Alternative genetic foundations for a key social polymorphism in fire ants

Area of Science:

• * Social organization and behavioral genetics in eusocial insects.
• * Evolutionary biology and population genetics.

Background:

• * Colony social organization in ants is crucial for their ecological success.
• * The odorant-binding protein gene Gp-9 has been linked to social organization (monogyny vs. polygyny) in some fire ant species.
• * Specific Gp-9 substitutions are hypothesized to affect queen recognition and regulate colony social structure.

Purpose of the Study:

• * To investigate if the same Gp-9 gene substitutions explain monogyny/polygyny in the distantly related fire ant Solenopsis geminata.
• * To compare the genetic basis of social organization evolution in S. geminata with that of the Solenopsis richteri clade.

Main Methods:

• * Sequencing of the Gp-9 coding region in monogyne and polygyne forms of S. geminata.
• * Comparative population genetic analyses of S. geminata and S. invicta.

Main Results:

• * Gp-9 coding sequences were identical in monogyne and polygyne S. geminata, refuting the hypothesis of specific amino acid substitutions driving social organization.
• * Polygyne S. geminata exhibited lower genetic diversity and different gene frequencies compared to the monogyne form.
• * These genetic differences in S. geminata contrast with findings in the S. richteri clade, indicating distinct evolutionary routes to polygyny.

Conclusions:

• * The evolution of polygyny in S. geminata is not driven by the same Gp-9 substitutions found in other fire ants.
• * Polygyny in S. geminata likely arose from a founder event, leading to reduced allelic variation and impaired queen recognition.
• * This study highlights alternative genetic mechanisms underlying the evolution of complex social systems in ants.