Abstract
The present study focused on the evolution of the karyotype in 21 taxa of the genus Isophya, which was done by mapping the location on the chromosomes of ribosomal RNA (rRNA) coding genes using fluorescence in situ hybridization (FISH) with an 18S rDNA probe and using silver staining (AgNO3) to evaluate the activity of major rDNA clusters. Since the chromosome number and sex determination do not vary in this genus, the above markers were used in a detailed comparison of the cytogenetic features of species of Isophya. The species analyzed were placed into three groups based on the location of rDNA on their chromosomes: (1) rDNA-FISH signals only on the two long pairs of autosomes, (2) rDNA-FISH signals on one long and one short pair of autosomes, and (3) rDNA-FISH signals on three to five different sized pairs of autosomes. These groupings partly correspond to the morphological groupings proposed in earlier studies. One long pair of autosomes frequently carried rDNA in all the Isophya species and probably is a plesiomorphic character for these taxa. The cytogenetic mapping revealed great variability among Isophya species in the chromosomal location of major rDNA clusters. Our results suggest that the observed variation in the number of rDNA clusters can be an important species-group specific phylogenetic marker. Analysis of 18S rDNA hybridization signals showed that the evolutionary dynamics of rDNA in this genus is remarkably high and accompanied by changes in the structure of chromosomes bearing rDNA at an inter- and intra-specific level. The telomeric sequence (TTAGG)n hybridized with the termini of most of chromosomes, however, some chromosome ends lacked signals probably due to a low copy number of telomeric repeats.
Highlights
The genus Isophya Brunner von Wattenwyl (1878) is one of the largest bushcricket genera in including 89 species (Eades et al, 2011) (I. medimontana Nedelkov, 1907 is regarded as a subspecies by Harz, 1969)
The present study reports the results of follow-up research on the reconstruction of the ancestral karyotype based on the number and distribution of rDNA clusters in 21 species/subspecies of the genus Isophya using fluorescence in situ hybridization (FISH) with 18S rDNA probe as a potentially useful marker
The present study focused on the evolution of the karyotype in Isophya by mapping the location of ribosomal RNA (rRNA) coding genes on chromosomes using FISH and using silver staining (AgNO3) to evaluate the activity of rDNA clusters
Summary
The genus Isophya Brunner von Wattenwyl (1878) is one of the largest bushcricket genera in including 89 species (Eades et al, 2011) (I. medimontana Nedelkov, 1907 is regarded as a subspecies by Harz, 1969). It occurs in Central Europe, the Carpathian Basin, the Balkans, southern Ukraine, Asia Minor and the Caucasus region, eastwards reaching north western Iran and Iraq and an isolated area of the Altai Mountains (Bey-Bienko, 1954). The status of many species remains unresolved because Isophya contains several morphologically very similar species (Heller, 1988, 2006; Warchaáowska-ĝliwa et al, 2008; Chobanov, 2009a, b). The development of new cytogeneticmolecular markers is important for a better understanding of the genome organization and phylogeny of this genus
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