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Morphometric Variation in Oaks of the Apostle Islands in Wisconsin: Evidence of Hybridization Between Quercus rubra and Q. ellipsoidalis (Fagaceae)
Abstract
The Apostle Islands in Lake Superior are populated by trees that are clearly related to Quercus rubra L. However, several islands have trees with morphological characteristics suggestive of hybridization with Q. ellipsoidalis Hill. Leaf specimens were collected from trees in five locations: the outermost island, an intermediate island, the nearest-shore island, the northeast shoreline, and an inland forest about 24 km from the shoreline. Seventeen landmarks were digitized for two to five leaves per tree. These landmarks were used to generate nine linear characters and three angles. These characters, along with the number of bristle tips per leaf, were used in various combinations for several principal component analyses. In addition, the landmark configurations were examined using rotational-fit methods. The patterns observed in both types of analysis indicate phenotypic variation coincident with a line connecting the two most distant sample sites. The location nearest the geographic center of this line is also nearest the center of the two-dimensional view of phenotypic variation. Trees at each site illustrate a distinctive pattern in the rotational-fit analyses, and patterns of co-variation in the morphometric characters are different for each site. The observed morphometric variation is consistent with the hypothesis that there is hybridization between these two species, most likely in the form of introgression from Q. ellipsoidalis into Q. rubra.
... Within this complex of Lobatae species, scientists observed a trend common within the genus Quercus; species level variation within leaf traits is in part caused by weakened boundaries between closely related species (Curtu et al., 2007(Curtu et al., , 2009Owusu et al., 2015;Valencia, 2010). Moreover, variation in leaf morphology for species in Quercus is related introgression and hybridization with closely related species (Jensen et al., 1993;Owusu et al., 2015;Sullivan et al., 2016). ...
... We measured leaf traits of Qe and Qr from common gardens to test the following hypotheses: (1) leaf trait phenotypes differ in mean and variance in response to common garden site, species, and between these independent variables. Evidence for this hypothesis is based on changes in leaf traits linked to environmental effects (Balaguer et al., 2001;Valladares, Martinez-Ferri, et al., 2000), and quantifiable differences in Qe and Qr leaf traits (Gailing et al., 2012;Jensen et al., 1993). ...
... Qe and Qr (Gailing et al., 2012;Jensen et al., 1993). The leaf landmarks used to measure traits 2-13 are shown in Figure 1. ...
This dissertation was written on topics related to the genus Quercus with a primary focus on Quercus ellipsoidalis (northern pin oak) and Quercus rubra (northern red oak). Within this dissertation are chapters related to the setup of experimental common gardens within the Ford and Kellogg experimental forest, a literature review describing drought adaptations of Quercus sect. Lobatae (red oak group), identification of transcription factors within the Q. robur (English oak) and Q. rubra genomes, a study comparing leaf trait phenotypic plasticity of Q. ellipsoidalis and Q. rubra, and an RNA-seq experiment studying ecological speciation between Q. ellipsoidalis and Q. rubra. Within these studies, I found that Q. ellipsoidalis and Q. rubra have similar leaf trait phenotypic plasticity, and unique molecular phenotypes related to upregulation of genes related to photosynthesis and innate immune response, respectively. Within the Q. rubra genome, I identified multiple regions of transcription factor gene clusters that could have a significant role related to drought adaptation for this species.
... Here we focus on the two North American red oak species Quercus rubra L. and Quercus ellipsoidalis E.J. Hill with different adaptations to drought such as differences in leaf conductance, root depth and leaf shape (Abrams 1990, Jensen et al. 1993. Both species are also differentiated at leaf morphometric and acorn traits and are characterized by different growth forms (Burns & Honkala 1990, Jensen et al. 1993. ...
... Here we focus on the two North American red oak species Quercus rubra L. and Quercus ellipsoidalis E.J. Hill with different adaptations to drought such as differences in leaf conductance, root depth and leaf shape (Abrams 1990, Jensen et al. 1993. Both species are also differentiated at leaf morphometric and acorn traits and are characterized by different growth forms (Burns & Honkala 1990, Jensen et al. 1993. However, no single trait is diagnostic for the species, only a combination of leaf morphometric traits is informative to assign most samples to genetically identified species (Gailing et al. 2012). ...
... However, no single trait is diagnostic for the species, only a combination of leaf morphometric traits is informative to assign most samples to genetically identified species (Gailing et al. 2012). Intermediate leaf morphologies between Q. rubra and Q. ellipsoidalis were interpreted as the result of interspecific hybridization and introgression (Jensen et al. 1993). However, genetic variation for species-discriminating leaf traits has also been found within species, e.g. for the European white oak species Quercus robur as revealed by QTL mapping in a Q. robur full-sib family , Gailing 2008. ...
Species boundaries in oaks are often not clear-cut, which is potentially a result of interspecific hybridization with trait introgression and phenotypic plasticity. Quercus rubra L. and Quercus ellipsoidalis E.J. Hill are two interfertile partially sympatric red oak species (section Lobatae) with different adaptations to drought. Quercus ellipsoidalis is the most drought tolerant of the North American red oak species and is characterized by deep tap roots, a shrubby growth and by deeply dissected leaves. Genetic differentiation between species is low for most molecular markers. However, one genic microsatellite in a CONSTANS-like (COL) gene, FIR013, was previously identified as outlier locus under strong divergent selection between species. In this study, we analyzed leaf morphometric traits in neighboring (parapatric) Q. rubra/Q. ellipsoidalis populations and in one sympatric population from the same region along an environmental gradient. Using multivariate statistics of leaf traits both species showed distinct bimodal frequency distributions for the first canonical discriminant function with some overlap in the phenotypic extremes, especially in the sympatric population. Leaf dissection traits showed strong and consistent differentiation between species in sympatric and parapatric populations, while differentiation for leaf size was lower in the sympatric population under more similar environmental conditions. Leaf phenotypes in F1 hybrids and introgressive forms suggested maternal effects and introgression of leaf traits between species. The association of outlier gene copy number at FIR013 with species-discriminating leaf traits in Quercus rubra can be a reflection of population differences since outlier gene copy number and population membership show significant collinearity. Similar environmental selection pressures on outlier alleles and leaf shape could also have resulted in this association. In future studies, segregating full-sib families could be used to test whether outlier alleles and associated genomic regions are indeed associated with leaf traits or other species-discriminating characters.
... Due to high variability in morphological characters and the absence of morphological and genetic diagnostic characters, it is difficult to distinguish between these closely related species at morphological traits or at a limited set of genetic markers. Thus, earlier studies of this species pair on the Apostle Islands in Wisconsin revealed continuous, clinal variation in leaf morphological characters and low genetic differentiation between populations, interpreted as the result of interspecific hybridization Jensen et al. 1993). Likewise, we observed a wide variation in leaf morphological characters on the Upper Peninsula of Michigan within populations but also pronounced differences in leaf size and growth habit between neighboring populations in different microenvironments (dry/mesic). ...
... For each of the 434 trees, the four largest leaves were measured at 13 leaf characters (12 dimensional and 1 counted character) that were used to discriminate between Q. rubra and Q. ellipsoidalis by Jensen et al. (1993) ( Table 2). Since most leaf dimensional characters showed strong correlation with leaf blade length (Table 3), four additional leaf shape characteristics (ratios of dimensional leaf characters) were calculated that describe shape differences between Q. rubra and Q. ellipsoidalis (Table 2; Fig. 2). ...
... Author's personal copy two bases, unambiguous attribution to loci was possible. performed on the directly measured leaf characters as used by Jensen et al. (1993) to discriminate between Q. rubra and Q. ellipsoidalis. Since most leaf dimensional characters showed strong correlation with leaf blade length (LBL), all analyses were also performed on all derived leaf characters including directly measured leaf characters and shape characters (Table 2). ...
Hybridization is considered to play an important role in speciation and evolution. Given the predicted northward tree migration in the eastern USA due to the impact of climate change, hybridization between related species is expected to become more frequent due to overlapping distribution ranges in the future. Oak species are “hot spots” of contemporary hybridization, serving as model organisms in the development of ecological species concepts. Q. rubra L. and Q. ellipsoidalis E.J. Hill were selected as study species, since they show different ecological requirements but hybridize with each other where both species co-occur. To identify morphological species and differentiation patterns in this species pair in ten populations on the Upper Peninsula of Michigan we investigated both leaf morphological variation, and genetic variation at highly variable microsatellite markers. Cluster analyses using leaf morphological characters revealed two distinct clusters for directly measured leaf characters and three clusters when additionally leaf shape characters were considered. Two populations growing on dry and sandy sites and identified as Q. ellipsoidalis in the field and by genetic assignment analyses were differentiated from the other eight populations at leaf morphological characters. Strong and significant correlations of leaf morphological differences with genetic distances at microsatellite markers but not with geographic distances are consistent with a pattern of isolation by adaptation. Differentiation at genetic and leaf morphological characters between neighboring populations in contrasting environments suggested reproductive isolation between populations of different species, possibly as the result of divergent selection. More extensive sampling along the distribution range of both species and reciprocal transplant experiments between parental environments are necessary to better understand the role of interspecific gene flow and selection in the maintenance of species identity in red oak species (Quercus section Lobatae).
... A similar pattern was observed by Manos and Fairbrothers (1987), Schnabel and Hamrick (1990), and Schwarzmann and Gerhold (1991). Another line of evidence indicative of high levels of gene flow among the Apostle region oaks involved patterns of morphological variation (see companion manu- Jensen et al., 1993). Using principle component analysis techniques, we found evidence of a morphological cline that paralleled the geographic layout of the region . ...
... Collections.-Five populations of oaks were studied in the Bayfield, Apostle Islands National Lakeshore region in northeastern Wisconsin ( Jensen et al., 1993). Samples were collected on five separate trips to the region. ...
... Another line of evidence indicative of high levels of gene flow among the Apostle region oaks involved patterns of morphological variation (see companion manuscript Jensen et al., 1993). Using principle component analysis techniques, we found evidence of a morphological cline that paralleled the geographic layout of the region. ...
Isozyme variability was examined in populations representing the red oak complex (Quercus subg. Erythrobalanus) on an island archipelago and adjoining peninsula in Lake Superior, near Bayfield, Wisconsin. A concomitant study of morphometric variation described in the companion manuscript, revealed a continuum in leaf morphology extending from an interior mainland site to the outermost island. The existence of this clinal variation presented an ideal opportunity to examine the genetic structure of a hybrid population along with the putative progenitor species. Dormant leaf bud samples were collected from specimens of Quercus rubra L., Q. ellipsoidalis Hill, and their putative hybrids from three islands and two locations on the peninsula. Acorns were collected from some of these same trees from one peninsula location and two islands. Twelve putative enzyme loci from six enzyme systems were analyzed. Allele frequency data indicated little differentiation between populations. Mean F(ST) values for the adult trees and acorns were 0.042 and 0.020. Genetic identities according to Nei ranged from 0.958 to 0.999. Despite these high levels of genetic similarity, the populations appeared to be highly inbred as indicated by positive mean F(IT) values of 0. 183 and 0.373 for the adult trees and acorns. Estimates of migration rate per generation (Nm) for the adult trees was 5.70, a value that is low when compared to estimates for other plant species with similar life history characteristics.
