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Variation and Evolution in Plants
... Identifying plant species with DNA-barcodes is already a well-established methodology that cost effectively promotes biodiversity assessment, conservation, ecological and life history studies of plants (Kress et al., 2005). As such, it is a widely used tool despite possibly being confounded by plant hybridisation, asexual reproduction, genome duplications and incomplete lineage sorting (Fazekas et al., 2009;Stebbins, 1950). Fast and efficient species determination of Camelina is of practical nature due to its agricultural implications and hybridisation potential. ...
... It has been stated that C. sativa is the ancestor of C. alyssum which has developed in flax fields as a result of directional selection, causing morphological changes in the plant's habitus, fruit morphology and ripening type to resemble flax (Barrett, 1983). Thus, it also shares the same distribution dynamics as flax (Stebbins, 1950;Vavilov, 1992). This is supported by our topology, previous crossing experiments and detailed morphological studies that all point towards a close relationship between C. sativa and C. alyssum (Sinskaia and Bezluzheva, 1931;Stebbins, 1950;Tedin, 1925;Zinger, 1909). ...
... Thus, it also shares the same distribution dynamics as flax (Stebbins, 1950;Vavilov, 1992). This is supported by our topology, previous crossing experiments and detailed morphological studies that all point towards a close relationship between C. sativa and C. alyssum (Sinskaia and Bezluzheva, 1931;Stebbins, 1950;Tedin, 1925;Zinger, 1909). With the abandonment of flax fields, the distribution range of C. alyssum also shrank and the species is nowadays considered extinct from most of Central Europe (Francis and Warwick, 2009). ...
Stretching 8000 km from the Pannonian basin and the Danube delta in the West to the Manchuria region in the East and reaching up to 1000 km in width, the Eurasian steppe belt is the vastest steppe region worldwide. However, our knowledge about the temporal and spatial patterns of floral origin and evolution of the Eurasian Steppe is limited and inconclusive. Case studies on typical steppe flora may help us close such gaps. The study subject of this project was Camelina – a taxon which occupies open dry habitats in temperate zones of Eurasia. To infer the evolutionary history of this genus, maximum likelihood optimisation in RAxML and Bayesian Inference approach were carried out, based on the nuclear external transcribed spacer region. Furthermore, we performed a secondarily calibrated time estimation analysis using Bayesian optimisation in BEAST to infer potential influence of climatic shifts and paleogeographic events on the distribution patterns of Camelina and carried out an ancestral area reconstruction analysis using a Bayesian Binary Method. Our study resulted in a well-supported phylogeny that corresponds with the species morphology and uncovered several genetically distinct inter- and intraspecific lineages which appear to correlate geographically. Time divergence estimation argue for the diversification of Camelina to have taken place in the Middle East around the transition from Pliocene to Pleistocene (3-2 mya), and its historical biogeography to have been under a strong influence of several glacial periods and their palaeoclimatic and palaeoenvironmental consequences. Its young age also explains the subtle morphological character differences among species and high interspecific hybridisation potential. We further discuss the rediscovery of wild Camelina sativa populations and propose the external transcribed spacer as a ribotype identifying region for young and rapidly evolving core eudicot lineages.
... Poa L. is known for its high frequency of polyploidy and large number of species (Stebbins 1950;Clayton and Renvoize 1986;Soreng 1990; Gillespie and Soreng 2005). The base chromosome number in Poa is x = 7, as it is across tribe Poeae s.l. ...
... Given the high degree of polyploidy in the genus, the expectation is that much of it is due to allopolyploidy (Stebbins 1950). However, few studies have directly addressed allopolyploid origins in Poa species (Darmency and Gasquez 1997;Brysting et al. 2000Brysting et al. , 2004Patterson et al. 2005). ...
... The combination of artificially produced hybrids, isozyme data, and our DNA data, provides solid support for P. annua having a hybrid origin of the parentage proposed by Nannfeldt (1935Nannfeldt ( , 1937 and Tutin (1957). We classify P. annua as a segmental allopolyploid (Stebbins 1950), as the parents are easily recognized as closely related, and distinguished subtly, though completely, by morphological and life-history traits. This suggests a different explanation for Koshy's result: that the P. annua karyotype differentiated after the original hybridization event. ...
d i v e r s i t y , p h y l o g e n y , a n d e v o l u t i o n i n t h e m o n o c o t y l e d o n s e d i t e d b y s e b e r g , p e t e r s e n , b a r f o d & d a v i s a a r h u s u n i v e r s i t y p r e s s , d e n m a r k , 2 0 1 0 Abstract—Poa is the largest grass genus, with over 500 species, most of which are polyploid. Only 13 to 15% of species with chromosome counts have diploid populations. We conducted two phylogenetic analyses of combined chloroplast trnT-trnL-trnF (TLF) and nuclear ribosomal ITS sequence data for 42 outgroups and 47 samples of 30 species of Poa. One analysis focused on Poa taxa with diploid populations, and a second analysis included six more polyploid, and three possible hybrid taxa for which the data were not combined. The results are mostly congruent with results in published studies and provide further support for the recent classification of Poa into five serially diverging subgenera: Sylvestres, Ochlopoa, Pseudopoa, Stenopoa, and Poa. Incongruent placements of separate plastid and ITS sequences of P. abbreviata and P. annua are attributed to reticulate evolution, and of P. trivialis to long branch attraction. A genome notation system is introduced to simplify and facilitate characterization of plastid and ITS contributions in each accession and higher-level grouping resolved, and to identify the parental contributions in the possible hybrids. For example, we provide new evidence that a tetraploid, Poa annua (M 1 m 2), is derived from hybridization between two diploids, P. infirma (M 1 m 1) and P. supina (M 2 m 2), where large capitals represent plastid and small capitals represent ITS genomes of P. subg. Ochlopoa sect. Micrantherae (Mm), and superscript numbers represent the genetically divergent genomes of the parental species within the section.
... The evolutionary potential of a species and its ability to withstand adverse environments depend on both genetic diversity of the species and its population genetic structure (Stebbins, 1950). Different levels of genetic variation and genetic structure of populations can be attributed to multiple factors, such as distribution ranges, life forms, breeding systems, seed dispersal mechanisms, evolutionary history, natural selection, and human interference (Hamrick and Godt, 1996;Sarin et al., 2015;Zhou et al., 2020). ...
