Climate microrefugia promote intraspecific trait variability of the Palaearctic ant species Myrmica ruginodis (Hymenoptera: Formicidae)

Topographic depressions in karst areas (dolines) play an outstanding role in maintaining small-scale environmental heterogeneity in homogeneous landscapes. Such depressions can serve as microrefugia for cool-adapted species, providing cooler and more humid conditions than the surrounding matrix (plateaus). Recent studies showed that dolines can maintain species with different functional traits compared with the surrounding areas, providing a more heterogeneous and competitive environment. However, we have limited knowledge pertaining to how microrefugia shape the functional traits of a single species. Here, we compared the functional traits of the Palaearctic ant species Myrmica ruginodis between microhabitats of dolines and the surrounding plateaus in a karst landscape. We found that the number of virgin queens was higher on the plateaus, while males were more numerous in dolines, but there was no significant difference in colony size between the two microhabitats. Dolines hosted more worker brood, suggesting potential for larger colonies. Interestingly, the repeatability of worker aggressiveness was higher and worker size was more variable in dolines, emphasizing the individual aspects of doline colonies. Our results highlight that dolines not only support species whose functional traits vary from those occurring on the surrounding plateaus, but these microhabitats also exert a filter effect on the functional traits of a given species, enriching our understanding of biodiversity maintenance. It seems that - although the biotic and abiotic conditions provided by these microrefugia are more favorable for M. ruginodis than the surrounding plateaus - the plasticity of their functional traits allows them to compensate and survive even in sub-optimal environmental conditions. This plasticity may prove to be a useful prospect in the light of the ongoing climate change.