Karenia brevis, le dinoflagellé produisant des brevetoxines (PbTx), est la principale espèce d’efflorescences d’algues toxiques dans le Golfe du Mexique. Les effets de cette algue sur Mercenaria mercenaria et Crassostrea virginica sont méconnus tandis que les efflorescences coïncident avec la période de reproduction de ces espèces. Ce projet avait pour but de déterminer les effets i) d’une exposition à K. brevis en laboratoire et naturelle de terrain sur les processus physiologiques associés à la reproduction de M. mercenaria et C. virginica, et ii) d’une exposition à K.brevis sur la qualité et le développement des gamètes, embryons et larve de ces espèces. Suite à l'exposition des adultes de clams et d’huîtres à K. brevis, les paramètres physiologiques de la reproduction ont été affectés. La présence de PbTx dans les tissus des gamètes et le potentiel transfert maternel de PbTx à la progénie via les ovocytes, pourraient avoir entraîné les effets négatifs observés lors du développement larvaire.Les effets négatifs similaires causés par l'exposition des stades précoces à différentes préparations de cellules de K. brevis suggèrent que d'autres composés toxiques, en plus de PbTx, pourraient être impliqués dans la toxicité et, que la majorité des effets délétères se produisent durant les divisions embryonnaires.Le clam et l’huître américaine sont sensibles à K. brevis. Les effets négatifs sur les adultes et jeunes stades de vie, combinés à une exposition quasi-annuelle aux efflorescences de K. brevis, pourraient engendrer des perturbations majeures sur le recrutement des populations de ces espèces importantes, et avoir des répercussions environnementales et économiques. / The brevetoxin (PbTx) producing dinoflagellate, Karenia brevis is the most prevalent harmful algal bloom species in the Gulf of Mexico. The effects of this alga on Mercenaria mercenaria and Crassostrea virginica are poorly understood yet, blooms typically overlap with periods of reproduction and spawning in these species.The aims of this project were to determine the effects of i) laboratory and field exposure of K. brevis on the reproductive and related physiological processes of adult M. mercenaria and C. virginica and the quality of the offspring that were produced and ii) K. brevis exposure on gamete, embryo and larval development in these species.Following exposure of adult clams and oysters to K. brevis, negative effects were recorded on reproductive and physiological parameters. PbTx was recorded in gamete tissues, and maternal transfer of this PbTx to the offspring via the oocytes, may have resulted in the significant negative effects recorded on larval development up to the end of the lecithotrophic phase.The similar dose-dependent negative effects caused by direct exposure of gamete and early life stages to different cell preparations of K. brevis suggests that other toxic compounds in addition to PbTx may be involved in toxicity and, that the majority of negative effects occur during embryonic divisions.Hard clams and eastern oysters are susceptible to K. brevis exposure. The negative effects on adult and early life stages combined with the near- annual exposure to blooms of K. brevis could cause significant bottle-necks on the recruitment and population dynamics of these important species and, have wider reaching environmental and economic impacts.

