Insect polyploid adaptation for cell number and size varies in longstanding versus neopolyploid lines of the wasp Nasonia vitripennis

Polyploidisation (whole genome duplication) is pervasive in eukaryotic evolution but poses significant challenges. Longstanding polyploid lines may have specialised coping mechanisms, but neopolyploids must overcome immediate impediments. In particular, larger polyploid cells disrupt development and physiological function. Some vertebrate polyploids have larger but fewer cells (cell reduction); in invertebrates, such coping mechanisms are unstudied. Here we study polyploid cellular and morphological responses by comparing wings of a longstanding polyploid line (Whiting Polyploid Line, WPL) and neopolyploid lines of the wasp Nasonia vitripennis. As with all hymenopterans, in wasps males are haploid and females are diploid. Polyploids are diploid males and triploid females. We created neopolyploid lines with RNA interference of female development genes transformer (TRA) and wasp-overruler-of-masculinisation (WOM). We analysed differences in wing cell counts, wing surface area, and wing cell size between these polyploid lines. There were sex-specific and line differences, with female WPL exhibiting no difference in cell count between the diploids and triploids, whereas the neopolyploid lines had significantly reduced cell counts in triploids. In males, both the WPL and WOM neopolyploid line had lower cell counts in diploids than in haploids, with a less pronounced effect in the TRA neopolyploid line. Wing surface area and cell size also varied, with the longstanding WPL having greater similarity between polyploids and non-polyploids than the newly generated TRA and WOM lines. Variation in cellular size and reduction between polyploid lines suggests greater stabilization and a possible signature of re-diploidisation in the long-standing line compared to the neopolyploid lines. We discuss implications for polyploid adaptation and evolution, including effects on reproductive success.