The dynamics of B chromosomes in populations of the Australian plague locust, 'Chortoicetes terminifera' (Walker)

Abstract

The B chromosomes of Chortoicetes terminifera possess an accumulation mechanism. B chromosomes were transmitted at a rate of 0.766 in one B(♂) × zero B(♀) crosses and 0.477 in zero B(♂) one × B(♀) crosses. In crosses where the female had a B chromosome, there were significant differences in transmission rates between pods, but these were not related to differences in G-banding patterns of the B chromosomes involved. In crosses where either the male or female parent had two B chromosomes the B chromosomes did not segregate perfectly, nor did they segregate in a random fashion. The closest resemblance to the behaviour of normal bivalents occurred when the two B chromosomes were of the same, rather than different, G-banding variants, and when they were present in the male rather than the female parent. B chromosomes occurred at eight localities scattered throughout New South Wales. No locality was found where they were not present. The average frequency of B chromosomes was 14.0% for one-B individuals and 0.8% for two-B individuals. There were no significant differences in B-chromosome frequency between males and females. Of the eight localities, only one had a B-chromosome frequency significantly different from any other locality. This relatively uniformity of B-chromosome distribution is interpreted as a consequence of the migratory nature of C. terminifera. A model was constructed to simulate the dynamics of B chromosomes in locust populations. Three main dynamic patterns were recognized, and these were related to differences in the fitness of one-B and two-B individuals. It was concluded that the B chromosome of C. terminifera is probably parasitic, although the simulation model revealed some difficulties which suggest that caution should be applied to the description of any B chromosome as purely parasitic.Key words: B chromosomes, locust, meiotic drive, G-banding, fitness. Chortoicetes terminifera (Walker).