This thesis was conducted to evaluate important epidemiological features of Gastro-Intestinal Nematode (GIN) infections in Ontario sheep flocks; namely, the PeriParturient Egg Rise (PPER), overwintering of GIN free-living stages on pasture, and Anthelmintic Resistance (AR). Three main studies were carried out: a longitudinal study was conducted on six sheep farms to evaluate the PPER in ewes lambing in different seasons and to determine whether total plasma protein (TPP) levels and packed cell volume (PCV) were associated with increased fecal GIN-egg shedding. Secondly, a pilot-study was conducted on three farms to describe pasture-level environmental conditions and over-wintering survival and infectivity of free-living GIN larvae, especially Haemonchus contortus. Lastly, a cross-sectional study was conducted on 47 sheep farms in Ontario, to evaluate the frequency of AR, compare different diagnostic tests for AR, and evaluate management practices associated with AR. In the longitudinal study, the PPER was observed in winter, spring and autumn lambing ewes, though the magnitude and distribution of the PPER varied with season. Lower TPP and PCV values were associated with increased fecal GIN-egg counts. The pilot-study suggested that H. contortus larvae did not overwinter successfully on pasture, while other GINs, such as Teladorsagia sp., Trichostrongylus spp. and Nematodirus spp., were able to overwinter on pasture, and were infective the following spring. Resistance to ivermectin, fenbendazole and levamisole was demonstrated on 97% (28/29), 95% (19/20) and 6% (1/17) respectively of the farms tested; most of the resistance observed was found in Haemonchus sp. The Fecal Egg Count Reduction percentage following treatment was influenced by which mean (i.e. arithmetic vs. geometric) was used in the formula; use of pre-treatment in addition to post-treatment faecal egg counts was not influential. Both the fecal egg count reduction test and the larval development assay diagnosed resistance, but there was poor agreement between the two tests, as indicated by the Kappa test. The prior use of benzimidazoles on farms was associated with higher levels of fenbendazole resistance. The information generated in this thesis will be used to develop a parasite control program for sheep flocks in Ontario and to guide future research on GIN parasitism. / New Directions - Ontario Ministry of Agriculture, Food and Rural Affairs; Ontario Sheep Marketing Agency; Ontario Agriculture Centre Canada; Merial; Animal Health Strategic Initiative - University of Guelph Partnership; Undergraduate Research Assistantship; Gartshore Memorial Sheep Scholarship;

Orientador: Claudio José Von Zuben / Banca: Aricio Xavier Linhares / Banca: Wesley Augusto Conde Godoy / Resumo: A ordem Diptera desperta grande interesse nos estudos científicos devido à importância agrícola, sanitária, veterinária e forense, dependendo da espécie em estudo. A espécie Chrysomya megacephala (Fabricius) foi introduzida há cerca de 30 anos no Brasil e é de considerável importância médico-sanitária, além de poder ser utilizada em estudos forenses, na estimativa de intervalo pós-morte (IPM) em humanos. A espécie Musca domestica (Linnaeus) tem distribuição cosmopolita e é bastante comum no ambiente urbano e pode também transportar formas infectantes de muitas doenças. Nessas moscas, após o desenvolvimento dos imaturos em substratos discretos e efêmeros, as larvas abandonam o substrato alimentar em busca de um sítio para pupação, processo chamado de dispersão larval pós-alimentar. No entanto, em ambiente natural, tanto a fonte alimentar como o substrato de pupação podem estar contaminados com substâncias químicas, sendo que algumas destas podem ser de interesse forense ou ser aplicadas no controle de pragas. Assim, o principal objetivo do presente trabalho é procurar dar contribuição a um melhor conhecimento dos efeitos do ansiolítico Diazepam [Diazepam NQ® 10mg] sobre o desenvolvimento larval e comportamento de dispersão larval e do inseticida Fipronil [Regent 800 WG®] sobre a dispersão pós-alimentar das larvas de duas espécies de moscas (C. megacephala e M. domestica). Na análise do desenvolvimento larval, pôde-se observar que a presença de Diazepam no substrato alimentar aumenta o tempo de desenvolvimento larval, retardando o ganho de massa por tempo nas duas espécies estudadas, quando se compara ao grupo controle. Já o comportamento de dispersão larval foi alterado na presença de Fipronil ou de Diazepam, em relação ao controle, sendo que a profundidade de enterramento e a distância das pupas do centro de irradiação... