Bacterial endosymbionts that provide nutrients to hosts often have genomes that are extremely stable in structure and gene content. In contrast, the genome of the endosymbiont has fractured into multiple distinct lineages in some species of the cicada genus To better understand the frequency, timing, and outcomes of lineage splitting throughout this cicada genus, we sampled cicadas over three field seasons in Chile and performed genomics and microscopy on representative samples. We found that a single ancestral lineage has split at least six independent times in over the last 4 million years, resulting in complexes of between two and six distinct lineages per host. Individual genomes in these symbiotic complexes differ dramatically in relative abundance, genome size, organization, and gene content. Each lineage retains a small set of core genes involved in genetic information processing, but the high level of gene loss experienced by all genomes suggests that extensive sharing of gene products among symbiont cells must occur. In total, complexes that consist of multiple lineages encode nearly complete sets of genes present on the ancestral single lineage and presumably perform the same functions as symbionts that have not undergone splitting. However, differences in the timing of the splits, along with dissimilar gene loss patterns on the resulting genomes, have led to very different outcomes of lineage splitting in extant cicadas.

The leafhopper Macrosteles laevis, like other plant sap-feeding hemipterans, lives in obligate symbiotic association with microorganisms. The symbionts are harbored in the cytoplasm of large cells termed bacteriocytes, which are integrated into huge organs termed bacteriomes. Morphological and molecular investigations have revealed that in the bacteriomes of M. laevis, two types of bacteriocytes are present which are as follows: bacteriocytes with bacterium Sulcia and bacteriocytes with Nasuia symbiont. We observed that in bacteriocytes with Sulcia, some cells of this bacterium contain numerous cells of the bacterium Arsenophonus. All types of symbionts are transmitted transovarially between generations. In the mature female, the bacteria Nasuia, bacteria Sulcia, and Sulcia with Arsenophonus inside are released from the bacteriocytes and start to assemble around the terminal oocytes. Next, the bacteria enter the cytoplasm of follicular cells surrounding the posterior pole of the oocyte. After passing through the follicular cells, the symbionts enter the space between the oocyte and follicular epithelium, forming a characteristic “symbiont ball.”

Sup-sucking hemipterans host ancient heritable microorganisms that supplement their unbalanced diet with essential nutrients and have repeatedly been complemented or replaced by other microorganisms. These symbionts need to be reliably transmitted to subsequent generations through the reproductive system, and often they end up using the same route as the most ancient ones.

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In mammals, the relationship between the immune system and behavior is widely studied. In fish, however, the knowledge concerning the brain immune response and behavioral changes during brain viral infection is very limited. To further investigate this subject, we used the model of tilapia lake virus (TiLV) infection of zebrafish (Danio rerio), which was previously developed in our laboratory. We demonstrated that TiLV persists in the brain of adult zebrafish for at least 90 days, even when the virus is not detectable in other peripheral organs. The virions were found in the whole brain. During TiLV infection, zebrafish displayed a clear sickness behavior: decreased locomotor activity, reduced food intake, and primarily localizes near the bottom zone of aquaria. Moreover, during swimming, individual fish exhibited also unusual spiral movement patterns. Gene expression study revealed that TiLV induces in the brain of adult fish strong antiviral and inflammatory response and upregulates expression of genes encoding microglia/macrophage markers. Finally, using zebrafish larvae, we showed that TiLV infection induces histopathological abnormalities in the brain and causes activation of the microglia which is manifested by changes in cell shape from a resting ramified state in mock-infected to a highly ameboid active state in TiLV-infected larvae. This is the first study presenting a comprehensive analysis of the brain immune response associated with microglia activation and subsequent sickness behavior during systemic viral infection in zebrafish.

Abstract. The organization and development of ovaries in representatives of two families (Putoidae and Monophlebidae) of scale insects are described. Developing ovaries of Puto albicans McKenzie, 1967 and Crypticerya morrilli (Cockerell, 1914) consist of numerous clusters of cystocytes that are arranged in the form of rosettes. At the end of the last nymphal instar these clusters start to protrude from the interior of the ovary into the body cavity and the ovarioles begin to be formed. The ovary of a young female is composed of about 200 spherical telotrophic ovarioles devoid of terminal filaments. The ovarioles of C. morrilli contain 8 germ cells (7 trophocytes and a single oocyte). From 25 to 45 germ cells (23-43 trophocytes and 2 or 3 oocytes) occur in the ovarioles of P. albicans. An ovariole of an adult female is subdivided into a trophic chamber (tropharium), vitellarium and ovariolar stalk (pedicel). At each stage of development, the ovaries are accompanied by large cells (termed bacteriocytes) that contain endosymbiotic microorganisms. The organization of the ovary in P. albicans is more similar to that in archaeococcoid scale insects than in neococcoid taxa. In contrast, the number of germ cells per ovariole in C. morrilli is not typical of other archaeococcoids, but resembles the derived condition seen in other iceryine taxa. The classification and phylogeny of scale insects are discussed in the light of these results.

Many insects, on account of their unbalanced diet, live in obligate symbiotic associations with microorganisms (bacteria or yeast-like symbionts), which provide them with substances missing in the food they consume. In the body of host insect, symbiotic microorganisms may occur intracellularly (e.g., in specialized cells of mesodermal origin termed bacteriocytes, in fat body cells, in midgut epithelium) or extracellularly (e.g., in hemolymph, in midgut lumen). As a rule, symbionts are vertically transmitted to the next generation. In most insects, symbiotic microorganisms are transferred from mother to offspring transovarially within female germ cells. The results of numerous ultrastructural and molecular studies on symbiotic systems in different groups of insects have shown that they have a large diversity of symbiotic microorganisms and different strategies of their transmission from one generation to the next. This chapter reviews the modes of transovarial transmission of symbionts between generations in insects.

Abstract. The ultrastructure, distribution and transovarial transmission of endosymbiotic bacteria in representatives of six aphid families: Eriosomatidae (Pemphigus spyrothecae, Prociphilus fraxini), Anoeciidae [Anoecia (Anoecia) corni], Drepanosiphidae [Mindarus abietinus, Sipha (Rungsia) maydis, Clethrobius comes, Myzocallis (Lineomyzocallis) walshii], Thelaxidae (Thelaxes dryophila), Aphididae (Delphiniobium junackianum, Aphis viburni, Cavariella theobaldi, Macrosiphoniella tanacetaria) and Lachnidae (Schizolachnus pineti, Eulachnus rileyi) were studied at the ultrastructural level. The ovaries of aphids are accompanied by large organs termed bacteriomes that consist of giant cells termed bacteriocytes. The bacteriocyte cytoplasm is tightly packed with endosymbiotic bacteria. Ultrastructural observations have shown that the bacteria Buchnera aphidicola (primary symbiont of aphids) present in various species are characterized by significant differences in both size and organization of their cytoplasm. In the aphids, Prociphilus fraxini, Sipha (Rungsia) maydis, Thelaxes dryophila, Aphis viburni, Cavariella theobaldi, Macrosiphoniella tanacetaria, Eulachnus rileyi and Schizolachnus pineti, in addition to Buchnera aphidicola, secondary endosymbionts are also present. The bacteriocytes containing secondary endosymbionts are less numerous than those with Buchnera. In Eulachnus rileyi (Lachnidae), in addition to primary and secondary endosymbionts, there is a third type of microorganism. In all species examined both the primary and secondary endosymbionts are transovarially transmitted from mother to offspring.