Abstract
The cytogenetic characteristics of the grasshopper Podisma sapporensis (two races 2n = 23♂ X0/XX and 2n = 22♂ neo-XY/neo-XX) were analysed through fluorescence in situ hybridization with rDNA and telomeric DNA probes, C-banding, fluorochrome and silver staining. For the first time, samples from the neighbourhood of a hybrid population (i.e., Mikuni Pass population) were studied. Our results indicated a significant degree of chromosomal differentiation between P. sapporensis races when comparing the number and position of the rDNA sites, as well as the heterochromatin composition and distribution obtained by C-banding and DAPI/CMA3 staining. Telomeric signals were usually detected at the distal and/or subdistal position of the autosomes; however, some chromosome ends lacked signals, probably due to a low number of telomeric repeats. On the other hand, telomeric DNA sequences were found as interstitial telomeric repeats in some autosomes, which can trigger a variety of genome instability. B chromosomes were found in specimens belonging to both main races from nine out of 22 localities. Four types of X chromosomes in the X0/XX race were identified. It was concluded that the physical mapping of rDNA sequences and heterochromatin are useful as additional markers for understanding the phylogeographic patterns of cytogenetic differentiation in P. sapporensis populations.
Highlights
Chromosomal changes are considered to have played an important role in evolution, diversification and speciation1–3 because they could be a trigger for impeded gene flow between populations (e.g
During the last glacial period, P. sapporensis probably experienced population fragmentations into two main refuges on two sides of the central mountain system separated by the ridges of the Daisetsu and Hidaka Mountains, causing significant genetic differentiation for contemporary populations owing to the disruption of gene flow
The comparison was achieved by molecular and classical (C-banding, silver impregnation and fluorochrome DAPI/CMA3 staining) cytogenetic methods
Summary
Chromosomal changes (e.g., peri- or paracentromeric inversions, mutual translocations) are considered to have played an important role in evolution, diversification and speciation because they could be a trigger for impeded gene flow between populations (e.g.). Podisma sapporensis Shiraki, 1910 (Orthoptera, Acrididae, Melanoplinae) is one of the most highly variable species with respect to karyotypes and it provides an excellent opportunity to determine the role of chromosomal rearrangements in speciation. Podisma sapporensis Shiraki, 1910 (Orthoptera, Acrididae, Melanoplinae) is one of the most highly variable species with respect to karyotypes and it provides an excellent opportunity to determine the role of chromosomal rearrangements in speciation7–10 This species is distributed in Hokkaido, southern Kuril Island (Kunashir Island) and Sakhalin. Hybrid individuals between the X0/XX and neo-XY/neo-XX chromosome races have occasionally been found in the boundary between different chromosomal populations; the number of hybrid individuals in the natural environment is very few and no distinctive hybrid zone between the two races has ever been found This suggests that some strong barriers are hampering hybridization, such as topographic factors and/or selection against the heterozygote. The principal objective was to ascertain: [1] how the individuals of P. sapporensis populations differed in the number and location of rDNA clusters; and [2] whether the combination of different cytogenetic markers led to a new facet of chromosomal differentiation compared to the standard cytogenetic markers alone
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