Evolution of alternative reproductive systems in Bacillus stick insects

Area of Science:

• Evolutionary Biology
• Genetics
• Reproductive Biology

Background:

• Organismal reproduction varies significantly across life.
• The stick insect genus Bacillus displays five distinct reproductive modes, including sexual reproduction, parthenogenesis, hybridogenesis, and androgenesis.
• Hybridogenesis involves paternal genome elimination and replacement, while androgenesis results in offspring with two paternal genomes.

Purpose of the Study:

• To reevaluate Bacillus lineages and the proposed F1 hybrid ancestries of hybridogenetic and obligately parthenogenetic lineages from Sicily.
• To genetically confirm species identification and hybrid lineage ancestry.
• To investigate the genome-wide retention of F1 hybrid constitution in these lineages.

Main Methods:

• Generation of a chromosome-level genome assembly for Bacillus rossius (a facultative parthenogenetic species).
• Extensive field sampling.
• Analysis of RADseq and mtDNA data.

Main Results:

• All previously described Bacillus species were identified and genetically corroborated.
• The F1 hybrid ancestry of hybrid lineages was confirmed.
• Hybrid lineages exhibit complete retention of their F1 hybrid constitution, indicating complete paternal genome elimination in hybridogens and stable heterozygosity in obligate parthenogenesis.

Conclusions:

• The study provides genetic evidence supporting the F1 hybrid origin of Bacillus hybrid lineages.
• Complete paternal genome elimination in hybridogenesis and stable heterozygosity in obligate parthenogenesis were observed.
• These findings offer insights into reproductive mode transitions and genome elimination mechanisms.