Orientadores: Sandra Maria Carmello-Guerreiro, Simone de Padua Teixeira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-09T03:29:24Z (GMT). No. of bitstreams: 1 Cortez_PriscilaAndressa_M.pdf: 142634667 bytes, checksum: 533aad1a400f13a4d678be944c37b495 (MD5) Previous issue date: 2007 / Resumo: Miconia albicans (Melastomataceae) mostrou-se uma espécie com agamospermia obrigatória do tipo diplosporia e viabilidade polínica nula em populações do Cerrado e da Floresta Atlântica. A inviabilidade polínica não esteve restrita a um único estádio de desenvolvimento dos andrófitos e a principal anormalidade observada nas anteras de flores em pré-antese foi a deformidade das células reprodutivas, principalmente aquelas em estádio de andrósporos livres. A intensa vacuolação das células androsporogênicas e tapetais, bem como a precoce degeneração das células do tapete, podem ser características relacionadas à esterilidade masculina da espécie. A ontogenia dos estratos parietais diferiu da observada em outros membros do gênero, corroborando a sua classificação como irregular. Anteras em estádio de pré-deiscência apresentaram a região de deiscência coberta por uma provável epiderme com características distintas daquela observada no restante da mesma. Diferenças ambientais foram observadas apenas na quantidade de células encontradas nas anteras de flores em pré-antese, cerca de 50% maior nos indivíduos provenientes do Cerrado. A ontogenia do óvulo e do ginófito se assemelhou àquela observada em outras espécies do gênero, exceção feita a divisão da célula arquesporial e a supressão da meiose em M. albicans. Os embriões agamospérmicos foram originados no interior do ginófito, a partir da oosfera ou de uma das duas sinérgides. Evidências sugerem que o endosperma autônomo do tipo nuclear foi originado por expansões de cada um dos núcleos da célula central, e não por sua fusão. A porcentagem de aborto de óvulos na espécie foi de cerca de 50% e as sementes maduras produzidas apresentaram uma porcentagem de germinação bastante variável, provavelmente em decorrência da alta incidência de fungos observada nos experimentos realizados. Os frutos formados em botões florais apresentaram características semelhantes às observadas nas demais unidades, incluindo a viabilidade das sementes / Abstract: Miconia albicans (Melastomataceae) is a species with diplosporic obligate agamospermy and no pollen viability in ¿Cerrado¿ and Atlantic Forest vegetations. The sterility of pollen grains wasn¿t restricted to one developmental stage and the major abnormality of the cells from pre-anthesis flower anthers was the deformation of the reproductive cell wall, mainly in the free microspore stage. Intense vacuolation of both sporogenous and tapetal cells as well as the precocious degeneration of the tapetal cells may be related to male sterility in this species. The ontogeny of the parietal layers was different from that observed in another species of the genus and was in agreement with its classification of irregular type. The anthers in predehiscence stage showed the dehiscence region probable closed with an epidermis with papilous cells, differently from that observed in the another anther regions. Ambient differences were restricted to the number of cells observed in the pre-anthesis anthers, which was about 50 percent up in the Atlantic Forest vegetation in relation to the Cerrado one. The ovule and embryo sac ontogeny was similar to that observed in another species of the genus, except for the division of the arquesporic cell and the suppression of the meiotic division during the gametogenesis, both observed only in M. albicans. The agamospermous embryos were originated in the embryo sac from the egg cell or one of two synergids. Evidence suggested that the nuclear autonomous endosperm was originated from expansions in both nucleus of the central cell, and not from the fusion of both. The percentage of ovule abortion was about 50 percent and the mature seeds showed a variable germination percentage probably due to fungi incidence which occurred in the seeds from both environments. The ontogenetic characteristics observed in fruits from both floral buds and flowers were similar, as well as the seeds viability / Mestrado / Biologia Vegetal / Mestre em Biologia Vegetal

