Interaction among different heterocromatic variants in the grasshopper Dichroplus elongatus

Simultaneous chromosome polymorphisms for supernumerary elements allow us to analyse the relationships among different forms of heterochromatic variation in nature. We report simultaneous variation patterns for supernumerary segments in chromosomes S10 (SS10), S9 (SS9) and S6 (SS6) and B chromosomes in nine populations of the grasshopper Dichroplus elongatus from two biogeographic provinces from east Argentina. Our results show spatial chromosome differentiation for three out of four supernumerary heterochromatic variants (B chromosomes, SS6 and SS10). The incidence of B chromosomes was negatively correlated with the SS10 frequency. The distribution pattern analysis shows different degree of differentiation among populations for each supernumerary heterochromatic variant suggesting that the detected chromosome variation cannot be explained by interaction between migration and genetic drift. Moreover, the observed population chromosome differentiation was not in agreement with the hierarchical analysis of molecular of heterogeneity at mitochondrial DNA level (mtDNA). The present results point out the importance of the interaction among heterochromatic variants in the chromosome intraspecific variation in east Argentina natural populations of the grasshopper D. elongatus.