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Sperm motility and postmating prezygotic isolation in two nightingale species
Baránková, Lucie ; Reifová, Radka (advisor) ; Frolíková, Michaela (referee)
The motility of male gametes (sperm) is one of the important factors influencing the reproductive success of males. Because sperms are often subjected to strong postmating sexual selection and even closely related species often differ in sperm morphology, sperm motility could also differ between species, which may contribute to reproductive isolation between species. As part of my diploma thesis, I studied sperm motility in two closely related species of songbirds, the common nightingale (Luscinia megarhynchos) and the thrush nightingale (Luscinia luscinia). These two species of nightingales are an ideal model system because the areas of these two species overlap in the secondary contact zone across Central and Eastern Europe, where they occasionally hybridize and thus allow the study of speciation mechanisms in the natural environment. Both species also differ greatly in total sperm length. As part of my diploma thesis, I studied the possible influence of different sperm morphology on their motility. I further tested whether the motility of nightingale sperm differs in the fluid from the cloaca of a female of the same species and a different species, which would demonstrate the presence of postmating prezygotic reproductive isolation between species. The results of my work showed that despite the...
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Haldne's rule and mechanisms of hybrid female sterility in birds
Baránková, Lucie ; Reifová, Radka (advisor) ; Jansa, Petr (referee)
Hybrid sterility is one of the mechanisms of intrinsic postzygotic reproduction barriers between species and plays a key role in the process of speciation, which is emergence of new species. In accordance with Haldane's rule, hybrid sterility affects preferably the heterogametic sex, which means that in organisms with XY chromosomes, such as mammals or drosophila, male sterility will be affected by sterility of hybrid offspring, while organisms with ZW chromosomes such as birds or butterflies, will be a sterile hybrid female. Symptoms and mechanisms of hybrid sterility are well studied in organisms with heterogametic males, whereas far fewer studies have been performed on organisms with heterogamous females. In my bachelor thesis I will introduce the basic theories explaining the two general rules of speculation, the Haldane rule and the associated great influence of chromosome X or Z on the occurrence of hybrid sterility. Furthermore, in my work I will deal with the manifestations of hybrid sterility of females in birds and in the selected species will introduce the mechanisms that cause this sterility. Key words: Haldane's rule, hybrid sterility, speciation, birds, postzygotic izolation
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