... Quercus L. species have a high level of intraspecific variability of morphometric parameters of leaves, which can vary significantly in different individuals within the same population or even one tree and depend on seasonal and ontogenetic changes (Jensen et al., 1993;Penas et al., 1994;Bruschi et al., 2003;González-Rodríguez and Oyama, 2005;Nikolić et al., 2005). In particular, the variability of the morphological and anatomical features of Q. robur (Borazan and Babaç, 2003;Nikolić et al., 2005Nikolić et al., , 2006Boratynski et al., 2008;Kryvoruchko and Bessonovа, 2018;Martins et al., 2022) and Q. rubra (Jensen et al., 1993;Ashton and Berlyn, 1994;Nagel et al., 1998;Kryvoruchko andBessonovа, 2017, 2018) leaf structure is shown in different growing conditions (moisture, lighting, increased UV radiation, influence of urban technogenic conditions). ...
... Quercus L. species have a high level of intraspecific variability of morphometric parameters of leaves, which can vary significantly in different individuals within the same population or even one tree and depend on seasonal and ontogenetic changes (Jensen et al., 1993;Penas et al., 1994;Bruschi et al., 2003;González-Rodríguez and Oyama, 2005;Nikolić et al., 2005). In particular, the variability of the morphological and anatomical features of Q. robur (Borazan and Babaç, 2003;Nikolić et al., 2005Nikolić et al., , 2006Boratynski et al., 2008;Kryvoruchko and Bessonovа, 2018;Martins et al., 2022) and Q. rubra (Jensen et al., 1993;Ashton and Berlyn, 1994;Nagel et al., 1998;Kryvoruchko andBessonovа, 2017, 2018) leaf structure is shown in different growing conditions (moisture, lighting, increased UV radiation, influence of urban technogenic conditions). ...
... Different techniques of multivariate analyses were increasingly applied to resolve some difficulties that may be confronted by a morphological overlap in flowering plants (e.g. Sokal and Sneath, 1963;Gilmartin, 1967;Jensen and Eshbaugh, 1976;McNeil, 1984;Jensen et al., 1993). Numerical taxonomy uses numeric algorithms to create groups of taxonomic units based on their character states. ...
... Two basic methodologies can be included within numerical analyses: phenetic and cladistic (phylogenetic); in phenetic analyses, classifications are Different techniques of multivariate analyses were increasingly applied to resolve some difficulties that may be confronted by a morphological overlap in flowering plants (e.g. Sokal and Sneath, 1963;Gilmartin, 1967;Jensen and Eshbaugh, 1976;McNeil, 1984;Jensen et al., 1993). Numerical taxonomy uses numeric algorithms to create groups of taxonomic units based on their character states. ...
This study aims at examining and confirming the patterns of phenetic relationships and the levels of variations within and among the species of Lotus L., 1753 in Egypt by using morphometric analysis techniques. We have evaluated 24 morphological characters from about 300 herbarium specimens representing 19 species of Lotus that are currently recognized. Based on numerical analyses of macromorphological characters (cluster analysis, principal coordinate analysis and principal component analysis), 19 species of Lotus were recognized from Egypt. These species were clustered in six species-specific groups: (I) Lotus halophilus Boiss. & Spruner, L. angustissimus L., L. glinoides Delile and L. schimperi Steud. ex Boiss., (II) Lotus glaber Mill. and L. palustris Willd., (III) Lotus polyphyllos E.D. Clarke, L. creticus L. and L. cytisoides L., (IV) Lotus gebelia Vent., L. lanuginosus Vent. and L. arenarius Brot., (V) Lotus edulis L., L. tetragonolobus L. and L. conjugatus L. and (VI) Lotus ornithopodioides L., L. peregrinus L., L. arabicus L. and L. hebranicus Hochst. ex Brand. As a result of this study, we proposed that some characters, not previously examined in detail, showed significant characters in species delimitation: pod length, seed dimensions, features of upper and lower leaflets, calyx, length of corolla, length of style, numbers of flowers and ovules.
... A. incana is less hygrophilous compared to A. glutinosa. Its range is more restricted to Central and Northern Europe, extending more to the north compared to A. glutinosa (Hegi 1981). Whereas A. glutinosa is indigenous in Flanders, A. incana reaches the utmost western edge of its range here and the native character in Flanders is doubted. ...
... Although leaves are plant organs suiting well geometric morphometric studies, botanists did not yet take as much advantage of this set of methods in comparison to zoologists, mostly restricted to taxonomic questions (Viscosi and Cardini 2011). For trees, several geometric morphometric studies have been conducted on the hybrid swarms of oaks (Jensen et al. 1993; Penaloza-Ramirez et al. 2010; Viscosi et al. 2009a Viscosi et al. , b, 2012) and other tree species (Jensen et al. 2002; Vit et al. 2012). Here, we dissected phenotypic traits of two sympatric and interfertile species A. glutinosa and A. incana applying geometric morphometric methods, principal component analyses and mixed modelling methods. ...
Key message
Spontaneous hybrids in natural regenerations of
A. glutinosa
cannot be excluded if
A. incana
is occurring in the neighbourhood, and has to be taken into account when restoring swamp forests.
Abstract
Swamp forests with A. glutinosa are endangered in Flanders due to habitat destruction and fragmentation, and therefore restoration is promoted. At the other hand, frequent plantations of A. incana, a non-native species in Flanders (northern part of Belgium), may facilitate spontaneous hybrids between the two species as they are interfertile. We assessed phenotypic variability of both species and putative hybrids using nine leaf, five infructescence and eight bud characters, and additionally height growth. We focussed on a field trial established with seeds collected in fifteen autochthonous A. glutinosa stands and on A. incana trees of unknown origin sampled at five locations in Flanders. We applied geometric morphometric methods, principal component analyses and mixed modelling methods. We found three individuals with intermediate morphological traits between A. glutinosa and A. incana among the eleven pedigrees in one of the two natural A. glutinosa populations where also planted A. incana was present. Their height growth was variable and only one of the three fructified, with seeds showing a normal germination success. These individuals can be hybrids with intermediate features between the parental species or they may display the natural variability of the latter with overlapping traits. Other individuals with intermediate leaf shape but less intermediate features for other leaf, bud and infructescence characters, found in the pedigrees of additional four A. glutinosa populations, may point to the relative wide natural variability for leaf shape within the parental species. Alternatively, these may concern backcrossed individuals or matro/patroclinal inheritance in hybrids. An inter-population variance study showed that several leaf characters are under a relative genetic control, underlining the importance of vegetative organs in taxonomic treatment of species complexes. The occurrence of spontaneous hybrids in natural regenerations of A. glutinosa cannot be excluded if A. incana is present in the neighbourhood, and has to be taken into account both in seed collections for the creation of autochthonous planting stock as when restoring swamp forests.
... Even leaf morphological traits that are frequently used for species identifi cation show a large variability within species and overlapping frequency distributions among species making the distinction of closely related species at single characters diffi cult. However, multivariate analyses using a set of morphometric, numeric and observed leaf characters in sympatric populations can often be used to differentiate between closely related species with some overlap in the phenotypic extremes (Jensen et al. 1993, Curtu et al. 2007a, Viscosi et al. 2012, Yucedag & Gailing 2013. Putative hybrids have been described based on morphological characters (Jensen et al. 1993, Rushton 1993 and/or genetic assignment analyses using discriminating genetic markers (e.g. ...
... However, multivariate analyses using a set of morphometric, numeric and observed leaf characters in sympatric populations can often be used to differentiate between closely related species with some overlap in the phenotypic extremes (Jensen et al. 1993, Curtu et al. 2007a, Viscosi et al. 2012, Yucedag & Gailing 2013. Putative hybrids have been described based on morphological characters (Jensen et al. 1993, Rushton 1993 and/or genetic assignment analyses using discriminating genetic markers (e.g. Neophytou et al. 2011. ...
Oak species show a wide variation in morphological and physiological characters, and boundaries between closely related species are often not clear-cut. Still, despite frequent interspecific gene flow, oaks maintain distinct morphological and physiological adaptations. In sympatric stands, spatial distribution of species with different ecological requirements is not random but constrained by soil and other micro-environmental factors. Here, we discuss factors that may influence the maintenance of the integrity of oak species in the face of interspecific gene flow. Pre-zygotic isolation (e.g. cross incompatibilities, asynchrony in flowering, pollen competition) and post-zygotic isolation (divergent selection) contribute to the maintenance of species integrity in sympatric oak stands. The antagonistic effects of interspecific gene flow and divergent selection are reflected in the low genetic differentiation between hybridizing oak species at most genomic regions interspersed by regions with signatures of divergent selection (outlier regions). In the near future, the availability of high-density genetic linkage maps anchored to scaffolds of a sequenced Q. robur genome will allow to characterize the underlying genes in these outlier regions and their putative role in reproductive isolation between species. Reciprocal transplant experiments of seedlings between parental environments can be used to characterize selection on outlier genes. High transferability of gene-based markers will enable comparative outlier screens in different oak species.
... Q. ellipsoidalis has smaller ellipsoid acorns and deeply lobed glabrous leaves, while Q. rubra has larger ovoid acorns with a short cap and leaves with shallower lobes (Barnes and Herbert Jr. 2004). While hybridization between the species was suggested based on the observation of continuous leaf morphological variation (Jensen et al. 1993) and low genetic differentiation between species at isozyme markers (Hokanson et al. 1993), these markers did not allow an assignment of individual samples to species. In the present study, a total of 582 individuals from 11 locations in the Upper Peninsula, where Q. rubra and Q. ellipsoidalis are the only species present, were characterized at both potentially selectively neutral non-genic microsatellites (nuclear simple sequence repeats or nSSRs) and at genic microsatellites (expressed sequence tag or (EST)- SSRs) (Aldrich et al. 2002; Durand et al. 2010; Steinkellner et al. 1997; Sullivan et al. 2012). ...
... Previous variation studies of the species pair Q. rubra and Q. ellipsoidalis were mainly restricted to morphological characters and isozyme markers (Hokanson et al. 1993; Jensen et al. 1993). Potential introgressive forms and hybrids could not be identified with these methods due the plasticity inherent in leaf morphological characters (Aldrich and Cavender-Bares 2011) and the limited amount of genetic variation within and among species at isozyme markers (Hokanson et al. 1993). ...
