title: Post-meiotic B chromosome expulsion, during spermiogenesis, in two grasshopper species.
abstract: Most supernumerary (B) chromosomes are parasitic elements carrying out an evolutionary arms race with the standard (A) chromosomes. A variety of weapons for attack and defense have evolved in both contending elements, the most conspicuous being B chromosome drive and A chromosome drive suppression. Here, we show for the first time that most microspermatids formed during spermiogenesis in two grasshopper species contain expulsed B chromosomes. By using DNA probes for B-specific satellite DNAs in Eumigus monticola and Eyprepocnemis plorans, and also 18S rDNA in the latter species, we were able to count the number of B chromosomes in standard spermatids submitted to fluorescence in situ hybridization, as well as visualizing B chromosomes inside most microspermatids. In E. plorans, the presence of B-carrying microspermatids in 1B males was associated with a significant decrease in the proportion of B-carrying standard spermatids. The fact that this decrease was apparent in elongating spermatids but not in round ones demonstrates that meiosis yields 1:1 proportions of 0B and 1B spermatids and hence that B elimination takes place post-meiotically, i.e., during spermiogenesis, implying a 5-25% decrease in B transmission rate. In E. monticola, the B chromosome is mitotically unstable and B number varies between cells within a same individual. A comparison of B frequency between round and elongating spermatids of a same individual revealed a significant 12.3% decrease. We conclude that B chromosome elimination during spermiogenesis is a defense weapon of the host genome to get rid of parasitic chromosomes.
authors.affiliation: Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, Granada, Spain.
authors.forename: Josefa
authors.initials: J
authors.lastname: Cabrero
authors.affiliation: Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, Granada, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Martín-Peciña
authors.affiliation: Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, Granada, Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Ruiz-Ruano
authors.affiliation: Departamento de Ciencia y Tecnología Agroforestal, E.T.S. de Ingenieros Agrónomos, Universidad de Castilla La Mancha, 02071, Albacete, Spain.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Gómez
authors.affiliation: Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Avda. Fuentenueva s/n, Granada, Spain. jpmcamac@ugr.es.
authors.forename: Juan Pedro M
authors.initials: JPM
authors.lastname: Camacho
mesh_terms: D000818:Animals; D059006:Chromosomes, Insect / Q000235:genetics*; D006110:Grasshoppers / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D013091:Spermatogenesis / Q000235:genetics*
keywords: FISH; Micronucleus; Microspermatids; Parasitic; Satellite DNA