The B chromosome system of the grasshopper Eyprepocnemis plorans has provided support for our dynamic model on the evolution of parasite B chromosomes, by which Bs are neutralized by the evolution of drive suppressor genes in the A genome, so that they are condemned to extinction through stochastic loss (and the low fitness of individuals carrying four or more Bs) lasting hundreds or thousands of generations (depending on population size), unless a new selfish B variant may emerge and regenerate the polymorphism. With the present project, we propose to reach three general objectives:

i) to determine the molecular composition of B chromosomes in this species, 
ii) to reveal the possible expression of the DNA contained in the Bs, or possible regulatory changes in genes located on the A chromosomes caused by B presence, and 
iii) to disentangle the coevolution mechanisms underlying the neutralization-regeneration process of these parasite chromosomes. 

In relation with the first objective, we will continue the analysis of the B2 and B24 DNA libraries built in the former project, we will characterize cytogenetically and molecularly the B chromosomes that have recently been reported in natural populations from the Caucasus, we will analyse the presence of retroelements in the B chromosomes that might explain their high mutability, and will compare the potential capability to capture centromere proteins among B chromosomes differing in transmission ratio. In relation with the second objective, we plan to build a cDNA library from individuals possessing B chromosomes, and to analyse the distribution of  5-metil-cytosin on the A chromosomes in the presence of different B chromosome types. With regard to the third objective, we will continue analysing the evolution of B frequency in the population where Bs were introduced in 1993, and will perform a population survey of the Torrox region, an interesting locality where B chromosome substitutions are presently taking place.