Phyllanthus emblica L. is a well-known medicinal and edible plant species. Various medicinal compounds in the fruit make it an important medicinal and promising economic material. The plant is widely distributed in Southwestern and Southern China. However, due to massive deforestation and land reclamation as well as deterioration of its natural habitat in recent years, the wild resources of this species have been sharply reduced, and it is rare to see large-scale wild P. emblica forests so far. In order to effectively protect and rationally utilize this species, we investigated the genetic diversity, genetic structure, and population dynamics of 260 individuals from 10 populations of P. emblica sampled from the dry climate area in Yunnan and wet climate area in Guangxi using 20 polymorphic EST-SSR markers. We found high genetic diversity at the species level (He = 0.796) and within populations (He = 0.792), but low genetic differentiation among populations (FST = 0.084). In addition, most genetic variation existed within populations (92.44%) compared with variation among the populations (7.56%). Meanwhile, the NJ tree, STRUCTURE, and hierarchical analysis suggested that the sampled individuals were clustered into two distinct genetic groups. In contrast, the genetic diversity of the dry climate group (He = 0.786, Na = 11.790, I = 1.962) was higher than that of the wet climate group (He = 0.673, Na = 9.060, I = 1.555), which might be attributed to the combined effects of altitude, precipitation, and geographic distance. Interestingly, only altitude and precipitation had significant pure effects on the genetic diversity, and the former was slightly stronger. In addition, DIYABC analysis suggested the effective population size of P. emblica might have contracted in the beginning of the Last Glacial Maximum. These genetic features provided vital information for the conservation and sustainable development of genetic resources of P. emblica, and they also provided new insights and guidelines for ecological restoration and economic development in dry-hot valleys of Yunnan and karst areas in Guangxi.
... The most widespread consequence of chromosome doubling in plants was called the "gigas" effect since the increase in cell size was achieved due to the larger number of gene copies. Usually, CSD individuals would exhibit larger organs compared to their diploid counterparts, mainly in the appearance of roots, leaves, tubercles, fruits, flowers and seeds (Stebbins, 1950). CSD often have lower growth rates, and tend to flower later or over a longer period of time than related diploids, which is a desirable feature for ornamental breeding (Levin, 2002). ...
Sedum alfredii Hance is a cadmium (Cd)/zinc (Zn) hyperaccumulator native to China.
However, its relatively low biomass restricted the large-scale application for heavy metal
contamination remediation. The chromosome set doubling of S. alfredii in vitro was achieved
by 0.1%–0.2% (W/V) colchicine treatment. The plant DNA ploidy was analyzed by flow
cytometry and chromosome set doubling plants (CSD) were identified based on the obvious
different sharp peak. A tissue culture experiment with different Cd treated levels and a field
trial with natural polluted mined soil were conducted to study the effects of chromosome
doubling on plant biomass and Cd accumulation in shoots. The results suggested that S.
alfredii is a mixoploid. Compared with the wild type plants (WT), CSD exhibited typical
“gigas” characteristics in morphology including stem thickness, root hair production,
number of leaves and size of stoma guard cell. Fresh weight and dry weight of CSD were
increased to 1.62–2.03-fold and 2.26–3.25-fold of WT. And Cd content of CSD showed a
17.49%–42.82% increase and 59% increase under tissue culture and field condition,
accordingly. In addition, the TF and in BCF of CSD were 2.37- and 1.59-fold of WT,
respectively. These results proved that it is feasible to promote phytoextraction efficiency of
S. alfredii in Cd contaminated soils through chromosomal engineering, which provides a
novel approach for hyperaccumulator application in phytoremediation.
... Hybridization and introgression have played a significant role in speciation, and have resulted in the production of new and evolutionarily stable lineages (Stebbins 1950, Dejoode and Wendel 1992, Rieseberg et al. 1995. Hybrid species can be classified into two types: allopolyploid, which involves a change in ploidy, and homoploid, in which the hybridization occurs with no change in chromosome number (Grant 1983, Rieseberg 1997, Gross and Rieseberg 2005. ...
... The fossil record thus supports the belief that the plants of the continental interiors were more highly evolved than the contemporaneous psilophytes which lived near the shore. The psilophytes were highly adapted to these lowland sites in which the environmental-organism relations were essentially unchanging, conditions now considered necessary for bradytelic lines (Simpson, 1944;1953;Stebbins, 1950). The view that most Devonian lowland plants are relict types which express various experiments in different ways of life, and which evolved long before the Devonian, not only comes closer to the actual situation as judged from stratigraphic and phylogenetic evidence, but is consistent with current opinions as to the nature of the evolutionary process. ...
... The evolution of the angiosperm genome is characterized by polyploidization through whole-genome duplication (WGD), followed by diploidization, which is typically accompanied by considerable homoeologous gene loss (Stebbins, 1950). A number of polyploidy events have been identified along different lineages of flowering plants. ...
ATP-binding cassette (ABC) proteins can act as transporters of different substrates across biological membranes by hydrolyzing ATP. However, little information is available about ABC transporters in Brassica rapa, an important leafy vegetable. In the present study, we carried out genome-wide identification, characterization and molecular evolution analyses of ABC gene family in B. rapa and 9 other plant species. A total of 179 B. rapa ABC genes (BraABCs) were identified. Among them, 173 BraABCs were identified on 10 chromosomes. Based on phylogenetic analysis and domain organization, the BraABC family could be grouped into eight subfamilies. BraABCs in the same subfamily showed similar motif composition and exon-intron organization. Common and unique cis-elements involved in the transcriptional regulation were also identified in the promoter regions of BraABCs. Tissue-expression analysis of BraABCs demonstrated their diverse spatiotemporal expression profiles. Influences of the whole genome triplication (WGT) on the evolution of BraABCs were studied in detail. BraABCs were preferentially retained compared with their neighboring genes during diploidization after WGT. Synteny analysis identified 76 pairs of syntenic BraABC paralogs among the three subgenomes of B. rapa, and 10 paralog pairs underwent positive selection with ω (= Ka/Ks) ratios greater than 1. Analyses of the expression patterns of syntenic BraABC paralogs pairs across five tissues and under stress treatments revealed their functional conservation, sub-functionalization, neo-functionalization and pseudogenization during evolution. Our study presents a comprehensive overview of the ABC gene family in B. rapa and will be helpful for the further functional study of BraABCs in plant growth, development, and stress responses.
... To explore the evolution of self-fertilization in perennials, Morgan et al. 7 first presented a life-history model with both overlapping generations and partial self-fertilization. Motivated by the observations that self-fertilization is comparatively more common in annual plants than among perennial plants 8 , the authors compared annual and perennial plant species and the conditions favoring self-fertilization. However, they neglected to explore how self-fertilization modifies the allocation of resources, and a similar oversight in other life-history models 1,6 . ...
By incorporating the effects of inbreeding depression (ID) on both juveniles and adults survivorship, we
developed a new theoretical model for hermaphroditic perennial plants. Our model showed that the
effect of the selfing rate on the evolutionarily stable strategy (ESS) reproductive allocation depends on
three parameters: (1) the self-fertilized juvenile relative survivorship (SFJRS), (2) the self-fertilized adult
relative survivorship (SFARS) and (3) the growth rate of self-fertilized adult, where the SFJRS is the
survivorship of self-fertilized juveniles divided by the survivorship of outcrossed juveniles, and likewise
for the SFARS. However, the ESS sex allocation decreases as the selfing rate increases. This relationship
seems independent of the SFJRS, the SFARS, and the growth rate of self-fertilized adults. Additionally,
our model showed that the complete outcrossing is an ESS when the fraction of juvenile inbreeding
depression (FJID) is less than 1/2 − τ, where τ is the self-fertilized adults mortality rate caused by ID. In
contrast, the complete selfing also acts as an ESS when the FJID is greater than 1/2 − τ. These results
could explain the diversity of mating strategies and related resource allocations for plants.
