Browsing by Author "Vieira, Vasco Manuel Nobre de Carvalho da Silva"
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- Controles demográficos da estrutura populacional de algas de ciclo de vida bifásico: caso de estudo de Gelidium sesquipedalePublication . Vieira, Vasco Manuel Nobre de Carvalho da Silva; Santos, Orlando PimentaGelidium sesquipedale é uma alga vermelha com um ciclo de vida bifásico haplo-diplóide. Esta alga, tal como muitas outras do mesmo tipo, têm demonstrado possuir um rácio de abundâncias desigual, estável ou instável, entre as gerações isomórficas gametófita e tetrasporófita: o rácio G:T.
- What drives distinct ploidy phases of isomorphic biphasic life cycles to occur at uneven abundancesPublication . Vieira, Vasco Manuel Nobre de Carvalho da Silva; Santos, RuiThroughout the history of eukariotic primary producers, namely the plant and algae, there was an evolution of the life cycles along with their morphological and physiological complexity and role on the ecosystems. The earlier, simpler ones, namely the bryophytes, have haploid life cycles. The most complex and evolved ones, namely the vascular plants, have diploid life cycles. In between there is a whole range of taxa with haploid-diploid life cycles. It most often occurs in brown or red algae. In the former the ploidy phases are heteromorphic whereas in the latter are frequently isomorphic, which raises the question about the reasons for their unbalanced occurrence in their habitats when these are expected to be even as a consequence of isomorphicity. The hypothesis that have been proposed may be resumed to two: (i) ploidy dissimilarities in their fecundities as a consequence of the differential cytological processes of spore production; and (ii) ploidy dissimilarities in growth and survival, of both spores and fronds, as a consequence of a conditional differentiation required to the stability and evolution of their biphasic life cycles. However, there is a gap between the hypotheses proposed and the observed pattern of phase dominance as the link has not been proved so far. The objective of the present thesis is to help filling this gap by establishing how ploidy dissimilarities in the life cycle may generate effective uneven abundances that match the observed in the field. To do that the thesis is divided into six chapters. In the first chapter there is a general introduction to the subject. In the second chapter it was accessed how different types of vital rates may be generally efficient, or inefficient, forcing functions upon the pattern of ploidy phase dominance. In the third chapter it was accessed how efficiently the different types of vital rates may impose a geographical variability of ploidy dominance like the ones reported for a few species. In the forth chapter it was accessed how the life cycle response to time instability is dependent on the ploidy dissimilarities in the vital rates, and how time variability may surge even in stable environments. In the fifth chapter it was accessed how efficiently, or inefficient, the different types of vital rates may impose an intra-population pattern of ploidy dominance with a fine resolution both over space and time, as it has been reported in the literature. In the sixth chapter are the final conclusions. It was found that ploidy phase dissimilarities upon the survival rates of the fronds and/or upon the performance of the spores are the most efficient and likeliest drives for the patterns of ploidy phase dominance observed in the field.