Evolution of long centromeres in fire ants

Area of Science:

• Genetics
• Evolutionary Biology
• Molecular Biology

Background:

• Centromeres are crucial for chromosome segregation but show low sequence conservation across species.
• Centromere drive theory predicts rapid turnover of centromeric sequences due to meiotic competition.
• Longer centromeres might possess a transmission advantage during reproduction.

Purpose of the Study:

• To investigate the phenomenon of extremely long centromeres in the red imported fire ant, Solenopsis invicta.
• To identify the major centromeric satellite DNA repeat and analyze its copy number variation between related species.
• To explore the correlation between centromere expansion and histone modifications.

Main Methods:

• Cytological examination of centromere size in Solenopsis species.
• Bioinformatics and molecular analyses to identify and quantify centromeric satellite DNA (CenSol).
• Comparative analysis of centromere characteristics across related fire ant species.

Main Results:

• Solenopsis invicta exhibits extremely long centromeres, averaging 34% of chromosome length, unlike Solenopsis geminata.
• CenSol was identified as the major centromeric satellite DNA repeat, with high sequence similarity but vastly different copy numbers between S. invicta and S. geminata.
• Centromere expansion in S. invicta was not linked to CenH3 duplication, and several related species also show long centromeres.

Conclusions:

• The findings support a model of centromere expansion driven by centromere drive.
• Expanded centromeres may be more common in Hymenoptera, particularly those with haplodiploid sex determination.