Phase transformation and chiasma frequency variation in locusts. I. Schistocerca gregaria.

Abstract

Locusts exhibit two basic forms or phases, one characteristic of swarming populations, termed phase gregaria, and the other characteristic of low density populations, termed phase solitaria. It has been claimed by Nolte that locusts living at low density, both in the field and in the laboratory, have a reduced chiasma frequency compared with animals living at high density. A postulated gregarisation pheromone is held to be responsible for the stimulation of melanin biosynthesis in the swarming animals and an unknown metabolite in this pathway causes the increase in chiasma frequency, as well as other phenotypic changes associated with phase transformation. According to Nolte this represents a means of releasing stored genetic variation necessary for adaptation in the areas invaded by swarms. — This claim has been re-examined in laboratory stocks of Schistocerca gregaria using a methodology comparable to that of Nolte. No reduction in the chiasma frequency of isolated animals was observed in any of the experiments. The isolated animals did, however, develop a phenotype characteristic of phase solitaria in terms of their pigmentation and morphometrics.