The genetics of asexual reproduction
Sexual reproduction is the predominant mode of reproduction in multicellular organisms and most likely evolved early in the history of eukaryotes. Species undergoing sexual reproduction maintain greater genetic diversity and should have greater prospects of adaptation and survival in changing environments despite a lower population growth rate. Although, asexual reproduction has been largely considered as an evolutionary dead-end, contemporary genomics technology now offers the prospect of shedding new light on this issue. Towards this goal, the EU-funded ODOGEN (Comparative genomics and gene expression profile of sexual and parthenogenetic Ischnura hastata (Insecta, Odonata)) project utilised the damselfly Ischnura hastata to investigate the consequences of switching from sexual reproduction to parthenogenesis. Researchers were interested in studying the mechanisms implicated in this transition. As a first step, they analysed meiosis-specific and meiosis-related genes in over 100 odonate insect species. Out of the eight meiosis-specific genes tested, a consistent absence of two genes (Rec8 and Cortex) was seen across all species. Further phylogenetic analyses of these data should provide invaluable information on the origin and evolution of these genes across different insect groups. Comparative gene expression analysis in sexual and parthenogenetic mature females revealed a significant number of differentially expressed transcripts. Sexual females exhibited higher levels of the CREB binding protein while asexual insects expressed high levels of aquaporins indicating a potential link with fertility. However, meiotic genes were not identified, suggesting that either meiosis did not occur in females of this age or that oocytes formed by mitotic divisions. Genome-wide sequencing methods allowed scientists to detect population differentiation in this species. Future research towards the study of patterns of gene expression throughout the development of both sexual and parthenogenetic females should help delineate important aspects regarding these processes.
Keywords
Genetics, asexual reproduction, ODOGEN, Ischnura hastata, meiotic gene