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Dylan O Burge - One of the best experts on this subject based on the ideXlab platform.
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evolution of leaf structure and drought tolerance in species of californian Ceanothus
American Journal of Botany, 2018Co-Authors: Leila R Fletcher, Dylan O Burge, Hongxia Cui, Hilary S Callahan, Christine Scoffoni, Grace P John, Megan K Bartlett, Lawren SackAbstract:PREMISE OF THE STUDY Studies across diverse species have established theory for the contribution of leaf traits to plant drought tolerance. For example, species in more arid climates tend to have smaller leaves of higher vein density, higher leaf mass per area, and more negative osmotic potential at turgor loss point (πTLP ). However, few studies have tested these associations for species within a given lineage that have diversified across an aridity gradient. METHODS We analyzed the anatomy and physiology of 10 Ceanothus (Rhamnaceae) species grown in a common garden for variation between and within "wet" and "dry" subgenera (Ceanothus and Cerastes, respectively) and analyzed a database for 35 species for leaf size and leaf mass per area (LMA). We used a phylogenetic generalized least squares approach to test hypothesized relationships among traits, and of traits with climatic aridity in the native range. We also tested for allometric relationships among anatomical traits. KEY RESULTS Leaf form, anatomy, and drought tolerance varied strongly among species within and between subgenera. Cerastes species had specialized anatomy including hypodermis and encrypted stomata that may confer superior water storage and retention. The osmotic potentials at turgor loss point (πTLP ) and full turgor (πo ) showed evolutionary correlations with the aridity index (AI) and precipitation of the 10 species' native distributions, and LMA with potential evapotranspiration for the 35 species in the larger database. We found an allometric correlation between upper and lower epidermal cell wall thicknesses, but other anatomical traits diversified independently. CONCLUSIONS Leaf traits and drought tolerance evolved within and across lineages of Ceanothus consistently with climatic distributions. The πTLP has signal to indicate the evolution of drought tolerance within small clades.
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Three Edaphic-Endemic Ceanothus (Rhamnaceae) New to Science
Systematic Botany, 2017Co-Authors: Dylan O Burge, Jon P. Rebman, Margaret R. Mulligan, Dieter H. WilkenAbstract:North America is home to approximately 55 species of Ceanothus (Rhamnaceae), more than 30 of them endemic to the biodiversity hotspot known as the California Floristic Province. Although several species of Ceanothus are widespread in North America, most of the species are micro-endemics, known from a small number of occurrences and generally associated with special ecological conditions. As botanical exploration of North America continues, it is expected that more such micro-endemics will be discovered. However, field work is not the only way in which additional Ceanothus diversity will come to light; the strongly variable morphology of Ceanothus means that specimens are difficult to identify, and many biological entities that probably deserve taxonomic recognition are already represented in herbaria but have not yet been recognized as new. We here describe three new taxa of Ceanothus, two initially noted among existing collections, and another discovered during botanical exploration in San Diego County. All three are edaphic micro-endemics found only in the southern California Floristic Province, California. These include 1) Ceanothus foliosus var. viejasensis D. O. Burge&Rebman, restricted to gabbro-derived soils on ViejasMountain in SanDiego County, 2) Ceanothus pendletonensis D. O. Burge, Rebman, &M. R. Mulligan, found on granodiorite-derived soils of the central Santa Margarita Mountains in San Diego County, and 3) Ceanothus thyrsiflorus var. obispoensis D. O. Burge, endemic to rhyolite-derived soils near Hollister Peak in San Luis Obispo County.
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A Taxonomic Conspectus of Ceanothus Subgenus Cerastes (Rhamnaceae)
Systematic Botany, 2016Co-Authors: Dylan O Burge, Katherine Zhukovsky, Dieter H. WilkenAbstract:Abstract The diverse New World shrub genus Ceanothus (Rhamnaceae) is made up of two deeply divergent, reciprocally monophyletic groups that are treated as subgenera in most recent systematic and flora treatments, Ceanothus subgenus Cerastes, and Ceanothus subgenus Ceanothus. The two groups are phylogenetically divergent and appear to have simultaneously diversified in western North America, particularly the California Floristic Province. Ceanothus subgenus Cerastes is easily distinguished from Ceanothus subgenus Ceanothus by its sclerophyllous (versus thin) leaves, stomata sequestered in pits (versus on the leaf surface), and swollen (versus papery) stipules. Low levels of genetic divergence among species, combined with highly variable, intergrading morphology makes taxonomic work in Ceanothus subgenus Cerastes difficult. To aid research in this diverse and ecologically important group of plants, we present a taxonomic conspectus of Ceanothus subgenus Cerastes, including formal recognition of Cerastes at ...
