Reevolution of sexuality breaks 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.oribatid mites ͉ parthenogenesis ͉ spanandric males ͉ automixis ͉ ancient asexuals

Reversing opinions on Dollo’s Law

“…This highlights that, in many cases, neither state can be determined with statistical significance. 11 Law, suggesting that stick insects can regain wings [12], lizards can regain digits [4], slipper limpets can regain a coiled shell [13], asexual mites can regain sex [14], frogs can regain tadpoles in their life histories [15] and marine snails can regain a feeding larval stage [16]. Possibly owing to publication bias, there is a single published study showing that a feature, self-incompatibility, has never been regained in a family of plants [17].…”

“…An ML approach can also be used to determine whether the rate of reversals is significantly different from zero. This has been widely used to show exceptions to Dollo's Law [4,[12][13][14][15][16][17]. The sensitivity of ML results to different rates of gains and losses can also be used to determine how unlikely losses must be before the re-evolution of a character is reconstructed on the phylogeny [46].…”

Multiple convergent evolution of arboreal life in oribatid mites indicates the primacy of ecology

“…In contrast to basal oribatid mite lineages, Brachypylina are predominantly sexual. The importance of the reproductive mode for arboreal oribatid mites can be inferred from the arboreal genus Crotonia that re-evolved sexual reproduction from a previously soil-living and parthenogenetic taxon, the Camisiidae/Crotoniidae (Domes et al 2007b). It is not known why sexual reproduction is advantageous for arboreal species but it is probably related to food resources.…”

Sperm-dependent parthenogens delay the spatial expansion of their sexual hosts

“…Dybdahl and Lively (1998), Paland et al (2006), West et al (1999)). It should however be noted that some findings of exceptional longevity of clones, their adaptive potential or even the reevolution of sex contrast traditional assumptions in some model groups (Vrijenhoek 1993, Judson et al 1996, Domes et al 2007, Normark et al 2003, Martens et al 2003). …”