Experimental hybridization between chromosome races of <i>Podisma sapporensis</i> Shiraki, 1910 (Orthoptera, Acrididae) from Sakhalin and Kunashir Islands
An experiment on the reproductive isolation of the Podisma sapporensis Shiraki, 1910 populations is aimed at elucidating the forms and mechanisms of evolutionary divergence and speciation in grasshopper distributed in the southern Kuril Islands and Sakhalin Island. During of a genetic experiment, hybrids were obtained for the first time between the chromosome races of the Sakhalin and Kunashir populations of P. sapporensis . Analysis of hybrid embryos in the crossing Sakhalin (female) x Kunashir (male) (C x K) revealed all theoretically expected genotypes of the offspring. Cytogenetic analysis of the testes of the first generation of F1 hybrids (C x K) did not reveal any disturbances in the meiosis. Homologous chromosomes in the prophase of meiosis segregate in the same way as in the control groups. Hybrid virgin females F1 (C x K) are able to give parthenogenetic generation, the genome of which corresponds to females of both the Kunashir and Sakhalin populations. In the (C x K) variant of crossing, the second (F2) viable generation of hybrids was obtained. Cytogenetic analysis of embryos from reciprocal crossing Kunashir (female) x Sakhalin (male) (K x C) showed the hybrid origin of only female embryos. However, they did not come out of diapause. The theoretically expected male genotypes (21 autosomes + neo-X) were not formed. These results indicate the non-viability of the offspring of this crossing. Our results indicate a partial reproductive isolation of the Sakhalin and Kunashir populations of P. sapporensis . We assume that geographic isolation, along with structural chromosomal rearrangements, played a key role in the formation of a reproductive barrier between the studied chromosomal races. In accordance with the principles of the biological concept of a species, the evolutionary divergence of these chromosomal races corresponds to the species taxonomic level.