Orientadores: Sandra Maria Carmello-Guerreiro, Simone de Padua Teixeira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-15T16:53:33Z (GMT). No. of bitstreams: 1 Caetano_AnaPauladeSouza_M.pdf: 5552395 bytes, checksum: ddd2d3795d5da107ef405fe68e7a02a3 (MD5) Previous issue date: 2010 / Resumo: Em Miconia fallax, uma espécie apomítica, e Miconia pepericarpa, uma espécie sexuada, os processos de esporogênese e gametogênese apresentam diversas características semelhantes, muitas delas compartilhadas com outros membros da família Melastomataceae. Entretanto, apesar das similaridades, algumas diferenças foram observadas. Em relação à antera, o formato da célula generativa no grão de pólen maduro é fusiforme em M. pepericarpa e esférico em M. fallax. Além disso, a quantidade de grãos de pólen viáveis produzidos é marcadamente menor na espécie apomítica. Quanto ao óvulo, as diferenças encontradas são ainda mais marcantes. Em M. fallax, células denominadas iniciais apospóricas se diferenciam juntamente com as células-mãe de megásporos, levando à formação de mais de um saco embrionário. Assim, enquanto M. fallax apresenta até três sacos embrionários no óvulo maduro, sendo um sexuado e até dois apospóricos, M. pepericarpa exibe apenas um saco embrionário. Além disso, na espécie apomítica M. fallax, constatou-se a formação de embriões adventícios em sementes jovens. Provavelmente, o desenvolvimento de embriões a partir dos sacos embrionários apospóricos juntamente com a formação do embrião zigótico e adventício levam à poliembrionia em M. fallax, com formação de até quatro embriões em uma mesma semente. Das diferenças encontradas entre as duas espécies, apenas o formato da célula generativa não foi relacionado à apomixia, sendo um caráter específico. Já as demais diferenças, são características exclusivas de M. fallax, e estão diretamente relacionadas à apomixia, sendo elas: 1) formação de uma proporção menor de grãos de pólen viáveis; 2) diferenciação de células iniciais apospóricas; 3) formação de múltiplos sacos embrionários; 4) desenvolvimento de embriões apomíticos; 5) poliembrionia. A espécie apomítica M. fallax é poliplóide e, neste caso, a viabilidade polínica baixa pode ser explicada pela ocorrência de alterações na meiose, comuns em espécies poliplóides. A poliembrionia, também tem sido bastante relacionada à apomixia, sendo esta relação confirmada pelos dados obtidos neste trabalho. Além disso, com os resultados alcançados, foi possível reconhecer que M. fallax é uma apomítica facultativa, uma vez que, além da possibilidade de produção de embriões apomíticos, a espécie ainda preserva os mecanismos de formação de grãos de pólen e sacos embrionários sexuados, com possibilidade de produção de embriões zigóticos. / Abstract: In Miconia fallax, an apomictic species, and Miconia pepericarpa, a sexual species, the processes of gametogenesis and sporogenesis have a number of similar characteristics, many of which are shared with other members of the family Melastomataceae. However, despite the similarities, some differences were observed. Concerning the anther, the generative cell in mature pollen grain is spindle shaped in M. pepericarpa and spherical in M. fallax. Furthermore, the quantity of viable pollen grains produced is markedly lower in apomictic species. Regarding the ovule, differences are even more striking. In M. fallax, cells called aposporous initials differentiate themselves along with the megaspore mother cell, leading to the formation of more than one embryo sac. Thus, while M. fallax exhibit up to three embryo sacs in mature ovule, one being sexed and a maximum of two aposporous, M. pepericarpa displays only one embryo sac. Moreover, in apomictic species M. fallax, we found the formation of adventitive embryos in young seeds. Probably the development of embryos from the aposporous embryo sac parallel to the formation of zygotic and adventitious embryos lead to polyembryony in M. fallax, with formation of up to four embryos in a single seed. About differences found between this two species, only the shape of the generative cell was not related to apomixis, as it is a specific character. The other differences are unique features of M. fallax and are directly related to apomixis, namely: 1) the formation of a smaller proportion of viable pollen grains, 2) the differentiation of aposporous initial cells 3) the formation of multiple embryo sacs, 4) the development of apomictic embryos (adventitious or aposporic), and 5) polyembryony. The apomictic species M. fallax is polyploid, and, in this case, the low pollen viability can be explained by the occurrence of changes in meiosis, common in polyploid species. The polyembryony, has also been frequently related to apomixis, and this relationship is confirmed by data obtained in this work. Furthermore, with these results, it was possible to recognize that M. fallax is a facultative apomictic, since in addition to the possibility of apomictic embryo production the species still preserves the mechanisms of the formation of pollen grain and sexual embryo sac, with the possibility of producing zygotic embryos. / Mestrado / Mestre em Biologia Vegetal