... Pairs that included variable mating species were excluded from this analysis. Mating system may coevolve and be correlated with traits such as polyploidy ( Stebbins, 1950 ; Barringer, 2007 ; Robertson et al., 2011 ) and lifespan ( Barrett et al., 1996 ). To ensure that these traits did not drive or obscure a relationship between mating system shift s and co-occurrence, we gathered published information on ploidy and lifespan when possible. ...
Premise of the study:
Automatic self-fertilization may influence the geography of speciation, promote reproductive isolation between incipient species, and lead to ecological differentiation. As such, selfing taxa are predicted to co-occur more often with their closest relatives than are outcrossing taxa. Despite suggestions that this pattern may be general, the extent to which mating system influences range overlap in close relatives has not been tested formally across a diverse group of plant species pairs.
Methods:
We tested for a difference in range overlap between species pairs for which zero, one, or both species are selfers, using data from 98 sister species pairs in 20 genera across 15 flowering plant families. We also used divergence time estimates from time-calibrated phylogenies to ask how range overlap changes with divergence time and whether this effect depends on mating system.
Key results:
We found no evidence that automatic self-fertilization influenced range overlap of closely related plant species. Sister pairs with more recent divergence times had modestly greater range overlap, but this effect did not depend on mating system.
Conclusions:
The absence of a strong influence of mating system on range overlap suggests that mating system plays a minor or inconsistent role compared with many other mechanisms potentially influencing the co-occurrence of close relatives.
... Plant life form related to life span (short vs. long lived) and growth form (herbaceous vs. woody) has also been considered as a key driver of mating system evolution. Stebbins (1950) discussed the possibility that shorter-lived species may be more associated with selfing than longer-lived species, and more recent studies have revealed that this pattern is robust (Barrett et al. 1996). Longer-lived species can be less constrained by pollen limitation, because they can reproduce several times, and can incur adult inbreeding depression (Morgan et al. 1997), which both favour outcrossing. ...
A number of plant traits influence the success of fertilization and reproduction in plants. Collectively these traits represent ecological syndromes that are of evolutionary significance. However, while an
association between mating system and colonizing ability has been proposed, the existence of a broader relationship between mating system and a species' position in ecological succession has not been extensively investigated. Grime’s CSR theory stresses that an ecological succession can
involve changes from colonizing to either competitive or stress-tolerant strategies. How distinct dimensions of competitiveness and stress tolerance covary with mating systems has still not been considered. We designed a comparative approach to evaluate the link between mating system, life
form and CSR strategies for 1,996 herbaceous and woody species. We found that CSR strategies are significantly related to mating systems. Ruderal species –colonizers in early succession– were mostly selfers while more competitive species were more often outcrossers. On the other hand,
greater physiological stress tolerance was associated with mixed mating systems. Outcrossing is classically expected to be advantageous for most life history strategies other than colonizers, but we suggest that reproductive assurance can counterbalance this effect in stressful environments where populations are sparse and pollinators are rare. Therefore, our results emphasize that competition and abiotic stresses are not equivalent selective pressures on the evolution of mating systems. Finally, we found plant life span to convey additional information on mating system variation, supporting its role for mating system evolution. These findings encourage further investigation of the evolutionary role of ecological strategies as syndromes of traits and suggest that the emergence of large databases of plant traits will help address the major evolutionary hypotheses on such syndromes.
... Consequently, hybrid zones among dominant and low-dispersal intertidal species of Fucus are likely to display substantial spatial and temporal differences compared with the equally dominant, but highdispersal intertidal mussels. Disturbance has long been recognized as an important mechanism of hybridization (Stebbins, 1950; Harrison, 1990). Natural disturbances in the marine environment are many, including influences of freshwater input, upwelling along coastal margins, and geological events ranging from formation of new land masses to Pleistocene cooling (Gardner, 1997). ...
... Polyploidy may confer evolutionary advantages for plant species, including lessening of hybrid outbreeding depression (Stebbins 1950; Soltis & Soltis 2000). Hybrids between alder species are difficult to distinguish from each other due to continuous phenotypic variation of distinguishing characteristics (Pīrāgs 1962, Parnell 1994, Banaev & Bazant 2007, Poikans 2014). ...
... In addition, if asexual dispersal follows a stepping-stone pattern , the geographical range of lineages dispersing by asexual diaspores but not by spores is expected to vary with their age, whereas distributional patterns resulting from long-distance dispersal of spores would not (Stebbins, 1950). ...
Aim
Why some species exhibit larger geographical ranges than others remains a fundamental, but largely unanswered, question in ecology and biogeography. In plants, a relationship between range size and mating system was proposed over a century ago and subsequently formalized in Baker's Law. Here, we take advantage of the extensive variation in sexual systems of liverworts to test the hypothesis that dioecious species compensate for limited fertilization by producing vegetative propagules more commonly than monoecious species. As spores are assumed to contribute to random long‐distance dispersal, whereas vegetative propagules contribute to colony maintenance and frequent short‐distance dispersal, we further test the hypothesis that monoecious species exhibit larger geographical ranges than dioecious ones.
Location
Worldwide.
Methods
We used comparative phylogenetic methods to assess the correlation between range size and life history traits related to dispersal, including mating systems, spore size and production of specialized vegetative propagules.
Results
No significant correlation was found between dioecy and production of vegetative propagules. However, production of vegetative propagules is correlated with the size of geographical ranges across the liverwort tree of life, whereas sexuality and spores size are not. Moreover, variation in sexual systems did not have an influence on the correlation between geographical range and production of asexual propagules.
Main conclusions
Our results challenge the long‐held notion that spores, and not vegetative propagules, are involved in long‐distance dispersal. Asexual reproduction seems to play a major role in shaping the global distribution patterns of liverworts, so that monoecious species do not tend to display, on average, broader distribution ranges than dioecious ones. Our results call for further investigation on the spatial genetic structure of bryophyte populations at different geographical scales depending on their mating systems to assess the dispersal capacities of spores and asexual propagules and determine their contribution in shaping species distribution ranges.
... Starting from the classical work of Stebbins (1950; 1957), two major selective forces have been proposed to promote a shift from outcrossing to selfing. The first one is the genetic transmission advantage: a selfing genotype transmits twice as many copies of its genes to offspring as does an outcrossing genotype. ...
In hermaphroditic plants, theory for mating system evolution predicts that populations will evolve to either complete autonomous selfing or complete outcrossing, depending on the balance between automatic selection favouring self-fertilization and costs resulting from inbreeding depression (ID). Theory also predicts that selection for selfing can occur rapidly and is driven by purging of genetic load and the loss of ID. Therefore, selfing species are predicted to have low levels of ID or even to suffer from outbreeding depression (OD), whereas predominantly outcrossing species are expected to have high levels of ID. To test these predictions, we related the capacity of autonomous selfing to the magnitude of early acting inbreeding or outbreeding depression in both allogamous and autogamous species of the orchid genus Epipactis. For each species, the level of autonomous selfing was assessed under controlled greenhouse conditions, whereas hand-pollinations were performed to quantify early costs of inbreeding or outbreeding depression acting at the level of fruit and seed production. In the autogamous species, the capacity of autonomous selfing was high (> 0.72), whereas in the allogamous species autonomous selfing was virtually absent (< 0.10). Consistent with our hypothesis, allogamous Epipactis species had significantly higher total ID (average: 0.46) than autogamous species, which showed severe costs of OD (average: -0.45). Overall, our findings indicate that strong early-acting ID represents an important mechanism that contributes to allogamy in Epipactis, whereas OD may maintain selfing in species that have evolved to complete selfing. This article is protected by copyright. All rights reserved.
