Genome Size and Chromosomal Evolution in Leaf Beetles (Coleoptera, Chrysomelidae)

Abstract

The DNA content of Feulgen-stained spermatids in 39 species of leaf beetles ranges from IC = 0.17 pg to 3.69 pg, and their chromosome numbers range from 2n = 16 to 2n = 46. The striking variability of genome sizes parallels that of chromosome number, and there is a significant correlation between these parameters (r = 0.39, P < 0.005). Significant direction correspondence was also obtained between genome size and (a) spermatid area (r = 0.88, P 0.001) and (b) whole chromosome area at metaphase I (r = 0.89, P < O.OOl), giving a substantial support to the nucleotypic hypothesis of genome size at the cellular level. The implications of genome size and chromosome number to the cytogenetic evolution in the Chrysomelinae leaf beetles is dealt with in some detail. The rate of chromosomal evolution per genus is not only significantly correlated with species richness (r = 0.53, P < 0.05). but also with the number of host plant families selected by the congeneric species (r = 0.84, P < 0.001), showing that specialized phytophagy increases the chance of chromosomal evolution and speciation, although these two latter aspects are not necessarily linked.