Resumen de Caracterización del género Pseudo-nitzschia en la Costa Catalana
Within the diatoms group, the genus Pseudo-nitzschia has raised interest for their capacity to produce domoic acid, a potent neurotoxin that causes ASP, (Amnesic Shellfish Poisoning). This thesis presents the study of the diversity of species of the genus Pseudo-nitzschia in the Catalan Coast (Mediterranean Sea) of the years 2005- 2007. The study has required a revision of their taxonomy for what has been used diverse tools as the morphology, molecular characterization and the study of the sexual compatibility to determine the existence of cryptic and semi-cryptic species.
In this thesis we obtained 72 clonal cultures, 8 of them, species described in the area for the first time. Also, 2 species of Pseudo-nitzschia have been identified in field samples.
Complementary studies of this strians have allowed to gain taxonomy information in the genus, therefore the clones of the laboratory were characterized through the optic and electronic microscopy, the sequence of the internal transcribers space ITS I, ITS II and 5.8S rDNA, the pigment analysis as well the studies of the growth rates, reduction of the cellular size and the study of the sexual compatibility. Taking all these characteristics the species are described in an unequivocal way. One of the main conclusions of this thesis is that all future material dedicated to the characterization of the genus Pseudo-nitzschia should include information of the morphotypes and genotypes as well as the system of sexual compatibility.
Several aspects have been described of the life cycle of the isolated species (e.g. fine structures of gametes, auxospores and cellular size) and a new form of sexuality has been described for the first time in the genus Pseudo-nitzschia. The genus Pseudo- nitzschia was considered heterothallic, but the P. brasiliana presents a homothallic sexual reproduction. For the first time, the auxopore development is described and formation of the initial cells in this species. It is proposed that the homothallism would be a desirable adaptation for this species which appears occasionally and in low densities in the Catalan Coast.
It is postulated that during the bloom of Pseudo-nitzschia sexual reproduction should occur, supporting the fact that during the proliferation the average size of the organisms increases. During the proliferations, only by means of the sexual reproduction, the maximum cells size can be recovered and it allows the species to maintain an appropriate physiologically's size. We propose the cell size in the genus Pseudo- nitzschia as indicator of in situ sexuality.
The proliferations of the genus Pseudo-nitzschia has been characterized in the Catalan Coast. Environmental factors such as temperature, salinity, inorganic nutrients do not seem to modulate the proliferations of Pseudo-nitzschia in the coastal area.
Nevertheless, the results obtained in the coastal area can not be generalised. The biotical and abiotical factors that accompany the blooms of the Pseudo-nitzschia species in an area such as the Delta of the Ebro, have been described for the first time. In this area, two statistically different groups were defined, one formed by winter samples and another for summer-autumn samples. The first one defined by high concentrations of NO3 and low concentrations of NH4, being these conditions associated to high abundance of P. delicatissima and low of P. calliantha. In the second group we find the opposed characteristics The study of the growth rates allows us to conclude that the species of the genus Pseudo-nitzschia can change between, quick growth, when conditions are good to favour a proliferation, to a slow rate of growth under adverse conditions. The species can be considered r-strategists. Regarding the beginning of the proliferations, a low density of organisms or diffuse basal population should exist, so that in case of good conditions an exponential growth begins.
The correct identification of the species has allowed us to conclude that there is a great diversity in the genus Pseudo-nitzschia in the Catalan coast. Two species (P. brasiliana, P. linea) have been detected for the first time in the sea Mediterranean and other 5 new detections in the Catalan coast (P. caciantha, P. calliantha, P. fraudulenta, P. galaxiae and P. multistriata). We discuss the implications in the distribution from the species to level of the Mediterranean and biogeography of the genus.
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