... Currently, with the identification of the primary components, including SnRK2, ABFs, AFPs, group-A PP2C, and PYRs in algal (Wang et al., 2015), the function of the ABA signaling pathway could traced back to before the divergence of land plants. Angiosperm genome evolution is characterized by polyploidization through whole-genome duplication (WGD) followed by diploidization, which is typically accompanied by considerable homoeologous gene loss (Stebbins, 1950). For example, the genome of Arabidopsis thaliana has experienced a paleohexaploidy (γ) duplication shared with most dicots and two subsequent genome duplications (α and β) since its divergence from Carica papaya along with a rapid DNA sequence divergence and extensive gene loss (fractionation; Bowers et al., 2003). ...
The sucrose non-fermenting 1-related protein kinase 2 (SnRK2) family members are plant-specific serine/threonine kinases that are involved in the plant response to abiotic stress and abscisic acid (ABA)-dependent plant development. Further understanding of the evolutionary history and expression characteristics of these genes will help to elucidate the mechanisms of the stress tolerance in Pak-choi, an important green leafy vegetable in China. Thus, we investigated the evolutionary patterns, footprints and conservation of SnRK2 genes in selected plants and later cloned and analyzed SnRK2 genes in Pak-choi. We found that this gene family was preferentially retained in Brassicas after the Brassica-Arabidopsis thaliana split. Next, we cloned and sequenced 13 SnRK2 from both cDNA and DNA libraries of stress-induced Pak-choi, which were under conditions of ABA, salinity, cold, heat, and osmotic treatments. Most of the BcSnRK2s have eight exons and could be divided into three groups. The subcellular localization predictions suggested that the putative BcSnRK2 proteins were enriched in the nucleus. The results of an analysis of the expression patterns of the BcSnRK2 genes showed that BcSnRK2 group III genes were robustly induced by ABA treatments. Most of the BcSnRK2 genes were activated by low temperature, and the BcSnRK2.6 genes responded to both ABA and low temperature. In fact, most of the BcSnRK2 genes showed positive or negative regulation under ABA and low temperature treatments, suggesting that they may be global regulators that function at the intersection of multiple signaling pathways to play important roles in Pak-choi stress responses.
... Therefore, proposing such an approach in breeding, he adopted what nature used in order to create a variety of species of natural flora. Experimental evidence of this assumption appeared later in the writings of L. Stebbins and colleagues (Stebbins, 1950 among others). ...
October 2015 marks the 160th anniversary of the birth of Ivan V. Michurin. As a scientist and plant breeder, he made a significant improvement of many fruit and berry plants, and flowers. He developed methods of plant breeding, especially regarding long-distance hybridisation of fruit plants, and promoted gardening to the north and east of Russia. He introduced some new berry species, such as Actinidia and black chokeberry, and was the first in Russia to use dwarf and semi dwarf stocks of apples. Michurin initiated the mass movement of gardeners and horticulture experimenters in USSR who changed and significantly extended the assortment and areas of fruit and berries cultivation in the country. He not only brought together a representative collection of species and varieties of fruit, berry and flower plants from around the world, but also used them in breeding by hybridization, including interspecific. He created some new artificial interspecific hybrids such as Cerapadus (cherry and bird cherry tree hybrid), and others. Michurin created 132 cultivars. Eleven of them are not only cultivated, but are also included in “The State Register of Protected Plant Breeding of the Russian Federation”.
... In addition, postzygotic barriers might be involved in reducing hybridization between K. arvensis and K. carinthiaca. Whereas hybrids are likely fertile (see above), hybrid progeny might be maladapted to the parental core niches, prospering only in intermediate habitats (Stebbins 1950; Arnold 2004). This hypothesis would require further study by reciprocal transplant experiments; however, such approach is not conceivable as it presents a strong conservational risk for K. carinthiaca. ...
Interspecific hybridization, especially when regularly followed by backcrossing (i.e., introgressive hybridization), conveys a substantial risk for many endangered organisms. This is particularly true for narrow endemics occurring within distributional ranges of widespread congeners. An excellent example is provided by the plant genus Knautia (Caprifoliaceae): Locally endemic K. carinthiaca is reported from two isolated populations in southern Austria situated within an area predominantly occupied by widespread K. arvensis. While K. carinthiaca usually inhabits low-competition communities on rocky outcrops, K. arvensis occurs mainly in dry to mesic managed grasslands, yet both species can coexist in marginal environments and were suspected to hybridize. Flow cytometry revealed that diploid K. carinthiaca only occurs at its locus classicus, whereas the second locality is inhabited by the morphologically similar but tetraploid K. norica. In the, therefore, single population of K. carinthiaca, flow cytometry and AFLP fingerprinting showed signs of introgressive hybridization with diploid K. arvensis. Hybridization patterns were also reflected in intermediate habitat preferences and morphology of the hybrids. Environmental barriers to gene flow seem to prevent genetic erosion of K. carinthiaca individuals from the core ecological niches, restricting most introgressed individuals to peripheral habitats. Efficient conservation of K. carinthiaca will require strict protection of its habitat and ban on forest clear cuts in a buffer zone to prevent invasion of K. arvensis. We demonstrate the large potential of multidisciplinary approaches combining molecular, cytometric, and ecological tools for a reliable inventory and threat assessment of rare species.
... Despite these challenges, noteworthy progress has been made recently in understanding the structure of apomictic complexes for a few groups using a diversity of molecular approaches (e.g., Schranz et al. 2005 iBoechera]; Grusz et al. 2009 ICheilanthes ]; Fehrer et al. 2009 [ Hieracium ]; Cosendai et al. 2011 [Ranuncu/us]). For incompletely or poorly known complexes however, the initial step must be to comprehensively characterize diploid populations that may be progenitors of the polyploids (Stebbins 1950; Grant 1981). One such complex is the Erigeron sect. ...
Erigeron strigosui (Asteraceae) is a complex species consisting of a diversity of sexual diploid and apomictic polyploid populations. Previous work has established the geographic distribution and phylogenetic relationships among sexual diploid populations in the extreme southeastern United States. In this work we investigated disjunct sexual diploid populations in Arkansas and Missouri We evaluated pollen quality and mapped geographic locations for 496 unique herbarium collections to determine that sexual populations are relatively common in Arkansas (37 out of 286 collections; 12.9%), especially in upland habitats in the western 2/3 of the state, but rare in Missouri (1 out of 210 collections; 0.596). Eight rDNA (ITS plus ETS) sequences for seven populations reveal that sexual diploid E. slrigosus from Arkansas is not genetically differentiated from other populations that have been studied. However, two genetic lineages were detected; those from the Ozark Highlands correspond to previously described rDNA haplotype II while samples from more southerly ecoregions correspond to previously described rDNA haplotype III. This work fills in a large gap in the knowledge of the distribution of genetic variation and lends insight into the phylogeography of the complex.
