Reproductive biology versus transposable elements load: the role of host reproductive strategy in the study of R2 dynamics in Bacillus stick insects (Phasmida, Bacillidae)

Transposable elements (TEs) are known to promote genome evolution, even if they are often defined as “genomic parasites”. According to the Red Queen hypothesis, conflicts between parasite TEs and the host genome are at equilibrium through strict competitive efforts. Host reproductive strategy is significantly involved in this dynamics. The R2 non-LTR retrotransposon activity was estimated, through insertions display analyses, in populations of the strictly gonochoric Bacillus grandii maretimi, the facultative parthenogenetic B. rossius and the obligatory parthenogenetic B. atticus. R2 activity was also evaluated in the progeny of parthenogenetic isolates of B. rossius and B. atticus, and in the male progeny of crosses between gonochoric individuals of B. rossius. Gonochoric populations showed higher R2 loads than the parthenogenetic ones, the lowest value being scored in B. atticus. In all samples low frequency insertions are the majority, with the only exception of a bisexual B. rossius population. R2 load was similar in unisexual and bisexual B. rossius offspring but lower in B. atticus progeny. Moreover, in B. rossius unisexual offspring high-frequency insertions were the most represented. Data on facultative unisexuals evidenced a low R2 elimination rate, with recombination having a major role, although a bisexual-like insertion profile emerge at the population level. In this regard, natural selection seems to predominate in bisexuals. Stick-insects obligatory parthenogenesis seems to allow only a very low R2 load, with possible burst of retrotransposition buffered at the population level. Our data agree in indicating TE dynamics deeply linked with host reproductive strategies.