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Thesis by publication. / Thesis (PhD) -- Macquarie University, School of Biological Sciences, 1990. / Bibliography: leaves 269-324. / Introduction -- Models of parental allocation -- Sex expression in homosporous pteridophytes -- The origin of heterospory -- Pollination and the origin of the seed habit -- Brood reduction in gymnosperms -- Pollination: costs and consequences -- Adaptive explanations for the rise of the angiosperms -- Parent-specific gene expression and the triploid endosperm -- New perspectives on the angiosperm female gametophyte -- Overview -- Glossary -- Kinship terms in plants -- Literature Cited. / Among vascular plants/ different life cycles are associated with characteristic ranges of propagule size. In the modern flora, isospores of homosporous pteridophytes are almost all smaller than 150 urn diameter, megaspores of heterosporous pteridophytes fall in the range 100-1000 urn diameter, gymnosperm seeds are possibly all larger than the largest megaspores, but the smallest angiosperm seeds are of comparable size to large isospores. -- Propagule size is one of the most important features of a sporophyte's reproductive strategy. Roughly speaking, larger propagules have larger food reserves, and a greater probability of successful establishment, than smaller propagules, but a sporophyte can produce more smaller propagules from the same quantity of resources. Different species have adopted very different size-versus-number compromises. The characteristic ranges of propagule size, in each of the major groups of vascular plants, suggest that some life cycles are incompatible with particular size-versus-number compromises. -- Sex expression in homosporous plants is a property of gametophytes (homosporous sporophytes are essentially asexual). Gametophytes should produce either eggs or sperm depending on which course of action gives the greatest chance of reproductive success. A maternal gametophyte must contribute much greater resources to a young sporophyte than the paternal gametophyte. Therefore, smaller gametophytes should tend to reproduce as males, and gametophytes with abundant resources should tend to reproduce as females. Consistent with these predictions, large female gametophytes release substances (antheridiogens) which induce smaller neighbouring ametophytes to produce sperm. -- The mechanism of sex determination in heterosporous species appears to be fundamentally different. Large megaspores develop into female gametophytes, and small icrospores develop into male gametophytes. Sex expression appears to be determined by the sporophyte generation. This is misleading. As argued above, the optimal sex expression of a homosporous gametophyte is influenced by its access to resources. This is determined by (1) the quantity of food reserves in its spore and (2) the quantity of resources accumulated by the gametophyte's own activities. If a sporophyte produced spores of two sizes, gametophytes developing from the larger spores' would be more likely to reproduce as females than gametophytes developing from the smaller spores, because the pre-existing mechanisms of sex determination would favor production of archegonia by larger gametophytes. Thus, the predicted mechanisms of sex determination in homosporous species could also explain the differences in sex expression of gametophytes developing from large and small spores in heterosporous species. / Megaspores of living heterosporous pteridophytes contain sufficient resources for female reproduction without photosynthesis by the gametophyte (Platyzoma excepted), whereas microspores only contain sufficient resources for male reproduction. Furthermore, many more microspores are produced than megaspores. A gametophyte's optimal sex expression is overwhelmingly determined by the amount of resources supplied in its spore by the sporophyte, and is little influenced by the particular environmental conditions where the spore lands. Gametophytes determine sex expression in heterosporous species, as well as homosporous species. A satisfactory model for the evolution of heterospory needs to explain under what circumstances sporophytes will benefit from producing spores of two distinct sizes. -- In Chapter 4, I present a model for the origin of heterospory that predicts the existence of a "heterospory threshold". For propagule sizes below the threshold, homosporous reproduction is evolutionarily stable because gametophytes must rely on their own activities to accumulate sufficient resources for successful female reproduction. Whether a gametophyte can accumulate sufficient resources before its competitors is strongly influenced by environmental conditions. Gametophytes benefit from being able to adjust their sex expression in response to these conditions. For propagule sizes above the threshold, homosporous