... Together, these pathways regulate the expression of the so-called flowering integrator genes FT and SOC1 depending on the environment, which will subsequently act on the flower identity genes (Andres & Coupland 2012). Classical garden studies of the natural quantitative variation for flowering time within species distributed across a wide range of climates have shown that this variation is involved in the genetically based (evolutionary) adaptation of plants to different climates (Stebbins 1950; Briggs & Walters 1997; Aspinwall et al. 2013; Shrestha et al. 2014). This is best illustrated with the wild species A. thaliana, whose native range spans Eurasia (Weigel 2012). ...
The timing of flowering initiation depends strongly on the environment, a property termed as the plasticity of flowering. Such plasticity determines the adaptive potential of plants since it provides phenotypic buffer against environmental changes, and its natural variation contributes to evolutionary adaptation. We addressed the genetic mechanisms of the natural variation for this plasticity in Arabidopsis thaliana by analysing a population of recombinant inbred lines derived from Don-0 and Ler accessions collected from distinct climates. QTL mapping in four environmental conditions differing in photoperiod, vernalization treatment and ambient temperature, detected: i) FLC as a large effect QTL affecting flowering time differentially in all environments; ii) numerous QTL displaying smaller effects specifically in some conditions; iii) significant genetic interactions between FLC and other loci. Hence, the variation for the plasticity of flowering is determined by a combination of environmentally sensitive and specific QTL, and epistasis. Analysis of FLC from Don identified a new and more active allele likely caused by a cis-regulatory deletion covering the non-coding RNA COLDAIR. Further characterization of four FLC natural alleles showed different environmental and genetic interactions. Thus, FLC appears as a major modulator of the natural variation for the plasticity of flowering to multiple environmental factors. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
... Early zoological workers envisioned two possible outcomes of hybridization: (1) the merger of the hybridizing taxa due to extensive introgression or (2) the cessation of hybridization due to the reinforcement of reproductive barriers [14] [41]. By contrast, botanists tended to view hybridization as a creative process often leading to the formation of stable hybrid lineages [3] [63]. Although the consequences of hybridization envisioned by botanists and zoologists were vastly different, both groups did agree, at least implicitly, that hybrid zones were ephemeral. ...
The role of hybridization in the origin, maintenance, and loss of biodiversity has been the subject of speculation and debate for more than two centuries (Linnaeus 1760; Kölreuter 1893; Arnold 1997). Some authors have emphasized the creative role of hybridization in fostering species or community diversity (Linnaeus 1760; Kerner von Marilaun 1894–1895; Lotsy 1916; Stebbins 1942; Anderson 1949; Whitham and Maschinski 1996; Arnold 1997), whereas others have focused on its role as a destructive evolutionary force, contributing to the extinction of rare populations or species (Cade 1983; Rieseberg 1991; Ell-strand 1992; Levin et al. 1996; Rhymer and Simberloff 1996; Carney et al. 2000). Although the emphasis of these authors may vary, most appear to recognize the diversity of possible evolutionary outcomes of hybridization.
... Thus, at the more western longitudes of its range, subspecies peninsularis' peduncles were similar to those of subspecies acuminata, which obscures its detection regardless of its relatively small leaves. Species distributed over one or more climatic belts spanning latitudes often possess clines for physiological characteristics and their associated vegetative characters (Stebbins 1950). These clines result from adaptive responses to the environmental conditions prevailing in the different parts of the species range (Fritsch and Lucas 2000, Spurr and Barnes 1980). ...
The Mecardonia acuminata complex is a classic example of a widespread endemic species in the southeastern US. Morphological variations in the complex resulted in the classification of at least three varieties or subspecies for the species by previous botanists. However, the distributions and diagnostic features of two of the subspecies, peninsularis and microphylla, are unclear due to shared morphological features and widespread distribution of the subspecies acuminata. The present study involved examination and biostatistical analyses of 3 vegetative and 5 reproductive characters that were known to serve as diagnostic features of 1 or more taxa of the species. Results of the study indicate that subspecies peninsularis can be distinguished by its ascending peduncle angle of suspension, diffuse basal branching habit (dendriform at base) of the shoot and small leaves, especially in the southern ranges of the complex. Subspecies microphylla can be distinguished based on its short (<20 mm) fruit peduncles and divaricate peduncle angle of suspension. Subspecies acuminata comprises individuals with divaricate peduncle angle of suspension and long fruit peduncles (>20 mm). Subspecies acuminata was also observed to comprise many individuals that were intermediates of 2 or 3 subspecies. Discriminant function analyses on longitude, latitude, and biogeography as well as Wilks' lambda estimates suggest moderate to low clinal variation and a much broader historical range distribution of subspecies peninuslaris. The morphological variations in the species complex may be due to secondary contact with ongoing integration into subspecies acuminata.
... The " modern synthesis " of the 1940s set the stage for scientific investigations of genetic and environmental variation in natural populations (Mayr 1942; Simpson 1944; Stebbins 1950; Dobzhansky 1951). One of the best and most illustrative examples in population biology of analyzing causes of phenotypic variation is the plant Achillea lanulosa (a relative of Milfoil), studied by Clausen et al. (1948). ...
Genes and environment make the organism. Darwin stood firm in his denial of any direct role of environment in the modification of heredity. His theory of evolution heralded two debates: one about the importance and adequacy of natural selection as the main mechanism of evolution, and the other about the role of genes versus environment in the modification of phenotype and evolution. Here, I provide an overview of the second debate and show that the reasons for the gene versus environment battle were twofold: first, there was confusion about the role of environment in modifying the inheritance of a trait versus the evolution of that trait, and second, there was misunderstanding about the meaning of environment and its interaction with genes in the production of phenotypes. It took nearly a century to see that environment does not directly affect the inheritance of a phenotype (i.e., its heredity), but it is nevertheless the primary mover of phenotypic evolution. Effects of genes and environment are not separate but interdependent. One cannot separate the effect of genes from that of environment, or nature from nurture. To answer the question posed in the title, it is partly because the 20th century has been a century of unending progress in genetics. But also because unlike physics, biology is not colorblind; progress in biology has often been delayed beyond the Kuhnian paradigm change due to built-in interest in negating the influence of environment. Those who are against evolution, of course, cannot be expected to understand the role of environment in evolution. Those for it, many biologists included, believing in the supremacy of genes empowers them by giving adaptation a solely gene-directed (self-driven) "teleological" interpretation.
