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Title: The involvement of a sex chromosome fusion and rDNA diversity in the grasshopper podisma pedestris hybrid zone
Author: Veltsos, Paris
ISNI:       0000 0001 3823 1419
Awarding Body: Queen Mary, University of London
Current Institution: Queen Mary, University of London
Date of Award: 2008
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A fusion involving the X chromosome has generated a Neo-XY race from the standard acridid XOIXX karyotype in the grasshopper Podisma pedestris. The two races meet and form a hybrid zone. However the specific targets of selection responsible for its maintenance have never been found. This thesis examines the possibility of involvement of ribosomal DNA and fitness regimes driven by early sex chromosome evolution in the maintenance of the hybrid zone. rDNA was studied with fluorescent in situ hybridisation (FISH) and at the sequence level. FISH reveals an astonishing polymorphism in the distribution of rDNA loci, both within individual populations and between spatially isolated populations, allowing their subdivision into previously undetected genetic races. It is suggested that rDNA differentiation between populations could maintain the hybrid zone either by random mixing of rDNA loci, expected to generate individuals with insufficient rDNA, or by rDNA sequence incompatibility. Data from diverse experimental approaches addressed the evolution of rDNA itself. In particular, it was possible to show that rDNA loci contain multiple pseudogenes and that concerted evolution is not successful in homogenising all loci. It was also possible to demonstrate mobility of active loci and to assess the effect of rDNA copy number on the previously described genome size difference between the two races. Sex chromosome incompatibilities maintaining the hybrid zone were assessed by fitting computer simulation data to ecological data obtained from the field. The fitness reduction of the chromosomal heterozygotes for the X, or the evolution of male beneficial and female deleterious alleles on the Neo- Y, could be involved with the maintenance of the P. pedestris hybrid zone. More generally it is shown that the fusion may mark the beginning of the inevitable establishment of the Neo-XY system.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available