Quantifying Cost Savings of Pleometrosis and Haplometrosis: Excavation Labor of the Seed-HArvester Ant Pogonomyrmex californicus

Studies of cooperation remain an important aspect in understanding the evolution of social cues and interactions. One example of cooperation is pleometrosis, an associative behavior of forming a colony with two unrelated, fertile queens. However, most ant species display haplometrosis, the founding of a colony by a single queen. In these associations, the queen typically rejects cooperation. In populations of Pogonomyrmex californicus, both pleometrosis and haplometrosis exists. It is not clear how associative -metrosis became a practiced behavior since haplometrotic queens tend to fight. However, as fighting in pleometrotic queens became less frequent, this induces benefit, in terms of cost savings, in having associative behaviors. The hypothesis tested was nest excavation of pleometrotic queens show sociality, while haplometrotic queens show association independence. Isolated pleometrotic queens (P) showed low excavation rate at 2.72cm2/day, compared to the rate when the task was shared in (PP) nests, 4.57cm2/day. Nest area of the (P) queens were also affected during days 3 and 4 of the experiment, where there was presence of nest area decrease. Furthermore, the excavation session of (P) was the only one determined as significant between all other nests. Although the (P) queens have low values, they eventually reach a similar point as the other nests by day 6. However, the lack of haste in excavation leads to longer exposure to the elements, substituting the risk of losing cuticles in excavation for the risk of predation. For the haplometrotic queens, nests of (H) and (HH) displayed no significant difference in excavation values, leading to having social effect in their association.