... The gesnerioids are a lineage that have basically diversified at the diploid level in South America. The coronantheroids are not a relict lineage as once thought, but apparently the result of recent long distance dispersals into Australasia from within the gesnerioids (Woo et al. 2011, Perret et al. 2013) for which polyploidy has been argued to be particularly advantageous (Stebbins 1950, Barrier et al. 1999) by allowing an increased fitness through fixed heterozygosity (e.g., Soltis et al. 2004). The epithematoids are an odd assemblage of morphologically discontinuous lineages that might have experienced a high level of extinction events. ...
Sparked by the publication of large phylogenetic studies and major generic redefinitions in the Gesneriaceae, we review this growing body of molecular studies on the family. Different aspects of molecular data and their use in Gesneriaceae systematics are considered including conceptual challenges on the phylogenetic work undertaken to date as well as an overview of taxon sampling in the family. Molecular data are currently available for 70 of 72 recognized New World genera and 64 of 68 Old World genera. Many of the smaller genera and some of the larger genera are completely sampled. Current knowledge of tribal and generic delineations and relationships among the New World genera is relatively advanced. In contrast, intergeneric relationships and tribal arrangements are mostly unresolved for the Old World genera. In this paper we illustrate and summarize the published phylogenetic work in composite phylogenies with an emphasis on the most pertinent and accurate molecular systematic studies. This paper provides the molecular-based background for a new formal classification of the family Gesneriaceae.
... Mientras es tan común en plantas, es rara en animales, en los que prácticamente es confinada a las formas hermafroditas o partenogenéticas. Stebbins (1950) sugiere que esto se debe a que la poliploidía interfiere con la diferenciación celular en los animales, pero no en las plantas, cuyo proceso de desarrollo es más sencillo. Muller (citado en Mayr, 1969) sostiene que la causa que provoca la esterilidad es la descompensación del equilibrio en los factores determinantes del sexo; de acuerdo con esta hipótesis, el equilibrio de los cromosomas sexuales es más delicado en los animales. ...
... Researchers have long identified the importance of both geographic and ecological barriers in the isolation of species (Stebbins 1950). Ecological barriers can influence adaptation to different environmental conditions and potentially affect the connection between populations which, in turn, promotes divergence (Rundell and Price 2009; Nosil et al. 2009). ...
The discovery of biotic and ecological factors that influence genetic isolation in populations contributes to our understanding of speciation, one of the most important issues in evolutionary biology. In this paper, we ask whether differences in climate preferences are influencing genetic isolation in two assemblages of populations of Berberis trifoliolata Moric., the Northeastern and the Mexican Plateau groups. Agarito, as this species is known, is a remarkable shrub in the arid regions of North America and found mostly in the Chihuahuan Desert. Ecological niche modeling and two tests of niche evolution were carried out. The Ecological Niche Modeling suggests that the potential distribution of the Northeastern group does not predict that of the Mexican Plateau group, and nor does the latter predict the former. Tests of niche evolution indicate a divergent niche between these two groups. Among the most important climate factors detected in the multivariate niche evolution test are mean annual temperature and annual precipitation. We concluded that the two lineages exemplify an incipient speciation process.
... Over the last 60 yr, an increased awareness of the importance of reticulate mechanisms of evolution has accumulated, both at shallow and deep levels (e.g. Anderson 1949; Stebbins 1950; Grant 1981; Rieseberg and Soltis 1991; Doolittle 1999; Mallet 2005, 2007; Arnold and Fogarty 2009). In plants, hybridization is considered a powerful and widespread process (e.g. ...
Abstract— The phylogeny of Amaryllidaceae tribe Hippeastreae was inferred using chloroplast (3′ ycf1, ndhF, trnL (UAA)-F (GAA)) and nuclear (ITS rDNA) sequence data under maximum parsimony and maximum likelihood frameworks. Network analyses were applied to resolve conflicting signals among data sets and putative scenarios of reticulate evolution. All analyses of all regions consistently revealed two major clades, which are formalized as subtribes: A) Traubiinae, formed by Traubia, Placea, Phycella, Rhodolirium, and Famatina maulensis, characterized by x = 8, rare polyploidy, and a capitate stigma, and B) Hippeastrinae, including Eithea, Habranthus, Haylockia, Hippeastrum, Rhodophiala, Sprekelia, Zephyranthes, and Famatina pro parte, characterized by a range of basic chromosome numbers (x = 6‐11) and frequent polyploidy and aneuploidy. No clear morphological features diagnose the latter clade, which contains ca. 90% of the tribe's species diversity. Our phylogenetic results question the monophyly of all genera in the tribe and show widespread cytonuclear discordance within the mainly Neotropical Hippeastrinae, further supporting putative ancient hybridization(s) preceding the radiation of this major clade. In contrast, the Traubiinae, endemic to Chile and Argentina, show a tree-like pattern of evolution, consistent with the apparent absence of allopolyploidy in this clade. A brief description, circumscription, and geographic distribution are provided for each subtribe.
... The success of polyploids may be attributable to one or several factors: the multiplication of chromosome sets can cause an immediate shift in phenotypic and physiological traits as a result of a larger genome size (Wendel 2000; Ramsey 2011); alternatively, the increased genetic buffering provided by having extra genome copies and changes in gene expression may induce a heterosis effect, confer a greater biochemical flexibility, and affect the potential for novel adaptive responses to selection (Levin 1983, 2002; Brochmann & Elven 1992; Bretagnolle & Thompson 1996; Soltis & Soltis 1999; Otto & Whitton 2000; Wendel 2000; Soltis et al. 2003). It has been suggested that polyploids often occupy wider or different ranges of habitats than their diploid parents (Stebbins 1950; Lewis 1980; Petit et al. 1999; Otto & Whitton 2000). Therefore, polyploids are considered to be more successful in terms of a wider geographic range or niche than their progenitors (Levin 1983, 2002). ...
To elucidate the mechanisms of the adaptive advantages of polyploidy, there is a need to identify physiological traits that participate in the success of polyploids. We studied selected photosynthetic characteristics, stomatal density, and specific leaf area of three ploidy levels (2n = 4x, 5x, 6x) of the geophyte Allium oleraceum that partially differ in their ecological niches. Although the cytotypes were on average similar with regard to most of the measured photosynthetic traits, the hexaploids showed more rapid initial photosynthetic induction and a tendency for a higher maximum photosynthetic rate per unit area. The stomatal density was not affected by ploidy, though the specific leaf area was reduced for the hexaploids compared to the other cytotypes. A lower intracytotype variation was found for most of the studied photosynthetic and anatomical traits for the hexaploids compared to the large variation found within other cytotypes. A comparison of the photosynthetic traits between the cytotypes showed that the ecological differentiation between cytotypes is only weakly related to the characteristics of their photosynthetic apparatus. However, contrasting ranges of variability in the measured traits between the cytotypes can be related to previously observed differences between cytotypes with regard to the ranges of intracytotype genetic variation, genome size variation, and niche breadth. A higher variability of photosynthetic traits in tetraploids and pentaploids may be related to the existence of a spectrum of types adapted to different environmental conditions. Hexaploids may represent a recently formed cytotype adapted to open environmental conditions.
