Parallel polymorphism for supernumerary segments in Chorthippus parallelus (Zetterstedt)

Abstract

French populations of Chorthippus parallelus like those from Britain are polymorphic with respect to supernumerary segments on the M₇ and S₈ chromosomes. The pattern of polymorphism parallels that of British material on both morphological and behavioural grounds. It agrees also in its effect on mean cell chiasma frequency and the absence of any effect on between cell variance. Finally the agreement extends also to the distribution of karyotypes within populations, those of the S₈ showing a Hardy-Weinberg distribution whereas those of the M₇ show a deficiency of structurally heterozygous types. All these parallels imply a common origin for the British and French material, an origin which, so we must suppose, antedated the physical separation of Britain and France some 8,000 years ago.