Elementi trasponibili in genomi di artropodi con strategie riproduttive non-canoniche.

Transposable elements (TEs) are universal components of all living organisms. TEs activity and movement have profound effects on host genome and today many researchers agree to consider them as important actors in genome evolution. The relationships between TEs and their host genomes are still under debate. Different hypotheses were proposed to explain TEs dynamics in host genome; one of these propose that host reproductive strategies can influence TEs evolutionary dynamics (Hickey, 1982). In fact, bisexual organisms, through homologous chromosomes recombination and reassortment during meiosis and amphimixis, can control the spread and proliferation of mobile elements, while unisexual organisms would experience an increase of these elements density due to the inability to eliminate them through exclusive mechanisms of sexual reproduction. In order to evaluate these hypothesis, I isolated and characterized TEs in organisms with non-canonical reproductive strategies. I performed my analyses in two organisms: the stick insects of the Bacillus genus and in the tadpole shrimps T. cancriformis. In both instances reproductive strategies range from bisexual gonochoric reproduction, to unisexual parthenogenesis, making them an excellent model for the study and characterization of TEs. In the Bacillus genus I focused on the R2 non-LTR retrotranposon. I isolated and sequenced by primer walking seven R2 complete elements; both gonochoric and parthenogenetic Bacillus species. I found a R2 degenerate element present in the B. rossius genome since 5 Myr ago. In addition, my analyses for the first time suggest that also R2 retrotransposons can use horizontal transfer as a strategy to colonize a new genome. My data showed a TEs overview in a T. cancriformis parthenogenetic population. In contrast with the theoretical, my analyses highlighted that the 20% of the library is composed by TEs, in which both TEs classes are widely represented (class I, 11.4% and class II, 8.9%).