reproduction is evolutionarily unstable, because the propagule's food reserves are more than sufficient for a "male" gametophyte to fertilize all eggs within its neighbourhood. A population of homosporous sporophytes can be invaded by sporophytes that produce a greater number of smaller spores which could land in additional locations and fertilize additional eggs. Such'spores would be male-specialists on account of their size. Therefore, both spore types would be maintained in the population because of frequency-dependent selection. -- The earliest vascular plants were homosporous. Several homosporous groups gave rise to heterosporous lineages, at least one of which was the progeniture of the seed plants. The first heterosporous species appear in the Devonian. During the Devonian, there was a gradual increase in maximum spore size, possibly associated with the evolution of trees and the appearance of the first forests. As the heterospory threshold was approached, the optimal spore size for female reproduction diverged from the optimal spore size for male reproduction. Below the threshold, a compromise spore size gave the highest fitness returns to sporophytes, but above the threshold, sporophytes could attain higher fitness by producing two types of spores. -- The evolution of heterospory had profound consequences. Once a sporophyte produced two types of spores, microspores and megaspores could become specialized for male and female function respectively. The most successful heterosporous lineage (or lineages) is that of the seed plants. The feature that distinguishes seed plants from other heterosporous lineages is pollination, the capture of microspores before, rather than after, propagule dispersal. Traditionally, pollination has been considered to be a major adaptive advance because it frees sexual reproduction from dependence on external fertilization by freeswimming sperm, but pollination has a more important advantage. In heterosporous pteridophytes, a megaspore is provisioned whether or not it will be fertilized whereas seeds are only provisioned if they are pollinated. / The total cost per seed cannot be assessed solely from the seed's energy and nutrient content. Rather, each seed also has an associated supplementary cost of adaptations for pollen capture and of resources committed to ovules that remain unpollinated. The supplementary cost per seed has important consequences for understanding reproductive strategies. First, supplementary costs are expected to be proportionally greater for smaller seeds. Thus, the benefits of decreasing seed size (in order to produce more seeds) are reduced for species with small seeds. This effect may explain minimum seed sizes. Second, supplementary costs are greater for populations at lower density. Thus, there is a minimum density below which a species cannot maintain its numbers. -- By far the most successful group of seed plants in the modern flora are the angiosperms. Two types of evidence suggest that early angiosperms had a lower supplementary cost per seed than contemporary gymnosperms. First, the minimum size of angiosperm seeds was much smaller than the minimum size of gymnosperm seeds. This suggests that angiosperms could produce small seeds more cheaply than could gymnosperms. Second, angiosperm-dominated floras were more speciose than the gymnosperm-dominated floras they replaced. This suggests that the supplementary cost per seed of angiosperms does not increase as rapidly as that of gymnosperms, as population density decreases. In consequence, angiosperms were able to displace gymnosperms from many habitats, because the angiosperms had a lower cost of rarity. -- Angiosperm embryology has a number of distinctive features that may be related to the group's success. In gymnosperms, the nutrient storage tissue of the seed is the female gametophyte. In most angiosperms, this role is taken by the endosperm. Endosperm is initiated by the fertilization of two female gametophyte nuclei by a second sperm that is genetically identical to the sperm which fertilizes the egg. Endosperm has identical genes to its associated embryo, except that there are two copies of maternal genes for every copy of a paternal gene. -- Chapter 9 presents a hypothesis to explain the unusual genetic constitution of endosperm. Paternal genes benefit from their endosperm receiving more resources than the amount which maximizes the fitness of maternal genes, and this conflict is expressed as parent-specific gene expression in endosperm. The effect of the second maternal genome is to increase maternal control of nutrient acquisition. -- Female gametophytes of angiosperms are traditionally classified as monosporic, bisporic or tetrasporic. Bisporic and tetrasporic embryo sacs contain the derivatives of more than one megaspore nucleus. Therefore, there is potential for conflict between the different nuclear types within an embryo sac, but this possibility has not been recognized by plant embryologists. In Chapter 10, I show that many previously inexplicable observations can be understood in terms of genetic conflicts within the embryo sac. / Mode of access: World Wide Web. / 324 leaves ill

