Sequenced diatoms Thalassiosira pseudonana and Phaeodactylum tricornutum belong to the chromist algae harboring secondary plastids, which display distinct evolutionary history when compared to photosynthetic organelles from rhodophytes, green algae and plants. Via secondary endosymbiosis, heterotrophic eukaryotic ancestor of diatoms engulfed red alga, and in addition to the new organelle, it obtained fitness increasing peculiarities in the chimerical cell metabolism and lifestyle. We examined phylogeny and in silico localization of the nuclear-encoded but plastid located enzymes of tryptophan biosynthesis. We suggest that the diatom tryptophan pathway represents an extreme in the trend of plastid (cyanobacterial) enzymes to be replaced by eukaryotic isoforms. In addition, the gene napped during the endosymbiotic gene transfer from the diatom plastid genome to the diatom nucleus (psb28) was described.

Relações de simbiose são comuns na natureza e tornaram-se fundamentais para a desconstrução do antigo conceito de indivíduo, único e indivisível, para o surgimento da ideia do holobionte, definido como o ser constituído de características próprias somadas aos simbiontes a ele associados. Tais relações são comuns em Insecta, sendo bactérias os microrganismos mais comumente encontrados em simbiose, influenciando diversos aspectos bioecológicos do hospedeiro. Dentre os insetos, pulgões são organismos modelos para o estudo de interações com simbiontes devido à associação com diversas espécies de bactérias, as quais produzem diferentes fenótipos do hospedeiro. Este trabalho teve por objetivo avaliar o papel do endossimbionte secundário Arsenophonus nas interações de seu hospedeiro Aphis citricidus (Kirkaldy) (Hemiptera: Aphididae) com o primeiro e terceiro níveis tróficos. Assim, isolinhagens de A. citricidus infectadas (Ars+) ou não (Ars-) por Arsenophonus foram estabelecidas e utilizadas para a condução de estudos comparativos para a exploração de plantas hospedeiras com diferentes valores nutricionais, Citrus sinensis (hospedeiro ótimo) e Murraya paniculata (hospedeiro subótimo). Foram observadas a sobrevivência, longevidade e fecundidade de A. citricidus Ars+ e Ars- em cada planta hospedeira, sendo os valores obtidos utilizados na construção de tabelas de vida de fertilidade. Para o estudo das interações com o terceiro nível trófico, foram realizados estudos comparativos do parasitismo de A. citricidus Ars+ e Ars-, criados em ambos hospedeiros, pelo parasitoide Aphelinus asychis (Walker) (Hymenoptera: Aphelinidae). Foram observados o desenvolvimento do parasitoide e o sucesso de parasitismo. Os resultados obtidos comprovaram ser C. sinensis o hospedeiro mais adequado e que o simbionte secundário beneficia seu hospedeiro na exploração do alimento, resultando na redução do período de desenvolvimento e em insetos de maior tamanho no hospedeiro subótimo. Os parâmetros de tabela de vida de fertilidade calculados para pulgões Ars+ foram superiores aos de Ars-. Além de beneficiar A. citricidus na utilização do alimento, o simbionte Arsenophonus também afetou a relação de seu hospedeiro com o parasitoide A. asychis. Pulgões Ars+ foram inadequados ao completo desenvolvimento do parasitoide. A relação de simbiose de A. citricidus e Arsenophonus estudada demonstrou a importância de simbiontes secundários nas interações multitróficas do hospedeiro e as implicações que elas podem ter para o controle do crescimento populacional de insetos de interesse econômico. / Symbiotic relationships are common in nature and have become essential for the deconstruction of the old concept of individual, as a single and indivisible entity, for the emergence of the holobiont idea, being consisted of its own characteristics added to the symbionts associated with it. Such relationships are common in Insecta, and bacteria are the microorganisms most commonly found in symbiosis, influencing many bioecological aspects of the host. Among insects, aphids are model organisms for the study of interactions with symbionts due to their association with various species of bacteria that produce different host phenotypes. This study aimed to evaluate the role of the secondary endosymbiont Arsenophonus on the interactions of its host Aphis citricidus (Kirkaldy) (Hemiptera: Aphididae) with the first and third trophic levels. Thus, isofemale strains of A. citricidus infected (Ars+) or not (Ars-) with Arsenophonus were established and used to conduct comparative studies on the use of host plants with different nutritional values, Citrus sinensis (optimum host) and Murraya paniculata (suboptimum host). We assessed survival, longevity and fecundity rates of Ars- and Ars+ A. citricidus in each host plant, and the obtained data were used in for calculation of fertility life tables. We also carried out comparative studies on the success of parasitization of Ars- and Ars+ A. citricidus reared on both host plants by the parasitoid Aphelinus asychis (Walker) (Hymenoptera: Aphelinidae). We assessed parasitoid development on aphids reared on both host plants and measured the success of parasitization on aphids reared on the optimum host plant. Our data proved C. sinensis as a more suitable host than M. paniculata, and that the secondary symbiont benefited infected aphids to explore the food source by reducing the time of development and producing larger adults in the suboptimal host. The fertility life table parameters calculated for Ars+ aphids were higher than those for Ars-. Besides benefiting A. citricidus in the use of food, Arsenophonus also affected the relationship of its host with the parasitoid A. asychis. Ars+ aphids were unsuitable to A. asychis and did not allow the full development of the parasitoid. The studied symbiotic relationship of A. citricidus and Arsenophonus showed the importance of secondary symbionts in multitrophic interactions of the host and the implications they may have for controlling the population growth of insects of economic interest.

