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Abstract

The analysis of 19 populations of the grasshopper Eyprepocnemis plorans, collected along four rivers belonging to the Segura basin (Mundo, Benamor, Taibilla and Segura itself), has shown that the presence of B chromosomes ends abruptly in each river, coinciding with the existence of a narrow pass in which this grasshopper cannot live because of the absence of the appropriate habitats. The existence of a broad inland region lacking grasshoppers with B chromosomes suggests that B chromosomes arose after the first colonization of the Iberian Peninsula by E. plorans specimens from North African populations. The B chromosome seems to have spread upstream along each of these four rivers until reaching geographical barriers that have impeded its advance and thus have preserved the non-B chromosome region. The available evidence indicates that the observed geographical distribution of the B chromosome polymorphism in this zone was shaped mainly by historical non-selective events.

Population Genetic Structure of the Grasshopper Eyprepocnemis plorans in the South and East of the Iberian Peninsula

“…This suggests higher isolation (i.e. lower gene flow) between the +B and -B populations and is consistent with the possibility that B chromosomes are absent in these latter populations because B chromosomes have not yet arrived to them [5].…”

“…plorans lives in moist habitats near river courses and coastal areas throughout the circum-Mediterranean region, also reaching the Caucasus and the Arabian Peninsula [3]. B chromosomes have been found in almost all natural populations of this subspecies so far analyzed from Spain, Morocco, Italy, Greece, Turkey, Armenia, and Dagestan [4], the only B-lacking region being located at the headwaters of the Segura River basin in Spain [5]. A recent study has suggested that B chromosomes in E. plorans plorans are rather young [6].…”

Protein-coding genes in B chromosomes of the grasshopper Eyprepocnemis plorans

“…The presence of a same type of B in populations from Spain, Morocco, Tunisia and Sicilia suggests a recent invasion into these areas25. The high success of these B chromosomes, which are present in almost all populations hitherto analyzed, except those in the headwaters area of the Segura River basin in Spain26, has arisen from the transmission advantage (drive) they show during female meiosis27. This drive is suppressed by the A chromosomes2829 as a consequence of the arms race between A and B chromosomes predicted by the near-neutral model of B chromosome evolution30.…”

Geographical Barriers Impeded the Spread of a Parasitic Chromosome

“…In the Iberian Peninsula, B-lacking populations have only been found in the headwaters of several rivers belonging to the Segura river basin, including the Segura River itself and several of its tributaries (e.g. Mundo, Benamor and Taibilla) [ 14 ]. Since in each of these rivers the border between B presence and absence coincided with the existence of a geographical barrier, e.g.…”