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The role of ecological factors in maintenance of sexuality
Toman, Jan ; Flegr, Jaroslav (advisor) ; Janko, Karel (referee)
The existence and widespread distribution of sexual reproduction despite its obvious disadvantages is an evolutionary enigma. According to the theory of frozen plasticity, the evolution of sexual and asexual species is fundamentally different. One of the implications of this theory are different ecological preferences of these species. Sexual species should prefer biotically and abiotically variable environments because of their ability to quickly and reversibly respond to unpredictable changes. On the other hand, asexual species should prosper in biotically and abiotically stable environments because of their ability to perfectly adapt even to extreme environmental factors in the long term. I decided to test these predictions in the metastudy comparing ancient asexual clades (in which we can be sure about their obligate asexuality and evolutionary longevity) with their sexual sister or closely related ecologically comparable clades. The hypothesis of the preference of asexual species to biotically and abiotically homogenous environments was supported by the results of this metastudy. On the other hand, the hypothesis of supposed ability of asexual species to perfectly adapt to a broader range of environmental conditions, tested on the comparison of temperature ranges of activity of previously...
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Ecological aspects of sexual reproduction
Toman, Jan ; Flegr, Jaroslav (advisor) ; Markoš, Anton (referee)
Sexual reproduction is one of the most interesting biological phenomena. No theory has ever entirely explained its wide occurrence among Eukaryotic clades despite its clear disadvantages (e.g. twofold price of sex). Theories can be divided into three groups according to the approach to solve this problem - molecular, genetic and ecological (environmental). Environmental theories are slightly preferred in the last decades and the opinion that the key to the sex enigma lies among them is widely accepted. Most of the environmental theories do not counter each other and there is possibility either to integrate them in several ways or presume that several of these theories might act simultaneously. According to theories, abiotically stable environments without biotic interactions (homogenous) should be suitable for and select for asexual species, whereas environments abiotically variable and rich in biotic interactions (heterogenous) should be suitable for and select for sexual species. The anagenetic phenomenon of punctuated equilibria and some of its explanations, e.g. P. R. Sheldon's Plus ça change hypothesis or J. Flegr's Frozen plasticity theory, also supports this division. There is a vast amount of empirical data supporting this division in ecological studies. Clearly homogenous environments...
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Geographical parthenogenesis: evolutionary and ecological significance of apomictic reproduction in vascular plants
Hartmann, Matthias ; Mráz, Patrik (advisor) ; Dobeš, Christoph (referee) ; Krahulec, František (referee)
It has been suggested that polyploidization affects the ecological niche of a species, possibly ultimately leading to a shift in the distribution of the species, such as in geographical parthenogenesis. The phenomenon describes the wider distribution and shift of asexuals towards higher altitudes, northern latitudes and more extreme habitats when compared with their closely related sexual relatives. Several hypotheses have been proposed to explain such patterns with lacking empirical evidence because investigations rather focused on single hypotheses, which were rather tested several times independently on multiple organisms than vice versa. Therefore, the present study aimed to tackle the phenomenon of geographical parthenogenesis from multiple angles, i.e. testing several hypotheses simultaneously using Hieracium alpinum as a model system. In the arcto-alpine Asteraceae H. alpinum sexually reproducing diploid individuals occur in a small isolated area in the Eastern and Southern Carpathians, while apomictically reproducing, i.e. asexual reproduction via seeds, triploid plants occupy the remaining and much larger part of the range from the Balkans to the arctic parts of Europe. This implies that asexual triploids have had some fitness / colonization advantage(s), leading to a replacement of sexual diploids...
