarching goal of my research is to understand adaptive evolution from mechanisms to landscapes. In this era of increased biological homogenization, where human activities have greatly reduced the uniqueness of local floras and faunas through species introductions and extirpations, it is essential to understand the processes that lead to the formation of locally differentiated forms if we are to successfully steward rare species, restore populations of species lost to landuse change, or manage invasive species spreading to new areas. To understand how locally differentiated forms arise, it is essential to understand how genotypes become phenotypes, as local differentiation can arise from both genetic and environmental differences.
To better understand how locally differentiated forms arise, I use two broad sets of complementary approaches that focus on genetic, developmental, and physiological mechanisms of differentiation, and landscape patterns of variation. Furthermore, I use in tandem two sets of focal organisms: emerging genetic model organisms in which it is possible to perform manipulative studies, and the rare and declining or invasive species that are most in need of management attention.
Population differentiation in fragmented landscapes
In my dissertation research I examined the mechanisms and landscape patterns of population differentiation in phenotypically plastic shade avoidance elongation in Impatiens capensis, a North American native annual which has become invasive in Europe. Forest understory populations of I. capensis have been observed to elongate less in response to reduced ratios of red:far red (R:FR) light, an important signal of foliage shade, than conspecific plants from open canopy sites. To determine whether the observed pattern of differentiation occurs consistently, I collected seedlings from five pairs of open and closed canopy habitats to determine if the pattern of differentiation is consistent across populations (1). By growing the progeny of the seedlings under two shade treatments to simulate responses to open and closed canopy sites, I was able to determine that populations differed between open and closed canopy sites, but that open canopy plants do not always respond more to shade than plants from open canopy sites. Furthermore, by developing AFLP molecular markers, I showed that this differentiation occurs despite extensive gene flow, and that the differentiation between habitats in morphological traits (Qst) is greater than expected from the marker based Fst. These results suggest that differentiating selection consistently acts on I. capensis between open and closed habitats over short spatial and temporal scales, but that the endpoints of this selection will differ depending on starting genetic variation, correlated features of different specific habitats, and the length of time over which differentiation occurs.
Reduced responsiveness to low R:FR in plants from closed canopy sites could be caused by two physiological mechanisms. First, closed canopy plants could have less sensitive “shade avoidance” elongation responses to low R:FR. Secondly, the high irradiance response to FR (FR-HIR), which allows seedlings to stop elongating out of the soil (ie, de-etiolating) under low R:FR, might persist longer in closed-canopy plants, counteracting shade avoidance responses to low R:FR in juvenile plants. I tested these hypotheses by using red and far-red light emitting diodes to distinguish the responses to altered R:FR of genotypes of I. capensis collected from a pair of open and closed canopy populations that differ in sensitivity to R:FR (2). Genotypes from the open site exhibited typical shade avoidance responses, elongating in response to supplemental FR. However, genotypes from the closed canopy site responded to supplemental FR by elongating less than under ambient control conditions, indicating a persistent FR-HIR. Thus, in a single focal pair of populations the observed population differentiation in response to low R:FR may be linked to differences in FR-HIR.
For more information on my work on shade avoidance in Impatiens, see (3), (4), and (5). I am continuing collaborative work on the relationship of flowering time and elongation with Kathleen Donohue and Annie Schmitt in the US, and work on the biomechanics of elongation and mechanical stimulation with Heidi Huber and Niels Anten at Nijmegan and Utrecht Universities in the Netherlands.
Invasion and Conservation Genetics
As popular ornamentals, many Impatiens species have been transported to new regions for their floral displays, and have subsequently spread from cultivation. In work mentoring Brown undergraduates, we have examined the dispersal behavior of two invasive Impatiens species (6) and the climate envelope of African ornamental Impatiens (7). I am reviewing this work and related work on Impatiens invasions with Nava Tabak at the University of Connecticut (8).
Grasslands currently cover a small portion of coastal New England, but host a large number of regionally rare species. I worked with Kelly Gravuer, now a botanist at NatureServe, to examine patterns of population differentiation in Liatris scariosa var. Novae Angliae, a rare New England grassland composite. Liatris is found in many coastal grasslands from New York to Maine. These populations differ greatly in size, in management strategy, and in surrounding landscape. In a greenhouse common garden, we found that populations differed in leaf traits more than expected by allozyme differentiation, implying that selection on leaf shape favors shorter leaves in populations that are regularly mowed compared to those that are burned or unmanaged (9). These results suggest that translocation and augmentation schemes should consider manage-ment history as well as genetic relatedness in choosing source populations. I am currently using similar methods to guide efforts by the Nantucket Conservation Foundation to bolster populations of Aster concolor, another declining grassland composite. For other work with Liatris, see (10) and (11).