Sympatric hybridizing oak species provide a model system for studying local adaptation. Disjunct populations of Quercus rubra L. and Quercus ellipsoidalis E. J. Hill at the northern edge of their distribution may harbor important reservoirs of adaptive genetic variation. Genic (expressed sequence tag- simple sequence repeat = EST-SSR) and non-genic nuclear microsatellite (nuclear SSR = nSSR) markers were used to estimate neutral and potentially adaptive genetic variation in these two supposedly interfertile oak species showing different adaptations to drought. Eleven populations of putative Q. rubra and Q. ellipsoidalis located in the Western Upper Peninsula of Michigan were characterized using seven EST-SSRs and eight nSSRs. Bayesian cluster analysis revealed two distinct groups corresponding to each species with evidence of low levels of potential introgression. A comparison of the genetic structure of adult trees and seedlings revealed no evidence for selection against hybrids. Overall, similar levels of genetic variation and differentiation between populations and species were found at both EST-SSRs and nSSRs indicating that most EST-SSRs chosen reflect neutral variation. Two loci, 3A05 (nSSR) and GOT021 (EST-SSR, putative histidine kinase 4-like), were identified as putative outlier loci between species showing largely reduced variation in Q. ellipsoidalis. Future analyses of an increased number of EST-SSRs located in functional genes will allow the identification of genes involved in the reproductive isolation between both species.
... The variability of oak leaf size and shape was analysed by different authors using morphometric methods, to determine the differences between species, their hybrids, or populations of the same species (e.g. Jensen, 1990;Jensen et al., 1993;Peňaloza-Ramirez et al., 2010;Viscosi and Cardini, 2011;Viscosi, 2015;Liu et al., 2018;Proietti et al., 2021;Jovanović et al., 2022aJovanović et al., , 2022b. The variability of woody species is most easily observed at the level of the phenotype, which represents adaptive variability (Nonić and Šijačić-Nikolić, 2021). ...
The pubescent oak (Quercus pubescens Willd.) leaves were analysed by the means of morphometric methods in the Outstanding Natural Landscape “Kosmaj” in Serbia. The main goals were to determine the level of intraspecific variability of pubescent oak leaves and to link it to local habitat conditions. Morphological analysis of size and shape (MASS) and landmark analyses were used for the investigation of the leaves, and observed differences were correlated to habitat conditions (altitude, slope, aspect) obtained by the digital terrain model. This study showed a clear pattern of intraspecific variability of leaf size and shape at a small spatial scale, and the presence of fluctuating asymmetry, length, and location differences as a response to local habitat conditions. The findings suggest that morphological variability can represent a useful tool for detecting changes in the environment, especially in areas where the pubescent oak is considered endangered.
... Images were used to record 10 semi landmarks on each achene due to the shape of the achene (Fig. 2). Semi landmarks were chosen to putatively represent homologous points (Jensen 1990;Jensen & al. 1993), and to embed diagnostic features of each species following various authors (Jensen 1990;Bruschi & al. 2000;Borazan & Babac 2003;Gonzalez-Rodriguez & al. 2004). Semilandmark coordinates were used in Morpho J software (Klingenberg 2011). ...
Alirezaei, Z., Zarei, R. & Pakravan, M. 2023.12.30: Comparison of different morphometric methods on three taxa of the genus Ceratocephala (Ranunculaceae) in Iran.-Iran. J. Bot. 29 (2): 122-131. Tehran. The genus Ceratocephala with about 14 species in the world, has two species in Iran, including C. falcata and C. testiculata which are widely distributed in different parts of the country. Ceratocephala falcata has variations in fruit shapes. Some botanists have considered several subspecies and varieties for this species. In this research, traditional morphometric and geometric morphometric methods have been used to determine the taxonomic position of these taxa. Traditional morphometric studies based on nineteen quantitative characters (including leaf and fruit traits) of 78 populations were performed using SPSS software with the Ward method. Geometric morphometry based on fruit traits was performed in 22 specimens using tps Dig 2.12 and morpho J software. Traditional morphometry was not successful in distinguishing varieties, but different varieties including C. falcata var. falcata and var. incurva were identified using geometric morphometric methods.
... H ybridization is a process that occurs in plants from ferns to angiosperms (Whitney et al. 2010) and is considered a process that impacts the speciation and evolution of the groups in which it is present (Anderson 1953, Arnold 2004, Soltis & Soltis 2009, Soltis 2013. It is a natural and common process in numerous families, with some classic examples of hybridization occurring in Asteraceae (Helianthus), Cactaceae (Opuntia), Fagaceae (Quercus), Iridaceae (Iris), Pinaceae (Pinus) and Rosaceae (Lachemilla, Rosa) (Critchfield 1986, Rieseberg 1991, Jensen et al. 1993, Pinkava 2002, Arnold 2006, Meng et al. 2011, Morales-Briones et al. 2018. Although numerous studies have been conducted in these families, it is still difficult to fully understand the dynamics and outcomes of hybridization in these groups. ...
Background: Hybridization in nature occurs in numerous botanical families. In particular, the Cactaceae family contains lots of genera in which hybridization is reported.
Questions: What are the patterns of reported natural hybridization in Cactaceae and their probable causes? Are there phylogenetic and evolutionary implications related to hybridization, particularly in Opuntioideae?
Data description: A total of 62 articles about natural hybridization and classical Cactaceae literature were reviewed.
Study site and dates: From 1900 to June 2021
Methods: A search for articles was performed in Web of Science and Google Scholar with the keywords "Cactaceae hybridization", for time span "1900 to 2021" and included information from classic family-specific monographs.
Results: Natural hybrids in Cactaceae occur in subfamilies, Cactoideae and Opuntioideae. There is evidence of nonselective mechanisms of reproductive isolation, but only for few taxa. For Cactoideae members the main approach used was morphological description, and the tribe with the highest number of natural hybrids was Trichocereeae. In Opuntioideae, the reviewed articles performed mostly chromosome counts, morphometric and phylogenetic analyses, and showed the highest number of natural hybrids.
Conclusions: It has been suggested that hybridization impacts the evolution of Cactoideae and Opuntioideae, but few studies have formally tested this hypothesis. In Cactoideae, we found only descriptive evidences of hybridization; therefore, previous statements suggesting an important role of hybridization in the evolution of Cactoideae should be supported by performing formal analyses. For the postulation that hybridization impacts the evolution of Opuntioideae, we found formal evidence supporting hybridization hypothesis unlike what we found in Cactoideae.
... GMM methods are used in many disciplines, within and beyond plant biology, and allow the analysis of the relative positions of landmarks and sets of points used to approximate curves (outlines) and surfaces to quantify size and shape (Jensen 2003, Claude 2008. In recent years botanists have also applied these types of analysis to study the shape of leaves (Jensen 1990, Jensen et al. 1993, Viscosi et al. 2009a, b, Asanidze et al. 2011, Adebowale et al. 2012, Morello and Sede 2016, Chitwood and Otoni 2017, De la Paz Pollicelli et al. 2018, Li et al. 2018, Morello et al. 2018, Sandner et al. 2019) and other plant organs (Yoshioka et al. 2004, Van der Niet et al. 2010, Hernández-Ramírez and Aké-Castillo 2014, Ros et al. 2014, Bonhomme et al. 2017, Savriama 2018, producing informative results with tools which are relatively simple to use. Leaf analysis, compared to the analysis of other plant organs, can, however, with equally simple tools, also provide useful information on the ecology of species. ...
Scientific and technological progress has led to the creation of analysis tools that have revolutionized traditional studies of morphology and plant ecology. Recent methods and tools which, on the basis of leaf samples, allow the development of geometric morphometric analyses and the evaluation of functional strategy are good examples. These methods, still little used, have never been applied on the same leaf samples to obtain information on their morphometry and on the ecology of the plants at the same time. This article discusses the effectiveness of modern leaf analysis tools for geometric morphometrics (outline analysis) and studies of functional strategies based on the competitor‐stress tolerator‐ruderal (CSR) scheme, using a study of a steno‐endemic plant of the Alps, Primula albenensis Banfi et Ferl. as an example. These aspects were analyzed using the same leaf samples collected in the only two areas where this species grows. CSR analyses revealed that P. albenensis is not a stress‐tolerant species (C:S:R = 37:1:62), as previously thought. Moreover, no significant intraspecific differences emerged as regards functional strategy. Instead, outline analysis highlighted a significant difference (p < 0.001) between the leaves collected in the two sampling areas which differ mainly in the width of the leaf blade and petiole. The results of this study and others reported in the literature therefore suggest that these modern methods of leaf analysis are cheap, effective and relatively simple to perform. Furthermore, researchers are able to carry out geometric morphometric and CSR analysis using the same samples of leaves in order to maximize the information content provided by the analysis of plant material which is sometimes not easily available. This article is protected by copyright. All rights reserved.
... Thus, when oak species with similar phenological stages grow in mixed populations as they often do, hybridization occurs either among different species in the same section or sub-genus or between species of different sections within the genus Quercus (Bacilieri et al., 1996;Borazan and Babac, 2003). These phenomena in addition to the high phenotypic plasticity of oaks cause a striking morphological variability and diversity, resulting into taxonomic confusion within the genus (Jawarneh et al., 2013;Jensen et al., 1993). ...
The seven oak species present in Lebanon show taxonomic ambiguity partly due to their great morphological variability among and within species. Very few investigations were conducted on oaks in Lebanon despite the presence of endemic species, and none tried to discriminate these according to their morphology, nor to determine subspecies or identify eventual hybrids. In this study 1328 leaves and 550 fruits were collected covering the whole range of oak species over the Lebanese territory; 24 leaf and 6 fruit traits were recorded and analyzed in order to differentiate among species, to define missing gaps for certain subspecies and to discriminate eventual hybrids and their possible parents. Environmental conditions were attributed in each sampling location to study the effect of selected environmental factors on leaf traits. PCA results showed that several leaf and fruit traits differ significantly among species, and that species leaf characteristics override the environmental influence. The interval between central nerve and apical leaf nerve, interval between apical and basal lobes, scale length and cupule diameter are the main contributors to differentiation among taxa. Oak species were grouped according to the 3 subgenus sections and species and subspecies were discriminated mainly according to fruit traits variance. Three potential hybrids were identified, with intermediate morphology or closer to one of their parents. Variation of morphological traits were discerned according to biogeographical gradients, and varied from one species to another.
... Systematists working with extant plants can study hundreds of herbarium specimens and sample populations. Consequently‚ they can circumscribe both parent species and the morphological intermediates among them that form a hybrid complex and use morphometrics to establish the boundaries of the species within the complex (e.g., Jensen et al. 1993) to create hypotheses that can be tested with molecular studies. However, this is not possible in the fossil record. ...