Insects are often infected with facultative endosymbiotic bacteria, which can have a range of important ecological effects. The grain aphid, Sitobion avenae, harbours diverse facultative symbionts, which suggests their importance in grain aphid biology. This thesis attempts to explain the ecological roles of the facultative endosymbionts in S. avenae. It also examines the question of whether the horizontal transmission of symbionts between aphid clones and species can be important for shaping the ecology and evolution of multi-species aphid communities. Novel techniques developed for research with the grain aphid study system are presented. Grain aphid clones vary in their tolerance to low temperatures, but this trait is not affected by their facultative endosymbionts. Strains of a symbiont Hamiltonella defensa do not protect grain aphids from hymenopterous parasitoids, regardless of the host genotype. However, experienced parasitoid females preferentially oviposit in aphids which do not harbour symbionts. Comparison of the fitness consequences of infection with the same Hamiltonella strains in their original and in novel grain aphid host clones reveal no consistent differences. Symbiont strains establish easily following artificial transfer between clones of the grain aphid, but the symbionts transferred from other aphid species form less stable infections. Hamiltonella strains do not affect the fecundity of their grain aphid host clones regardless of their host species of origin, but also do not generally confer protection against parasitoids. There are no clear patterns in the distribution of parasitoid-resistant phenotypes across phylogenetic trees of Hamiltonella and its bacteriophage APSE. Strains of four unrelated species of endosymbionts, Rickettsia, Spiroplasma, Rickettsiella and Regiella, confer the same pathogen-resistant phenotype to a single pea aphid clone. The same symbiont strains can confer resistance to clones of two different aphid species. Some strains in multiple infections may compensate for the costs of infections with other symbionts. The importance of these results for understanding the ecological and evolutionary role of facultative endosymbionts in aphids and other insects are discussed, and directions for further research are proposed.

Phylum Euglenozoa contsists of four groups - Euglenoidea, Kinetoplastea, Symbiontida and Diplonemea. Phototrophic euglenids, which constitute a clade, possess green plastid acquired via secondary endosymbiosis from green alga related to recent genus Pyramimonas. According to generally accepted plastid-late hypothesis, the endo- symbiosis took place after split between phototrophic euglenids and all other euglenozo- ans. Endosymbiotic event is always associated with gene transfer from endosymbiont to nuclei of host. Even if the endosymbiont is completely lost we should be able to observe enrichment of the host genome with the genes derived from endosymbiont. Some recent phylogenetic analyses uncovered genes related to green algae in trypanosomas (Kineto- plastea: Trypanosomatida). Based on this observation, authors postulated a hypothesis that the plastid was present already in common ancestor of kinetoplastids and euglenids and was lost in kinetoplastids and some euglenids including osmotrophic Rhabdomonas costata. During analysis of transcriptome of R. costata we found 63 genes, which could originated from green (24 genes) or other (49 genes) algae. In phylogenetic trees only one was robustly related to green and four were robustly related to other algae. Since the number of genes related to...