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The Role of Soil Chemistry in the Geographic Distribution of Ceanothus otayensis (Rhamnaceae)
Madroño, 2014Co-Authors: Dylan O BurgeAbstract:Abstract Ceanothus otayensis McMinn (Rhamnaceae) was previously known only from metavolcanic-derived soils of the northern Peninsular Ranges—predominantly the San Ysidro Mountains—in San Diego County, California, and adjacent Baja California, Mexico. Recently, a new population of C. otayensis was discovered on sedimentary soils at Marine Corps Air Station Miramar, 25 km northwest of the next nearest known population. Sedimentary deposits at the new locality are thought to produce unusual soils. It is possible that the disjunct distribution of C. otayensis is a response to soil conditions, a phenomenon frequently seen in other members of Ceanothus, for instance on serpentine. The present study uses soil chemistry data for seven populations and subpopulations of C. otayensis (metavolcanic: n = 5; sedimentary: n = 2), as well as 22 populations of closely related Ceanothus, to determine whether soils of C. otayensis are chemically distinct from those of closely related Ceanothus, and answer the following ...
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limited hybridization across an edaphic disjunction between the gabbro endemic shrub Ceanothus roderickii rhamnaceae and the soil generalist Ceanothus cuneatus
American Journal of Botany, 2013Co-Authors: Dylan O Burge, Robin Hopkins, Yihsin Erica Tsai, Paul S ManosAbstract:UNLABELLED PREMISE OF THE STUDY Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • METHODS AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • KEY RESULTS Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • CONCLUSIONS There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.
Paul S Manos - One of the best experts on this subject based on the ideXlab platform.
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limited hybridization across an edaphic disjunction between the gabbro endemic shrub Ceanothus roderickii rhamnaceae and the soil generalist Ceanothus cuneatus
American Journal of Botany, 2013Co-Authors: Dylan O Burge, Robin Hopkins, Yihsin Erica Tsai, Paul S ManosAbstract:PREMISE OF THE STUDY: Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • METHODS: AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • KEY RESULTS: Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • CONCLUSIONS: There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.
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limited hybridization across an edaphic disjunction between the gabbro endemic shrub Ceanothus roderickii rhamnaceae and the soil generalist Ceanothus cuneatus
American Journal of Botany, 2013Co-Authors: Dylan O Burge, Robin Hopkins, Yihsin Erica Tsai, Paul S ManosAbstract:UNLABELLED PREMISE OF THE STUDY Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • METHODS AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • KEY RESULTS Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • CONCLUSIONS There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.
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diversification of Ceanothus rhamnaceae in the california floristic province
International Journal of Plant Sciences, 2011Co-Authors: Dylan O Burge, Dieter H. Wilken, Steven W Kembel, Diane M Erwin, Melissa B Islam, Jurgen Kellermann, Paul S ManosAbstract:High diversity and endemism in the California Floristic Province (CFP) are an alleged response to the late Cenozoic advent of Mediterranean-type climate in this region. Ceanothus comprises two divergent subgenera with centers of diversity in the CFP. We reconstruct the evolution of Ceanothus by using DNA sequence data from the nuclear gene nitrate reductase. We find that the timing of diversification events is related to geological and climatic history. In both subgenera, diversification is characterized by recent divergence of extant taxa and geographically structured phylogenetic relationships. A strong north-south divergence of subgenus Cerastes across the Transverse Ranges indicates that phylogenetic relationships may be structured by climatically divergent regions of the CFP. Divergence-time estimation suggests that the age of extant diversification in both subgenera is ∼6 Ma. This agrees with the fossil record but predates the hypothesized Quaternary (2-Ma) origin of Mediterranean-type climate in th...
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edaphic ecology and genetics of the gabbro endemic shrub Ceanothus roderickii rhamnaceae
Madroño, 2011Co-Authors: Dylan O Burge, Paul S ManosAbstract:Abstract Edaphic-endemic plant taxa are often interpreted as recently derived entities that evolved in situ, with genetic divergence driven by substrate specialization. However, little is known about the evolution of specific edaphic-endemic taxa, particularly the role that soil conditions may play in their initial divergence and continued persistence. Our study focuses on Ceanothus roderickii, a strict specialist on soils derived from a single outcrop of the geological material gabbro located in south-western El Dorado County, California. In order to elucidate the evolutionary history of C. roderickii we sequenced the third intron of the low-copy nuclear gene nitrate reductase (NIA) for individuals representing four populations of C. roderickii and a wide taxonomic and geographic sampling of closely related plants, including 37 populations of Ceanothus cuneatus and a single representative from 16 other taxa. Analysis of NIA shows that C. roderickii is closely related to C. cuneatus var. cuneatus, a widel...
