Molecular cytogenetic analysis reveals the existence of two independent neo-XY sex chromosome systems in Anatolian Pamphagidae grasshoppers

Abstract

Background: Neo-XY sex chromosome determination is a rare event in short horned grasshoppers, but it appears with unusual frequency in the Pamphagidae family. The neo-Y chromosomes found in several species appear to have undergone heterochromatinization and degradation, but this subject needs to be analyzed in other Pamphagidae species. We perform here karyotyping and molecular cytogenetic analyses in 12 Pamphagidae species from the center of biodiversity of this group in the previously-unstudied Anatolian plateau.

Results: The basal karyotype for the Pamphagidae family, consisting of 18 acrocentric autosomes and an acrocentric X chromosome (2n♂ = 19, X0; 2n♀ = 20, XX), was found only in G. adaliae. The karyotype of all other studied species consisted of 16 acrocentric autosomes and a neo-XY sex chromosome system (2n♂♀ = 18, neo-XX♀/neo-XY♂). Two different types of neo-Y chromosomes were found. One of them was typical for three species of the Glyphotmethis genus, and showed a neo-Y chromosome being similar in size to the XR arm of the neo-X, with the addition of two small subproximal interstitial C-blocks. The second type of the neo-Y chromosome was smaller and more heterochromatinized than the XR arm, and was typical for all Nocarodeini species studied. The chromosome distribution of C-positive regions and clusters of ribosomal DNA (rDNA) and telomeric repeats yielded additional information on evolution of these neo-XY systems.

Conclusion: Most Pamphagidae species in the Anatolian region were found to have neo-XY sex chromosome systems, belonging to two different evolutionary lineages, marked by independent X-autosome fusion events occurred within the Trinchinae and Pamphaginae subfamilies. The high density of species carrying neo-XY systems in the Anatolian region, and the different evolutionary stage for the two lineages found, one being older than the other, indicates that this region has a long history of neo-XY sex chromosome formation.

Keywords: FISH; Karyotype; Neo-sex chromosome evolution; Pamphagidae grasshoppers; Telomeric repeats; The neo-X; The neo-Y; rDNA.

Fig. 1

C-banding (a,c,e,g) and fluorescence in situ hybridization (FISH) with both rDNA (green) and telomeric DNA (red) probes (b,d,f,h) in diakinesis/metaphase I for the following Glypotmethis species from Trinchinae subfamily: G. adaliae (a,b); G. dimorphus (c,d); G. efe (e,f); G. holtzi pukhripes (g,h). Red arrowheads indicate ITSs. The inset in the top right corner shows neo-X and neo-Y chromosomes in mitotic metaphase

Fig. 2

Features of karyotypes of species studied. a L₁ and L₂ chromosome pairs with polymorphic small second arms in species form Glyphotmetis genus; b Neo-X-neo-Y bivalent of Nocaracris sp. in early diplotene. Arrowheads indicate conjugation of terminal part of XL arm of neo-X chromosomes with two small dot-like B-chromosomes

Fig. 3

C-banding (a,c,e,g,i,k,m,o,q,s) and FISH using both rDNA (green) and telomeric (red) probes (b,d,f,h,j,l,n,p,r,t) of chromosomes in Nocarodeini tribe: Oronothrotes furvus (a,b); Paranocaracris cytripes cytripes (c,d); Nocaracris sp. (e,f) - arrowheads indicate dot-like B-chromosomes; P. cytripes idrisi (g,h); P. sureyanus (i,j); Paranocarodes fieberi anatoliensis (k,l); P. fieberi tolunai (m,n); P. straubei (o,p); P. turkmen (q,r); Pseudosavalania karabagi (s,t). Red arrowheads indicate ITSs (n and t)

Fig. 4

Ideograms of karyotypes of Pamphagidae grasshoppers. Black blocks indicates C-bands, green blocks indicate rDNA clusters. Striped blocks indicate colocalisation of rDNA clusters and C-bands. Block on one chromosome indicates polymorphic sites