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Some species of Diptera have a great medical and veterinary importance, acting as vectors of many diseases, addiction of having a considerable agricultural, commercial and ecological importance and other ones having forensic importance. Flies utilize discrete and ephemeral breeding sites for larval nutrition. After the exhaustion of food, larvae begin dispersing in search of sites to pupate or to additional food sources, a process referred as post feeding larval dispersal. However, in natural environments these breeding or feeding sites can be contaminated with chemical substances. Some of these substances can be of forensic interest or be applied in pest control. In the present study, the main objective was to investigate the effect of Diazepam® [Diazepam NQ® 10mg] and Fipronil® [Regent 800 WG®] on immature stages of Chrysomya megacephala (Diptera: Calliphoridae) and Musca domestica (Diptera: Muscidae). The larvae were reared on artificial diet and rabbit liver on which different dosages of Diazepam were administrated in order to study the effects of this drug on the development and post feeding larval dispersal of the two species. Different dosages of the insecticide Fipronil were disposed in circular arena used as pupation substrate to investigate the effects on post feeding larval dispersal. The results showed that time required for larval development were significantly longer in colonies fed in contact with Diazepam than in the control ones, delaying the increase of mass per unit time in the two studied species. The larval dispersal behavior was modified in the presence of Fipronil and Diazepam, in comparison to arenas without the drugs. It was also observed that the burial depth and distance of the irradiation center were shorter than in the control groups for the two species... (Complete abstract click electronic address below) / Mestre

Made available in DSpace on 2014-06-11T19:30:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-08-17Bitstream added on 2014-06-13T18:40:14Z : No. of bitstreams: 1 gomes_g_me_rcla.pdf: 2270133 bytes, checksum: d4e2f6bb8bc021e8025a823eb3f7a791 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A ordem Diptera desperta grande interesse nos estudos científicos devido à importância agrícola, sanitária, veterinária e forense, dependendo da espécie em estudo. A espécie Chrysomya megacephala (Fabricius) foi introduzida há cerca de 30 anos no Brasil e é de considerável importância médico-sanitária, além de poder ser utilizada em estudos forenses, na estimativa de intervalo pós-morte (IPM) em humanos. A espécie Musca domestica (Linnaeus) tem distribuição cosmopolita e é bastante comum no ambiente urbano e pode também transportar formas infectantes de muitas doenças. Nessas moscas, após o desenvolvimento dos imaturos em substratos discretos e efêmeros, as larvas abandonam o substrato alimentar em busca de um sítio para pupação, processo chamado de dispersão larval pós-alimentar. No entanto, em ambiente natural, tanto a fonte alimentar como o substrato de pupação podem estar contaminados com substâncias químicas, sendo que algumas destas podem ser de interesse forense ou ser aplicadas no controle de pragas. Assim, o principal objetivo do presente trabalho é procurar dar contribuição a um melhor conhecimento dos efeitos do ansiolítico Diazepam [Diazepam NQ® 10mg] sobre o desenvolvimento larval e comportamento de dispersão larval e do inseticida Fipronil [Regent 800 WG®] sobre a dispersão pós-alimentar das larvas de duas espécies de moscas (C. megacephala e M. domestica). Na análise do desenvolvimento larval, pôde-se observar que a presença de Diazepam no substrato alimentar aumenta o tempo de desenvolvimento larval, retardando o ganho de massa por tempo nas duas espécies estudadas, quando se compara ao grupo controle. Já o comportamento de dispersão larval foi alterado na presença de Fipronil ou de Diazepam, em relação ao controle, sendo que a profundidade de enterramento e a distância das pupas do centro de irradiação... / Some species of Diptera have a great medical and veterinary importance, acting as vectors of many diseases, addiction of having a considerable agricultural, commercial and ecological importance and other ones having forensic importance. Flies utilize discrete and ephemeral breeding sites for larval nutrition. After the exhaustion of food, larvae begin dispersing in search of sites to pupate or to additional food sources, a process referred as post feeding larval dispersal. However, in natural environments these breeding or feeding sites can be contaminated with chemical substances. Some of these substances can be of forensic interest or be applied in pest control. In the present study, the main objective was to investigate the effect of Diazepam® [Diazepam NQ® 10mg] and Fipronil® [Regent 800 WG®] on immature stages of Chrysomya megacephala (Diptera: Calliphoridae) and Musca domestica (Diptera: Muscidae). The larvae were reared on artificial diet and rabbit liver on which different dosages of Diazepam were administrated in