Fungus-growing ants are a remarkable taxon of New World ants that engage in a mutualistic symbiosis with basidiomycete fungi. Their fungus-gardens are valuable resources and are exploited in countless ways by parasites and other beneficiaries outside of the ant-fungi mutualism. Here, for the first time, we report on the agro-predatory behavior of the ant Megalomyrmex incisus on Mycetophylax conformis and Mycetophylax morschi fungus-growers from sand dunes near Ilhéus, Brazil. Me. incisusworkers raided colonies of My. conformis and My. morschi and aggressively antennated, pulled, bit, and stung the fungus-growers, which played dead or retreated on the fungus. Me. incisus quickly usurped the fungus-garden and expelled all Mycetophylax workers. The usurpation closely resembled that described for raids of Me. wettereri on Cyphomyrmex longiscapus, in that the fungus-growers remained passive and avoided confrontation. This passive behavior suggests that Me. incisus uses chemical weapons that facilitate the exploitation of the host colony resources.
Past climate changes often have influenced the present distribution and intraspecific genetic diversity of organisms. The objective of this study was to investigate the phylogeography and historical demography of populations of Acromyrmex striatus (Roger, 1863), a leaf-cutting ant species restricted to the open plains of South America. Additionally, we modeled the distribution of this species to predict its contemporary and historic habitat. From the partial sequences of the mitochondrial gene cytochrome oxidase I of 128 A. striatus workers from 38 locations we estimated genetic diversity and inferred historical demography, divergence time, and population structure. The potential distribution areas of A. striatus for current and quaternary weather conditions were modeled using the maximum entropy algorithm. We identified a total of 58 haplotypes, divided into five main haplogroups. The analysis of molecular variance (AMOVA) revealed that the largest proportion of genetic variation is found among the groups of populations. Paleodistribution models suggest that the potential habitat of A. striatus may have decreased during the Last Interglacial Period (LIG) and expanded during the Last Maximum Glacial (LGM). Overall, the past potential distribution recovered by the model comprises the current potential distribution of the species. The general structuring pattern observed was consistent with isolation by distance, suggesting a balance between gene flow and drift. Analysis of historical demography showed that populations of A. striatus had remained constant throughout its evolutionary history. Although fluctuations in the area of their potential historic habitat occurred during quaternary climate changes, populations of A. striatus are strongly structured geographically. However, explicit barriers to gene flow have not been identified. These findings closely match those in Mycetophylax simplex, another ant species that in some areas occurs in sympatry with A. striatus. Ecophysiological traits of this species and isolation by distance may together have shaped the phylogeographic pattern.
Fragmentation of tropical forests is one of the major threats to biodiversity and viable natural populations. Brazilian seasonally dry tropical forests (SDTF) are endangered because of human occupation, conversion of lands to agriculture and high deforestation rates in these fertile soils. Enterolobium contortisiliquum has been removed from SDTF natural areas due to the advance of cattle grazing and agriculture in Brazilian SDTFs. To aid conservation efforts of this species we used molecular markers to study the genetic diversity and population structure of E. contortisiliquum in Brazilian SDTF remnants. A total of 263 individuals in 13 forest patches were analyzed with 103 ISSR fragments. In spite of being found scattered among the SDTF patches, E. contortisiliquum populations exhibited high genetic diversity (mean Shannon's index of diversity = 0.384; mean genetic diversity = 0.280) and genetic divergence between populations was detected (ΦST = 0.155, p < 0.0001). UPGMA dendrogram, principal coordinate analysis and Bayesian analysis showed that E. contortisiliquum populations were clustered into three groups that were not related to geographic distance (r = 0.119, p = 0.197). However, these populations are spatially structured into groups distributed in the West, Central and East of the study area. This genetic structure may be related with landscape and both the Espinhaço Range and São Francisco River may act as a partial geographic barrier limiting the gene flow. Because the highest rates of genetic diversity were found outside of conservation units, we propose the creation of protected areas in different geographic regions that include E. contortisiliquum populations from different genetic clusters.