Origin and maintenance of sex: the evolutionary joys of self sex

Abstract

Sex is generally thought of as meiosis, conjugation, and syngamy, with the primary function of sex believed to be genetic mixing. However, conjugation does not occur with complete automixis, whereas syngamy does not occur with restitutional automixis. Self sex in the forms of automixis and autogamy does not include genetic mixing. Yet sex, including self sex, is necessary for most eukaryotic lineages. What is the purpose of sex without genetic mixing? Obligate self sex is not an evolutionary dead end, but holds the key to understanding the evolutionary origin, function, maintenance, and ubiquity of sex. We extend the rejuvenescence hypothesis that sex provides a necessary developmental reset for multicellular eukaryotes and even many unicellular eukaryotes. Sex reduces additive genetic variance of epigenetic signals, especially cytosine methylation, and of ploidy levels. Furthermore, we argue that syngamy is a modified form of meiosis that maintains ploidy and resets epigenetic signals. Epigenetic resetting is consistent with sex being induced by starvation or desiccation. Diminution of additive genetic variance is consistent with the origin and maintenance of an adaptive trait, sex, that has been present for approximately two billion years.

Sex produces as numerous and long-lived offspring as parthenogenesis in a new parthenogenetic insect

“…We suggest it should be considered a renovation and genetic dispersal process (Gorelick and Carpinone 2009). Parthenogenesis could also be an alternative reproductive tactic when good partners are unavailable (Neaves and Baumann 2011).…”

Genome constraint through sexual reproduction: application of 4D-Genomics in reproductive biology

“…Application of genome theory and 4D-Genomics recently led to the establishment of a new paradigm for sexual reproduction [Gorelick and Carpinone 2009;Gorelick and Heng 2011;Heng 2007b;Wilkins and Holliday 2009]. In contrast to the century-old reasoning that the function of sexual reproduction increases genetic variation, under the new paradigm sexual reproduction mainly acts to reduce genome alterations despite its secondary function of mixing genes.…”

The Paradox of Sexual Reproduction and the Levels of Selection: Can Sociobiology Shed a Light?

“…This imprinting could be a reason for the absence of parthenogenesis in mammals (Jaenisch andWilmut 2001, Engelstädter 2008). Various hypotheses about the adaptive significance of DNAmethylation exist (e.g., Wolffe and Matzke 1999;Gorelick and Carpinone 2009). …”