In flowering plants, apomixis is asexual reproduction by seeds. Apomixis allows the production of offspring with the same genetic characteristics as the mother plant. Fertilization is not required. Apomixis could become a tool for naturally cloning high-yielding crop hybrids through their own seed. However, apomixis does not occur in major crop plants, except for citrus. In the present study, genes that might cause apomixis in naturally occurring apomictic plants were investigated. Sexual and apomictic species of the genus Boechera were exposed to stressed and non-stressed conditions. Effects of these treatments on the expression of apomixis was then measured. Stress triggered an increase in the frequency of sexual development in apomictic plants, but continuation of sexual development to form sexual seeds did not occur. Stress also triggered alterations in the expression of stress-related genes.

<p>This dissertation investigates the processes of hybridation, polyploidy, and apomixis and their roles in the evolution of myriopterid ferns. First, I examine patterns of hybridization in members of the Cheilanthes yavapensis complex using a suite of techiniques, ranging from molecules to morphology--including isozymes, spore measurements, and molecular phylogenetics based on chloroplast and nuclear DNA markers--to elucidate relationships in this notorious group of ferns. Second, I utilize the rules of traditional taxonomy set by the International Code of Botanical Nomenclature to recircucmscribe and resurrect the genus Myriopteris from within cheilanthoid ferns. This revised classification is bolstered by results from my molecular phylogenetic analysis of DNA sequence data in the subsequent chapter. Then, using morphological and cytological analyses, I examine the evolution of indument, leaf and rachis shape, vernation, chromosome number, and reproductive mode across the myriopterid tree. In my concluding chapter I develop microsatellite markers for the apomictic triploid, M. lindheiemeri, and explore whether premeiotic chromosome duplication facilitates the production of genetically distinct offspring in this otherwise asexual lineage.</p> / Dissertation

Hieracium lepidulum is an invasive weed in New Zealand. It colonises a wide range of habitats including pine plantations, scrubland, native Nothofagus forest, and mid-altitude to alpine tussock grassland, where it is competing with indigenous species. Understanding the breeding systems and population genetic structure of H. lepidulum is important for biocontrol, and aids in the understanding of evolutionary colonisation processes. H. lepidulum is a triploid, diplosporous, obligate apomict. This type of reproduction through clonal seed does not involve meiosis or fertilisation, and theoretically populations should contain very low levels of genetic variation, the only source being somatic mutation. Common garden experiments and microsatellite markers were used to determine the population genetic structure of H. lepidulum populations in the Craigieburn Range, Canterbury. Both experiments revealed that populations, sampled from three replicate altitudes within three geographically-separated locations, contained no genetic variation; individuals all possessed the same microsatellite genotype. These results strongly suggest that the Craigieburn Range H. lepidulum individuals reproduce solely by apomixis and populations belong to the same clonal lineage. Populations were also examined for their response to two abiotic environmental ‘stresses’, drought and shade. H. lepidulum populations’ exhibited high drought tolerance, yet appeared to be shade-intolerant. Low levels of reproduction in light-limiting habitats will prevent the invasion of H. lepidulum into closed-canopy forest habitats. H. lepidulum appears to have overcome the reduction in fitness associated with apomictic reproduction by phenotypic plasticity, fixed heterozygosity and polyploidy – all associated with increased vigour, fitness, and the ability to occupy broader ecological niches. This study’s results are hopeful for the development of biocontrol programs involving genotype-specific pathogens but suggest that grazing management may not succeed. The data will be useful for future comparisons of genetic structure during the course of H. lepidulum invasions and will contribute to the management of this invasive weed.

No description available.