The evolution of plant ecosystems during the Cenophytic was complex and influenced by both abiotic and biotic factors. Among abiotic forces were tectonics, the distribution of continents and seas, climate, and fires; of biotic factors were herbivores, pests, and intra- and interspecific competition. The genus QuercusL. (Quercoideae, Fagaceae) evolved in this context to become an established member of the plant communities of the Northern Hemisphere, commencing in the Paleogene and spreading to a diverse range of environments in the later Cenozoic. Its palaeontological record, dominated by leaves and pollen, but also including wood, fruits and flowers, is widespread in Eurasia and North America. Consequently, a great number of species have been described, from the 19th century to the present day. Although Quercus is currently an ecologically and economically important component of the forests in many places of the Northern Hemisphere and Southeastern Asia, no comprehensive summary of its fossil record exists. The present work, written by an international team of palaeobotanists, provides the first synthesis of the fossil history of the oaks from their appearance in the early Paleogene to the Quaternary.
... Landmark-based geometric morphometrics provides a powerful technique in quantitative biology for the study of shape variation in a wide range of disciplines . In plant sciences, a geometric morphometric approach is more commonly used to study interspecific variations in shape and it is extremely useful when dealing with hybridogenous species (Jensen et al. 1993(Jensen et al. , 2002Viscosi et al. 2009;Vít et al. 2012;Vander Mijnsbrugge 2015). However, multivariate morphometric analyses can also be applied to assess intraspecific variations in shape related to sexual dimorphism, fluctuating asymmetry and variation along geographic and ecological transects (Loy 1996). ...
Key message
Multivariate morphometric analyses were used for the first time to examine sexual dimorphism and shape variability of needles in natural populations of relict speciesTaxus baccataL.
Abstract
Needle morphology and intraspecific variability of Taxus baccata L. were examined for the first time in Serbian natural populations (in the central Balkans). A geometric morphometric approach was used to assess size and shape variation of needles and to address questions of sexual dimorphism and phenotypic plasticity. Population-specific sexual size dimorphism was found. In the Tara population, females had larger needles than males and this was in accordance with earlier reports on T. baccata dimorphism. We found it unusual that in the other two populations, Kopaonik and Malinik, sexual size dimorphism was constrained and the sexes had needles of equal size. Multivariate analysis of needle shape revealed that the Tara population differed from the other two populations and was characterized by straighter, more symmetric needles. The absence of sexual size dimorphism and the less symmetrical shape of needles could be signs of a deviation from optimal conditions for yew in the Kopaonik and Malinik populations as regards mean annual temperature, precipitation, humidity and soil quality. There is also an indication that sexual size dimorphism in needles arises from a modification in female morphology and that female yews carry more information about climate. However, the conclusions presented in this study have certain limitations because of the small number of individuals in the Tara population (only 3 female and 4 male plants) that represent the quasi-total of adult yews at this site.
... Among the red oaks of eastern North America, hybridization and introgression are reported with varying frequencies among different age classes. Parentage analysis of seedlings indicated hybridiza- tion rates > 20% ( Moran et al., 2012), whereas adult hybrids are apparently much more rare, on the order of 1-5% ( Jensen et al., 1993;Aldrich et al., 2003;Hipp & Weber, 2008;Moran et al., 2012;. Similarly, gene flow is apparently more restricted between some species than others: hybridization was limited between all age classes of neighbouring stands of northern pin oak (Q. ...
Oaks (Quercus: Fagaceae) commonly interbreed yet retain their morphological, genetic, and ecological distinctiveness. Post-zygotic isolation mechanisms, such as ecologically-dependent selection on adaptive loci, may therefore limit introgression. To test this hypothesis, we quantified hybridization and genetic divergence across the contact zone of four red oaks (Quercus section Lobatae) in the Great Lakes region of North America using a suite of 259 AFLPs and 27 genic and genomic microsatellite markers. First, we identified hybrids using genetic structure analysis and confirmed the reliability of our assignments via simulations. Then, we identified candidate loci for species maintenance with three complementary tests for directional selection and obtained partial gene sequences linked to an outlier locus and three other highly-differentiated loci. We detected evidence of recent hybridization among all species and considerable gene-flow between Q. ellipsoidalis and Q. velutina. Overall, about 20% of Q. velutina had recent ancestry from Q. ellipsoidalis while nearly 30% of Q. ellipsoidalis had a Q. velutina ancestor. Most loci were negligibly to weakly differentiated among species, but two gene-linked microsatellites significantly deviated from neutral expectations in multiple, complementary outlier tests. Both outlier loci were located within the same 15 cM bin on the existing Q. robur linkage map, a region targeted by divergent selection in other oak species. Adaptive loci in this highly-differentiated genomic region may contribute to ecological divergence among species and limit introgression.
... V dendrologii byla GMM využita např. pro sledování hybridizace amerických dubů (Jensen 1990;Jensen et al. 1993) nebo pro taxonomické studie dubů evropských (Viscosi et al. 2009a, b). Další studie se týkají planých růží (Olsson, Prentice 2001) nebo kříženců Prunus spinosa s P. domestica ssp. ...
Variability in leaf lamina shape among different taxa of Betula L. genus in the Czech Republic was assessed using the quantitative evaluation of outline shapes. The study was especially focused on the border mountains and the central part of the republic. 342 specimens were tested in total. The specimens of the tetraploid and diploid birch taxa were clearly distinguishable. The location of the widest part of blade seems to be the most relevant sign for the determination between two above-mentioned groups. On the contrary, distinguishing between the tetraploid taxa was not successful. Even though it was observed that the geographic area and the height of the specimen have a significant impact on the variability of the blade shape of tetraploid taxa, preliminary in situ taxa determination did not coincide with the geometric morphometry results. Other tested variables (wetness of the site and the altitude) also did not significantly correlate with the leaf shape. The failure of discrimination among the tetraploid Betula populations thus might imply either insufficient discriminative power of the leaf shape characters or an incorrect taxonomy. Final conclusions on discrimination of Czech Betula L. taxa, however, will need an employment of genetic analyses.
... Las especies mexicanas del género Quercus se encuentran distribuidas desde climas cálidos hasta templados, donde predominan junto con los pinos y constituyen la mayor parte de la cubierta vegetal de esos lugares (Rzedowski, 1978). La sistemática de Quercus ha sido difícil de estudiar (Jensen et al., 1993) debido a la diversidad morfológica que presenta el género, asociada a la variabilidad dentro de las especies y la aparente facilidad de formar híbridos, lo cual puede generar morfologías intermedias que dificultan la identificación taxonómica entre especies (Palmer, 1948; Cristofolini y Crema, 2005; Albarrán-Lara et al., 2010; Peñaloza-Ramírez et al., 2010). Valencia (2004) ...
A morphometric study was carried out in order to evaluate morphological variation of Quercus sartorii and Q. xalapensis and to contribute to their taxonomic delimitation. Herbarium specimens and material of 11 populations from Mexico in the states of Hidalgo, San Luis Potosí, Tamaulipas, and Veracruz, including 2 sympatric populations, were studied. Characters from foliar architecture, fruits and anatomical features of periderm and wood were analyzed through multivariate and phenetic methods. Principal component and discriminant analyses showed that fruit characters such as acorn, nut, and cupule diameters contributed to group individuals in their species, the acorn of Q. sartorii being smaller than that of Q. xalapensis. Variation was not attributed to latitude or elevation. The resulted phenogram revealed 2 groups in which individuals grouped in their own species if fruit features were included. In addition to the quantitative characters mentioned, 3 traits of the venation pattern plus 2 anatomical features distinguished the individuals of each species. These differences were maintained in the individuals from sympatric populations, supporting the distinctness of Quercus sartorii and Q. xalapensis.
... Although leaves are plant organs suiting well geometric morphometric studies, botanists did not yet take as much advantage of this set of methods in comparison to zoologists, mostly restricted to taxonomic questions (Viscosi and Cardini 2011). For trees, several geometric morphometric studies have been conducted on the hybrid swarms of oaks (Jensen et al. 1993; Viscosi et al. 2009a Viscosi et al. , b, 2012 Penaloza-Ramirez et al. 2010) and other tree species (Jensen et al. 2002; Vit et al. 2012; Vander Mijnsbrugge 2015) but, to our knowledge, not yet on elm species. Because of their rarity, the relicts of U. laevis in Flanders were hardly known before the end of the nineties of last century, when Flanders was inventoried specifically for autochthonous relict populations of woody species (Vander Mijnsbrugge et al. 2005). ...
Ulmus laevis Pallas is a rare and endangered tree species in the northern part of Belgium, restricted to a minimal amount of natural populations that mainly consist of a strongly reduced number of individuals. Probably isolated for several generations, random phenotypic variation in the strongly declined populations can be hypothesised. We analysed U. laevis trees grown in a field trial with a single-tree-plot design (completely randomised). The plants were vegetatively propagated through cuttings from nearly all known natural relict populations in Flanders. We analysed three short-shoot leaves from different ramets from different genotypes from eleven natural populations. Leaf size and shape variables were computed using landmark and procruste methods. We visualised the variability in leaf morphology in a principal component analysis (PCA) including shape, size, and categorical morphological variables. The variance structure of the morphological variables was studied applying mixed modelling methods. The overall PCA distinguished two deviating natural populations. The Zandhoven population showed a deviating simple leaf margin toothing, correlated with larger numbers of split secondary veins. The Halle population is characterised by absence of pubescence at the lower side of the leaves. Both relict populations with deviating morphological leaf characteristics may point to an ecotype evolution putatively due to isolation combined with greatly diminished population sizes. The variance structure analysis of individual leaf variables showed that the deviating categorical leaf characters are under stronger genetic control (specialist characters) compared to the more plastic variables.
... Geometric morphometrics (GM) methods enable studying the entire shape as a single character instead of inferring shape based on independent measurements (Adams et al. 2004). Morphological shape has important implications for taxonomic distinctions (Viscosi and Cardini 2011), examining hybridization patterns (Jensen et al. 1993), exploring relationships between floral structure and pollinators (van derNiet et al. 2010), and for correlating with climatic components (Conesa et al. 2012). Analysis of shape parameters may be more appropriate than linear measurement data for elucidating the relationship between leaf trait variation and environmental factors that contribute to observed variation. ...
Morphological variation in plants can be affected by climate, which influences how species are identified as well as hypotheses of species divergence. We tested whether climatic niches were correlated with the observed morphological (leaf) variation of four geographically overlapping and reproductively similar Helichrysum species (Hilliard’s Group 4 in the southern African flora). We found that two species, H. gymnocomum and H. odoratissimum, showed clear evidence for climatic niche conservatism and that across all species leaf shape was not significantly correlated with climatic niche. Interestingly, there did appear to be a pattern, albeit statistically non-significant, that linked cold, dry climates to leaf shape, particularly for the variable and widespread H. odoratissimum. For example, smaller, narrower leaf shapes were generally found in cooler, drier regions, while large, broad leaves (particularly those of H. odoratissimum) are found in warmer, more humid regions. In addition, the data also showed that two species, H. odoratissimum and H. gymnocomum, comprised a single variable group. The climate-leaf shape patterns could potentially reflect the morphological variation between these two species. Collectively, these findings suggest further work is necessary to determine the role of climate and leaf shape variation in species divergence in the Eastern Mountain Region.
