Central-marginal dynamics in Dinoponera quadriceps (Hymenoptera, Formicidae): activity density, body reduction and functional divergence.

The Central-marginal hypothesis predicts that populations occurring at the periphery of a species' geographic distribution experience more adverse environmental conditions, resulting in reduced population density, lower fitness, and potential morphological changes. In insects, morphological traits are strongly associated with ecological performance and resource acquisition, making them useful indicators of how populations respond to environmental gradients. Here, we investigated whether populations of the ant Dinoponera quadriceps differ in activity density and morphofunctional traits between the center and edge of the species' geographic distribution along the Espinhaço Mountain Range, Brazil. Ants were sampled using pitfall traps in two sites approximately 610 km apart. Generalized Linear Mixed Models were used to evaluate differences in activity density and trait variation between sites, and a Principal Component Analysis summarized multivariate body size variation. The activity density of D. quadriceps was -higher in the central population in the full dataset but this difference was not robust to the removal of a single outlier trap. A positive correlation between D. quadriceps activity density and richness of other ant species was observed in the full dataset but also disappeared after outlier exclusion. Individuals from the marginal population exhibited significantly smaller overall body size. Additionally, trait-specific differences emerged, with marginal individuals displaying larger cephalic index, longer femora, and larger eyes. These findings suggest that peripheral environments impose energetic constraints that reduce body size while favoring morphological adjustments that enhance locomotor and sensory efficiency, highlighting the importance of intraspecific functional variation in understanding species responses at geographic range limits.