Effect of Supernumerary Chromosomes on Sex Ratio in Calligrapha philadelphica L. (Coleoptera: Chrysomelidae)

Abstract

SUPERNUMERARY chromosomes occur sporadically in plants and animals. In the animal kingdom, they have been observed in at least 50 insects and two turbellarians, and they may be present or absent in different populations of the same species¹. They are generally considered to be inert as they are usually heterochromatic and their carriers are not distinguishable morphologically. The chromosomal polymorphism that they confer on some populations suggests that they play an adaptive part in the success of the population^1,2. In plants supernumerary chromosomes have a harmful effect on vigour and fertility, and the effect becomes more pronounced as their number increases³. The work of Lewis⁴ and Fröst⁵ has suggested that their presence may be an adaptation to arid regions³.