... magnoliifolia predominating at lower altitudes and Q. resinosa predominating at higher altitudes), whereas intermediate phenotypes are favored at middle elevations. Morphological clines along altitudinal or geographical gradients have been observed in other studies of oak species in sympatry (e.g., Jensen et al. 1993; Spellenberg 1995, TovarSánchez and, and they are usually interpreted as supporting the hypothesis that hybrid zones with extensive interspecific gene flow are by-products of secondary contact of species. However, this pattern is not always found. ...
We tested the effects of hybridization and introgression on the levels of leaf fluctuating asymmetry (FA) in a hybrid zone between Quercus magnoliifolia and Quercus resinosa at the Tequila volcano, Jalisco state, Mexico, in which the species are distributed along an altitudinal gradient ranging from 1400 to 2100 m. Bayesian clustering analysis was performed with STRUCTURE on data for eight nuclear microsatellite loci to assign individuals from reference populations and from the hybrid zone to pure or hybrid genotypic classes. To test the performance of the assignment procedure and to determine optimal thresholds for genetic assignment pure, hybrid and backcrossed genotypes were simulated (from the allelic frequencies found in real pure populations of the two species) and reanalyzed with STRUCTURE. Leaf FA and morphological identification of parental and hybrid individuals were obtained using geometric morphometric techniques. We found genetic and morphological evidence of a hybrid zone by secondary contact at the Tequila volcano. The genotypes and phenotypes were significantly correlated with altitude along the mountain, but no correlation between them was found. FA was higher in F1 hybrids and backcrossed genotypes than in pure species. Levels of FA were more correlated with the proportion of genetic ancestry of each individual than with leaf morphology or altitude, supporting the hypothesis that hybridization is associated with development instability potentially caused by disruption of coadapted gene complexes characteristic of each species.
... The two interfertile red oak species Q. rubra and Q. ellipsoidalis provide a model to study pre-zygotic and post-zygotic isolation mechanisms. Both species hybridize where they co-occur in gene flow distance (Jensen et al. 1993; Lind and Gailing 2013; Owusu et al. in press) but they tend to occupy different micro-environments with regard to water availability (Abrams 1990). While the more widespread Q. rubra occupies well-drained uplands and mesic slopes, Q. ellipsoidalis shows a more restricted distribution on very dry sandy sites and can maintain high photosynthesis rates even at low leaf potentials during drought (Abrams 1988Abrams , 1990). ...
Key message
Highly elevated differentiation in different life stages between two interfertile oak species at a
CONSTANS
-like gene suggests a role of this gene in pre-zygotic isolation and adaptive divergence between species.
Abstract
Genome-wide differentiation patterns among oak species suggest that divergent selection can maintain species-specific adaptations and morphological integrity by reducing effective interspecific gene flow. While there is evidence for both pre- and post-zygotic isolation mechanisms in oaks (e.g., differences in flowering time, selection against hybrids), these mechanisms are rarely studied at each life stage from acorns to adult trees within the same forest. To assess the reproductive isolation mechanisms between two ecologically divergent species, we (1) quantified the number of hybrids in different life stages in Quercus rubra and Quercus ellipsoidalis, two interfertile red oaks with different adaptations to drought, and (2) assessed the timing of bud burst in both natural populations and in a seedling common garden trial. The low number of hybrids in all life stages suggested pre-zygotic isolation between species or selection in very early life stages that have not been sampled (e.g., early seed abortion). Significant differences in bud burst were found in two consecutive years between species in a common garden seedling trial but not in natural populations of the same provenance. In addition, we found evidence for divergent selection on several gene loci between species in each life stage. In particular, an SSR repeat located within the coding sequence of a CONSTANS-like gene, a locus involved in the photoperiodic regulation of flowering time and development, showed very high interspecific differentiation between species in all life stages (mean F
ST = 0.83), compared to the average neutral differentiation of 3.7 %.
... ANCOVA analyses using seed size as covariate were performed in SPSS ver. 20 (Inc 2002). Differentiation at quantitative traits was calculated as percentage of among population variation in a one way ANOVA. ...
Related oak species with different ecological requirements often hybridize where they co-occur. Even though interspecific gene flow is consideredto be common in closely relatedoaks, species identity in sympatric oak species with different local adaptations is generally maintained with a low number of hybrids andintrogressive forms in the adult tree generation. Quercus rubra and Q.ellipsoidalis offer a goodmod el to study characters that are related to different local adaptations and reproductive isolation of the species. Both species are interfertile, but grow in different micro-environments with Q.ellipsoidalis as the most drought tolerant red oak species occurring often on very dry sites. In an earlier study, genetic assignment analysis at 15 highly variable microsatellite markers revealeda low number of hybrids (0-2%) andintrogressive forms (0-4%) in neighboring Q.ellipsoidalis and Q.rubra populations in both the adult tree and seedling generation. In the present study, pronounced differences in growth and survival, the timing of bud burst and leaf senescence between seedlings of both species in a common garden experiment suggested reproductive isolation between species and genetic differences in fitness-related traits. Future studies should focus on the analysis of fitness traits in parental environments using reciprocal transplant studies.
... The application of multivariate clustering techniques may, being in some cases based on geometric data, be capable of identifying and extracting species despite overlap (Fraley and Raferty 2002). Analysing shape as an integrated whole avoids problems of non-independence often encountered in studies employing traditional morphometric methods to quantifying form, particularly in studies of hybridisation (Jensen et al. 1993Jensen et al. , 2002 Viscosi et al. 2009b) where measurement of genetically correlated traits may lead to failure to detect recombinant hybrids (Lexer et al. 2009). In bryophytes, geometric morphometric methods have been employed in a purely descriptive capacity, to quantify differences among new species (Renner et al. 2009b), to explore breadths of species-level variation (Renner et al. 2010b), and to facilitate model-based tests of whether morphological variation is best explained by the existence of one polymorphic species or two monomorphic species (Renner et al. 2009a). ...
Molecular data have revealed many morphologically cryptic species. More surprising than lack of difference, however, is that morphological variation and complex patterns of overlapping features can mask cryptic species. We employ geometric morphometric methods (GMM) to explore patterns of variation within four liverwort species, three of which were previously attributed to Lejeunea tumida Mitt. Each species exhibited considerable variation within, and overlap among, species in size and shape, independent of degree of relatedness. Most variation was expressed within individuals, suggesting that the observed breadth of variation was within the developmental capacity of single genotypes. Size and shape variation within, and consequently overlap among, individuals resulted primarily from variance in growth of shoots. Inter-specific differences were swamped by intra- and inter-individual variation. We coupled GMM with multivariate methods for outlier removal, and simple averaging of individuals to explore whether intra-individual variation could be reconciled to maximise the inter-species difference, facilitating resolution of cryptic species despite extensive morphological continuity and overlap. Unfortunately, outlier removal did not achieve separation among species, because removing extremes failed to eliminate overlap resulting from within-species variation. Individual averaging was partially successful in extracting L. tumida as a discrete entity but did not segregate the remaining three species. Although the challenges for morphology-based identification of cryptic species are significant, GMM provide one of the best sets of methods for identifying and communicating any subtle morphological differences that may exist.
... S1? elgi FRON NORF A poorly known taxon in the province. See Grant & Epling (1943 (1982)(1983)(1984)(1985)(1986)(1987), Ball (1981), Jensen et al. (1984Jensen et al. ( , 1993, Maycock et al . (1980), Overlease (1977), Sutherland (1987) (1982)(1983)(1984)(1985)(1986)(1987), COSEWIC (1999), Hess (1990), Meyers (1983Meyers ( , 1984, Morsink & Pratt (1984), Waldron (1983) (1982)(1983)(1984)(1985)(1986)(1987). ...
... Hybrid zones in Quercus may form through a complicated history of hybridization and backcrossing Gonzalez-Rodriguez et al. 2004). Hybridization in Quercus has been detected from morphological (Hardin 1975;Jensen et al. 1993;Gonzalez-Rodriguez and Oyama 2005;Scareli-Santos et al. 2007) and genetic variation Bacilieri et al. 1996;Gonzalez-Rodriguez et al. 2004;Tovar-Sanchez and Oyama 2004). Most oak hybridization studies to date have focused on oaks of North America and Europe (Stebbins et al. 1947;Muller 1952;Tucker et al. 1961;Rushton 1993;Spellenberg and Bacon 1996;Howard et al. 1997;Ishida et al. 2003;Gonzalez-Rodriguez and Oyama 2005;Lexer et al. 2006). ...
Natural hybridization is known to be a potential threat to rare and endangered species due to the risk of extensive genetic swamping or assimilation. However, hybridization may also beneficial for rare species by increasing their genetic variation and adaptive potential. Quercus austrocochinchinensis is an endangered oak species that overlaps geographically with the common, widespread Q. kerrii. Morphological intermediates are common in contact zones between the species, suggesting interspecific hybridization. This phenomenon may lead to pure Q. austrocochinchinensis facing a larger threat. Given the importance of leaf morphology for hybrid identification in oaks, we characterized leaf morphological and anatomical features of pure populations of Q. kerrii and Q. austrocochinchinensis and a population of probable hybrids at the contact zone. The results demonstrate that (1) leaf morphological features of putative hybrids are stable and distinct from the parental taxa, and more similar to those of Q. kerrii; (2) anticlinal wall patterns of abaxial epidermal cells show the most significant differences between parental species and probable hybrids, providing an important character for species identification; and (3) putative hybrids were intermediate in leaf anatomical features between the two parental species. The leaf traits for identified Q. austrocochinchinensis, Q. kerrii and hybrids can be used to estimate the hybridization ratio at the contact zone. The morphological evidence, sympatry and phenology strongly suggest that the rare Q. austrocochinchinensis forms hybrids with the more widespread Q. kerrii. Natural hybridization might play an important future role in both migration and adaptation of the species to novel environments. Thus, the characters we identify here for diagnosing hybrids provide an important tool for conserving species and genetic diversity. We suggest that a management plan for Q. austrocochinchinensis should address the conservation of both of the pure species, investigation of gene flow dynamics in the hybrid zone and investigation of the impacts of gene flow on fitness of the two species.
... The application of multivariate clustering techniques may, being in some cases based on geometric data, be capable of identifying and extracting species despite overlap (Fraley and Raferty 2002). Analysing shape as an integrated whole avoids problems of non-independence often encountered in studies employing traditional morphometric methods to quantifying form, particularly in studies of hybridisation (Jensen et al. 1993Jensen et al. , 2002 Viscosi et al. 2009b) where measurement of genetically correlated traits may lead to failure to detect recombinant hybrids (Lexer et al. 2009). In bryophytes, geometric morphometric methods have been employed in a purely descriptive capacity, to quantify differences among new species (Renner et al. 2009b), to explore breadths of species-level variation (Renner et al. 2010b), and to facilitate model-based tests of whether morphological variation is best explained by the existence of one polymorphic species or two monomorphic species (Renner et al. 2009a). ...
