Multilocus evolution in fire ants: effects of selection, gene flow and recombination

Area of Science:

• Genetics
• Evolutionary Biology
• Behavioral Ecology

Background:

• Reproductive success in fire ants (Solenopsis invicta) is linked to queen genotype at the Pgm-3 gene.
• A second gene, Gp-9, is also under strong selection, particularly in the polygyne social form.

Purpose of the Study:

• To investigate the role of the Gp-9 gene in fire ant reproductive success.
• To understand the independent and combined effects of Pgm-3 and Gp-9 selection in different social forms.

Main Methods:

• Analysis of gene selection pressures in polygyne and monogyne fire ant social forms.
• Examination of genetic linkage and gametic phase disequilibrium between Pgm-3 and Gp-9.

Main Results:

• Strong directional selection on Pgm-3 (worker destruction of Pgm-3AA queens) and complex selection on Gp-9 (lethality of Gp-9bb, advantage for Gp-9Bb) in polygyne ants.
• Tight linkage (rf=0.0016) and strong gametic phase disequilibrium between Pgm-3 and Gp-9 in U.S. and native Argentine populations.
• Disequilibrium origin likely due to independent selection and gene flow, not founder effects.

Conclusions:

• Both Pgm-3 and Gp-9 are critical loci under independent selection in polygyne fire ants.
• The observed gene associations are maintained by selection and gene flow, shaping reproductive strategies.
• Understanding these genetic factors is key to fire ant population dynamics and control.