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

Apomixis (asexual reproduction by seeds) has the considerable potential in agriculture and crop breeding due to its ability to produce genetically identical progenies in a form of persistent propagules, i.e. seeds. However, the processes laying behind the origin of apomixis and connected molecular mechanisms are still unknown. Despite the fact, that apomicts are considered to be an evolutionary dead-ends, they are often more widely distributed than their sexual relatives (this phenomenon is commonly referred to as geographical parthenogenesis (GP). Although this phenomenon is studied for decades, its causes are still not fully understood. Importantly, several recent studies pointed out that apomicts with limited genetic variability can at some extent react to changing environment through changes in gene transcription by epigenetic modifications. It is generally assumed, that hybridisation and polyploidization played a crucial role in the emergence of apomixis. For this reason, presented studies test the putative origin of selected polyploid apomicts and if the interspecific hybridisation between diploid sexuals triggers polyploidization using predominantly polyploid and apomictic genus Hieracium s. str. Surprisingly, the presented study demonstrates the hybrid origin of almost all investigated...

Les systèmes reproducteurs déterminent comment le matériel génétique est transmis d’une génération à la suivante […]. Les espèces qui combinent de la reproduction sexuée et asexuée/clonale sont très répandues [… mais] l’effet de leur système reproducteur sur leur évolution reste énigmatique et discuté.L’objectif de cette thèse est de modéliser la dynamique des fréquences génotypiques d’une population avec une combinaison de reproduction sexuée et/ou clonale dans des cycles de vie principalement diploïdes [. … Un] modèle du type chaine de Markov avec temps et états discrets sert de base mathématique pour décrire [leurs] changements […] au cours du temps.Les résultats montrent que la reproduction partiellement asexuée peut en effet modifier la dynamique de la diversité génomique par rapport à une reproduction strictement sexuée ou strictement asexuée. […] L’histoire démographique a un rôle important pour les organismes partiellement clonaux et doit être prise en compte dans toute analyse […].Cette thèse fait des recommandations pour la collecte des données et une hypothèse de base pour l’interprétation des données de génétique/génomique […]. Ces résultats ont des retombées dans plusieurs domaines, allant de la recherche fondamentale […] à des applications en agriculture […], pêche […] et protection de la nature […]. / Reproductive systems determine how genetic material is passed from one generation to the next, making them an important factor for evolution. Organisms that combine sexual and asexual/clonal reproduction are very widespread [… yet] the effects of their reproductive system on their evolution are still controversial and poorly understood.The aim of this thesis was to model the dynamics of genotype frequencies under combined sexual/clonal reproduction in dominantly diploid life cycles [. … A] state and time discrete Markov chain model served as the mathematical basis to describe [their] changes […] through time.The results demonstrate that partial clonality may indeed change the dynamics of genomic diversity compared to either exclusively sexual or exclusively clonal populations. […] Time has a crucial role in partially clonal populations and needs to be taken into account in any analysis of their genomic diversity.This thesis provides recommendations for data collection and a null hypothesis for the interpretation of population genetic/genomic data […]. Moreover, it includes new methods for the analysis of genotype-based population genetic Markov chain models. These results have a high potential relevance in several areas, ranging from basic research […] to applications in agriculture […], fisheries […] and nature conservation […].