Abstract
There is wide interest in understanding how genetic diversity is generated and maintained in parthenogenetic lineages, as it will help clarify the debate of the evolution and maintenance of sexual reproduction. There are three mechanisms that can be responsible for the generation of genetic diversity of parthenogenetic lineages: contagious parthenogenesis, repeated hybridization and microorganism infections (e.g. Wolbachia). Brine shrimps of the genus Artemia (Crustacea, Branchiopoda, Anostraca) are a good model system to investigate evolutionary transitions between reproductive systems as they include sexual species and lineages of obligate parthenogenetic populations of different ploidy level, which often co-occur. Diploid parthenogenetic lineages produce occasional fully functional rare males, interspecific hybridization is known to occur, but the mechanisms of origin of asexual lineages are not completely understood. Here we sequenced and analysed fragments of one mitochondrial and two nuclear genes from an extensive set of populations of diploid parthenogenetic Artemia and sexual species from Central and East Asia to investigate the evolutionary origin of diploid parthenogenetic Artemia, and geographic origin of the parental taxa. Our results indicate that there are at least two, possibly three independent and recent maternal origins of parthenogenetic lineages, related to A. urmiana and Artemia sp. from Kazakhstan, but that the nuclear genes are very closely related in all the sexual species and parthenogegetic lineages except for A. sinica, who presumable took no part on the origin of diploid parthenogenetic strains. Our data cannot rule out either hybridization between any of the very closely related Asiatic sexual species or rare events of contagious parthenogenesis via rare males as the contributing mechanisms to the generation of genetic diversity in diploid parthenogenetic Artemia lineages.
Highlights
There is wide interest in understanding how genetic diversity is generated and maintained in parthenogenetic lineages, as it will help clarify the debate of the evolution and maintenance of sexual reproduction
Cyst samples from Asiatic sexual species were obtained from the same cyst bank collection, including A. urmiana from Urmia lake and from Koyashskoe lake, A. tibetiana from four lakes of the Tibetan plateau (Lagkor Co, Gaize, Hayan, Jingyu), an undescribed sexual Artemia population from Kazakhstan and A. sinica from Yuncheng (China) (Figure 1)
Kazakhstan in agreement with Munoz et al [30], and revealed a possibly new lineage of parthenogenetic lineages represented by KUJ [29]
Summary
There is wide interest in understanding how genetic diversity is generated and maintained in parthenogenetic lineages, as it will help clarify the debate of the evolution and maintenance of sexual reproduction. Several different genetic mechanisms underlie transitions from sexual reproduction to asexuality, and these mechanisms influence in turn the genetic diversity of parthenogenetic lineages and their success and persistence [3,4]. One mechanism for the polyphyletic origin of parthenogenetic lineages diversity is contagious parthenogenesis [3], in which parthenogenetically produced functional rare males mate with sexual females and transmit parthenogenesis to their offspring. In the presence of sexual females of related lineages or species, rare males could produce fertile hybrid offspring which would inherit the parthenogenesis-inducing alleles
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