Marescalchi et al. 1998

Marescalchi O, Scali V, Zuccotti M. 1998. Flow-cytometric analyses of intraspecific genome size variations in Bacillus atticus (Insecta, Phasmatodea). Genome 41: 629-635.

These authors measured nuclear DNA contents of 12 populations of a walking-stick insect distributed around the shores of the eastern Mediterranean sea. This species is thelytokous (see Boivin and Candau, 2007), and includes both diploid and triploid populations. Chromosome number is mostly conserved across populations of the same ploidy level.

Their flow cytometry methodology is more fully described in an earlier paper (Marescalchi et al. 1990), but seems fairly good (at this level of detail) as they describe copreparation of a standard, mouse thymocytes in all samples.

A clear correlation of genome size and longitude was found, with the smallest genomes in Sardinia at the species’ western extent. As one moves west, genomes in this species become gradually smaller, a situation that the authors argue can be explained by the relative ages of the populations. The high diversity within this species among and within eastern populations suggests that the eastern Mediterranean houses the oldest populations. The authors argue for a pattern of reduced genome size with younger populations, though the details of what type of DNA has changed or been lost is not known, no mechanism linking colonization versus nondispersal and genome size evolution is proposed, and the theory discussed includes apparently long-since-discounted ideas about ecological specialization.