David W Huffman - One of the best experts on this subject based on the ideXlab platform.
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production losses and germination of Ceanothus fendleri seeds in an arizona ponderosa pine forest
Western North American Naturalist, 2006Co-Authors: David W HuffmanAbstract:Abstract I quantified seed production and ovule losses for Ceanothus fendleri Gray (Fendler Ceanothus) plants protected from large ungulate herbivores in a ponderosa pine (Pinus ponderosa [Laws]) forest of northern Arizona. I also tested seed germination responses to cold stratification and heat treatments in the laboratory. Fruit production on fecund stems ranged from 7.4 to 38.2 fruits per stem, which equated to 22.2–118.2 potential seeds based on 3 ovules per fruit. Stems that produced fruit were significantly large relative to their expected sizes. Predispersal ovule losses ranged from 70.7% to 91.4% across the 2 years studied. A chalcidoid seed parasite (Eurytoma squamosa Bugbee) consumed 11%–28% of the total number of seeds produced. Postdispersal seed predation varied from 0% to 24% and was significantly affected by forest floor substrate in 1 study year. Cumulative ovule losses were estimated to be 71%–92%. Cold stratification did not significantly affect seed germination, and exposure to 90°C res...
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responses of fendler Ceanothus to overstory thinning prescribed fire and drought in an arizona ponderosa pine forest
Forest Ecology and Management, 2004Co-Authors: David W Huffman, Margaret M MooreAbstract:Abstract Overstory tree thinning and prescribed fire are used to restore ecosystem structure and function in ponderosa pine (Pinus ponderosa Laws.) forests of the southwest but little research has examined constraints on population-level responses of understory plants. In order to study growth and reproduction of a common shrub species after forest restoration treatments, we monitored Fendler Ceanothus (Ceanothus fendleri Gray) plants from 1999 to 2002 in thinned and unthinned overstory units. To study effects of tree thinning, we analyzed relationships of overstory stand density (Reineke’s SDI) and current-year branch length, number of branches, and biomass, and also evaluated the importance of mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus) herbivory (Browsing) as a predictor in linear models. To study effects of prescribed fire, we examined mortality, seedling emergence, and growth response on experimentally burned and unburned plots. SDI and browsing were significantly and negatively correlated with F. Ceanothus current-year branch length, biomass, and leaf area but relationships were generally weak. Across the 4 years, browsing appeared to be consistently more important than SDI in explaining variation in growth. Although SDI and browsing were significant predictors of growth in years with near normal precipitation, models failed in drought years. Burning resulted in 17–32% mortality whereas 0–5% of plants died on unburned plots. Mortality of burned plants was positively related to amount of forest floor consumed during prescribed fires. One growing season after fire, surviving burned plants responded by producing long resprouts. Current-year branches were consistently longer on burned than unburned plants only where plots were protected from large herbivores. Unburned plants had more current-year branches and greater biomass than burned plants. No seedlings emerged on unburned plots but were found on 44% of burned plots. A quadratic function represented the relationship between seedling emergence and forest floor consumption. Our results suggest that restoration treatments in ponderosa pine forests of northern Arizona can help increase abundance of F. Ceanothus but population responses may be slow, particularly when constrained by ungulate herbivory, fire-related mortality of plants and dormant seeds, and drought.
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population ecology of fendler Ceanothus responses to herbivory and forest restoration treatments
2003Co-Authors: David W HuffmanAbstract:To understand responses of Fendler Ceanothus to forest restoration treatments and large ungulate herbivory, I focused research on four areas: 1) effects of large ungulate herbivores on Fendler Ceanothus stem size, morphology, and flower production, 2) production, fate, and germination of Fendler Ceanothus seeds, 3) importance of overstory density, ungulate herbivory, prescribed fire, and drought for Fendler Ceanothus growth and regeneration, and 4) simulation of population dynamics under various management scenarios. After two seasons (1999, 2000), plants protected from large ungulate herbivores were larger and produced greater biomass, leaf area, and flowering stems than plants that were not protected. These results showed that large herbivores such as mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus elaphus) constrained growth and reproduction of Fendler Ceanothus in thinned forest units. Fendler Ceanothus stems that were not protected from large herbivores did not produce fruit over the four-year study (1999-2002). Seed production (2000-2001) was affected by stem size and probably drought. Predispersal seed parasites and postdispersal predators were important sources of ovule loss. Seed germination after iii exposure to 90C (10-minute duration) was greater than without heat treatment. These results increase our understanding of Fendler Ceanothus seed production and losses. Stand density index (SDI) and browsing by ungulates were negatively related to Fendler Ceanothus growth. Prediction of growth from SDI and browsing was poor in years of drought. Plant mortality was positively related to depth of forest floor consumed in experimental burning. Fendler Ceanothus seedlings emerged on burned plots but not on unburned plots. These results indicate that overstory tree thinning and prescribed fire can increase growth and reproduction of Fendler Ceanothus but responses are constrained by herbivory and drought. Simulation of Fendler Ceanothus population dynamics suggested that restoration treatments and herbivory interact to affect long-term persistence and population structure. Populations that did not experience fire were generally dominated by dormant seeds whereas burned populations had relatively even life stage structures at the end of the 25- year simulation. Frequent fire (2-5 yr) stimulated growth of protected populations but negatively affected populations exposed to intense herbivory.