Landscape genomics of endemism and stress tolerance
In my postdoctoral research, I am using emerging genomic tools to examine how extreme soils such as serpentinic soils can drive local differentiation between populations. Serpentinic soils, which occur globally in small patches along fault lines, are extreme in having low Ca:Mg and high concentrations of nickel and other heavy metals, and host communities of regionally rare plants that are frequently threatened by development, mining, and invasive species. It is impossible to make informed management decisions about serpentinic areas without knowledge of the mechanisms by which serpentinic soils are tolerated and how tolerance evolves. If tolerance is achieved easily and can evolve quickly in any one species, it is feasible for plants from nearby non-serpentinic sites to establish on serpentinic areas. Conversely, if tolerance can only be achieved with difficulty and evolves infrequently in any one species, only plants from another serpentinic area are likely to establish on a particular serpentinic outcropping.
As genomic tools are required to fully characterize tolerance, I am developing Arabidopsis lyrata, a near relative of the model plant A. thaliana with an ongoing genome project, as an ecological model for serpentinic tolerance. In eastern North America A. lyrata naturally occurs on both serpentine soils with low Ca:Mg and high Ni levels as well as less extreme soils. The genetic underpinnings of tolerance of these soils are currently not understood, but as A. thaliana and A. lyrata genomic tools mature, the potential to use these tools in related species that naturally occur on these soils grows. I take a multi-pronged approach to the study of tolerance of these soils that uses a mix of 1) historic herbaria records and landcover data to characterize how soil types and landuse change have impacted the persistence of A. lyrata in the area between Philadelphia and Baltimore where there are “islands” of serpentic soil, 2) phenotypic characterization of differences in serpentine and non-serpentine populations in Ni and Ca:Mg tolerance both under controlled hydroponic and field conditions, and 3) emerging genomic tools to find candidate pathways and genes for tolerance of Ni and low Ca:Mg.
As the potential to take genomic resources from model organisms to related non-model organisms grows, I intend to also work on salinity tolerance in salt marsh grasses and in relatives of alfalfa. Alterations to water salinity is a significant contributor to degradation of many coastal plant communities, and salinization of agricultural soils is a major challenge to crop yields in arid regions. I am currently working with the groups of Brian Silliman and Mark Bertness to characterize differential effects of increased salinity on the competitive ability of native North American and exotic Eurasian ecotypes of Phragmites australis. There are already substantial genomic resources for rice; as all grass genomes are largely co-linear, it will be possible to extend these tools to other grasses. Similarly, I am beginning work on salinity tolerance among Tunisian ecotypes of Medicago truncatula, a relative of the crop alfalfa for which a genome sequence is nearly complete.
Future research goals
As a faculty member, I intend to maintain a research program that uses interdisciplinary approaches to characterize mechanisms and landscape patterns of tolerance to extreme soils, both naturally occurring and human created. My goals are to increase our knowledge of how tolerance is achieved so that tolerance can be improved in 1) plants that we maintain economically, as well as 2) provide information necessary to maintain and restore the populations of rare species that can naturally tolerate these soils, and 3) to prevent unwanted species from spreading. I will continue to use both emerging genetic model species and rare or noxious species for which management information is needed.
1. E. J. Von Wettberg, D. L. Remington, J. Schmitt, Am. Nat. (in review).
2. E. J. von Wettberg, J. Schmitt, Am. J. Bot. 92, 868 (May, 2005).
3. E. J. von Wettberg, H. Huber, J. Schmitt, Evolutionary Ecology Research 7, 531 (May, 2005).
4. H. Huber et al., Am. Nat. 163, 548 (Apr, 2004).
5. E. J. von Wettberg, J. Schmitt, Evolution (in review).
6. D. Auyeung, E. J. Von Wettberg, J. Schmitt, Plant Ecol. (in review).
7. L. A. Mandle, E. J. von Wettberg, M. Hoffman, J. Schmitt, Proc Natl Acad Sci U S A (in review).
8. N. M. Tabak, E. J. von Wettberg, (in preparation).
9. K. Gravuer, E. J. von Wettberg, J. Schmitt, Biological Conservation 124, 155 (2005).
10. K. Gravuer, E. J. von Wettberg, J. Schmitt, Am. J. Bot. 90, 1159 (2003).
11. M. Vadeboncoeur, E. J. von Wettberg, J. Schmitt, (in preparation).
The overarching goal of my research is to understand adaptive evolution from mechanisms to landscapes. In this era of increased biological homogenization, where human activities have greatly reduced the uniqueness of local floras and faunas through species introductions and extirpations, it is essential to understand the processes that lead to the formation of locally differentiated forms if we are to successfully steward rare species, restore populations of species lost to landuse change, or manage invasive species spreading to new areas. To understand how locally differentiated forms arise, it is essential to understand how genotypes become phenotypes, as local differentiation can arise from both genetic and environmental differences.
