"Sex-ratio" citoplasmatico em Drosophila melanogaster
Horacio Montenegro
TESE
Português
(Broch.)
T/UNICAMP M764s
[Cytoplasmatic sex-ratio in Drosophila melanogaster]
Campinas, SP : [s.n.], 2005.
67p. : il.
Orientador: Louis Bernard Klaczko
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
Resumo: Elementos genéticos egoístas são partículas herdáveis de etiologia e mecanismos de ação variados, mas com a caracterítica em comum de modificar a segregação mendeliana dos alelos em favor próprio, aumentando a própria freqüência. Elementos citoplásmaticos egoístas são um caso especial de...
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Resumo: Elementos genéticos egoístas são partículas herdáveis de etiologia e mecanismos de ação variados, mas com a caracterítica em comum de modificar a segregação mendeliana dos alelos em favor próprio, aumentando a própria freqüência. Elementos citoplásmaticos egoístas são um caso especial de elementos genéticos egoístas, como são herdados apenas pelo citoplasma materno, eles sofrem seleção para causar desvios na proporção sexual, em favor de um excesso de fêmeas. A proporção sexual nas progênies de organismos que se reproduzem sexualmente é, em geral, 1.___.__)LVKHU________SURS{V_D_SULPHLUD_H[SOLFDoão baseada em seleção natural para esta proporção. O princípio de Fisher prediz que o sexo mais raro tem maior valor adaptativo, pois sua contribuição média por indivíduo é maior. Assim, a seleção favorecerá alelos que aumentem a freqüência do sexo raro nas progênies. Quando a proporção chegar a 1.___.__indivíduos dos dois sexos terão o mesmo valor adaptativo. Parasitas reprodutivos, endosimbiontes herdados maternalmete, representam a maior parte dos elementos citoplasmáticos egoístas, e uma das causas mais comuns de desvios à proporção de 1.___.__ Agentes androcidas, endossimbiontes que matam os embriões machos, são um destes parasitas reprodutivos. Como conseqüência, a proporção sexual da prole das fêmeas infectadas afasta-se de 1.___.__apresentando excesso ou totalidade de fêmeas. Agentes androcidas foram encontrados em mais de 40 espécies de 6 ordens de insetos. Várions táxons de bactérias já foram associados com o fenótipo, e a filogenia dos parasitas e hospedeiros não é congruente, indicando transmissão horizontal freqüente. Neste trabalho, estudamos o agente androcida de Drosophila melanogaster, descrito recentemente. Sistemática molecular mostrou que trata-se de uma bactéria do gêneroSpiroplasma, muito próxima ao agente androcida encontrado em D. nebulosa. As seqüências comparadas (3000 pares de base, representando seqüências parciais de 3 genes) são idênticas, portanto, as duas bactérias têm um ancestral comum muito recente. De fato, possivelmente as duas espécies de Drosophila só entraram em contato há 4 ou 5 séculos, com a expansão mundial de D. melanogaster, e a transmissão do Spiroplasma de D. nebulosa para D. melanogaster deve ter ocorrido depois disso. Em uma coleta em Recife, foi encontrado que 2,3% das fêmeas estavam infectadas com Spiroplasma; outro parasita reprodutivo, a bactéria Wolbachia (que causa incompatibilidade citoplasmática) infectava 96% das fêmeas. Além disso, as duas bactérias co-infectavam os mesmos indivíduos, uma observação até agora incomum para parasitas reprodutivos com fenótipos diferentes. Como parasitas reprodutivos tem transmissão exclusivamente materna, seu valor adaptativo é altamente correlacionado com o das fêmeas hospedeiras. Desta forma, espera-se que parasitas reprodutivos não tenham efeitos deletérios no valor adaptativo das fêmeas hospedeiras, ou até que sejam benéficos. Por outro lado, a eficiência de transmissão ou a intensidade do fenótipo de manipulação reprodutiva podem estar positivamente correlacionados com a densidade de bactérias no hospedeiro, de forma que parasitas mais eficientes causem efeitos deletérios no valor adaptativo da fêmea. Para verificar se existem efeitos de Spiroplasma e Wolbachia no valor adaptativo de fêmeas, medimos a viabilidade larval e a fecundidade de fêmeas adultas, comparando com a de fêmeas não-infectadas. Nenhuma das duas características parece ser afetada por Spiroplasma ou Wolbachia, nem por infecção com as duas bactérias simultaneamente. Finalmente, foi verificado que temperaturas baixas (em torno de 16,5°C) interrompem a transmissão do agente androcida para a progênie das moscas infectadas
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Abstract: Selfish genetic elements are inheritable particles with diverse ethiology and mechanisms, but sharing the fact that they modify the Mendelian segregation for their own benefit, thus increasing their own frequency. Selfish cytoplasmic elements are a special instance of selfish genetic...