CAPES / As fruteiras nativas vêm ganhando atenção pelos produtores e consumidores, já que são consideradas como alimento funcional. No caso da pitangueira, é uma das únicas fruteiras nativas com plantio comercial, sendo atualmente, explorada pela indústria de sucos e de cosméticos. Para a indústria, em geral, é importante que os frutos da pitangueira apresentem o máximo rendimento de polpa. Entretanto, os frutos desta fruteira não possuem tal característica, por produzirem geralmente sementes grandes comparativamente, ao tamanho dos frutos. Contudo, foi identificado na coleção de fruteiras nativas da UTFPR - Câmpus Dois Vizinhos um genótipo produtor de pitangas sem sementes, o que pode revolucionar o mercado, atraindo mais fruticultores interessados em seu plantio. Porém, as causas desta característica devem ser elucidadas para que se possa futuramente, lançar no mercado, genótipos produtores de frutos com qualidade superior e sem sementes. O objetivo deste trabalho foi buscar elucidar as possíveis causas da apirenia em pitangueira (Eugenia uniflora L) e caracterizar comparativamente a qualidade do fruto produzido pela mesma . Os trabalhos foram realizados nos Laboratórios de Microscopia e de Fisiologia Vegetal e, na área da coleção de frutas nativas da UTFPR – Câmpus Dois Vizinhos – Paraná e, na Estação experimental de Aula Dei (Zaragoza, Espanha). Foram utilizados genótipos de pitangueira (E. uniflora L.) que produzem frutos com e sem sementes (pirênicos e apirênicos, respectivamente), pertencentes à coleção da referida Instituição. Foram realizados experimentos envolvendo a biologia floral e reprodutiva da pitangueira; feitos cortes histológicos para descrição da embriogênese e ontogênese; níveis de ploidia e avaliação da qualidade de frutos. Pode-se constatar que o acesso apirênico, em muitas características não se diferenciou do acesso pirênico, mas foi verificado que este último tem maior período de floração e frutificação, maior número de polén por flor, comparado ao acesso apirênico. O acesso apirênico encontrado poderá servir de base para cruzamentos dirigidos no melhoramento genético da cultura, buscando-se novos híbridos, com essa característica, pois seus frutos apresentaram qualidades que permitem enquadrá-las para dupla finalidade. / The native fruit trees have gained attention by producers and consumers, already that it is consider as functional food. In the case of Surinan Cherry tree, it is one of native fruit trees with commercial cultive, it being currently exploited by the juice and cosmetics industry. For the industry, in general, it is important that the Surinan Cherry fruit to present the maximum pulp content. However, the fruits of this specie do not have this characteristic, because they generally produce large seeds comparatively to the fruit size. Nevertheless, there is a genotype that produces fruit withou seed from UTFPR - Câmpus Dois Vizinhos, Paraná State, Brazil, what to change the market, and itcan attracted more fruit growers interested its cultive. But, the causes of this characteristic have to be elucidated for in the future for it be posible have in the market genotypes producing fruit quality superior and without seed. The aim of this work was to elucidate the causes of fruit without seed in the Surinan Cherry (Eugenia uniflora L) and its fruit quality was comparated with of the other Surinan Cherry trees. The works were carried out at the Microscopy and Plant Physiology Laboratories and at the native fruit collection area from UTFPR - Câmpus Dois Vizinhos - Paraná State, Brazil. In addition, to have works at Aula Dei Experimental Station (Zaragoza, Spain). Genotypes of Surinan cherry (Eugeia uniflora L.), which produce fruits with and without seeds (pirenics and apirenic, respectively) it was studied. Experiments were carried out involving floral and reproductive biology of Surinan cherry tree; it was realized histological sections for description of embryogenesis and ontogenesis; levels of ploidy and evaluation of the fruit quality. It can to be observed that the apirenic genotype in many characteristics was not different to pirenic genotype. It was verified that the pirenic genotype presented a longer period of flowering and fruiting and, presented a higher number of pollen by flower compared to apirenic genotype. The apirenic genotype can to serve as a basis for crosses directed in the fruit breeding of Surinan cherry, to try obtaining new hybrids, with this characteristic, already that, this fruit present quality to in nature or industry market.