POPULATION CYTOLOGY OF BRITISH GRASSHOPPERS. I. CHIASMA VARIATION IN CHORTHIPPUS BRUNNEUS, CHORTHIPPUS PARALLELUS AND OMOCESTUS VIRIDULUS.

Abstract

1. The chiasma frequencies of three species of British grasshoppers, C. brunneus, C. parallelus and O. viridulus have been studied in detail. These have been analysed in terms of two metrics, the individual mean chiasma frequency per cell and the individual variance between cells. 2. These three species have significantly different chiasma frequencies (C. brunneus 13.51, C. parallelus 15.39 and O. viridulus 18.04), but only C. parallelus shows significant differences between populations. 3. The species with the higher chiasma frequencies have greater variation for this character both within and between individuals. 4. Long and Medium bivalents both contribute to the differences in chiasma frequency between species and populations — they are positively correlated. 5. It is suggested that a higher chiasma frequency is more difficult to control and consequently more liable to variation. 6. It is further postulated that greater inbreeding is reflected in a higher chiasma frequency — the latter compensating for any reduction in the rate of release of variation caused by the former.