order to study the effects of this drug on the development and post feeding larval dispersal of the two species. Different dosages of the insecticide Fipronil were disposed in circular arena used as pupation substrate to investigate the effects on post feeding larval dispersal. The results showed that time required for larval development were significantly longer in colonies fed in contact with Diazepam than in the control ones, delaying the increase of mass per unit time in the two studied species. The larval dispersal behavior was modified in the presence of Fipronil and Diazepam, in comparison to arenas without the drugs. It was also observed that the burial depth and distance of the irradiation center were shorter than in the control groups for the two species... (Complete abstract click electronic address below)

Cette étude a pour but de comparer la reproduction et le recrutement des coraux entre les récifs subtropicaux d'Afrique du Sud et les récifs tropicaux de la Réunion représentant des milieux contrastés. D'autres part, afin de simuler le réchauffement climatique, l'effet de l'augmentation de la température de l'eau en aquarium a été testé sur le développement des larves et les juvéniles de coraux. Les deux espèces étudiées, Acropora austera et Platygyra daedalea ont un mode de reproduction (hermaphrodite ‘pondeur’), un développement des gamètes (5-6 mois) et une période de reproduction (d'Octobre à Février) similaires en Afrique du Sud et à la Réunion. La fécondité de ces coraux est néanmoins supérieure en Afrique du Sud par rapport à la Réunion. Les deux espèces produisent 43-100% plus d'ovocytes en Afrique du Sud qu'à la Réunion. Le taux de recrutement des coraux est aussi supérieur sur les récifs subtropicaux d'Afrique du Sud (548 recrues m2 an-1) comparé à ceux de la Réunion (305 recrues m2 an-1). Le recrutement est dominé par les Pocilloporidae dans les deux régions, suivis par les Acroporidae en Afrique du Sud et les Poritidae à la Réunion. En Afrique du Sud, l'augmentation de la température de l'eau de 2°C a une influence négative sur le développement larvaire du sensible A. austera alors que P. daedalea est plus vigoureux et supporte des températures de 4°C supérieures à la normale (30°C). À la Réunion, le faible taux de fécondité et de recrutement semble être un indicateur de perturbation des récifs. Au contraire en Afrique du Sud, l'effort de reproduction des coraux et l'important approvisionnement en larves, associés à la faible anthropisation des récifs, pourraient favoriser l'adaptation des coraux aux changements climatiques dans une certaine limite. / Coral reproduction and recruitment in Scleractinia were compared between the subtropical reefs of South Africa and the tropical reefs of Reunion to assess variations between contrasting environments. In addition, coral larvae and juvenile polyps were exposed to elevated temperature in aquarium to simulate global warming. The two targeted species, Acropora austera and Platygyra daedalea, exhibited the same reproductive mode (hermaphroditic broadcast spawner), gamete development (5-6 months) and breeding seasonality (October to February) in South Africa and Reunion. Coral fecundity was nevertheless higher in South Africa than in Reunion. A. austera and P. certaine limite.AbstractCoral reproduction and recruitment in Scleractinia were compared between the subtropical reefs of South Africa and the tropical reefs of Reunion to assess variations between contrasting environments. In addition, coral larvae and juvenile polyps were exposed to elevated temperature in aquarium to simulate global warming. The two targeted species, Acropora austera and Platygyra daedalea, exhibited the same reproductive mode (hermaphroditic broadcast spawner), gamete development (5-6 months) and breeding seasonality (October to February) in South Africa and Reunion. Coral fecundity was nevertheless higher in South Africa than in Reunion. A. austera and P. daedalea produced respectively 43 and 100% more oocytes per polyp than their Reunion counterparts. The recruitment rate was also higher on the subtropical reefs of South Africa (548 recruits m2 year-1) compared to Reunion (305 recruits m2 year-1). Recruitment was dominated by Pocilloporidae at the two localities, followed by Acroporidae in South Africa and Poritidae in Reunion. In South Africa, an increase in sea temperature of 2°C strongly affected the larval development of the sensitive A. austera, while the more robust P. daedalea sustained temperatures up to 4°C (i.e. 30°C) above ambient. In Reunion, diminished fecundity and recruitment rate seemed to be an indicator of reef perturbation. In contrast in South Africa, the high reproductive effort and larval supply in corals associated with the low levels of disturbance on the reefs may favour coral adaptation, to some extent, under global change.

