Lessons to learn from ancient asexuals

Abstract

This chapter reviews current hypotheses on the prevalence of sex in the eukaryotic world and presents four examples of putative ancient asexuals. We evaluate theoretical and practical concepts on how to demonstrate long-term asexuality. These are either derived from classical biological research (e.g. absence of males in fossil or recent populations) or from molecular biology (e.g. the Meselson effect, presence of functional transposable elements). Testing for the presence of conserved meiotic core proteins is a novel and especially promising way to verify ancient asexuality. We further re-evaluate statistical methods that utilize existing DNA sequence information on how to test for meiotic recombination. Molecular mechanisms counteracting the accumulation of deleterious mutations might be the most important avenue for ancient asexuals to persist in long, evolutionary time frames. Such mechanisms are reassessed and linked to molecular data from putative ancient asexuals. In particular, the purging of deleterious mutations by ameiotic recombination appears to be more effective than previously anticipated. © 2007 Springer-Verlag Berlin Heidelberg.