B₁ Was the Ancestor B Chromosome Variant in the Western Mediterranean Area in the Grasshopper <b><i>Eyprepocnemis plorans</i></b>

Abstract

We analyzed the distribution of 2 repetitive DNAs, i.e. ribosomal DNA (rDNA) and a satellite DNA (satDNA), on the B chromosomes found in 17 natural populations of the grasshopper Eyprepocnemis ploransplorans sampled around the western Mediterranean region, including the Iberian Peninsula, Balearic Islands, Sicily, and Tunisia. Based on the amount of these repetitive DNAs, 4 types of B variants were found: B₁, showing an equal or higher amount of rDNA than satDNA, and 3 other variants, B₂, B₂₄ and B₅, bearing a higher amount of satDNA than rDNA. The variants B₁ and B₂ varied in size among populations: B₁ was about half the size of the X chromosome in Balearic Islands, but two-thirds of the X in Iberian populations at Alicante, Murcia and Albacete provinces. Likewise, B₂ was about one-third the size of the X chromosome in populations from the Granada province but half the size of the X in the populations collected at Málaga province. The widespread geographical distribution of the B₁ variant makes it the best candidate for being the ancestor B chromosome in the whole western Mediterranean region.

B-chromosome effects on Hsp70 gene expression does not occur at transcriptional level in the grasshopper Eyprepocnemis plorans

“…The B chromosomes observed in Salobreña and Torrox corresponded to the B2 and B24 variants, respectively, previously reported in these same populations (Cabrero et al 2014). PCR amplification of the Hsp70 gene on E. plorans cDNA using degenerate primers yielded a single product which was visualized as a 391 bp fragment in electrophoresis gels.…”

Geographical Barriers Impeded the Spread of a Parasitic Chromosome

“…Our analysis of a B-specific sequence-characterized amplified region (SCAR) marker in populations from the Iberian Peninsula, Morocco, Greece and Armenia revealed scarce DNA sequence changes thus suggesting a recent origin for B chromosomes [ 18 ]. In fact, a same type of B chromosome (B 1 ) is predominant in populations from the Iberian Peninsula, Balearic Islands, Morocco, Tunisia and Sicily, suggesting the recent spread of this B chromosome through Western Mediterranean areas [ 20 ]. Bearing also in mind that B 1 is the most widespread variant in the Iberian Peninsula, on which basis it is considered the original B variant [ 6 ], we conclude that the arrival of B chromosomes to the Spanish Mediterranean coasts was a recent event, in consistency with the low Fst values found between the B-carrying and B-lacking populations analyzed here.…”

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

“…E. plorans individuals were collected in Torrox (Málaga) (Table 4), a population where the prevalent B chromosome variant is B2425. Males were anaesthetized before dissecting out testes, one of which was fixed in 3:1 ethanol-acetic acid for cytological analysis, while the other testis and body remains were frozen in liquid nitrogen for nucleic acid extraction.…”

“…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.…”