... Selfing or autogamy is accompanied also by several advantages, such as the non-dependence on crossing partners and, therefore, the certainty of reproduction, the cohesion of unlinked well-adapted genes to a specific environment, and an increased colonizing ability for new habitats (Barrett, 2010; Charlesworth and Wright, 2001). Already Stebbins (1950, 1957, 1974) mentioned that the shift from out-crossing to self-fertilizing is classically regarded as one of the most prevalent evolutionary transitions in flowering plants, and Baker (1955) stated that colonizing species which disperse over long distances are generally self-compatible (Bakers rule!). These statements were formulated earlier by European scientists like Thellung (1930) and support the remarkable significance of the breakdown of genetic selfincompatibility as an evolutionary key event. ...
Bellevalia turcica was described as a new species in the Pozantı district, Adana province in the south of Turkey. The palynological, ecological, and phenological characteristics were determined. Bellevalia turcica is similar to Bellevalia fominii Woronow, but can easily be distinguished from the differences in the flower and leaf trait characteristics. Full description and detailed photographs of this new species were provided. The somatic chromosome number of B. turcica was determined to be 2n = 2x = 8. B. turcica was attributed into the “Vulnerable” category after assessment based on the International Union for Conservation of Nature (IUCN) Categories. The distribution patterns of B. turcica and other related Bellevalia species were also presented.
[DRAFT] A comparative morphological study of Bolboschoenus species based on a critical analysis of extensive herbarium material, their types, observations of plants in nature, comparative carpological study (Tatanov, 2004a), analysis of literature data on the anatomy of pericarp and sculpture of the surface of fruits (Browning, Gordon -Gray, 1992, 1993, 2000; Browning et al., 1995, 1996, 1997a, b, 1998a, b; Hroudová et al., 1997, 1998b, 2001; Hayasaka, Ohashi, 2002; Egorova, Tatanov, 2002, 2003 ), also a number of other data on morphology, anatomy, embryology and karyology, allowed us to identify features for solving the problems of species independence of taxa and for creating of system of the genus Bolboschoenus (Tatanov, 2004b). The original system of the genus proposed by us on a global scale includes 3 sections, 5 subsections and 14 species. The following features were used for distinguish sectiones: morphology of inflorescence, presence or absence of perianth bristles in mature fruits, number of stigmas, shape of fruit in cross-section, sculpture of fruit surface, shape of exocarp cells and presence or absence of a silica body in them. The subsections was based on morpholohy of inflorescence and the degree of its branching, number of stigmas, shape of spikelet, color of covering scales, shape of fruit in outline and cross-section, size of fruit, thickness of pericarp, number of sclereids layers in the mesocarp. An additional basis for distinguishing of sections and subsections was also provided their clearly defined geographically ranges.
Extreme habitats have a fascination of their own. They are occupied by only a few very characteristic species, and they are easy to recognize ecologically and spatially. In extreme environments a single physical factor is usually dominating and other factors subsidiary. This makes it easy to understand what is going on, and to define the intensity of the factor. Extreme habitats are so distinctive that it is also easy to see where they begin and end. Because of this they have important advantages for the study of evolution.
A metatheoretical and historiographical re-analysis of the Evolutionary Synthesis (the process) and the Synthetic Theory (the result) leads to the following conclusion: The Synthetic Theory is not a reductionistic, but rather a structuralistic theory with a limited range of relevant hierarchical levels. Historically the Synthesis was not a sudden event but a rational long-term project carried out between 1930 and 1950 by a large number of biologists in several countries. In the second part of our paper the contributions of several German biologists to the Synthesis are analyzed.
Pollen grains of the Euphorbiaceae show a number of pollen types which can be clearly distinguished. Generally different genera are characterized by a specific pollen type. Euphorbia obesa Hook. f. and Croton gratissimus Burch, subsp. subgratissimus (Prain) Burtt Davy, represent two genera within the Crotonoideae with different morphology, each type characteristic for the respective genus.
Taxonomically, the genus Euphorbia with apetalous flowers consisting of a naked pistil surrounded by several staminate flowers within a cyathium, is considered more advanced than the genus Croton. In Croton the inflorescence is a raceme with unisexual flowers. The floral whorls of the male show numerous anthers and both calyx and a showy corolla are present. Both genera are insect pollinated.
In both Euphorbia obesa and Croton gratissimus the pollen wall in section shows columellae, a structure characteristic of angiosperms. However the present ontogenetic studies show that the formation of the columellae differs entirely in the two pollen types. The final stratification of the wall as well as the morphology of the grains differ and evaluation of the exine structure indicates that phylogenetically Croton pollen shows more advanced characters than Euphorbia — contradicting the floral phylogeny.
This study conducted at light and electron microscope level compares the two pollen types morphologically and ontogenetically, concentrating mainly on the formation of the exine which is tectate-perforate in the prolate tricolpate grain of Euphorbia obesa and semi-tectate in the anaperturate, spheroidal grain of Croton gratissimus.
The aim of the study was to evaluate the significance of pollen characters in taxonomic and phylogenetic relationships within the Euphorbiaceae. The differing pollen morphology which is related to the taxonomic grouping of tribes within the subfamily (Crotonoideae) emphasizes diversity, which may result from physiological adaptation. The study shows that the same functional end may well be achieved in different ways and this may be a factor underlying the diversity in the heterogeneous family Euphorbiaceae.
The Brassicaceae include several major crop plants and numerous important model species in comparative evolutionary research such as Arabidopsis, Brassica, Boechera, Thellungiella, and Arabis species. As any evolutionary hypothesis needs to be placed in a temporal context, reliably dated major splits within the evolution of Brassicaceae are essential. We present a comprehensive time-calibrated framework with important divergence time estimates based on whole-chloroplast sequence data for 29 Brassicaceae species. Diversification of the Brassicaceae crown group started at the Eocene-to-Oligocene transition. Subsequent major evolutionary splits are dated to ∼20 million years ago, coinciding with the Oligocene-to-Miocene transition, with increasing drought and aridity and transient glaciation events. The age of the Arabidopsis thaliana crown group is 6 million years ago, at the Miocene and Pliocene border. The overall species richness of the family is well explained by high levels of neopolyploidy (43% in total), but this trend is neither directly associated with an increase in genome size nor is there a general lineage-specific constraint. Our results highlight polyploidization as an important source for generating new evolutionary lineages adapted to changing environments. We conclude that species radiation, paralleled by high levels of neopolyploidization, follows genome size decrease, stabilization, and genetic diploidization.
The potential of using Fragaria vesca L. as a bridge species for interspecific hybridization to F. nilgerrensis Schlect, F. nubicola Lindl., F. pentaphylla Losinsk, and F. viridis Duch. was investigated using a wide germplasm base of 40 F. vesca accessions. This study was successful in producing many hybrids between F. vesca and other diploid species indicating its value as a bridge species. Of the species used as males, F. nubicola, F. pentaphylla, and F. viridis accessions were more successful, averaging 8 to 16 fruit and 16 to 25 seeds/fruit. It was most difficult to obtain hybrids with F. nilgerrensis, which had only three seeds per fruit. Differences among pollen donors were minimal when hybrid seeds were germinated in vitro. For different species combinations, 75% to 99% of seeds had embryos and 77% to 89% of these embryos germinated. The lack of significant differences in crossability variables among the four F. vesca subspecies [i.e., ssp. americana (Porter) Staudt, ssp. bracteata (Heller) Staudt, ssp. vesca L., and ssp. vesca var. semperflorens L.] demonstrated the similarity between these species and the strong potential for gene flow between F. vesca and other diploid species. As European and North American F. vesca subspecies are not sufficiently divergent to differ in interspecific hybridization, F. vesca may be a younger species rather than an older progenitor species.
