Mechanismy sekundárního vzniku a udržování asexuálního rozmnožování. Metaanalýza a studie modelového systému rodu Cobitis

Bc. Oldřich BARTOŠ

Master's thesis

The mechanisms of secondary origin of asexuality and its maintenance; metaanalysis and case study of a model group Cobitis

Abstract:

The "paradox of sex" constitutes one of the most interesting themes in the evolutionary biology and despite the fact that it has attracted considerable amount of attention for decades, it probably still deserves the designation of "the queen of problems in evolutionary biology" (Bell 1982). The Muller´s ratchet theory is one of the most influential theories, which aim to explain the evolution or persistence of sex (Muller 1964). Despite the fact that the "modern" mathematical interpretation of the theory described the dynamics or behaviour on the intra-population level (e.g. Lynch et al. 1993), its conclusions are in general rather uncritically applied also to the inter-species level, i.e. to the macroevolutionary processes of phylogenesis (e.g. Beck et al. 2011). In this thesis, I do not question the role of ratchet-like processes on species-level. Rather, I address whether and how such processes may be detected from phylogenetic trees using some macroevolutionary tools. Here I use birth-death models whose design was accomodated to allow the incorporation of the ratchet-like process, i.e. the age dependent process of clonal decay. We then tested whether commonly applied gamma statistic, which is sensitive to changes in speciation and extinction rates, could measure the impacts of the "ratchet". Surprisingly it turned out that such form of summary statistic is unsuitable for our purposes. I have therefore tested other sorts of summary statistics and proved their systematic behaviour in response to the strength of clonal decay. I didnt have time and opportunity so far to validate these measures but I show potentially fruitful way how species-level phylogenies may be tested for the presence of age-dependent degeneration of asexual taxa. It will be our next aim to study the validity and robustness of the statistical methods presented in the thesis. For these reasons, the second part of the thesis, analysis of a model group Cobitis and possibly others, had to be delayed.

Abstract:

The "paradox of sex" constitutes one of the most interesting themes in the evolutionary biology and despite the fact that it has attracted considerable amount of attention for decades, it probably still deserves the designation of "the queen of problems in evolutionary biology" (Bell 1982). The Muller´s ratchet theory is one of the most influential theories, which aim to explain the evolution or persistence of sex (Muller 1964). Despite the fact that the "modern" mathematical interpretation of the theory described the dynamics or behaviour on the intra-population level (e.g. Lynch et al. 1993), its conclusions are in general rather uncritically applied also to the inter-species level, i.e. to the macroevolutionary processes of phylogenesis (e.g. Beck et al. 2011). In this thesis, I do not question the role of ratchet-like processes on species-level. Rather, I address whether and how such processes may be detected from phylogenetic trees using some macroevolutionary tools. Here I use birth-death models whose design was accomodated to allow the incorporation of the ratchet-like process, i.e. the age dependent process of clonal decay. We then tested whether commonly applied gamma statistic, which is sensitive to changes in speciation and extinction rates, could measure the impacts of the "ratchet". Surprisingly it turned out that such form of summary statistic is unsuitable for our purposes. I have therefore tested other sorts of summary statistics and proved their systematic behaviour in response to the strength of clonal decay. I didnt have time and opportunity so far to validate these measures but I show potentially fruitful way how species-level phylogenies may be tested for the presence of age-dependent degeneration of asexual taxa. It will be our next aim to study the validity and robustness of the statistical methods presented in the thesis. For these reasons, the second part of the thesis, analysis of a model group Cobitis and possibly others, had to be delayed.

Keywords

evolution of sex, Muller´s ratchet, clonal decay, birth-death model

Language used: English

Date on which the thesis was submitted / produced: 22. 8. 2015

Accessible from:: 22. 8. 2015

Thesis defence

• Date of defence: 24. 8. 2015
• Supervisor: RNDr. Karel Janko, Ph.D.

University of Ostrava

Faculty of Science

Master programme / field:
Biology / Systematic Biology and Ecology