Comparative Analysis of Facial Coloration between Introduced and Source Populations of the Red Wood Ant Formica paralugubris

SIMPLE SUMMARY: Animals’ body coloration can be implied in several ecological and behavioral processes, but it is understudied in ants. In this study, we compared the differences between the facial coloration of sixty-year-old imported populations of the red wood ant Formica paralugubris and their source populations, using a shape-based analytical approach for the first time. We found that, except for a case we discuss, the facial coloration is overall similar between introduced and source populations, suggesting a stable genetic background. Interestingly, we found that the large difference in the habitat in which populations naturally dwell or were established—forests dominated by spruce, beech, fir, and a mix of these—has a low effect on shaping this trait, as we might expect from previous studies. However, the within-population variability suggests that facial coloration is probably affected by very localized external factors at the population and nest level. Finally, we found that the ant size affects the trait, a result in line with previous studies. ABSTRACT: The variation in the typical black-reddish color of red wood ants (Formica rufa group) has been recently suggested as a good indicator of habitat quality, being dependent on environmental conditions. However, the relative contribution of external factors and heritability in shaping this trait is poorly investigated. In this study, we compared the facial coloration of workers from four introduced populations of Formica paralugubris with those of the two Alpine populations from which they had been taken. We used a Relative Warp Analysis to describe the variations in the shape of this trait. We expected each introduced population to be more similar to its population of origin if the color pattern was predominantly genetically determined. On the contrary, due to the considerable differences in habitat type and climate between the Alps and the Apennines, we expected to observe differences between the introduced population and their origin population if the coloration was mostly environmentally determined. With one exception that we discuss, the results showed that ants from the two source populations had different phenotypes, and that the introduced populations had a shape similar to the population of origin, suggesting a stable genetic background. Surprisingly, the habitat type seems to have a less clear effect, even if within-population differences suggest the influence of very localized environmental factors. Finally, we found that the facial coloration shape is affected by the ant’s size, a result in line with previous studies.