Reevolution of sexuality breaks Dollo's law

TLDR

The dominance of sexual reproduction remains an unresolved enigma, yet only a few parthenogenetic taxa persist long‑term, and oribatid mites provide notable exceptions to the rule that parthenogenetic taxa are recent and doomed to extinction. The study positions oribatid mites as a unique model to investigate the evolutionary significance of parthenogenetic versus sexual reproduction. Reevolution of sexuality depends on the long‑term maintenance of ancestral male‑production genes, which appears plausible in oribatid mites due to the presence of spanandric males, though the underlying storage mechanisms remain unclear. Phylogenetic and model‑based analyses reveal that Crotoniidae have reevolved sexuality from parthenogenetic ancestors, a unique reversal in the animal kingdom that violates Dollo's law.

Abstract

The dominance of sexual reproduction is still an unresolved enigma in evolutionary biology. Strong advantages of sex have to exist, because only a few parthenogenetic taxa persist over evolutionary timescales. Oribatid mites (Acari) include outstanding exceptions to the rule that parthenogenetically reproducing taxa are of recent origin and doomed to extinction. In addition to the existence of large parthenogenetic clusters in oribatid mites, phylogenetic analyses of this study and model-based reconstruction of ancestral states of reproduction imply that Crotoniidae have reevolved sexuality from parthenogenetic ancestors within one of those clusters. This reversal in reproductive mode is unique in the animal kingdom and violates Dollo's law that complex ancestral states can never be reacquired. The reevolution of sexuality requires that ancestral genes for male production are maintained over evolutionary time. This maintenance likely is true for oribatid mites because spanandric males exist in various species, although mechanisms that enable the storage of genetically ancestral traits are unclear. Our findings present oribatid mites as a unique model system to explore the evolutionary significance of parthenogenetic and sexual reproduction.