The botanist is confronted with a remarkably diverse group of organisms that nonetheless have identical or very similar metabolic requirements. Apart from a relatively few parasitic species, the majority of plants require similar resources to synthesize their primary and secondary metabolites (Farquhar, Caemmerer and Berry, 1980; Mooney and Gulmon, 1979; Troughton, Card and Hendy, 1974). And with a few exceptions, such as CAM and C4 metabolism, the biosynthetic pathways leading to these metabolites are virtually identical (Pearcy and Ehleringer, 1984; Schmitt and Edwards, 1981). Hence the physiological diversity among many algae, bryophytes, pteridophytes and seed plants is much more limited than is that of the vertebrates. Yet among the land plants, and the embryophytes in particular, the divergence in form and structure often requires that biochemical and ultrastructural evidence be used to prove common ancestry (Stewart and Mattox, 1975). The combination of metabolic homogeneity and structural heterogeneity has produced a dilemma for the functional morphologist. The growth and survival of a green plant is predicated on a photosynthetic imperative, yet form can be highly variable.
The paper is meant to explain and, where possible, briefly to substantiate the following central principles:
Until recently, only one species of baobab was thought to exist on mainland Africa, namely the tetraploid Adansonia digitata. However, a second, diploid species, Adansonia kilima, has recently been described and its presence has been confirmed in Tanzania, Kenya, Zambia, Namibia and South Africa. In this study, we use morphological analysis to confirm the presence of A. kilima in Zimbabwe. Leaves were collected from four different sites around Zimbabwe and the size and density of the stomata were measured. We found that the trees could be divided into two distinct groups, with the stomatal size and density in each group corresponding with those found previously. This suggests that both species do occur in Zimbabwe and their occurrence is sympatric.
Species' geographic ranges vary enormously, and even closest relatives may differ in range size by several orders of magnitude. With data from hundreds of species spanning 20 genera in 15 families, we show that plant species that autonomously reproduce via self-pollination consistently have larger geographic ranges than their close relatives that generally require two parents for reproduction. Further analyses strongly implicate autonomous self-fertilisation in causing this relationship, as it is not driven by traits such as polyploidy or annual life history whose evolution is sometimes correlated with selfing. Furthermore, we find that selfers occur at higher maximum latitudes and that disparity in range size between selfers and outcrossers increases with time since their evolutionary divergence. Together, these results show that autonomous reproduction-a critical biological trait that eliminates mate limitation and thus potentially increases the probability of establishment-increases range size.
© 2015 John Wiley & Sons Ltd/CNRS.
Population biology studies during 1966-2010 have revealed that the proportion of bisexual plants has declined in natural populations of Isoetes pantii at Narsinghgarh (Central India), where it has been growing with the parental species I. coromandelina L. and I. sampathkumaranii Rao. Since many fundamental discoveries have been observed from within the microsporangia (male sporangia) over four decades the decline of production of male sporangia by this species has been briefly presented in the light of chromosomal as well as ecological factors. Directional selection appears to have favoured this decline.
The genus Leontopodium (Pers.) R.Br. (Asteraceae, Compositae) is economically important for both pharmaceutical and horticultural purposes. This importance, however, has not led to a good understanding of species coherence and the delimitation of species. One fundamental aspect of a good understanding of a species is how many chromosomes it has and any possible indication of polyploidy. Here we present somatic chromosome numbers for 16 Leontopodium species, of which six are new for science. The results indicate basic chromosome numbers of x = 6, 8, 9 and 11, with x = 8 being most frequent among the species examined. While obviously including several distantly related lineages, the x = 8 species have distributions that are concentrated in the centre of diversity of the genus in southwest China. We identified two ‘species-pairs’ (Leontopodium dedekensii–L. sinense and L. souliei–L. calocephalum) in which the tetraploid species has more vigorous growth, but is confined geographically to the centre of diversity. The diploid species ascend to generally higher elevations and extend more towards the Tibetan Plateau. In contrast, our data also suggest range expansions in other polyploid species, such as the hexaploid Leontopodium ochroleucum extending into the mountains of Central Asia. Deviations from x = 8 are found at the edges of the wide Eurasian distribution of the genus. These may relate to subsequent range expansions into the Himalayas, northern Asia, the Far East, and a far disjunctive expansion to the mountains of Europe. This implies an increased ability of these species to colonise mountain floras and adapt to different environmental conditions. Thus, formation of higher ploidy levels in general might be significant for a successful radiation process.
Ecology joins forces with quantum theory on the pages of “Quantum Ecology” to create a holistic approach in energy studies. The infusion of quantum theoretical principles allows the study focus of ecological energetics to shift from the conventional calorific (trophic) flow in ecosystems to the potential energy structure of the vegetation. The books contents cover the theory and techniques in a unique account centred on the energy equation. The equation’s component terms define energy footprints specific to ecology’s basic processes, such as historic phylogeny, current environmental mediation of transience, and chance. What gives practical value to the energy equation is its ability to be parameterised by the usual type of survey or experimental data.
Availability:
Orlóci, L. 2015. Quantum Ecology. The energy structure and its analysis. SCADA Publishing, Canada. Order Online Edition from: https://createspace.com/5750582 or 4406077
Alternative source for information: https://sites.google.com/site/statisticalecology/
Whole genome duplication (WGD), which gives rise to polyploids, is a unique type of mutation that duplicates all the genetic material in a genome. WGD provides an evolutionary opportunity by generating abundant genetic "raw material," and has been implicated in diversification, speciation, adaptive radiation, and invasiveness, and has also played an important role in crop breeding. However, WGD at least initially challenges basic biological functions by increasing cell size, altering relationships between cell volume and DNA content, and doubling the number of homologous chromosome copies that must be sorted during cell division. Newly polyploid lineages often have extensive changes in gene regulation, genome structure, and may suffer meiotic or mitotic chromosome mis-segregation. The abundance of species that persist in nature as polyploids shows that these problems are surmountable and/or that advantages of WGD might outweigh drawbacks. The molecularly especially tractable Arabidopsis genus has several ancient polyploidy events in its history and contains several independent more recent polyploids. This genus can thus provide important insights into molecular aspects of polyploid formation, establishment, and genome evolution. The ability to integrate ecological and evolutionary questions with molecular and genetic understanding makes comparative analyses in this genus particularly attractive and holds promise for advancing our general understanding of polyploid biology. Here, we highlight some of the findings from Arabidopsis that have given us insights into the origin and evolution of polyploids.
Questa memoria è dedicata alla discussione sul modo di origine delle razze triploidi, esaploidi e ottoploidi di Sisymbrium irlo.
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