Genetic diversity and evolutionary age of parthenogenetic oribatid mites (Acari: Oribatida).
Technische Universität, Darmstadt
[Ph.D. Thesis], (2004)
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|Item Type:||Ph.D. Thesis|
|Title:||Genetic diversity and evolutionary age of parthenogenetic oribatid mites (Acari: Oribatida)|
Theories on the evolution and maintenance of sex are challenged by the existence of ancient asexual lineages like bdelloid rotifers and darwinulid ostracods. Ancient asexual origin of several speciose taxa has also been proposed for oribatid mites (Acari). In the present work, I analysed genetic divergences in different parthenogenetic and sexual lineages of oribatid mites to estimate the age of these lineages and to evaluate if the evolution of oribatid mites was without recombination. Age estimations were based on genetic distances of the mitochondrial gene for cytochrome oxidase I (COI) between clonal lineages of different parthenogenetic oribatid mite species. Species from two parthenogenetic taxa (Platynothrus peltifer, P. yamasakii, P. sibiricus, Heminothrus thori and Camisia horrida (Camisiidae) and Mucronothrus nasalis (Trhypochthoniidae)) were sampled in different sites in Europe, North America, South America, Australia and Asia. Corrected distances reached up to 157% on DNA level and 10% on amino acid level. Using different calibrations for a molecular clock, an age of up to 240 million years since the separation of the lineages was estimated. With this age, oribatid mites contain the oldest living parthenogenetic metazoan taxa. Further analyses investigated if the high evolutionary age of Platynothrus and other oribatid mite taxa (Mucronothrus nasalis, Tectocepheus velatus, Atropacarus striculus, Steganacarus magnus and Metabelba pulverulenta) was attained without gene recombination. To address this question, the two alleles of the hsp82 gene (coding for the 82 KD heat shock protein) were analysed for their genetic divergence. Due to gene recombination, sexual species in general have maximum divergences of 4% for this gene; higher amounts of divergence indicate absence of gene recombination as expected for parthenogenetic organisms. Genetic distances were up to 70% on DNA level and 15% on amino acid level indicating ancient lack of recombination. The absence of recombination in hsp82 was estimated to have happened 350 million years ago. The amount of genetic divergences between the alleles was in the same range in sexual and asexual oribatid mite species. High allelic divergence between hsp82 alleles in sexual and asexual species may be explained by the special mechanism of inheritance in oribatid mites: chromosomes are holokinetic and inverted meiosis has been inferred. If inverted meiosis occurs together with chiasma terminalisation gene recombination is suppressed in both sexual and parthenogenetic species. Together with terminal fusion in parthenogenetic species this mechanism resembles mitotic cloning. Inverted meiosis is a simple form of meiosis and it is discussed if this mechanism might be ancestral to “normal” meiosis. A scenario is proposed on how “normal” meiosis and monocentric chromosomes evolved from inverted meiosis and holokinetic chromosomes. Particular conditions may favour the frequent independent evolution and persistence of parthenogenetic clusters in oribatid mites. The absence of gene recombination in sexual and asexual oribatid mite species for at least 350 million years and the evolution of perhaps 100,000 oribatid mite species without gene recombination is an evolutionary mystery contradicting theories on sex and recombination and is unique in the animal kingdom.
|Place of Publication:||Darmstadt|
|Classification DDC:||500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie|
|Divisions:||10 Department of Biology|
|Date Deposited:||17 Oct 2008 09:21|
|Last Modified:||07 Dec 2012 11:49|
|Referees:||Norton, Prof. Dr. Roy A. and Göringer, Prof. Dr. H. Ulrich|
|Advisors:||Scheu, Prof. Dr. Stefan|
|Refereed:||16 December 2003|