Genes involved in the convergent evolution of asexuality in 1 stick insects 2

The ability to reproduce is one of the most fundamental traits that distinguishes living organisms 16 from inorganic matter, yet, organisms use a panoply of strategies for reproduction. The evolution 17 of these strategies, especially sexual and asexual reproduction, has been the focus of intensive 18 study. By contrast, the molecular underpinnings of sexual and asexual reproduction remain 19 relatively unknown. We investigated convergent gene expression changes and patterns of 20 molecular evolution across five independent transitions to asexuality in stick insects. We 21 compared gene expression of asexual females to those of females from close sexual relatives in 22 whole-bodies and two tissues: the reproductive tract and legs. We identified a striking amount of 23 convergent gene expression change, ranging from 5 to 8% of genes examined. Convergent 24 changes were also tissue-specific, with most convergent genes changing in only one tissue type. 25 Functional enrichment tests found that genes showing convergent changes in the reproductive 26 tract were associated with meiotic spindle formation and centrosome organization. These genes 27 are particularly interesting as they can influence the production of unreduced eggs, a key barrier 28 to asexual reproduction. Changes in legs and whole-bodies were likely involved in female sexual 29 trait decay, with enrichment in terms such as sperm-storage and pigmentation. By identifying 30 changes occurring across multiple independent transitions to asexuality, our results provide a rare 31 insight into the molecular basis of asexual phenotypes and suggest that the evolutionary path to 32 asexuality is highly constrained, requiring repeated changes to the same key genes. 33