Frequent colony relocations do not result in effective dispersal in the gypsy ant Aphaenogaster senilis

Does social thermal regulation constrain individual thermal tolerance in an ant species?

In ants, social thermal regulation is the collective maintenance of a nest temperature that is optimal for individual colony members. In the thermophilic ant Aphaenogaster iberica, two key behaviours regulate nest temperature: seasonal nest relocation and variable nest depth. Outside the nest, foragers must adapt their activity to avoid temperatures that exceed their thermal limits. It has been suggested that social thermal regulation constrains physiological and morphological thermal adaptations at the individual level. We tested this hypothesis by examining the foraging rhythms of six populations of A. iberica, which were found at different elevations (from 100 to 2,000 m) in the Sierra Nevada mountain range of southern Spain. We tested the thermal resistance of individuals from these populations under controlled conditions. Janzen's climatic variability hypothesis (CVH) states that greater climatic variability should select for organisms with broader temperature tolerances. We found that the A. iberica population at 1,300 m experienced the most extreme temperatures and that ants from this population had the highest heat tolerance (LT50 = 57.55°C). These results support CVH's validity at microclimatic scales, such as the one represented by the elevational gradient in this study. Aphaenogaster iberica maintains colony food intake levels across different elevations and mean daily temperatures by shifting its rhythm of activity. This efficient colony-level thermal regulation and the significant differences in individual heat tolerance that we observed among the populations suggest that behaviourally controlled thermal regulation does not constrain individual physiological adaptations for coping with extreme temperatures.

To reunite or not: A study of artificially fragmented Diacamma indicum ant colonies

Social insects live together in groups and maintain cohesion to enhance their chances of survival and productivity. Colony cohesion is severely challenged during relocation. We examined the dynamics of colony reunification and the factors affecting nest choice of artificially fragmented colonies of the queenless ant Diacamma indicum. None of the twelve undisturbed colonies fragmented or relocated when a good nest was available in their neighbourhood. When colonies were artificially fragmented, they mostly (25/30) reunified into a single nest unlike in randomized time-ordered network models, indicating that reunification is not the result of random recruitment acts. When the reproductive individual was present in a good nest, the colonies reunified at this address. However, when she was present in a suboptimal nest, colonies relocated her to a better quality nest and reunified there, illustrating that quality of the new nest is more important. The work distribution and relocation dynamics of reunification were comparable to intact colonies relocating to a single new nest. This is made possible by enhanced exchange of information among tandem leaders in the form of increased number of tandem runs among them. We conclude that colony cohesion is very important and is maintained after incorporating the risks of relocation and preference for nest quality during decision making.

Social and population structure in the ant Cataglyphis emmae

Dispersal has consequences not only for individual fitness, but also for population dynamics, population genetics and species distribution. Social Hymenoptera show two contrasting colony reproductive strategies, dependent and independent colony foundation modes, and these are often associated to the population structures derived from inter and intra-population gene flow processes conditioned by alternative dispersal strategies. Here we employ microsatellite and mitochondrial markers to investigate the population and social genetic structure and dispersal patterns in the ant Cataglyphis emmae at both, local and regional scales. We find that C. emmae is monogynous and polyandrous. Lack of detection of any population viscosity and population structure with nuclear markers at the local scale suggests efficient dispersal, in agreement with a lack of inbreeding. Contrasting demographic differences before and during the mating seasons suggest that C. emmae workers raise sexuals in peripheric nest chambers to reduce intracolonial conflicts. The high genetic differentiation recovered from the mtDNA haplotypes, together with the significant correlation of such to geographic distance, and presence of new nuclear alleles between areas (valleys) suggest long-term historical isolation between these regions, indicative of limited dispersal at the regional scale. Our findings on the ecological, social and population structure of this species increases our understanding of the patterns and processes involved under independent colony foundation.