First report on the chromosomes of Aeolosoma viride and Aeolosoma hemprichi (Aeolosomatidae; Annelida).

Abstract Aeolosomatidae are cosmopolitan meiofaunal Annelida characterised by small size and almost exclusively asexual reproduction. This study is the first report on the chromosome morphology of two aeolosomatid species. Giemsa staining and propidium iodide labelling were performed. The somatic chromosome number of Aeolosoma viride was 2n=30 with many biarmed elements, whereas A. hemprichi showed 60 small chromosomes with a dot-like appearance. Asexual reproduction, with its clonal transmission of chromosomal repatternings, probably ensures the fixation of new karyotypes in species of Aeolosoma .

Centrosome dynamics and inheritance in related sexual and parthenogenetic Bacillus (Insecta Phasmatodea).

In animals, some general features of centrosome dynamics and inheritance have been widely recognized. The most acknowledged model assigns to sperm the contribution of a centriole to the fertilized egg, which in turn provides the pericentriolar materials, including gamma-tubulin, recruiting them from the cytoplasm: the main zygote microtubule organizing center (MTOC) is thus reconstituted to organize first the spermaster and then the full first embryonic spindle. Obviously the model cannot apply to parthenogenetic systems, which actually rely on egg components alone. In stick insects of the Bacillus genus, the spindle of both somatic and germ cells is clearly anastral, therefore we have been investigating their centrosome in sexual and parthenogenetic taxa by analyzing its component dynamics and transmission through the use of monoclonal beta- and gamma-tubulin antibodies and transmission electron microscopy (TEM). It has been shown that in sexually reproducing species the spermatozoon does not contribute the centriole, so that the egg wholly provides the MTOC and the ensuing anastral spindle of the embryo: MTs appear to derive from pronuclear chromatin surroundings and no asters are observed. The parthenogenetic embryo development is the same as the sexual one if syngamy is excepted. The parthenogenetic mechanism realized by these panoistic insects appears to differ from that observed in the meroistic hymenopteran and drosophilid species, where the embryo spindle derives from asters formed in the egg cortex. In stick insects, the lack of sperm contribution to embryonic centrosome appears to be a major trait accounting for the widespread occurrence of facultative and obligate parthenogenesis within the order.