The thelytokous hybrid
Bacillus whitei (2n=35, XX female) endemic to Southeastern Sicily, is clearly derived from
B. rossius×
grandii, but a variety of cytotypes have been found in these parthenogens. The most widespread, standard karyotype perfectly fits the suggested hybrid derivation except for the fourth metacentric element, certainly deriving from
B. rossius, in which, however, nowadays invariably shows a corresponding acrocentric chromosome; on the other hand the acrocentric “modern” element has been found in hybridogenetic strains of
B. whitei, very recently discovered among clonal ones. Linking together reproductive biology and geographical distribution of the “metacentric” and “acrocentric” standard karyotypes, two hybridization events between
B. grandii and either a “paleo” or “neo”
B. rossius, respectively, are here suggested.
C-positive satellites and corresponding Ag-NOR, are found on a wide array of chromosomes, mostly reflecting those of both parental species, but also on new locations. The high dinamics of rDNA cistrons, mainly evidenced in the
B. rossius genome, makes NORs not entirely reliable as long-term cytotaxonomical markers, but rather useful in short-term comparisons.
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