Numerical variations of chromosomes in the natural populations of Indian acridids

Abstract

Nine natural populations of Indian acridids belonging to seven species were cytologically analysed to study the numerical variations of chromosomes in the male germline cells. Of these, two allopatric populations of A. humbertianus and two of O. nitidula were chosen for intraspecies interpopulational studies. Both aneuploidy and polyploidy were encountered as intraindividual variations. Two kinds of polyploid cells—one with and another without multivalents-were found to occur. The former signified the occurrence of premeiotic mitotic breakdown of spindle whereas the latter was due to the failure of cytokinesis. While many tetraploid cells without multivalents successfully consummated meiosis producing dimegalous spermatids, tetraploid cells with multivalents and higher polyploids degenerated without completing meiosis. Analysis of quantitative data indicated that failure of cytokinesis is more frequent than spindle in premeiotic mitotic divisions. The frequency of second meiotic polyploid cells was significantly higher than those of first meiosis. The probable reasons for the increased incidence have been discussed. Comparative analysis of qualitative and quantitative data of these anomalies for the allopatric populations of A. humbertianus and O. nitidula showed that the population structure and breeding systems have an impact on the origin and incidence of the numerical chromosomal variations.