Alvarez-Fuster et al. 1991

Alvarez-Fuster A, Juan C, Petitpierre E. 1991. Genome size in Tribolium flour-beetles: inter- and intraspecific variation. Genetical Research 58: 1-5.

These authors measured genome size in nine species of tenebrionid beetles in the tribe Ulomini; all but one of which are members of the genus Tribolium. Tribolium castaneum was and remains an exceptionally well-studied beetle, but genome size information was lacking, and few studies of insects had sought information about intraspecific variation in a comprehensive manner prior to this study.

Genome size was estimated by Feulgen densitometry measures of spermatids. Twenty spermatid nuclei from each of 10 individuals (five individuals of Alphitobius diaperinus) per species were measured, with spermatids of Dermestes maculatus used as a standard. For reasons not clear to me, detailed comparisons between D. maculatus and T. castaneum were carried out prior to studies of the other species. The procedure for isolation, fixation, and staining nuclei is similar to what we currently use but has some differences. Fixation was carried out for only 10 minutes in 10% formalin, rather than > 12 hours in MFA, hydrolysis lasted only 45 minutes (rather than 120) but used 5N-HCl as we use, and staining was for two hours (like what we do), but details of the chemical preparation of the stain are not given, though the cited Juan & Petitpierre (1989) may provide more information.

Statistical analysis included measures derived from Gold & Amemiya (1987) of within and between taxa comparisons. Nested ANOVA was also used to support an argument about the significance of intraspecific variation.

The discussion section includes an argument that large and uniform sampling as carried here provides a “solid base from which to analyze the pattern of distribution of genome sizes both inter- and intraspecifically.” Later discussion includes an odd argument that one species, T. brevicornis, with the largest genome size measured here, may be ancestral to the other species (including, presumably, the one species in another genus) and that genome evolution has proceeded by reduction and associated specialization of the type proposed by e.g. Hinegardner (1976).

Within each species, two to four significantly different groups of genome sizes were found, with the exception of one species (T. destructor), which did not show such structure. This, plus the nested ANOVA that indicated significant variation due to between-individuals-within-species comparisons, is taken as evidence in favour of (biologically) significant intraspecific variation in these beetles. The authors acknowledge that such intraspecific variation is surprising, but their arguments for evolutionary trends are not well constructed, so I do not know what to make of this intraspecific variation.