Sternorrhyncha display a staggering diversity of genetic systems -- more than in all other insects put together. In addition to all the major genetic systems found in other insects (diploid-male and haploid-male amphimixis, paternal genome elimination, automictic and apomictic thelytoky), Sternorrhyncha include the only regularly hermaphroditic insects, and the only case of diploid arrhenotoky. More fundamentally, Sternorrhyncha are unique in having regular genomic chimerism, in which one tissue (the bacteriome) has a different genome from the rest of the insect. In Pseudococcidae and Diaspididae, the bacteriome is polyploid and includes genomes derived from maternal polar bodies. In Putoidae, the bacteriome is derived directly from the maternal bacteriome and appears to constitute a second germ line. Sternorrhyncha rely on stable, low-quality food sources -- the phloem of woody plants -- and I will argue that this has led by two routes to the de-stabilization of their genetic systems. First, they rely on maternally transmitted bacterial or fungal endosymbionts for complete nutrition. Such endosymbionts will benefit from a female-biased sex ratio, and the instability of sex-determination mechanisms in Sternorrhyncha may reflect a history of host-endosymbiont conflict. Second, there are often close and prolonged associations between maternal kin in Sternorrhyncha. As in the evolution of genomic imprinting in angiosperms and mammals, this may have contributed to the extreme diversity of the fates of paternally-derived alleles in Sternorrhyncha. I will present circumstantial evidence to support these views, and preliminary molecular-phylogenetic and flow-cytometric data leading towards more direct tests.
Keywords: genetic systems
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