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Hannes Becher


PhD student




Project Title: Sex chromosome evolution in an alpine grasshopper hybrid zone

Summary: Sex chromosomes are subject to evolution, and sex chromosome systems are not necessarily stable. For instance, the ancestral sex chromosome system in Acridid grasshoppers is X0 (i.e., males carry on X and females two), but this system has been replaced independently in several lineages. In my PhD, I want to extend our knowledge on what forces are acting during sex chromosome evolution.

In the alpine grasshopper species, Podisma pedestris, two different chromosome races occur. One carries the ancestral X0 system. The other one underwent an X-to-autosome fusion creating a large neo-X-chromosome, and leaving behind a single chromosome that only occurs in males, the neo-Y. Both races meet and form a narrow hybrid zone, in which heterozygous individuals occur, and where neo-Ys can potentially occur in females. Due to its male-only inheritance outside the hybrid zone, the neo-Y is likely to be subject to sexually antagonistic selection (it might be advantageous in males, but deleterious in female hybrids.)

Modelling suggests this kind of sexually antagonistic selection could drive the replacement of the ancestral sex chromosomes by the neo-X and neo-Y. The selection actually acting on these chromosomes can be inferred from locations and shapes of their distribution clines. However, the neo-Y is indiscernible microscopically from its ancestral autosome and no molecular markers are known. Not yet.

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