GENETIC STRUCTURE AND EVOLUTION OF A FIRE ANT HYBRID ZONE

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Two invasive fire ant species, Solenopsis invicta and S. richteri, hybridize across a wide area in the United States.
• Hybrid zones are dynamic ecological and evolutionary arenas shaped by species interactions and environmental factors.

Purpose of the Study:

• To investigate the genetic and morphological patterns within a fire ant hybrid zone in Mississippi.
• To determine the model that best describes the observed distributional patterns of fire ant genotypes.
• To understand the role of intrinsic and extrinsic selection in shaping the hybrid zone.

Main Methods:

• Sampling ants along transects across the hybrid zone.
• Analyzing gene frequency and size distributions for numerous genetic and morphological markers.
• Comparing observed patterns with the mosaic hybrid zone model.

Main Results:

• Distributional patterns are consistent with the mosaic hybrid zone model, influenced by historical colonization.
• Recent species contact (<60 years) and habitat dynamics suggest the zone is not at equilibrium.
• Evidence suggests reduced fitness of hybrid genotypes due to intrinsic selection (gene complex disruption) and extrinsic selection (competition with parental species).

Conclusions:

• Colonization history initially structures the hybrid zone, but differential fitness of hybrid genotypes becomes increasingly important over time.
• Both intrinsic and extrinsic selective pressures contribute to the structuring of the fire ant hybrid zone.
• The future distribution of genotypes and the ultimate fate of the hybrid zone remain difficult to predict due to spatial and temporal variations in selective forces.