University of Edinburgh Edinburgh, Scotland, United Kingdom
Reproductive strategies vary significantly across the tree of life, but little is known about reproductive systems outside of the familiar Mendelian inheritance method. We explore the Arthropod-specific alternative Paternal Genome Elimination (PGE). Under PGE: males are functionally haploid, with their father’s genetic contribution transcriptionally repressed, and can only pass on their maternally inherited genes to offspring. Females, in contrast, are transcriptionally diploid and pass on both sets of alleles. PGE applies to the whole genome, and as such, these insects have no sex chromosomes, only autosomes with diploid or haploid expression. This unusual genetic system should create drastically different selective pressures for genes expressed by males versus females but has never been studied in a population genomic framework. Here, we use the citrus mealybug, Planococcus citri, as a model to test predictions of differing selection between males and females. We have generated DNA resequencing and RNAseq and show that adult males and females have incredible sexual dimorphism in gene expression and that genes expressed primarily in females hold more variation than those expressed in males. In the long term, the few genes expressed in both sexes evolve most adaptively. Thus, PGE accentuates sex differences but hinders adaptive evolution.
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