Background: Over the relatively short period of its evolutionary history, Boechera (Brassicaceae) has undergone rapid radiation that has produced 70+ morphologically distinct, sexual diploids. However, reproductive isolation has moved more slowly than morphological divergence in this group and the diploids appear to hybridize frequently where they coexist. Boechera duchesnensis appears to be the result of hybridization between its putative parents Boechera thompsonii and Boechera formosa. Objectives: The objectives of this study are to (i) analyze and document genetic diversity patterns in the population structure, - including allelic and heterozygosity frequencies - of B. thompsonii and B. formosa in concert with their geographic distribution to determine clustering relationships within these populations, (ii) confirm and expand the morphological characteristics of B. thompsonii and B. formosa, as initially proposed in the literature, including pollen and trichome structure using Scanning Electron Microscopy (SEM) to confirm ploidy level and to determine whether both putative parent species share morphological characteristics with their apomictic diploid offspring, and (iii) use genetic and morphologic evidence to show that B. thompsoii and B. formosa are, in fact, the parents of B. duchesnensis by comparing the genetic diversity patterns, population structure, and morphological characteristics of B. duchesnensis, to those of its proposed putative parents (B. thompsonii and B. formosa) and to confirm that B. duchesnensis shares characteristics of Boechera. Methods: Microsatellite data from 14 loci previously identified in Boechera were used to reexamine the current classifications and taxonomic foundations of three Boechera spp. GenAlEx 6.501 (Peakall and Smouse, 2006, 2012) was used to analyze genetic population structures of two divergent sexual diploids in the genus Boechera: B. thompsonii and B. formosa and to later compare those with the population structure of B. duchesnensis. Geographicaldata were plotted using ArcGIS 10.1 (Esri, 2012) to map heterozygosity distribution. Cluster analysis was run with STRUCTURE 2.3.3 (Pritchard et al., 2000; Falush et al., 2003, 2007) and distribution of allelic diversity and heterozygosity was subsequently compared within each taxon and correlated with geographic distribution characteristics. Resultant data were then compared with B. duchesnensis data to document genetic diversity patterns, population structure, and morphological characteristics. Key Results: Analysis of genetic diversity patterns, allelic distribution of the populations, and heterozygosity of B. thompsonii and B. formosa across their geographic range identified four genetically distinct clusters within B. thompsonii, and one genetically distinct cluster in B. formosa. Allelic frequencies in all four discrete population clusters of B. thompsonii and in one discrete population cluster of B. formosa were close to values found in species on the decline. Reproductive isolation, genetic variability, and allelic frequencies were determined, specimen elevations reported, and morphological characteristics reported in the literature were confirmed and expanded. A codominant genetic analysis performed for 14 different loci for B. duchesnensis against those of its parents showed that B. duchesnensis inherits alleles from both putative parents and confirms B. thompsonii and B. formosa as the parents of B. duchesnensis. Observed levels of heterozygosity of B. thompsonii and B. formosa were lower than expected levels and lower than those of other outcrossing diploids. The mean overall observed heterozygosities for each cluster were determined and documented by geographic location. A substantially higher level of observed heterozygosity in B. duchesnensis (Ho = 0.908) consistent with genetic fixation of a heterozygote and apomixis, supports hybridization as a speciation mechanism and apomixis as a mode of reproduction accounting for genotypic and phenotypic diversity. Morphological characteristics, especially those of pollen and trichomes were confirmed, expanded, and documented with SEM imagery. Discussion: This study provides an analysis of the genetic diversity patterns inherent in the population structure, allelic frequencies, allelic variation among individuals of the rare sexual diploids B. thompsonii, B. formosa, and the apomictic diploid B. duchesnensis in correlation with their geographic distribution. There is an implication of a reproductive barrier, within populations of the same species, that contributes to genetic isolation between clusters. I analyze the tendency of reduced heterozygosity to lead to genetic fixation, reproductive isolation, and how the heightened heterozygosity supports the classification of B. duchesnensis as an apomict. Assessing potential populations that might exist based on similar characteristics could possibly provide inferences about where future research might find similar examples of this hybridization. Reproductive isolation is hypothesized to limit gene flow between identified clusters of B. thompsonii and B. formosa exacerbating low observed heterozygosity levels and low allelic frequency levels. Population studies and cluster analysis have implications for offering future conservation strategies for both taxa.

Polyploidization is exceptionally cosmopolitan in plants. One common observation is that polyploids inhabit larger geographic distributions than their diploid progenitors. Differences in distribution between cytotypes are largely attributed to differences in mating system and ecological breadth among cytotypes. In Crataegus series Douglasianae, allopolyploids have larger ranges than their diploid progenitors. Range size increase is coupled with a shift to predominant asexuality in polyploids. This thesis explores 2 additional hypotheses that may contribute to differences in distribution among cytotypes: ecological breadth and dispersal ability. We find evidence that tetraploid C. douglasii occurs in a wider range of habits and has a greater dispersal ability than diploid C. suksdorfii. Overall, we suggest that differences in mating system, ecological breadth, and dispersal ability have contributed individually and collaboratively to differences in distribution among cytotypes of Crataegus series Douglasianae. Large ranges in polyploids may help maintain cytotype diversity by providing buffering capacity against demographic stochasticity.

