Insights about the evolutionary history of the southern black ant, Acromyrmex lobicornis, widely distributed species in western Argentina

SÁNCHEZ RETREPO, A. F.; CONFALONIERI, V.; CALCATERRA, L. A.

Curitiba

Simposio; XXIII Simpósio de Mirmecología, An International Ant Meeting; 2017

Universidad Federal de Paraná

The southern black ant, Acromyrmex lobicornis, is a species of leaf-cutting ant with a wide distribution in southern South America. Mostly distributed in Argentina, it extends from southern Brazil, Bolivia and Paraguay to the province of Chubut in Patagonia, and it is apparently in process of expansion into the southwest in direction to Chile. Its good adaptability to colonize different environments is explained by capacity to support extreme climatic conditions, like their nests have an external dome that minimizes environmental climate variability, thereby maintaining the optimum temperature and internal humidity, ensuring the survival of the fungus. A. lobicornis have four valid subspecies differentiated by variations in coloration and sculpturing. However, these characters seem ambiguous and made difficult to establish whether these really correspond to different subspecies or just resemble a phenotypic variability of the species. Defining the limits and range of variation of species is essential to maintain reliable biological information, especially those species with economic importance like this one. Samples from different populations of A. lobicornis throughout their range of distribution were sequenced for two mitochondrial genes in order to explore the distribution of the genetic variation among their populations, resolve the status of the subspecies and determine the historical demographic processes that could be related to a possible adaptation to lower temperatures and lower rainfall. We found that the geographical distribution of A. lobicornis is disjunct, with populations distributed along the ecoregión of the Monte in Argentina and populations distributed in rocky and dry zones near the Atlantic Forest in the south of Brazil and Uruguay, with scarce intermediate populations in the ecoregion of the Espinal in Argentina. Our preliminary results indicated that A. lobicornis forms a well-supported monophyletic and suggest that A. lobicornis is composed by differentiated clades located at lower latitudes (areas with higher temperature, which is more similar to the tropics) and clades distributed at higher latitudes. In spite of some haplotypes were widespread within the distribution range, at least three to four distinguishable haplogroups can be recognizable: one corresponding to the Monte, a second group to southernmost populations in Patagonia, and a third group to populations of the Espinal and the north of the distribution range. Understanding the evolutionary history of the southern black ant will provide insights into the evolutionary history of leaf-cutting ants in southern South America and the role of historical geo-climatic processes in their diversification. (CONICET, PICT-FONCyT)