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a seed chalcid eurytoma squamosa bugbee parasitizes buckbrush Ceanothus fendleri gray seeds in a ponderosa pine forest of arizona
Western North American Naturalist, 2002Co-Authors: David W HuffmanAbstract:Predispersal seed parasitism rates were quantified for buckbrush ( Ceanothus fendleri Gray) in 3 Arizona ponderosa pine ( Pinus ponderosa Laws.) forest units that had been thinned for ecological restoration objectives. The chalcidoid wasp Eurytoma squamosa Bugbee (Eurytomidae) was responsible for 35% of total seed loss in a single year. These findings represent an expansion of the known range and host list for E. squamosa and increase our understanding of factors that may constrain regeneration of C. fendleri in Southwest ponderosa pine forests.
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a seed chalcid eurytoma squamosa bugbee parasitizes buckbrush Ceanothus fendleri gray seeds in a ponderosa pine forest of arizona
Western North American Naturalist, 2002Co-Authors: David W HuffmanAbstract:Predispersal seed parasitism rates were quantified for buckbrush (Ceanothus fendleri Gray) in 3 Arizona ponderosa pine (Pinus ponderosa Laws.) forest units that had been thinned for ecological restoration objectives. The chalcidoid wasp Eurytoma squamosa Bugbee (Eurytomidae) was responsible for 35(percent) of total seed loss in a single year. These findings represent an expansion of the known range and host list for E. squamosa and increase our understanding of factors that may constrain regeneration of C. fendleri in Southwest ponderosa pine forests.
David D Myrold - One of the best experts on this subject based on the ideXlab platform.
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population size and diversity of frankia in soils of Ceanothus velutinus and douglas fir stands
Soil Biology & Biochemistry, 2001Co-Authors: Soonchun Jeong, David D MyroldAbstract:Abstract The influence of host plants on Frankia populations was investigated using soils from Ceanothus velutinus (Dougl.) and Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) stands. Population sizes of Ceanothus -infective Frankia in the soils were measured using plant bioassays with C. velutinus, C. sanguineus (Pursh), and C. integerrimus (H. & A.) as trap plants. The Frankia population in soil from the C. velutinus stand soil was about 10 times higher than that from the Douglas-fir stand. This result supports previous reports that, although the presence of host plants increases Frankia populations, Frankia persist without host plants. Nodulation capacities of the three trap plants were not significantly different. All nodules showed N 2 fixation activity using the acetylene reduction assay. The diversity of Frankia that nodulated trap plants was examined using repetitive intergenic DNA and the polymerase chain reaction (rep-PCR). A newly designed, direct repeat sequence and a BOX sequence were used as rep-PCR primers. The results showed that infective Frankia in the two soils contained a common group of Frankia as well as some Frankia strains unique to each soil. The level of host specificity of the infective Frankia was low; however, one group of Frankia nodulated only C. integerrimus seedlings. Taken together, the results suggest that the higher populations in the soil from the C. velutinus stand may be due to preferential increases in particular groups of Frankia .
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genomic fingerprinting of frankia microsymbionts from Ceanothus copopulations using repetitive sequences and polymerase chain reactions
Botany, 1999Co-Authors: Soonchun Jeong, David D MyroldAbstract:Specificity between Ceanothus species and their microsymbionts, Frankia, were investigated with nodules collected from three geographically separated copopulations of Ceanothus species. Nodules wer...
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phylogenetic placement of uncultured Ceanothus microsymbionts using 16s rrna gene sequences
Botany, 1999Co-Authors: Nancy J Ritchie, David D MyroldAbstract:Full-length 16S rDNA sequences were amplified directly from the nodules of Ceanothus americanus L. and Ceanothus thyrsiflorus Eschsch. using the polymerase chain reaction. Sequences were determined...