Polyploidization is exceptionally cosmopolitan in plants. One common observation is that polyploids inhabit larger geographic distributions than their diploid progenitors. Differences in distribution between cytotypes are largely attributed to differences in mating system and ecological breadth among cytotypes. In Crataegus series Douglasianae, allopolyploids have larger ranges than their diploid progenitors. Range size increase is coupled with a shift to predominant asexuality in polyploids. This thesis explores 2 additional hypotheses that may contribute to differences in distribution among cytotypes: ecological breadth and dispersal ability. We find evidence that tetraploid C. douglasii occurs in a wider range of habits and has a greater dispersal ability than diploid C. suksdorfii. Overall, we suggest that differences in mating system, ecological breadth, and dispersal ability have contributed individually and collaboratively to differences in distribution among cytotypes of Crataegus series Douglasianae. Large ranges in polyploids may help maintain cytotype diversity by providing buffering capacity against demographic stochasticity.

<p>What evolutionary processes and ecological patterns underlie the maintenance of asexual reproduction in natural populations? Although a vast body of literature offers theory to explain the existence of sexual and asexual reproduction, there has been little study of these forms of reproduction in the natural environment. In this dissertation I use a combination of field experiments, greenhouse studies, and genetic techniques to answer this question in the model plant system Boechera. </p><p>In Chapter 1, I review the utility of this system for studying ecological and evolutionary questions in general. Boechera offers an array of genetic and genomic tools, facilitated in part by a close evolutionary relationship with the model plant Arabidopsis thaliana, as well as undisturbed ecology and habitat that extends across much of North America. Additionally, the presence of apomixis (asexual reproduction via parthenogenetic formation of seeds) at the diploid level makes Boechera an ideal system for studying sex without the often-confounding factor of polyploidy; Boechera is one of very few plant groups in which this is possible. </p><p>In Chapter 2, I use a combination of microsatellite markers, flow cytometry, chromosome squashes, and morphological work to characterize apomixis, polyploidy, and species diversity in over 100 natural populations collected from central Idaho and western Montana. As in many other apomictic systems, I find that apomixis in Boechera is strongly linked to hybridization between species or between genetically divergent intraspecific lineages. I then explore associations between apomixis and ecological and topographical variables, as well as variables underlying differentiation between apomictic and sexual lineages. I find that ecological variables associated with apomixis are largely in congruence with the hypothesis of geographic parthenogenesis, and that geographic parthenogenesis is likely driven by the consequences of interspecific hybridization. We also find that apomixis is linked with disturbance and slope, with apomicts occurring in flatter locations than sexuals. </p><p>In Chapter 3, I use a large-scale field experiment comprising three years of data from two cohorts of sexual and asexual lineages to compare fitness between these two groups. I find that, despite herbivory levels that are much higher in apomicts than sexuals, apomictic fitness is consistently higher than sexual. Viability selection strongly favors apomicts, which results in a total fitness advantage for apomicts, despite variable fecundity selection. Selection varies in intensity between cohorts and among gardens. The results of a complementary greenhouse experiment show that the effects of herbivory differ by reproductive mode. Together, these experiments suggest that Red Queen dynamics may contribute to the coexistence of sex and asex in this group.</p><p>In Chapter 4, I use inter- and intraspecific F2 crosses to conduct a greenhouse study and a field experiment to explore the effects of hybridization and heterozygosity on fitness. I find that heterozygosity is favored in the field, with viability selection strongly favoring outcrossed over inbred lineages. However, hybridization results in lower survival, reproduction, and total fitness of interspecific F2 crosses, although hybrids that do reproduce produce more fruits than selfed parental lineages of both species, resulting in fecundity selection for hybrids. It is clear that the benefits of apomixis are due to hybridization, as hybrids are less fit overall. Evidence for both heterosis and outbreeding depression, dependent on lineage and on trait, are found in the field; these phenomena are not clearly associated with geographic distance between parental populations. Ongoing SNP genotyping will facilitate assessment of heterozygosity-fitness correlations as well as correlation of fitness and heterozygosity.</p> / Dissertation