Plants attributed to Lejeunea tumida comprise a heterogeneous aggregate of four morphologically distinct species, each circumscribed by subtle yet significant differences in perianth morphology, oil bodies, lobule morphology and lobe ornamentation. Size and shape also have utility in delimiting species, despite morphological overlap. We employ geometric morphometric methods to quantify and communicate diagnostic differences in lobule shape. Two new species, Lejeunea oracola M.A.M.Renner and Lejeunea rhigophila M.A.M.Renner are described, and a previously described species of Taxilejeunea reinstated as a new combination, Lejeunea colensoana (Steph.) M.A.M.Renner. Descriptions and illustrations of these three species and Lejeunea tumida Mitt. are presented. All four species occur in New Zealand. Although L. tumida has been reported for New South Wales, Victoria, and Tasmania, the identities of Australian plants comprising these records are largely unresolved, and require further investigation.
... Crosses frequently occur in mixed forests, where multiple oak taxa coexist, and the resulting variability is increased by the high phenotypic plasticity which currently characterizes this genus. As a consequence, the identification of species and subspecies can very often be wrong or misleading (Jensen 1988; Jensen et al. 1993; Ponton et al. 2004). From a taxonomical viewpoint, the genus Quercus has always been considered an intricate case among botanists and the debate concerning the species concept or the role of hybridism is still open. ...
Macro-morphological leaf traits and genetic assignments were combined to study the differentiation and
hybridization of three sympatric and inter-fertile white oak species (Quercus frainetto, Q. petraea, and Q.
pubescens). The sampling was performed in a single forest stand of central Italy (Mount Vairano) in which
the cover percentages of each of these three oak species were almost equal. The individuals classified as pure
species and the hybrid individuals were divided into two subsets (A and B) which were subsequently
statistically analysed. The results regarding the subset of pure individuals showed a clear separation between
the three species on the basis of differences observed in the following leaf traits: basal leaf shape, petiole
ratio, petiole length, number of intercalary veins, pubescence of the petiole, leaf area, number of lobes, lamina
length, and percentage of venation. Regarding the subset of hybrid individuals, as expected, a wider pattern
of leaf traits compared to that exhibited by the pure individuals was observed. The leaf traits of the pure
species that had provided the greater genetic contribution in the hybridization process were easily identifiable.
... Las especies mexicanas del género Quercus se encuentran distribuidas desde climas cálidos hasta templados, donde predominan junto con los pinos y constituyen la mayor parte de la cubierta vegetal de esos lugares (Rzedowski, 1978). La sistemática de Quercus ha sido difícil de estudiar (Jensen et al., 1993) debido a la diversidad morfológica que presenta el género, asociada a la variabilidad dentro de las especies y la aparente facilidad de formar híbridos, lo cual puede generar morfologías intermedias que dificultan la identificación taxonómica entre especies (Palmer, 1948; Cristofolini y Crema, 2005; Albarrán-Lara et al., 2010; Peñaloza-Ramírez et al., 2010). Valencia (2004) ...
A morphometric study was carried out in order to evaluate morphological variation of Quercus sartorii and Q. xalapensis and to contribute to their taxonomic delimitation. Herbarium specimens and material of 11 populations from Mexico in the states of Hidalgo, San Luis Potosí, Tamaulipas, and Veracruz, including 2 sympatric populations, were studied. Characters from foliar architecture, fruits and anatomical features of periderm and wood were analyzed through multivariate and phenetic methods. Principal component and discriminant analyses showed that fruit characters such as acorn, nut, and cupule diameters contributed to group individuals in their species, the acorn of Q. sartorii being smaller than that of Q. xalapensis. Variation was not attributed to latitude or elevation. The resulted phenogram revealed 2 groups in which individuals grouped in their own species if fruit features were included. In addition to the quantitative characters mentioned, 3 traits of the venation pattern plus 2 anatomical features distinguished the individuals of each species. These differences were maintained in the individuals from sympatric populations, supporting the distinctness of Quercus sartorii and Q. xalapensis.
... Many workers have attempted to quantify morphological differences using shape characteristics to solve a variety of taxonomic questions (Kendall, 1984;Bookstein, 1986Bookstein, , 1991Bookstein, , 1996Bookstein, , 1997Rohlf and Bookstein, 1990;Rohlf, 1993;MacLeod, 1999). This method has been useful in taxonomic and environmental studies of leaves (Jensen et al., 1993(Jensen et al., , 2002McLellan and Endler, 1998;Premoli, 1996;MacLeod, 2002;Krieger et al., 2007), ontogenetic shape variation in fossil ostracod carapaces (Baltanas et al., 2000), and sexual dimorphism in isopods (Bertin et al., 2002). This technique has also been applied successfully to the classifi cation of both modern (Warheit, 1992;MacLeod, 1999MacLeod, , 2002 and fossil taxa (Kowalewski, 1993;Baltanas et al., 2000). ...
... The high degree of gene flow among species of oak (Tomlinson et al. 2000; Williams et al. 2001), in addition to their high phenotypic plasticity (Cooperrider 1957; Jensen et al. 1984; Jensen 1988; Kashani and Dodd 2002), makes it difficult to delineate species boundaries based on morphological trait analysis. Hybridization among species of oak (Stebbins 1950; Burger 1975; Jensen et al. 1993) and the maintenance of distinct morphological types despite apparent weak reproductive barriers (Whittemore and Schaal 1991; Howard et al. 1997) have cast doubt on the taxonomic status of some species (Muir et al. 2000 ). It remains an unresolved question whether oak species maintain differences in a few distinct morphological traits despite extensive introgression , whether reduced fitness of hybrids keeps gene pools largely distinct (Coyne and Orr 2004 ), or whether hybridization is actually limited (Craft et al. 2002). ...
We used microsatellite DNA analysis to examine population differentiation among three species of white oak, Quercus alba L., Quercus bicolor Willd., and Quercus macrocarpa Michx., occurring in both pure and mixed stands in northeastern Illinois. Using individual-based Bayesian clustering or principal components analyses, no strong genetic groupings of individuals were detected. This suggests that the three species do not represent distinct and differentiated genetic entities. Nevertheless, traditional approaches where individuals are pre-assigned to species and populations, including F statistics, allele frequency analysis, and Nei's genetic distance, revealed low, but significant genetic differentiation. Pairwise F statistics showed that some intraspecific comparisons were as genetically differentiated as interspecific comparisons, with the two populations of Q. alba exhibiting the highest level of genetic differentiation (θ = 0.1156). A neighbor-joining tree also showed that the two populations of Q. alba are distinct from one another and from the two other species, while Q. bicolor and Q. macrocarpa were genetically more similar. Pure stands of Q. macrocarpa did not show a higher degree of genetic differentiation than mixed stands.
... Eigenshape analysis seems particularly appropriate for leaf-climate studies when compared with other morphometric methods. Landmark methods, which record measurements between corresponding points representing leaf features (e.g., lobes, leaf tip, and sinuses between lobes), have been used extensively in analyses of leaf shape within a single species (Ray, 1992;Jones, 1993;Farley and McNeilly, 2000) or in comparing two closely related species (Jensen et al., 1993;McLellan and Dengler, 1995;Premoli, 1996;McLellan, 2000;Jensen et al., 2002). The diversity of leaf forms at the community level, however, results in a paucity of landmarks with correspondence among specimens. ...
Paleobotanists have developed numerous methods for quantifying correlations between leaf form and climate, so that fossil leaves can be used to estimate past terrestrial climate. Approaches currently used can be broken into two classes: those using categorical, primarily qualitative shape characters (such as round base) and those describing shape as ratios or other abstract mathematical descriptors (such as perimeter-to-area ratio). Both classes of approach have limitations and are hard to compare to one another. We show how eigenshape analysis provides both interpretable characters and measures of continuous variation, thus potentially overcoming the limitations of both current approaches. We applied eigenshape analysis to a sample of 394 nonlobed leaves from extant assemblages to empirically identify independent leaf shape characters. This resulted in the identification of 20 shape characters. Of these, 13 reflected variation due to broad-scale asymmetry as well as asymmetry localized to the tip, base, and lamina-petiole junction. The remaining seven characters, in order of variance explained, corresponded roughly to base shape, tip angle, location of widest portion of the leaf (ovate to obovate variation), extent of widest portion of the leaf (elliptic to oblong variation), tip shape (blunt to drip tip), ovate to obovate variation localized to the middle of the leaf, and extension of the lamina along the petiole at the lamina-petiole junction. All 7 of these characters and only 1 of the 13 asymmetry characters had an association with climate. These characters corresponded to five of the seven broad categories of Wolfe's Climate-Leaf Analysis Multivariate Program shape descriptors, excluding only tooth shape and lobing. The results of this study indicate that eigenshape-generated measures of leaf shape merit further exploration.
... Palms frequently present complex patterns of variation, leading to taxonomic problems in differentiating species (Uhl and Dransfield 1987;Quero 1989). Interspecific hybridization and shared ancestral polymorphisms are two of the most common explanations for the observed patterns of variation (Jensen et al. 1993;Kleinschmit et al. 1995;Bruschi et al. 2000;Tovar-Sánchez and Oyama 2004). Brahea dulcis and B. nitida form hybrids, but they remain morphologically distinct in their allopatric and sympatric distribution, except in one (Xochipala) of the four sympatric zones, where B. nitida pure individuals were not able to be genetically identified. ...
Gene introgression usually results from spontaneous hybridization among closely related species in sympatric populations. This phenomenon has recently become a frequent topic of interest in evolutionary and conservation biology. A palm species complex occurring in Mexico formed by two native species, Brahea dulcis (Kunth) C. Martius and Brahea nitida André, and their putative hybrids, was analyzed with morphological and molecular markers in four hybrid zones and two pure sites for each parental species. Our results showed that the closeness of the hybrids to an allopatric site of either parental species (B. nitida, mesic habitat, and B. dulcis, xeric habitat) is directly related to their morphological and genetic similarity. Also, B. dulcis differed significantly from B. nitida in all the examined characters. Morphological and molecular data were highly coincident and supported the hypothesized hybridization. Hybrid phenotypes were morphologically parent-like for 46.4% of traits, intermediate for 33.2% of traits, and transgressive for 10.0% of traits. Thus, individual hybrids appear to be a mosaic of parent-like, intermediate, and transgressive phenotypes. Our results suggest that B. nitida has been genetically assimilated by B. dulcis in Xochiapala, and in the remaining hybrid zones a unidirectional pattern of gene flow towards B. nitida exists. Therefore, hybridization may threaten the conservation status of species through genetic assimilation and may confound the ability to distinguish among taxa.