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The role of ecological factors in maintenance of sexuality
Toman, Jan ; Flegr, Jaroslav (advisor) ; Janko, Karel (referee)
The existence and widespread distribution of sexual reproduction despite its obvious disadvantages is an evolutionary enigma. According to the theory of frozen plasticity, the evolution of sexual and asexual species is fundamentally different. One of the implications of this theory are different ecological preferences of these species. Sexual species should prefer biotically and abiotically variable environments because of their ability to quickly and reversibly respond to unpredictable changes. On the other hand, asexual species should prosper in biotically and abiotically stable environments because of their ability to perfectly adapt even to extreme environmental factors in the long term. I decided to test these predictions in the metastudy comparing ancient asexual clades (in which we can be sure about their obligate asexuality and evolutionary longevity) with their sexual sister or closely related ecologically comparable clades. The hypothesis of the preference of asexual species to biotically and abiotically homogenous environments was supported by the results of this metastudy. On the other hand, the hypothesis of supposed ability of asexual species to perfectly adapt to a broader range of environmental conditions, tested on the comparison of temperature ranges of activity of previously...
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|
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Ecological aspects of sexual reproduction
Toman, Jan ; Flegr, Jaroslav (advisor) ; Markoš, Anton (referee)
Sexual reproduction is one of the most interesting biological phenomena. No theory has ever entirely explained its wide occurrence among Eukaryotic clades despite its clear disadvantages (e.g. twofold price of sex). Theories can be divided into three groups according to the approach to solve this problem - molecular, genetic and ecological (environmental). Environmental theories are slightly preferred in the last decades and the opinion that the key to the sex enigma lies among them is widely accepted. Most of the environmental theories do not counter each other and there is possibility either to integrate them in several ways or presume that several of these theories might act simultaneously. According to theories, abiotically stable environments without biotic interactions (homogenous) should be suitable for and select for asexual species, whereas environments abiotically variable and rich in biotic interactions (heterogenous) should be suitable for and select for sexual species. The anagenetic phenomenon of punctuated equilibria and some of its explanations, e.g. P. R. Sheldon's Plus ça change hypothesis or J. Flegr's Frozen plasticity theory, also supports this division. There is a vast amount of empirical data supporting this division in ecological studies. Clearly homogenous environments...
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(A)sexual Life of Liverworts
HOLÁ, Eva
This thesis comprises of two published papers and one accepted manuscript, focused on various aspects of liverwort reproduction. Treated aspects include patterns of asexual reproduction, sex ratio and sex-specic pattern in vegetative growth, and patterns of genetic variation and spatial genetic structure of populations differing in availability of substrate on localities and the population connectivity, and consequently in size, density, and prevailing reproductive mode. These characteristics were studied on representatives of the family Scapaniaceae s.l., belonging to the largest liverwort order Jungermanniales. The results showed that asexual propagules were formed and present in course of the whole growing season and can be considered as a sufficient substitution for sexual reproduction. In contrast with the female-biased sex ratio observed earlier in most dioicous bryophytes, unexpectedly high male-biased sex ratio was observed in the aquatic liverwort, which was speculated to represent a strategy to overcome sperm dilution in aquatic environment. In addition, no size differences between female and male shoots were detected, although the evidence for higher cost of sexual reproduction in females was found. The study of population genetic structure has shown that even small and predominantly asexually reproducing populations are important sources of genetic variation. However, we were able to demonstrate notably low levels of gene flow among populations where habitat fragmentation poses a significant barrier to dispersal of diaspores. The fine scale study of spatial genetic structure revealed a strong aggregation of genotypes, particularly in smaller populations, and at the same time showed that asexual reproduction is an efficient mean of maintaining the populations at not only the short distances, given the spatial extent of clones spanning dozens of meters.
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Ecology and distribution of the moss \kur{Helodium blandowii} in the Czech Republic
BRADÁČOVÁ, Jitka
Recent and historical localities of the moss Helodium blandowii in the Czech Republic were written up in this thesis and various ecological charakteristics of this species were studied. It was grown with Sphagnum teres on hummocks and in hollows and these two species were compared in their high above water-table where they grow best. Further regeneration abilities of Helodium blandowii were examined.
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