Les plantes envahissantes sont considérées comme l'une des plus grandes menaces sur les espèces, mais leurs impacts sur les amphibiens demeurent peu connus. L’objectif de ce projet est de déterminer l’effet de l’établissement du roseau commun (Phragmites australis) sur la répartition des amphibiens et sur leur développement larvaire. Il est présumé que cette plante s'accapare l'espace et les ressources disponibles en produisant une importante biomasse, qu’elle peut modifier l’hydrologie des marais et la structure des communautés d’amphibiens. J’ai évalué les facteurs influençant la répartition des amphibiens selon les caractéristiques des étangs et du paysage dans 50 sites envahis ou non à divers degrés. Des expériences ont également été menées afin d’étudier les répercussions de trois densités de roseau sur des têtards de la Grenouille des bois (Lithobates sylvaticus) et sur la qualité de son habitat. Mes résultats suggèrent que le roseau à forte densité ralentit le développement larvaire de la grenouille des bois et influence les assemblages phytoplanctoniques. Cependant, il n’y a aucune relation entre la densité de la plante et la survie, la morphologie des têtards et les caractéristiques biotiques et abiotiques de l’eau. Dans notre aire d’étude, le paysage autour des étangs a une plus grande influence sur la répartition des amphibiens que l'établissement du roseau. Toutefois, la probabilité d’assèchement est plus élevée lorsque la plante est établie en grande quantité, ce qui, si l’envahissement s’intensifie, aura un effet néfaste sur la survie des têtards et mettra en péril la persistance des populations. / Invasive plants are considered one of the greatest threats to species, but their impact on amphibians is still poorly understood. The objective of this project is to determine the effect of the establishment of common reed (Phragmites australis) on amphibian distribution and larval development. It is thought that this plant monopolizes space and resources by producing a large biomass, and may alter wetland hydrology and amphibian community structure. I evaluated the factors influencing amphibian distribution according to the characteristics of ponds and the surrounding landscape in 50 sites invaded or not by reeds to varying degrees. Experiments were also conducted to study the impacts of three reed densities on wood frog tadpoles (Lithobates sylvaticus) and the quality of their habitat. My results suggest that high reed density slows wood frog larval development and influences phytoplankton assemblages. However, there is no relationship between, plant density and survival, tadpole morphology and water biotic and abiotic characteristic. In our study area, the landscape surrounding ponds has a greater influence on amphibian distribution than does reed establishment. However, the desiccation probability is higher when the plant is established in high quantities, which, if the invasion intensifies, will have an adverse effect on tadpole survival and therefore population persistence.

Les plantes envahissantes sont considérées comme l'une des plus grandes menaces sur les espèces, mais leurs impacts sur les amphibiens demeurent peu connus. L’objectif de ce projet est de déterminer l’effet de l’établissement du roseau commun (Phragmites australis) sur la répartition des amphibiens et sur leur développement larvaire. Il est présumé que cette plante s'accapare l'espace et les ressources disponibles en produisant une importante biomasse, qu’elle peut modifier l’hydrologie des marais et la structure des communautés d’amphibiens. J’ai évalué les facteurs influençant la répartition des amphibiens selon les caractéristiques des étangs et du paysage dans 50 sites envahis ou non à divers degrés. Des expériences ont également été menées afin d’étudier les répercussions de trois densités de roseau sur des têtards de la Grenouille des bois (Lithobates sylvaticus) et sur la qualité de son habitat. Mes résultats suggèrent que le roseau à forte densité ralentit le développement larvaire de la grenouille des bois et influence les assemblages phytoplanctoniques. Cependant, il n’y a aucune relation entre la densité de la plante et la survie, la morphologie des têtards et les caractéristiques biotiques et abiotiques de l’eau. Dans notre aire d’étude, le paysage autour des étangs a une plus grande influence sur la répartition des amphibiens que l'établissement du roseau. Toutefois, la probabilité d’assèchement est plus élevée lorsque la plante est établie en grande quantité, ce qui, si l’envahissement s’intensifie, aura un effet néfaste sur la survie des têtards et mettra en péril la persistance des populations. / Invasive plants are considered one of the greatest threats to species, but their impact on amphibians is still poorly understood. The objective of this project is to determine the effect of the establishment of common reed (Phragmites australis) on amphibian distribution and larval development. It is thought that this plant monopolizes space and resources by producing a large biomass, and may alter wetland hydrology and amphibian community structure. I evaluated the factors influencing amphibian distribution according to the characteristics of ponds and the surrounding landscape in 50 sites invaded or not by reeds to varying degrees. Experiments were also conducted to study the impacts of three reed densities on wood frog tadpoles (Lithobates sylvaticus) and the quality of their habitat. My results suggest that high reed density slows wood frog larval development and influences phytoplankton assemblages. However, there is no relationship between, plant density and survival, tadpole morphology and water biotic and abiotic characteristic. In our study area, the landscape surrounding ponds has a greater influence on amphibian distribution than does reed establishment. However, the desiccation probability is higher when the plant is established in high quantities, which, if the invasion intensifies, will have an adverse effect on tadpole survival and therefore population persistence.

