Abstract
Although previous cytogenetic analysis of Pamphagidae grasshoppers pointed to considerable karyotype uniformity among most of the species in the family, our study of species from Armenia has discovered other, previously unknown karyotypes, differing from the standard for Pamphagidae mainly in having unusual sets of sex chromosomes. Asiotmethis turritus (Fischer von Waldheim, 1833), Paranocaracris rubripes (Fischer von Waldheim, 1846), and Nocaracris cyanipes (Fischer von Waldheim, 1846) were found to have the karyotype 2n♂=16+neo-XY and 2n♀=16+neo-XX, the neo-X chromosome being the result of centromeric fusion of an ancient acrocentric X chromosome and a large acrocentric autosome. The karyotype of Paranothrotes opacus (Brunner von Wattenwyl, 1882) was found to be 2n♂=14+X1X2Y and 2n♀=14+X1X1X2X2., the result of an additional chromosome rearrangement involving translocation of the neo-Y and another large autosome. Furthermore, evolution of the sex chromosomes in these species has involved different variants of heterochromatinization and miniaturization of the neo-Y. The karyotype of Eremopeza festiva (Saussure, 1884), in turn, appeared to have the standard sex determination system described earlier for Pamphagidae grasshoppers, 2n♂=18+X0 and 2n♀=18+XX, but all the chromosomes of this species were found to have small second C-positive arms. Using fluorescent in situ hybridization (FISH) with 18S rDNA and telomeric (TTAGG)n DNA repeats to yield new data on the structural organization of chromosomes in the species studied, we found that for most of them, clusters of repeats homologous to 18S rDNA localize on two, three or four pairs of autosomes and on the X. In Eremopeza festiva, however, FISH with labelled 18S rDNA painted C-positive regions of all autosomes and the X chromosome; clusters of telomeric repeats localized primarily on the ends of the chromosome arms. Overall, we conclude that the different stages of neo-Y degradation revealed in the Pamphagidae species studied make the family a very promising and useful model for studying sex chromosome evolution.
Highlights
About 600 species of Pamphagidae, or “toad grasshoppers” as they are commonly known, are distributed in the desert and mountainous landscapes of Africa, Central Asia, and the Western and Eastern Mediterranean (Uvarov 1966, Massa 2013), including some species found in Armenia (Avakian 1968)
Asiotmethis turritus (Fischer von Waldheim, 1833), Paranocaracris rubripes (Fischer von Waldheim, 1846), and Nocaracris cyanipes (Fischer von Waldheim, 1846) were found to have the karyotype 2n♂=16+neo-XY and 2n♀=16+neo-XX, the neo-X chromosome being the result of centromeric fusion of an ancient acrocentric X chromosome and a large acrocentric autosome
We have found Armenian Pamphagidae grasshopper species to be characterized by intensive karyotypic evolution
Summary
About 600 species of Pamphagidae, or “toad grasshoppers” as they are commonly known, are distributed in the desert and mountainous landscapes of Africa, Central Asia, and the Western and Eastern Mediterranean (Uvarov 1966, Massa 2013), including some species found in Armenia (Avakian 1968). The family Pamphagidae remains one of most poorly karyotyped groups among the grasshoppers. One reason for this lies in the very low densities of the toad grasshopper populations. Reciprocal translocation between an ancient acrocentric X chromosome and one of the acrocentric autosomes was discovered to have taken place in some pamphagid species (Bugrov 1986, Bugrov and Warchałowska-Śliwa 1997, Bugrov and Grozeva 1998, Li et al 2005), leading to the formation of a large, biarmed neo-X chromosome. The autosome homologous to the XR arm is referred to as the neo-Y chromosome
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