Nesting and distribution of Trachymyrmex holmgreni in Brazilian restinga.

Abstract

The genus Trachymyrmex falls within an intermediate behavior between the “leaf-cutters” and “non-cutters” fungus-farming ants, since they can use both fresh cut and detritus as a substrate to grow symbiotic fungus. In addition to this behavior, the genus Trachymyrmex falls in an intermediate phylogenetic position in recent molecular and phylogenomic studies. These aspects make the study of the natural history of the Trachymyrmex species interesting in terms of understanding the steps in the evolution of fungus agriculture. Thus, the objective of this study was to describe the nest architecture, colony demography as well as the distribution pattern of the fungus-farming ant Trachymyrmex holmgreni colonies in the Restinga ecosystem. Our results allowed us to suggest that the architecture and demography of the nest varied between seasons. Surprisingly, in the autumn, the nest presented three fungus chambers and many winged ants, while in the spring, there were five fungus chambers and a significant number of immature individuals. These results indicate that T. holmgreni seems to invest in reproduction during the autumn and establishes new nests during the winter, which promotes growth during the spring and summer. In addition, we found an aggregate distribution pattern of the nests, suggesting that abiotic factors such as resource availability and microclimatic soil conditions probably interfered with the successful establishment of the colonies. We concluded that the demography and architecture of the nest reaffirmed the intermediate position of the genus and corroborated the hypothesis that the evolution of small to large nests went through intermediate sizes.