[ES] Los ácidos grasos de cadena muy larga (VLC-FA; >C24), aunque presentes en pequeñas cantidades, juegan un importante papel para el correcto desarrollo y funcionalidad de los tejidos neurales en vertebrados, especialmente durante su desarrollo temprano. Sin embargo, a pesar de su aparente importancia, los estudios sobre estos compuestos en peces son escasos. La biosíntesis de los VLC-FA se lleva a cabo mediante las denominadas proteínas de elongación de los ácidos grasos de cadena muy larga 4 (Elovl4) y, en consecuencia, la dotación y la función de estas enzimas determinan la capacidad endógena que una determinada especie tiene para satisfacer las demandas fisiológicas de VLC-FA, especialmente durante su desarrollo temprano. Además, esta producción endógena de los ácidos grasos poliinsaturados de cadena muy larga (VLC-PUFA) es dependiente de los sustratos. Así, para su biosíntesis se requiere de ácidos grasos más cortos, es decir ácidos grasos poliinsaturados de cadena larga (LC-PUFA; C20-24) que actúen como precursores, los cuales son incorporados principalmente a través de la dieta. Teniendo esto en mente, el presente trabajo de investigación tuvo como objetivos caracterizar los genes elovl4 en dorada (Sparus aurata) y en lenguado senegalés (Solea senegalensis), determinar la función de sus correspondientes proteínas codificadas, así como analizar el patrón de expresión tisular de elovl4. Además, se ha investigado la regulación nutricional de los genes implicados en la biosíntesis de VLC-PUFA (elovl4a, elovl4b) y LC-PUFA (fads2, elovl5) durante las primeras etapas del ciclo de vida de ambas especies (larvas y poslarvas), mediante el uso de dietas adaptadas a cada etapa del desarrollo. Los resultados confirmaron que ambas especies de peces poseen dos genes elovl4 distintos, denominados elovl4a y elovl4b según su homología con sus ortólogos de pez cebra. Asimismo, los ensayos funcionales de sus correspondientes proteínas, llevados a cabo en levaduras, indicaron que tanto Elovl4a como Elovl4b tienen la capacidad de elongar los ácidos grasos precursores (C20-24) hasta VLC-FA en ambas especies. Sin embargo, Elovl4b mostró mayor actividad que Elovl4a para elongar todos los ácidos grasos poliinsaturados a productos de cadena más larga, especialmente de la serie n-3. Además, los resultados de expresión génica indicaron que, aunque fueron detectados transcritos de elovl4 en la mayoría de los tejidos analizados, ambos genes elovl4 se expresaron más intensamente en los tejidos neurales de ambas especies, como el cerebro y los ojos, que mostraron los niveles de expresión más altos de elovl4a y elovl4b, respectivamente. Además, los resultados procedentes de los ensayos de regulación nutricional indicaron que los genes fads2, elovl5, elovl4a y elovl4b pueden ser regulados a través del contenido en LC-PUFA presente en la dieta. Es importante destacar que elovl4a y elovl4b fueron regulados de manera distinta según las hipotéticas necesidades de VLC-PUFA asociadas, de manera específica, con cada etapa del desarrollo temprano y dependiendo de disponibilidad dietaria de LC-PUFA. Estos hallazgos pueden contribuir a alcanzar una mejor comprensión de la vía biosintética de los VLC-FA en los teleósteos marinos, resaltando así el papel crucial que los productos de Elovl4 desempeñan para el correcto desarrollo y mantenimiento de las funciones neurofisiológicas durante las primeras etapas del desarrollo de los peces. Asimismo, estos resultados pueden ayudar a esclarecer el mecanismo molecular que controla la biosíntesis de VLC-PUFA, así como a establecer sus requerimientos específicos a lo largo del desarrollo de los teleosteos marinos en función de la especie. De esta manera, se abre la posibilidad de incorporar con éxito fuentes lipídicas alternativas a través de una programación nutricional temprana que estimule la biosíntesis de los VLC-PUFA durante las primeras etapas de alimentación exógena. / [CA] Els àcids grassos de cadena molt llarga (VLC-FA; >C24), encara que presents en petites quantitats, juguen un important paper per al