Chromosomal and NOR patterns in the polyclonal stick insect Bacillus atticus atticus (Insecta; Phasmatodea)

Area of Science:

• Cytogenetics
• Evolutionary Biology
• Entomology

Background:

• Bacillus atticus atticus is a thelytokous parthenogenetic complex related to Bacillus grandii.
• This complex is distributed across Sardinia and Near Eastern regions.
• Previous understanding of its cytogenetic differentiation was limited.

Purpose of the Study:

• To investigate the karyotypic and cytogenetic differentiation within Bacillus atticus atticus.
• To analyze the patterns and locations of nucleolar organizer regions (NORs).
• To contribute to understanding the phylogeny of B. atticus.

Main Methods:

• Karyotypic analysis of diploid unisexual isolates.
• Silver staining (Ag-NOR) to identify NORs.
• Fluorescence in situ hybridization (FISH) using rDNA probes for confirmation.

Main Results:

• Observed higher-than-expected karyotypic and cytogenetic differentiation.
• Identified a standard karyotype of 2n=34 chromosomes, with instances of repatterned and aneuploid complements.
• Found diverse NOR patterns, including homozygous and hemizygous strains, confirmed by FISH.

Conclusions:

• The observed chromosomal variations, particularly NOR patterns, are not artifacts.
• Mechanisms like transpositions, translocations, or hybridizations between NOR-bearing races likely explain the observed patterns.
• This chromosomal survey enhances the understanding of Bacillus atticus phylogeny.