To better understand how locally differentiated forms arise, I use two broad sets of complementary approaches that focus on genetic, developmental, and physiological mechanisms of differentiation, and landscape patterns of variation. Furthermore, I use in tandem two sets of focal organisms: emerging genetic model organisms in which it is possible to perform manipulative studies, and the rare and declining or invasive species that are most in need of management attention.
Population differentiation in fragmented landscapes
In my dissertation research I examined the mechanisms and landscape patterns of population differentiation in phenotypically plastic shade avoidance elongation in Impatiens capensis, a North American native annual which has become invasive in Europe. Forest understory populations of I. capensis have been observed to elongate less in response to reduced ratios of red:far red (R:FR) light, an important signal of foliage shade, than conspecific plants from open canopy sites. To determine whether the observed pattern of differentiation occurs consistently, I collected seedlings from five pairs of open and closed canopy habitats to determine if the pattern of differentiation is consistent across populations (1). By growing the progeny of the seedlings under two shade treatments to simulate responses to open and closed canopy sites, I was able to determine that populations differed between open and closed canopy sites, but that open canopy plants do not always respond more to shade than plants from open canopy sites. Furthermore, by developing AFLP molecular markers, I showed that this differentiation occurs despite extensive gene flow, and that the differentiation between habitats in morphological traits (Qst) is greater than expected from the marker based Fst. These results suggest that differentiating selection consistently acts on I. capensis between open and closed habitats over short spatial and temporal scales, but that the endpoints of this selection will differ depending on starting genetic variation, correlated features of different specific habitats, and the length of time over which differentiation occurs.
Reduced responsiveness to low R:FR in plants from closed canopy sites could be caused by two physiological mechanisms. First, closed canopy plants could have less sensitive “shade avoidance” elongation responses to low R:FR. Secondly, the high irradiance response to FR (FR-HIR), which allows seedlings to stop elongating out of the soil (ie, de-etiolating) under low R:FR, might persist longer in closed-canopy plants, counteracting shade avoidance responses to low R:FR in juvenile plants. I tested these hypotheses by using red and far-red light emitting diodes to distinguish the responses to altered R:FR of genotypes of I. capensis collected from a pair of open and closed canopy populations that differ in sensitivity to R:FR (2). Genotypes from the open site exhibited typical shade avoidance responses, elongating in response to supplemental FR. However, genotypes from the closed canopy site responded to supplemental FR by elongating less than under ambient control conditions, indicating a persistent FR-HIR. Thus, in a single focal pair of populations the observed population differentiation in response to low R:FR may be linked to differences in FR-HIR.
For more information on my work on shade avoidance in Impatiens, see (3), (4), and (5). I am continuing collaborative work on the relationship of flowering time and elongation with Kathleen Donohue and Annie Schmitt in the US, and work on the biomechanics of elongation and mechanical stimulation with Heidi Huber and Niels Anten at Nijmegan and Utrecht Universities in the Netherlands.
Invasion and Conservation Genetics
As popular ornamentals, many Impatiens species have been transported to new regions for their floral displays, and have subsequently spread from cultivation. In work mentoring Brown undergraduates, we have examined the dispersal behavior of two invasive Impatiens species (6) and the climate envelope of African ornamental Impatiens (7). I am reviewing this work and related work on Impatiens invasions with Nava Tabak at the University of Connecticut (8).
Grasslands currently cover a small portion of coastal New England, but host a large number of regionally rare species. I worked with Kelly Gravuer, now a botanist at NatureServe, to examine patterns of population differentiation in Liatris scariosa var. Novae Angliae, a rare New England grassland composite. Liatris is found in many coastal grasslands from New York to Maine. These populations differ greatly in size, in management strategy, and in surrounding landscape. In a greenhouse common garden, we found that populations differed in leaf traits more than expected by allozyme differentiation, implying that selection on leaf shape favors shorter leaves in populations that are regularly mowed compared to those that are burned or unmanaged (9). These results suggest that translocation and augmentation schemes should consider manage-ment history as well as genetic relatedness in choosing source populations. I am currently using similar methods to guide efforts by the Nantucket Conservation Foundation to bolster populations of Aster concolor, another declining grassland composite. For other work with Liatris, see (10) and (11).