correcte desenvolupament i funcionalitat dels teixits neurals en vertebrats, especialment durant el seu desenvolupament inicial. No obstant, malgrat la seua aparent importància, els estudis sobre aquests compostos en peixos son escassos. La biosíntesi dels VLC-FA es porta a terme mitjançant les denominades proteïnes d'elongació dels àcids grassos de cadena molt llarga 4 (Elovl4) i, en conseqüència, la dotació i la funció d'aquests enzims determinen la capacitat endògena que una determinada espècie té per a satisfer les demandes fisiològiques de VLC-FA, especialment durant el seu desenvolupament inicial. A més, aquesta producció endògena dels àcids grassos poliinsaturats de cadena molt llarga (VLC-PUFA) és depenent dels substrats. Així, per a la seua biosíntesi es requereix d'àcids grassos més curts, és a dir àcids grassos poliinsaturats de cadena llarga (LC-PUFA; C20-24) que actuen com a precursors, els quals són incorporats principalment a través de la dieta. Tenint això en compte, el present treball de recerca va tindre com a objectius caracteritzar els gens elovl4 en orada (Sparus aurata) i llenguado (Solea senegalensis), determinar la funció de les seues corresponents proteïnes codificades, així com analitzar el patró d'expressió tissular de elovl4. A més, es va investigar la regulació nutricional dels gens implicats en la biosíntesi de VLC-PUFA (elovl4a, elovl4b) i LC-PUFA (fads2, elovl5), durant les primeres etapes del cicle de vida d'ambdues espècies (larves i poslarves), mitjançant l'ús de dietes adaptades a cada etapa del desenvolupament. Els resultats van confirmar que totes dues espècies de peixos posseeixen dos gens elovl4 diferents, denominats elovl4a i elovl4b segons la seua homologia amb els seus ortòlegs en peix zebra. Així mateix, els assajos funcionals de les corresponents proteïnes, duts a terme en llevats, van indicar que tant Elovl4a com Elovl4b tenen la capacitat d'elongar els àcids grassos precursors (C20-24) fins a VLC-FA en totes dues espècies. No obstant això, Elovl4b va mostrar major activitat que Elovl4a per a elongar tots els àcids grassos poliinsaturats (substrats) fins a productes de cadena més llarga, especialment de la sèrie n-3. A més, els resultats d'expressió gènica van indicar que, encara que van ser detectats trànscrits de elovl4 en la majoria dels teixits analitzats, tots dos gens elovl4 es van expressar més en teixits neurals de totes dues espècies, com el cervell i els ulls, que van mostrar els nivells d'expressió més alts d'elovl4a i elovl4b, respectivament. A més, els resultats procedents dels assajos de regulació nutricional van indicar que els gens fads2, elovl5, elovl4a i elovl4b poden ser regulats a través del contingut en LC-PUFA present en la dieta. És important destacar que elovl4a i elovl4b van ser regulats de manera diferent segons les hipotètiques necessitats de VLC-PUFA associades, de manera específica, amb cada etapa del desenvolupament inicial i depenent de la disponibilitat dietaria de LC-PUFA. Aquestes troballes poden contribuir a tenir una millor comprensió de la via biosintètica dels VLC-FA en els teleostis marins, ressaltant així el paper crucial que els productes d'Elovl4 exerceixen en el correcte desenvolupament i manteniment de les funcions neurofisiològiques durant les primeres etapes del desenvolupament dels peixos. De la mateixa forma, aquests resultats poden ajudar a esclarir el mecanisme molecular que controla la síntesi endògena de VLC-PUFA, així com a establir els requisits específics de cada espècie al llarg del desenvolupament dels teleostis marins. D'aquesta manera, s'obri la possibilitat d'incorporar amb èxit fonts lipídiques alternatives a través d'una programació nutricional inicial que estimuli la biosíntesi de VLC-PUFA durant les primeres etapes d'alimentació exògena. / [EN] Very long-chain fatty acids (VLC-FA; >C24), although present in small amounts, play important roles for the correct development and functionality of neural tissues, especially during early development of vertebrates. However, despite their putative importance, their study