Timema stick insects retain functional sex-linked genetic systems after million years of asexual reproduction

New research published in the Proceedings of the National Academy of Sciences (PNAS) reveals that certain species of Timema stick insects have maintained fully functional genetic systems for sex-based gene regulation despite reproducing asexually for approximately one million years.

Led by Dr. Darren Parker of Bangor University, the study focused on the process of dosage compensation. In sexually reproducing species, this mechanism balances gene expression between males and females who possess different numbers of X chromosomes. Because the asexual Timema species reproduce through parthenogenesis—where eggs develop without fertilization—males are largely absent from the population.

Scientists expected these unused biological systems to have degraded due to a lack of evolutionary pressure. Instead, the findings show the dosage compensation machinery remains intact, challenging the traditional evolutionary assumption that biological systems will rapidly deteriorate once they are no longer useful.