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geographic distribution and genetic diversity of Ceanothus infective frankia strains
Applied and Environmental Microbiology, 1999Co-Authors: Nancy J Ritchie, David D MyroldAbstract:Little is known about Ceanothus-infective Frankia strains because no Frankia strains that can reinfect the host plants have been isolated from Ceonothus spp. Therefore, we studied the diversity of the Ceonothus-infective Frankia strains by using molecular techniques. Frankia strains inhabiting root nodules of nine Ceanothus species were characterized. The Ceanothus species used represent the taxonomic diversity and geographic range of the genus; therefore, the breadth of the diversity of Frankia strains that infect Ceanothus spp. was studied. DNA was amplified directly from nodular material by using the PCR. The amplified region included the 3′ end of the 16S rRNA gene, the intergenic spacer, and a large portion of the 23S rRNA gene. A series of restriction enzyme digestions of the PCR product allowed us to identify PCR-restriction fragment length polymorphism (RFLP) groups among the Ceanothus-infective Frankia strains tested. Twelve different enzymes were used, which resulted in four different PCR-RFLP groups. The groups did not follow the taxonomic lines of the Ceanothus host species. Instead, the Frankia strains present were related to the sample collection locales.
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molecular phylogeny of the genus Ceanothus rhamnaceae using rbcl and ndhf sequences
Theoretical and Applied Genetics, 1997Co-Authors: Soonchun Jeong, Aaron Liston, David D MyroldAbstract:Intrageneric phylogeny among ten representative Ceanothus species was investigated using DNA sequences of the chloroplast encoded ndhF and rbcL genes. Parsimony analysis of the ndhF sequences identified two main clades corresponding to two subgenera Ceanothus and Cerastes. The phylogenetic results suggest that three monophyletic clades within the subgenus Ceanothus can be delimited on the basis of (1) evergreen or (2) deciduous leaves and (3) thorn presence within the evergreen clade. The estimated divergence time based on rbcL sequences suggests that the two subgenera diverged 18–39 million years ago whereas species within each subgenus diverged more recently. Taken together, the results support the division of Ceanothus into two monophyletic subgenera and are consistent with the postulated recent divergence of many species within each subgenus.
Robin Hopkins - One of the best experts on this subject based on the ideXlab platform.
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limited hybridization across an edaphic disjunction between the gabbro endemic shrub Ceanothus roderickii rhamnaceae and the soil generalist Ceanothus cuneatus
American Journal of Botany, 2013Co-Authors: Dylan O Burge, Robin Hopkins, Yihsin Erica Tsai, Paul S ManosAbstract:UNLABELLED PREMISE OF THE STUDY Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • METHODS AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • KEY RESULTS Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • CONCLUSIONS There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.
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limited hybridization across an edaphic disjunction between the gabbro endemic shrub Ceanothus roderickii rhamnaceae and the soil generalist Ceanothus cuneatus
American Journal of Botany, 2013Co-Authors: Dylan O Burge, Robin Hopkins, Yihsin Erica Tsai, Paul S ManosAbstract:PREMISE OF THE STUDY: Hybridization is thought to have played an important role in diversification of the speciose shrub genus Ceanothus; putative hybrid species have been described, and data suggest that intrinsic barriers may not exist among closely related species. However, the extent to which hybridization occurs in the wild is not known, and little is understood about how extrinsic factors such as soil chemistry may influence the process. The present research focuses on the gabbro-endemic C. roderickii and the closely related soil-generalist C. cuneatus. Though the species occur peripatrically, they remain distinct across an edaphic disjunction. • METHODS: AFLP was used to quantify hybridization and introgression. Biological data and experiments were used to test for prezygotic isolation. Growth trials were used to test for local adaptation and selection against hybrids. • KEY RESULTS: Ceanothus cuneatus and C. roderickii were strongly differentiated morphologically and genetically, despite a lack of evidence for prezygotic barriers. Hybrids and back-crosses were present but infrequent. Finally, there was selection against hybrids in nonnative soil. • CONCLUSIONS: There is little genetic exchange between the focal species across an edaphic disjunction, despite the absence of prezygotic barriers. This result implies that soil conditions, as well as other extrinsic factors, should be considered as forces that may restrict hybridization and gene flow in Ceanothus, influencing local adaptation and speciation. Findings presented here are significant because they imply that exchange of genetic material between plants may be limited directly by the abiotic environment, rather than by the biology of the plants.