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Abstract: Selfish genetic elements are inheritable particles with diverse ethiology and mechanisms, but sharing the fact that they modify the Mendelian segregation for their own benefit, thus increasing their own frequency. Selfish cytoplasmic elements are a special instance of selfish genetic elements, as they are inherited only by maternal cytoplasm, they suffer strong selection to alter the sexual proportion, in direction to an excess of females. The usual sexual proportion in sexually reproducing organisms is 1.___.__)LVKHU________ was the first to propose an explanation based on the natural selection for this proportion. Fisher¿s
principle predicts that, if one of the sexes is rarer, it will have higher fitness, because its individual average contribution will be larger. Thereafter, selection will favour alleles that increase the frequencies of the rarer sex in broods. When the proportion reaches 1.___.__both sexes will have the same fitness. Reproductive parasites, maternally inherited endosymbionts, are the majority of selfish cytoplasmic elements, and one of the most common causes of departures from the 1.___._sexual proportion. Male killers, endosymbionts that kill male embryos, are one of these reproductive parasites. Consequently, the sexual proportion of infected females deviates from 1.___.__towards an excess or totality of females. Male killers have been found in more than 40 species of 6 insect orders. Several bacterial taxa have been associated with male-killing phenotype, and the phylogeny of parasites ad hosts is not congruent, indicating frequent horizontal transmission. In this work, we studied the recently described male killer agent found in Drosophila melanogaster. Molecular systematics showed that this agent is a Spiroplasma bacterium, closely related to the D. nebulosa male-killer. The compared sequences (3000 base pairs, partial sequence from 3 genes) are identical, thus both bacteria share a very recent common ancestral. Indeed, only since D. melanogaster worldwide expansion, 4 or 5 centuries ago, both Drosophila
species overlap in their distribution, and the Spiroplasma transmission from D. nebulosa to D. melanogaster probably occurred after this. In one collection in Recife, Spiroplasma has been found infecting 2.3% of all females, another reproductive parasite, the bacterium Wolbachia (which causes cytoplasmic incompatibility) infected 96% of all females. Wolbachia was also found co-infecting flies alongside with Spiroplasma, a rather uncommon observation for reproductive parasites with different phenotypes. As reproductive parasites have exclusively maternal transmission, their fitness is highly correlated with its female host fitness. Consequently, it is expected that reproductive parasites do not pose deleterious fitness effects to their female hosts, or even be beneficial. However, transmission efficiency or the intensity of the reproductive manipulation phenotype could be
positively correlated to the bacterial load on the host, in a way that more efficient parasites will have a deleterious fitness effect on females. In order to verify if Spiroplasma and Wolbachia have any kind of fitness effects on female hosts, we assessed larval viability and fecundity of adult females, in relation to uninfected females. Both characteristics showed signs of being affected by Spiroplasma or Wolbachia, nor by double-infection with both bacteria. Finally, low temperature (approximately 16.5°C) interrupts transmission of the male killing agent to the progeny of infected females Ver menos
principle predicts that, if one of the sexes is rarer, it will have higher fitness, because its individual average contribution will be larger. Thereafter, selection will favour alleles that increase the frequencies of the rarer sex in broods. When the proportion reaches 1.___.__both sexes will have the same fitness. Reproductive parasites, maternally inherited endosymbionts, are the majority of selfish cytoplasmic elements, and one of the most common causes of departures from the 1.___._sexual proportion. Male killers, endosymbionts that kill male embryos, are one of these reproductive parasites. Consequently, the sexual proportion of infected females deviates from 1.___.__towards an excess or totality of females. Male killers have been found in more than 40 species of 6 insect orders. Several bacterial taxa have been associated with male-killing phenotype, and the phylogeny of parasites ad hosts is not congruent, indicating frequent horizontal transmission. In this work, we studied the recently described male killer agent found in Drosophila melanogaster. Molecular systematics showed that this agent is a Spiroplasma bacterium, closely related to the D. nebulosa male-killer. The compared sequences (3000 base pairs, partial sequence from 3 genes) are identical, thus both bacteria share a very recent common ancestral. Indeed, only since D. melanogaster worldwide expansion, 4 or 5 centuries ago, both Drosophila
species overlap in their distribution, and the Spiroplasma transmission from D. nebulosa to D. melanogaster probably occurred after this. In one collection in Recife, Spiroplasma has been found infecting 2.3% of all females, another reproductive parasite, the bacterium Wolbachia (which causes cytoplasmic incompatibility) infected 96% of all females. Wolbachia was also found co-infecting flies alongside with Spiroplasma, a rather uncommon observation for reproductive parasites with different phenotypes. As reproductive parasites have exclusively maternal transmission, their fitness is highly correlated with its female host fitness. Consequently, it is expected that reproductive parasites do not pose deleterious fitness effects to their female hosts, or even be beneficial. However, transmission efficiency or the intensity of the reproductive manipulation phenotype could be
positively correlated to the bacterial load on the host, in a way that more efficient parasites will have a deleterious fitness effect on females. In order to verify if Spiroplasma and Wolbachia have any kind of fitness effects on female hosts, we assessed larval viability and fecundity of adult females, in relation to uninfected females. Both characteristics showed signs of being affected by Spiroplasma or Wolbachia, nor by double-infection with both bacteria. Finally, low temperature (approximately 16.5°C) interrupts transmission of the male killing agent to the progeny of infected females Ver menos
Klaczko, Louis Bernard, 1953-
Orientador
Loreto, Élgion Lúcio da Silva
Avaliador
Carvalho, Antonio Bernardo de
Avaliador
Solferini, Vera Nisaka, 1957-
Avaliador
Peixoto, Alexandre Afranio
Avaliador
Reis, Sérgio Furtado dos, 1952-
Avaliador
"Sex-ratio" citoplasmatico em Drosophila melanogaster
Horacio Montenegro
"Sex-ratio" citoplasmatico em Drosophila melanogaster
Horacio Montenegro
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