Karyotype structure and cytogenetic markers of Amoimyrmex bruchi and Amoimyrmex silvestrii: the contribution to understanding leafcutting ant relationships

Leafcutting ants are considered the most important herbivores in terrestrial environments throughout the Neotropics. <i>Amoimyrmex</i> is the sister clade of the remaining leafcutter ants from the genera <i>Atta</i> and <i>Acromyrmex</i>. <i>Amoimyrmex striatus</i> was the only species cytogenetically studied within the genus and shares the same chromosomal number with <i>Atta</i>, bearing 22 chromosomes, whereas <i>Acromyrmex</i> bears 38 chromosomes, with the exception of the social parasite <i>Acromyrmex ameliae</i> (2n=36). Our objective here was to analyze cytogenetically the species of <i>Amoimyrmex bruchi</i> and <i>Amoimyrmex silvestrii</i>, as well as to describe the karyotype of these sister species, by means of an integrative approach using classical and molecular cytogenetics. We aimed to characterize cytogenetic markers that contribute to the systematics and taxonomy of the genus. Our results showed that the karyotypes of these two species are very similar, with an identical chromosome number (2n=22), chromosome morphology (2K=20m+2sm), and location of 18S rDNA and the telomeric repeat TTAGG on the chromosomes. Yet, the microsatellite probe GA(15) showed variation across the species and populations studied. We suggest that both species diverged relatively recently and are unmistakably sisters because of the many shared characteristics, including the highly conserved karyotypes.

The multidimensional nutritional niche of fungus-cultivar provisioning in free-ranging colonies of a neotropical leafcutter ant

The foraging trails of Atta leafcutter colonies are among the most iconic scenes in Neotropical ecosystems, with thousands of ants carrying freshly cut plant fragments back to their nests where they are used to provision a fungal food crop. We tested a hypothesis that the fungal cultivar’s multidimensional requirements for macronutrients (protein and carbohydrates) and minerals (Al, Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn) govern the foraging breadth of Atta colombica leafcutter ants in a Panamanian rainforest. Analyses of freshly cut plant fragments carried by leafcutter foragers showed that the combination of fruits, flowers, and leaves provide for a broad realized nutritional niche that can maximize cultivar’s performance. And, while the leaves that comprised the most harvested resource also delivered an intake target containing protein in excess of the amounts that can maximize cultivar growth, in vitro experiments showed that the minerals P, Al, and Fe can enhance the cultivar’s tolerance to protein-biased substrates, and potentially expand the ants’ foraging niche. Yet, the cultivar also exhibits narrow margins between mineral limitation and toxicity that may render plant fragments with seemingly optimal blends of macronutrients unsuitable for provisioning. Our approach highlights that optimal foraging is inherently multidimensional and links the foraging behavior of a generalist insect herbivore to the fundamental nutritional niche of its microbial symbiont.Significance StatementColonies of Atta colombica leafcutter ants can contain millions of specialized workers exhibiting large-scale generalist herbivory. Yet, this generalist foraging niche also depends on the poorly understood physiological needs of the ants’ domesticated fungal cultivar. We show the cultivar’s fundamental nutritional niche is broad for carbohydrates but narrower for protein and a suite of minerals, but that the cultivar’s sensitivity to excess protein is also mediated by Al, Fe, and P. More generally, this study decouples the multidimensional foraging strategies that enable a generalist herbivore to navigate a complex nutritional landscape and mix many imbalanced foods to achieve balanced cultivar provisioning.

Meaningful Clearings: Human-Ant Negotiated Landscapes in Nineteenth-Century Brazil

This article explores the conflicts between people and Atta leafcutter ants over the meaning of anthropogenic deforestation in nineteenth-century Brazil. As human agricultural settlement advanced, ants followed in its wake, harvesting leaves, flowers, fruits, and other plant parts from crops to supply their underground fungus gardens. In so doing, the ants, as semiotic selves, interpreted what humans had done and acted accordingly, producing historically consequential environmental change in the process. An examination of primary sources such as legislation, travel journals, agricultural manuals, government administrative documentation, and newspapers for human-ant conversations demonstrates how interspecies sense making has fueled social innovations and rearrangements, shaping technical developments, legal-administrative practices, parliamentary discussions, and even local electoral arenas. By taking written documents as surviving structures of embodied, more-than-symbolic conversations, this analysis both takes its cue from, and helps substantiate, what Ewa Domanska has termed a “multispecies co-authorship” approach to human-animal relations. It argues that such a theoretical-methodological stance helps environmental historians account for nonhuman agency by allowing the exploration of animals’ truly creative, rather than merely resistive, behavior.

Comparative FISH-mapping of TTAGG telomeric sequences to the chromosomes of leafcutter ants (Formicidae, Myrmicinae): is the insect canonical sequence conserved?

Telomeric sequences are conserved across species. The most common sequence reported among insects is (TTAGG)n, but its universal occurrence is not a consensus because other canonical motifs have been reported. In the present study, we used fluorescence in situ hybridization (FISH) using telomeric probes with (TTAGG)6 repeats to describe the telomere composition of leafcutter ants. We performed the molecular cytogenetic characterization of six Acromyrmex Mayr, 1865 and one Atta Fabricius, 1804 species (Acromyrmex ambiguus (Emery, 1888), Ac. crassispinus (Forel, 1909), Ac. lundii (Guérin-Mèneville, 1838), Ac. nigrosetosus (Forel, 1908), Ac. rugosus (Smith, 1858), Ac. subterraneus subterraneus (Forel, 1893), and Atta sexdens (Linnaeus, 1758)) and described it using a karyomorphometric approach on their chromosomes. The diploid chromosome number 2n = 38 was found in all Acromyrmex species, and the karyotypic formulas were as follows: Ac. ambiguus 2K = 14M + 12SM + 8ST + 4A, Ac. crassispinus 2K = 12M + 20SM + 4ST + 2A, Ac. lundii 2K = 10M + 14SM + 10ST + 4A, Ac. nigrosetosus 2K = 12M + 14SM + 10ST + 2A, and Ac. subterraneus subterraneus 2K = 14M + 18SM + 4ST + 2A. The exact karyotypic formula was not established for Ac. rugosus. FISH analyses revealed the telomeric regions in all the chromosomes of the species studied in the present work were marked by the (TTAGG)6 sequence. These results reinforce the premise that Formicidae presents high homology between their genera for the presence of the canonical sequence (TTAGG)n.

Cytogenetic data for sixteen ant species from North-eastern Amazonia with phylogenetic insights into three subfamilies

Ants play essential roles in most terrestrial ecosystems and may be considered pests for agriculture and agroforestry. Recent morphological and molecular data have challenged conventional ant phylogeny and the interpretation of karyotypic variations. Existing Neotropical ant cytogenetic data focus on Atlantic rainforest species, and provide evolutionary and taxonomic insight. However, there are data for only 18 Amazonian species. In this study, we describe the karyotypes of 16 ant species belonging to 12 genera and three subfamilies, collected in the Brazilian state of Amapá, and in French Guiana. The karyotypes of six species are described for the first time, including that of the South American genus Allomerus Mayr, 1878. The karyotype of Crematogaster Lund, 1831 is also described for the first time for the New World. For other species, extant data for geographically distinct populations was compared with our own data, e.g. for the leafcutter ants Acromyrmex balzani (Emery, 1890) and Atta sexdens (Linnaeus, 1758). The information obtained for the karyotype of Dolichoderus imitator Emery, 1894 differs from extant data from the Atlantic forest, thereby highlighting the importance of population cytogenetic approaches. This study also emphasizes the need for good chromosome preparations for studying karyotype structure.