... Hybridization phenomena in the genus Quercus is particularly important because it is one of the most controversial examples of the convenience of the ''biological species concept'' (Muir et al. 2001). Oaks have a high frequency of hybridization in nature (Palmer 1948;Muller 1952;Tucker 1961;Cottam et al. 1982;Jensen et al. 1993;Spellenberg 1995;Howard et al. 1997;Ishida et al. 2003) and this is believed to be related to a poor development of sterility barriers between Quercus species (Grant 1981;Whittemore and Schaal 1991;Rushton 1993;Bacilieri et al. 1995;Dumolin-Lapègue et al. 1997). This plant group shows complex patterns of variation, leading to problems in species identification (Burger 1975). ...
Quercus crassifolia H. & B. and Quercuscrassipes H. & B. are two common temperate forest species in Mexico that form hybrids when they occur in mixed (sympatric) areas. In this study, we used chloroplast microsatellite haplotypes to infer phylogeographic patterns onto the genetic structure of populations of both parental species, thus defining probable colonization routes throughout Mexico. Haplotype diversity in seven hybrid zones and four allopatric sites with nonmixed (allopatric) populations of both putative parental species was analyzed. To determine the expansion and colonization routes for the two species, we carried out a nested clade phylogeographic analysis that would allow us to infer the haplotype correspondence to a phylogeographical approach. In spite of sharing many common populations, we determined that there is a different genetic historical colonization for Q.crassipes and for Q.crassifolia. Hybrid populations had the highest levels of genetic variation (Gv), Shannon diversity index (H), and haplotype number (nh) in comparison with nonmixed/allopatric populations of their putative parentals. Furthermore, populations of hybrid zones showed the highest values of genetic differentiation FST, RST . Moreover, both species share four distinctive cpDNA haplotypes, which were most likely acquired by introgression through hybrids located in several populations throughout the Eje Neovolcnico area. This last region was confirmed to be a hot spot for oak diversity, a place in which different maternal lineages merged.
... For example, I have argued that in many angiosperm leaves the juncture of leaf blade and petiole constitutes a biologically homologous landmark (Jensen, 1990). No one who has reviewed my papers (e.g., Jensen, 1990; Jensen & al., 1993 Jensen & al., , 2002) has challenged this view, perhaps because of the rather narrow context in which it was applied; in each case, the comparisons involved leaf structure of two species clearly closely related phylogenetically . I would not presume to make the claim that the juncture of leaf blade and petiole in Quercus velutina Lam. is biologically homologous to that in Eupatorium rugosum Houtt.; it may very well be, but experience (consider the juncture of leaf blade and petiole in leaves of Prunus serotina Ehrh.) has taught that such superficial similarities can have quite distinct evolutionary/developmental origins. ...
In this study, we used leaf geometric morphometrics to quantify the
differences among Quercus cerris L. and Quercus frainetto Ten. and their
populations in the Šumadija region in Serbia. We sampled 2200 leaves from
eight populations and on each leaf recorded 13 landmarks. To analyze how
leaf morphology varies across species and populations, we used Procrustes
ANOVA, a two-block partial least-squares analysis, a principal component
analysis and a canonical variate analysis. The results showed a clear
discrimination between species, followed by different levels of leaf shape
variability in Q. cerris and Q. frainetto. The leaves of Q. cerris displayed
higher levels of variability and higher differences among populations
compared to Q. frainetto. The patterns of population grouping in the two
species greatly differed, indicating that in these species different factors
contribute to intraspecific variability. This study provides preliminary
results of the leaf morphometric variability of oak species in the Šumadija
region in Serbia. Future studies should include genetic and environmental
analyses to understand the origins of phenotypic differences between species
and populations, and to fully recognize which factors mostly determine
relationships between taxa.
This account presents information on all aspects of the biology of Quercus rubra L. (Red Oak, Northern Red Oak; syn. Q. borealis, Q. maxima) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution; habitat; communities; responses to biotic factors; responses to environment; structure and physiology; phenology; floral and seed characters; herbivores and disease; history; and conservation.
Quercus rubra is a large deciduous tree native to eastern North America. In its native range this species is one of the most important mid‐successional tree species. Since the 18th century Q. rubra has been introduced into forest management in Europe and elsewhere. Currently, Q. rubra is a naturalized species in 23 countries. It is an important source of wood, and this was one of the most important reasons for its introduction in forests. In forest management this species is valued for its high growth rate and drought resistance. Red Oak is also widely cultivated in Europe for its ornamental value—red leaves in autumn and smooth, grey bark.
Red Oak is a threat to native species within its introduced range as it can alter environmental conditions beneath its canopy, especially by decreasing light availability and litter decomposition rate. Such conditions also contribute to biotic homogenization of the understorey vegetation. Q. rubra is widely dispersed by small mammals and birds, up to 1,500 m from seed sources, thereby increasing its potential invasiveness.
In Europe Q. rubra seems to be less prone to herbivores and fungi, in contrast to its native range, where it is grazed by ungulates and insects, and infected by Phytophthora and oak wilt. Due to its higher tolerance to drought than native European oaks, Q. rubra is claimed to be one of the species replacing native trees which are decreasing due to climate warming. However, consideration of all possible consequences is needed in wide‐scale introduction of alien species, such as Q. rubra, due to negative impacts on native ecosystems.
Isozyme variability was examined in populations representing the red oak complex (Quercus subg. Erythrobalanus) on an island archipelago and adjoining peninsula in Lake Superior, near Bayfield, Wisconsin. A concomitant study of morphometric variation described in the companion manuscript, revealed a continuum in leaf morphology extending from an interior mainland site to the outermost island. The existence of this clinal variation presented an ideal opportunity to examine the genetic structure of a hybrid population along with the putative progenitor species. Dormant leaf bud samples were collected from specimens of Quercus rubra L., Q. ellipsoidalis Hill, and their putative hybrids from three islands and two locations on the peninsula. Acorns were collected from some of these same trees from one peninsula location and two islands. Twelve putative enzyme loci from six enzyme systems were analyzed. Allele frequency data indicated little differentiation between populations. Mean FST values for the adult trees and acorns were 0.042 and 0.020. Genetic identities according to Nei ranged from 0.958 to 0.999. Despite these high levels of genetic similarity, the populations appeared to be highly inbred as indicated by positive mean FST values of 0.183 and 0.373 for the adult trees and acorns. Estimates of migration rate per generation (Nm) for the adult trees was 5.70, a value that is low when compared to estimates for other plant species with similar life history characteristics.
Morphometric methods were used with 40 morphological characters from each of 110 individuals collected from 11 populations of the Ixeris chinensis complex to test hypotheses regarding infraspecific taxa. Individuals of the nearest relative I. tamagawaensis were included as an outgroup. To utilize structual associations of the original data and the cumulative values of character variation, a modified data set was generated by matching factor scores with the large original data set. As a result, the original data was reduced to about 10% of its original size. The modified data also emphasized the cumulative values of character variations. Structural associations among characters measured, however, were not significant for most factors extracted even though some obvious trends appeared. Relationships between cumlative values of variation and taxa in the complex are discussed based on the results of the canonical discriminant function analysis, ANOVA, multiple comparison test, and cluster analysis, using the modified data. This study supports Kitamura's (1956) classification of infraspecific taxa in the I. chinensis complex. Given that there is no overlap of cumulative values of variation between the species complex and I. tamagawaensis, there is probably a 75% character overlap within the complex.
The genus Quercus (the oaks) is an important tree taxon and we review here several aspects of its biology relevant to domestication and summarize progress to date in breeding and improvement. The oaks are not very far along the domestication route and so wild populations are still important in the establishment and development of managed populations. We consider several aspects of oak ecology and genetics along with the challenging topic of oak taxonomy since these all influence gene pool management. We then turn to describe the successes already made in the areas of oak breeding, especially with regards to marker-assisted breeding and the development of molecular markers, linkage maps, and QTL studies. We also consider several new initiatives in oak genomics that will likely change the rate of progress in the domestication of this important group of trees.
Genetic differentiation between co-occurring crops and their wild relatives will be greatly modified by crop-to-weed gene flow and variation between human and natural selective pressures. The maintenance of original morphological features in most natural populations of Medicago sativa in Spain questions the relative extent of these antagonistic forces. In this paper, we measured and compared the pattern of population differentiation within and among the wild and cultivated gene pool with respect to both allozymes and quantitative traits. Patterns of diversity defined three kinds of natural populations. First, some populations were intermediate with respect to both allozymes and quantitative traits. This suggests that crop-to-weed gene flow may have created hybrid populations in some locations. Second, some populations were different from all the cultivated landraces with respect to both allozymes and quantitative traits. This probably results from variable gene flow in space and in time, due to demographic stochasticity in either natural or cultivated populations. Third, differentiation from cultivated landraces was only achieved for the quantitative traits but not for allozymes in two populations. This suggests that natural selection in some locations may oppose gene flow to establish cultivated traits into the natural introgressed populations.
This account presents an analysis of allopatric, sympatric and juxtaposed populations of the pinyon pines, Pinus cembroides Zucc. and P. johannis M.-F. Robert, based on phenetic analysis of morphological data, and draws on a comparison and differentiation of P. culminicola Andresen & Beaman. A qualitative and quantitative database for populations has been assembled and used for a cluster and ordination analysis using NTSYS. It was found that individual populations of the taxa were distinguishable. The emergence of morphological intermediate populations between P. cembroides and P. johannis was confirmed. The pattern of variation in P. johannis was found to be discrete, showing three geographical groups. The phenetic similarity between P. johannis from Zacatecas and P. johannis from San Luis Potosi and Queretaro was lower than that of P. johannis from Zacatecas and P. culminicola from Nuevo Leon. The following traits distinguish P. cembroides and the other two species: colour and fertility of seeds; cone shape; colour and width of needles; physiognomy; seed dimensions. This last trait can be used to distinguish three subgroups of pines with white endosperm in the northern, central and southern regions of the Mexican highlands.
Changes in lobule morphology in Radula subgenus Cladoradula show liverworts have the capacity for dramatic, relatively rapid morphological change by heterochrony. In individuals of R. bipinnata, R. boryana and R. tenax, lobules on secondary and tertiary shoots are progenetic with respect to lobules on primary shoots, in that the slope of the relationship between growth duration and shape does not change. However, in R. campanigera, lobules on secondary and tertiary branches exhibit different slopes from primary branches, but have the same growth duration, a pattern consistent with neoteny. The trajectory of allometric growth is extended or truncated in different species compared with outgroup and ancestral nodes. Changes in duration of lobule growth explain 85% of variation in lobule shape between species. Species are related by relatively shallow nodes in the crown of the Radula subgenus Cladoradula clade, suggesting that divergence and associated heterochronic changes have occurred relatively recently. The rapid morphological diversification in the crown contrasts with the relative stasis between the ancestral node and R. brunnea, the outgroup used in this analysis. A robust primary axis may be required to hold shoots away from vertical surfaces to maximize light interception, and hypermorphosis in lobule ontogeny could be a by‐product of the longer growth durations required to build axes sufficiently large to perform this structural role. Alternatively, the large auriculate lobules could function in external water transport systems by providing continuity of surfaces for solute transport via capillary action. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 153–175.
