FLOW-CYTOMETRIC ANALYSES OF INTRASPECIFIC GENOME SIZE VARIATIONS IN BACILLUS-ATTICUS (INSECTA, PHASMATODEA)

The stick insect Bacillus atticus comprises several populations with d ifferent chromosome numbers that are distributed over a large range of the Mediterranean basin. Here we have analyzed the DNA content of nin e diploid and three triploid populations by flow-cytometry. The mean g enome size of the diploids showed a significant decrease from east to west, ranging from 5.29 +/- 0.12 pg for the population from Crete (eas t) to 4.28 +/- 0.10 pg for the population from Sardinia (far west). Th is longitudinal trend of a decrease in genome size from east to west w as also found for the triploid populations (from 6.80 pg for the popul ation in Turkey to 6.08 +/- 0.01 pg for the population on the Isle of Rhodes). Differences in DNA content between populations belonging to t he same species have been described in animals, but the evolutionary i mplications of these differences are as yet unclear. What emerges from the present study is a correlation between genome-size variations and geographic distribution. The adaptive nature of genome-size variation s in response to environmental changes is discussed, and the class of DNA involved hypothesized.