2.1 ǀ Study species and collection
C. elegans Emery 1869 is a thermophilic ant that builds its nests in the soil in barely vegetated, sandy patches, e.g., along rivers in Iberia, France, and Italy. Populations in the Eastern Mediterranean are now considered to represent a separate species, C. dalmaticaSoudek 1925 (Seifert, 2018). From 2014 to 2017 we studied several populations of C. elegans along the rivers Gardon and Rhone in Southern France. In 2018 and 2019 we concentrated our study on one site south of Remoulins on Gardon (N 43° 55′ 43.9″, E 4° 34′ 5.1″), where we repeated our investigation in August 2020 to corroborate earlier results and retrieve additional detail about the peculiar phenomenon. For genetic analyses, we also used samples collected at the same site in August 2019.
The locations of nests were identified by following foragers back to the nest entrance. Samples of workers were stored in EtOH for the determination of nestmate relatedness by genotyping the individuals. By observing nest entrances and following individual pairs of carrying workers and carried female sexuals, over several minutes, we attempted to identify the direction of the transfer. For genetic analyses, we collected the ants with an aspirator immediately before the female sexual was placed into the entrance of the recipient colony. In addition, we collected pairs of unknown origin and destination and either stored them in 100% EtOH for the determination of genetic relatedness or kept them alive for later experiments.