in fish is scarce. Biosynthesis of VLC-FA is carried out by the so-called elongation of very long-chain fatty acid 4 (Elovl4) proteins and, consequently, the complement and function of these enzymes determine the endogenous capacity that a given species has for satisfying the physiological demands for VLC-FA, especially during its early development. Moreover, this endogenous production of very long-chain polyunsaturated fatty acid (VLC-PUFA) is substrate-dependent. Therefore, shorter fatty acid precursors, i.e. long-chain polyunsaturated fatty acids (LC-PUFA; C20-24), are required. These nutrients are mostly incorporated by the diet and their bioavailability can influence the capacity of Elovl4 for satisfying the physiological VLC-PUFA demands in marine fish. Thus, nutritional regulation of elovl4, as well as other elongase and desaturase genes involved in LC-PUFA biosynthesis (elovl5, fads2) has been proposed as a strategy to enhance endogenous production of LC-PUFA and VLC-PUFA in fish farming. The present thesis aimed to characterize elovl4 genes from the marine teleosts Sparus aurata and Solea senegalensis, to determine the function of the corresponding encoded proteins, and to analyze the tissue expression pattern of these genes. Moreover, we investigated the nutritional regulation of genes involved in the biosynthesis of the VLC-PUFA (elovl4a, elovl4b) and the LC-PUFA (fads2, elovl5) in early life-cycle stages (larvae and post-larvae) of both fish species fed diets adapted to each development stage. Live preys were supplied to larvae (early and late larvae) and microdiets for post-larvae, with a variable content in VLC-PUFA precursors, i.e. LC-PUFA. The results confirmed that both fish species possess two distinct elovl4 genes termed as elovl4a and elovl4b based on their homology to the zebrafish orthologs. Functional assays of the corresponding proteins in yeast denoted that Elovl4a and Elovl4b from both species have the capability to elongate C20-24 fatty acid precursors to VLC-FA products. However, Elovl4b appeared to have a higher activity than Elovl4a elongating all the polyunsaturated fatty acid substrates assayed to longer chain polyunsaturated products, especially those of the n-3 series. Moreover, gene expression results indicated that, although elovl4 transcripts were detected in most of the tissues analyzed, elovl4 genes were more strongly expressed in the neural tissues of both species, such as brain and eyes, which showed the highest expression levels of elovl4a and elovl4b, respectively. Furthermore, the results from nutritional regulation assays denoted that fads2, elovl5, elovl4a and elovl4b genes could be regulated by the dietary LC-PUFA content. It is important to highlight that elovl4a and elovl4b genes were differently regulated according to the species-specific VLC-PUFA putative needs, associated with each early life-stage and the LC-PUFA dietary availability. Importantly, these findings can contribute to a better understanding of the VLC-FA biosynthetic pathway in marine teleosts, highlighting the crucial role that the Elovl4 products carry out for the correct development and maintenance of neurophysiological functions during early stages of the fish development. Therefore, these results can help to elucidate the molecular mechanism controlling the VLC-PUFA biosynthesis and their species-specific requirements along the marine fish development, opening the possibility to incorporate successfully alternative lipid sources, through an early nutritional programming that stimulates the VLC-PUFA biosynthesis during the first exogenous feeding stages. / Para desarrollarel trabajo de investigación descrito en esta memoria, Miguel Torres Rodríguez recibió una beca predoctoral de la Excma. Diputación de Castellón. / Torres Rodríguez, M. (2021). Estudio de los patrones de expresión de genes implicados en la síntesis de ácidos grasos de cadena muy larga durante el desarrollo de la dorada y el lenguado, y su regulación nutricional [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/166619 / TESIS