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Title: Exploring the biology of the trioecious nematode Auanema rhodensis
Author: Tandonnet, Sophie
ISNI:       0000 0004 8497 7344
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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The free-living nematode Auanema rhodensis is a rare example of a species with three sexes, in which males, females and hermaphrodites coexist. Hermaphrodites (XX) reproduce primarily by selfing, and females (XX) and males (XO) by crossing, generating a mixed system in which selfing and outcrossing entwine. In A. rhodensis, females and hermaphrodites follow different developmental trajectories, as hermaphrodites always pass through a resistant larval stage called dauer, whereas females (and males) never do. Here I report that the meiosis programme controlling the segregation of the X chromosome in XX animals also varies according to the sex and type of gametogenesis, as well as within the same gametogenesis. Females undergo a conventional meiosis, yielding predominantly haplo-X (1X) oocytes. Hermaphrodites, on the other hand, produce diplo-X sperm and nullo-X oocytes. These results complement previous findings in males, in which an atypical meiosis also occurs, resulting in the exclusive production of haplo-X sperm. Consequences of these unusual patterns are that (i) aneuploidy can be readily observed in most gametes of self-fertilising hermaphrodites, which is then 'rescued' during self-fertilisation as the nullo-X oocytes are fertilised by the diplo-X sperm, (ii) the X homologues do not recombine in hermaphrodites and (iii) crosses between hermaphrodites and males result exclusively in male progeny. The X chromosome, apart from following atypical segregation patterns, presents various differences compared to autosomes (e.g., it is smaller, more polymorphic and has fewer genes). These characteristics can be, at least partially, explained by major removals of X material to autosomes in the lineage leading to A. rhodensis and by the lower recombination rate of the X resulting in the maintenance of heterozygosity. The sex determination mechanism controlling the production of females versus hermaphrodites is unknown. Here, I present the first steps undertaken to understand the female-hermaphrodite specification. Through empirical studies, I found that the females are generated mainly by hermaphrodite mothers and are always produced early in the brood, suggesting a maternal sex determination mechanism.
Supervisor: Not available Sponsor: Ciência sem fronteiras
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QL Zoology