Landscape genomics of endemism and stress tolerance
In my postdoctoral research, I am using emerging genomic tools to examine how extreme soils such as serpentinic soils can drive local differentiation between populations. Serpentinic soils, which occur globally in small patches along fault lines, are extreme in having low Ca:Mg and high concentrations of nickel and other heavy metals, and host communities of regionally rare plants that are frequently threatened by development, mining, and invasive species. It is impossible to make informed management decisions about serpentinic areas without knowledge of the mechanisms by which serpentinic soils are tolerated and how tolerance evolves. If tolerance is achieved easily and can evolve quickly in any one species, it is feasible for plants from nearby non-serpentinic sites to establish on serpentinic areas. Conversely, if tolerance can only be achieved with difficulty and evolves infrequently in any one species, only plants from another serpentinic area are likely to establish on a particular serpentinic outcropping.
As genomic tools are required to fully characterize tolerance, I am developing Arabidopsis lyrata, a near relative of the model plant A. thaliana with an ongoing genome project, as an ecological model for serpentinic tolerance. In eastern North America A. lyrata naturally occurs on both serpentine soils with low Ca:Mg and high Ni levels as well as less extreme soils. The genetic underpinnings of tolerance of these soils are currently not understood, but as A. thaliana and A. lyrata genomic tools mature, the potential to use these tools in related species that naturally occur on these soils grows. I take a multi-pronged approach to the study of tolerance of these soils that uses a mix of 1) historic herbaria records and landcover data to characterize how soil types and landuse change have impacted the persistence of A. lyrata in the area between Philadelphia and Baltimore where there are “islands” of serpentic soil, 2) phenotypic characterization of differences in serpentine and non-serpentine populations in Ni and Ca:Mg tolerance both under controlled hydroponic and field conditions, and 3) emerging genomic tools to find candidate pathways and genes for tolerance of Ni and low Ca:Mg.
As the potential to take genomic resources from model organisms to related non-model organisms grows, I intend to also work on salinity tolerance in salt marsh grasses and in relatives of alfalfa. Alterations to water salinity is a significant contributor to degradation of many coastal plant communities, and salinization of agricultural soils is a major challenge to crop yields in arid regions. I am currently working with the groups of Brian Silliman and Mark Bertness to characterize differential effects of increased salinity on the competitive ability of native North American and exotic Eurasian ecotypes of Phragmites australis. There are already substantial genomic resources for rice; as all grass genomes are largely co-linear, it will be possible to extend these tools to other grasses. Similarly, I am beginning work on salinity tolerance among Tunisian ecotypes of Medicago truncatula, a relative of the crop alfalfa for which a genome sequence is nearly complete.
Future research goals
As a faculty member, I intend to maintain a research program that uses interdisciplinary approaches to characterize mechanisms and landscape patterns of tolerance to extreme soils, both naturally occurring and human created. My goals are to increase our knowledge of how tolerance is achieved so that tolerance can be improved in 1) plants that we maintain economically, as well as 2) provide information necessary to maintain and restore the populations of rare species that can naturally tolerate these soils, and 3) to prevent unwanted species from spreading. I will continue to use both emerging genetic model species and rare or noxious species for which management information is needed.
1. E. J. Von Wettberg, D. L. Remington, J. Schmitt, Am. Nat. (in review).
2. E. J. von Wettberg, J. Schmitt, Am. J. Bot. 92, 868 (May, 2005).
3. E. J. von Wettberg, H. Huber, J. Schmitt, Evolutionary Ecology Research 7, 531 (May, 2005).
4. H. Huber et al., Am. Nat. 163, 548 (Apr, 2004).
5. E. J. von Wettberg, J. Schmitt, Evolution (in review).
6. D. Auyeung, E. J. Von Wettberg, J. Schmitt, Plant Ecol. (in review).
7. L. A. Mandle, E. J. von Wettberg, M. Hoffman, J. Schmitt, Proc Natl Acad Sci U S A (in review).
8. N. M. Tabak, E. J. von Wettberg, (in preparation).
9. K. Gravuer, E. J. von Wettberg, J. Schmitt, Biological Conservation 124, 155 (2005).
10. K. Gravuer, E. J. von Wettberg, J. Schmitt, Am. J. Bot. 90, 1159 (2003).
11. M. Vadeboncoeur, E. J. von Wettberg, J. Schmitt, (in preparation).
posted by Eric von Wettberg at 11:55 AM
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