C-banding, ag-nor localization and chromosomal repatterning in sardinian bacillus atticus (Insecta, phasmatodea)

All demcs of Sardinian Bacillus atticus share a 2n = 33 karyotype which is fully comparable to the standard one (2n = 34), except for a Robertsonian fusion of the two chromosomes of pair 11. Furthermore, the San Vito population shows a cytotype with 34 elements, derived from the common 33-chromosomes with the addition of an unusual, all-heterochromatic large acrocentric one. C-banding and silver staining have revealed a rather constant heterocromatin and NOR localizations in all samples; this suggests a most likely derivation of all Sardinian demes from common founder(s). The cytogenetic degree of differentiation of Sardinian B. atticus from other conspecific Italian demes, and from the bisexual B. grandii, is discussed. No cytogenetic evidence supporting the repeatedly stated hybrid structure of B. atticus is revealed from karyological studies, and the hybrid origin of B. atticus can be maintained on genetical grounds only. It is also suggested that the odd chromosome in the San Vito cytotype derives from a fission of a large satellite with the gain of a centromeric function. Since a paleointrogression of B. atticus genes into syntopic B. rossius had been evidenced in the Sardinian B. atticus range, the role of the 11–11 Robertsonian fusion in the hybrid zone is taken into account. © 1991, Taylor & Francis Group, LLC.