This paper examines micromorphological characteristics (trichomes, waxes, stomata) of the abaxial leaf surface of European and Mediterranean oaks. Observation were performed by scanning electron microscopy, and the purpose of the investigation was to ascertain whether it is possible to distinguish the different species taxonomically using these features. Several species, as well as some subspecific entities and taxa considered doubtful, were taken into consideration. Subgenera appear to be well-defined: e.g. the subgenus Quercus is characterized by waxes arranged in vertical scales, the subgenera Cerris and Sclerophyllodris by smooth waxes. They differ because the former has markedly elliptical stomata, while the latter two have roundish stomata. The different species are also fairly easy to distinguish, and this fact confirms the taxonomical validity of the parameters we have taken into consideration. In some cases subspecific entities and doubtful species do not differ at all from the related species, but in others they present such marked variations that it is difficult even to classify them with certainty. The most critical taxonomic groups (i.e. those which include a number of specific and subspecific entities often too difficult to distinguish from each other) are the series Quercus robur Quercus petraea Quercus pubescens and the Quercus faginea Quercus lusitanica Quercus canariensis group.
The pre-Neogene basement of the Pannonian domain is built up by a collage of terranes deriving from different parts of the Tethys, which finally accreted in the Late Oligocene–Early Miocene times. Combined stratigraphical, sedimentological, palaeomagnetic and tectonic investigations have revealed the palaeogeographic position of the Palaeogene Basin, including the Buda and Bükk tectonic units However, despite floristic similarities, the Buda and Bükk regions also show important physiognomic differences. In the vicinity of Budapest (Buda unit), the large size and width of leaves are conspicuous, whereas in Eger-Kiseged (Bükk unit), leaves are definitely smaller and narrower. In order to define the differences quantitatively, morphometrical measurements were adopted. The shape and size of leaf fossils were compared by means of a circular grid (Hill, 1980). Leaves of 4 dominant species (Sloanea elliptica (Andreánszky) Z. Kvaček & Hably, Engelhardia orsbergensis (Wessel & Weber) Jähnichen, Mai & Walther, Eotrigonobalanus furcinervis (Rossmässler) Walther & Kvaček, and Zizyphus zizyphoides (Unger) Weyland were the target of our study. The average leaf area is 1.4–2.3 times larger in the Buda tectonic unit (Budapest locality) than in the Bükk tectonic unit (Eger-Kiseged locality). Statistical tests proved highly significant differences between these values. Regarding the asymmetry of the leaf lamina, the four species differed considerably. Nevertheless, a significant difference between the two localities was shown only in one of them (Sloanea elliptica). Consequently, a significant alteration of measures of asymmetry as a function of habitat conditions was not indicated. Smaller leaf area and significantly narrower leaf blade are possible indicators of drier climatic conditions in the Bükk unit.
We examined responses of phytophagous insects to hybrids between Quercus crispula Blume and Quercus dentata Thunberg in a natural population in northern Japan. The abundance of leafminers and leaf area loss by chewing insects in hybrids were intermediate between those in the parental species (additive mode), close to those of either of the parental species (dominance mode), or similar to those of both parental species (no difference). Hybrids were neither more susceptible nor resistant to the insect herbivores we monitored. In Phyllonorycter (Gracillariidae) species, which are specialized to either of the parental oak species, the mortality of sap-feeding early instar larvae did not differ between hybrids and the parental species. The abundance of four leafminer taxa was correlated with environmental conditions (i.e., distance from the coastal edge of the forest or the timing of budbreak) as well as genetic factors.
The genus Quercus represents an important component of the scrublands and low forests of the Four
Corners area of northeastern Arizona, southeastern Utah, southwestern Colorado, and northwestern New Mexico. The
area is dominated by the widespread Quercus gambelii, although relictual and marginal populations of Q. turbinella and
Q. havardii are also present. Hybridization among these 3 species is common, leading to much variability in phenotypic
traits, and this hybridization forms part of the widespread complex of hybrid oaks recognized as Q. x undulata. Multivariate
analysis of leaf morphology was performed in 9 populations, representing the various taxa and levels of hybridization.
This analysis was intended to determine the distinctiveness conferred by, and extent of influence from, hybridi -
zation and successive introgression. It was found that, though common, hybridization seems to act at very restricted
spatial scales and not in the production of a region-wide hybrid swarm. Most hybridization occurs between the predominant
Q. gambelii and Q. turbinella. Quercus havardii appears to maintain itself as a fairly discrete taxon, with little gene
exchange among congener species. Though morphological introgression actively occurs only at the local population
level, it seems to have significantly altered the morphology of the parental species. This seems to be supporting evidence
for extensive introgression toward the southern Q. turbinella when its distribution was more widespread. This asymmetric
introgression toward Q. turbinella suggests a pattern of character coherence and the presence of a suite of advantageous
traits, which may allow the species to enlarge its niche via hybridization.
Superimposition methods for comparing configurations of landmarks in two or more specimens are reviewed. These methods show
differences in shape among specimens as residuals after rotation, translation, and scaling them so that they align as well
as possible. A new method is presented that generalizes Siegel and Benson's (1982) resistant-fit theta-rho analysis so that
more than two objects can be compared at the same time. Both least-squares and resistant-fit approaches are generalized to
allow for affine transformations (uniform shape change). The methods are compared, using artificial data and data on 18 landmarks
on the wings of 127 species of North American mosquitoes. Graphical techniques are also presented to help summarize the patterns
of differences in shape among the objects being compared.
Rotational-fit methods were used to examine shape variation in oak leaf morphology by reference to a set of 14 landmarks for each leaf. Within-tree, between-tree, and between-species variations were examined. Generalized least-squares and generalized resistant-fit analyses revealed patterns of landmark variation that could be related to leaf architecture. The two species (Quercus palustris and Q. velutina) did not illustrate the same patterns of within-tree variability nor did they reveal similar degrees of between-tree variability. Incorporating an affine transformation algorithm resulted in little insight in some comparisons but suggested strong uniform shape change in other comparisons (especially between species). Resistant-fit mean square statistics were equally variable 1) in upper vs. lower crown samples within trees, 2) between trees within each species, and 3) between species. In addition, resistant-fit mean square statistics were found to be a poor measure of similarity, whether derived by comparison to a single reference object or by way of pairwise comparisons. Fundamental species differences in leaf shape are suggested by relationships among particular sets of landmarks, although overall shape differences cannot be explained fully by these analyses.
Isozyme variability was examined in populations representing the red oak complex (Quercus subg. Erythrobalanus) on an island archipelago and adjoining peninsula in Lake Superior, near Bayfield, Wisconsin. A concomitant study of morphometric variation described in the companion manuscript, revealed a continuum in leaf morphology extending from an interior mainland site to the outermost island. The existence of this clinal variation presented an ideal opportunity to examine the genetic structure of a hybrid population along with the putative progenitor species. Dormant leaf bud samples were collected from specimens of Quercus rubra L., Q. ellipsoidalis Hill, and their putative hybrids from three islands and two locations on the peninsula. Acorns were collected from some of these same trees from one peninsula location and two islands. Twelve putative enzyme loci from six enzyme systems were analyzed. Allele frequency data indicated little differentiation between populations. Mean F(ST) values for the adult trees and acorns were 0.042 and 0.020. Genetic identities according to Nei ranged from 0.958 to 0.999. Despite these high levels of genetic similarity, the populations appeared to be highly inbred as indicated by positive mean F(IT) values of 0. 183 and 0.373 for the adult trees and acorns. Estimates of migration rate per generation (Nm) for the adult trees was 5.70, a value that is low when compared to estimates for other plant species with similar life history characteristics.
The “shear” method of Humphries et al. (1981) is based on a path model intended to explain differences in form by multiple factors: one for size and one or more for shape differences. Its adaptation for “removing” the effects of a within-population size-factor from between-group morphometric analyses is presented in compact matrix form, simplified, and compared to the method of orthogonal projection proposed by Burnaby (1966). While the sizecorrection methods give similar results for most real data sets, Burnaby's procedure with k = 1 (i.e., using a single composite size variable) is recommended for this purpose owing to its geometrical and computational simplicity. An example based on artificial data demonstrates that sheared principal components are not necessarily uncorrelated with size. Path modeling of size and shape together is a different purpose than size-correction, and is better served by a different procedure.
Wilson, P.: On inferring hybridity from morphological intermediacy. ‐ Taxon 41: 11–23. 1992. ‐ ISSN 0040‐0262.
The type of intermediacy that separates hybridity from divergence is not multivariate intermediacy; it is the coincidence of intermediate character states. For the purpose of showing hybridity, analyses should distinguish between the two types of intermediacy. (1) Hybrid indices fail to do so. (2) Principal components analysis does so only in an ambiguous way. (3) Pictorialized scatter diagrams properly present the evidence for an interpretation that is intuitive. (4) Counting characters as intermediate or not‐intermediate is an explicit approach that allows for statistical evaluation given that certain assumptions are made. Simulated data representing hybridity and divergence are presented to illustrate each method and to provide a prototype of how to document hybridity using the favored methods.
Previous study of a community of red oaks in New Jersey provided evidence of hybridization involving all three species present: Quercus ilicifolia, Q. marilandica, and Q. velutina. The research reported here attempts to a) clarify further the extent and directon of hybridization, and b) determine if patterns of hybridization detected with morphologic and chromatographic data sets illustrate congruence. Twenty-two morphological variables for each of 87 trees were analyzed by analysis of variance, principal components analysis, and discriminant analysis. Three statistically defined species groups and intermediately positioned hybrids were recognized, suggesting that hybridization is restricted to crosses of Q. ilicifolia-marilandica and Q. marilandica-velutina. Chromatographic profiles of the same trees (methanolic leaf extracts) revealed distinctive profiles for each species and permitted detection of putative hybrids. Principal coordinate analysis of a similarity matrix based on the presence or absence of thirty phenolic compounds produced a two-dimensional plot very similar to that produced with principal components analysis of the morphological data. Further, a discriminant analysis of phenolic characters, in which the individual trees were assigned to groups defined by the morphological analyses, resulted in no misclassification. The patterns of phenolic variation strengthened the conclusion that hybridization is not occurring between Q. ilicifolia-velutina. Additionally, there is agreement between these data and previously hypothesized evolutionary relationships among the three taxa.
Individuals representing five taxa and numerous unidentified OTU's of red oaks native to the western Great Lakes region of the United States were examined through principal components analysis. Two data sets, one consisting of twenty untransformed characters and one in which various characters were redefined as ratios, were employed for comparative analyses. Although minor differences are noted, the two data sets provide essentially the same view of the relationships between the included OTU's. The five taxa appear to form more or less discrete groups with the unidentified OTU's occupying positions of intermediacy. The results support previous conclusions that extensive hybridization occurs among the red oaks of this geographic region.
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