Recurring adaptive introgression of a supergene variant that determines social organization

Introgression has been proposed as an essential source of adaptive genetic variation. However, a key barrier to adaptive introgression is that recombination can break down combinations of alleles that underpin many traits. This barrier might be overcome in supergene regions, where suppressed recombination leads to joint inheritance across many loci. Here, we study the evolution of a large supergene region that determines a major social and ecological trait in Solenopsis fire ants: whether colonies have one queen or multiple queens. Using coalescent-based phylogenies built from the genomes of 365 haploid fire ant males, we show that the supergene variant responsible for multiple-queen colonies evolved in one species and repeatedly spread to other species through introgressive hybridization. This finding highlights how supergene architecture can enable a complex adaptive phenotype to recurrently permeate species boundaries

Desert Ants Learn Vibration and Magnetic Landmarks

The desert ants Cataglyphis navigate not only by path integration but also by using visual and olfactory landmarks to pinpoint the nest entrance. Here we show that Cataglyphis noda can additionally use magnetic and vibrational landmarks as nest-defining cues. The magnetic field may typically provide directional rather than positional information, and vibrational signals so far have been shown to be involved in social behavior. Thus it remains questionable if magnetic and vibration landmarks are usually provided by the ants' habitat as nest-defining cues. However, our results point to the flexibility of the ants' navigational system, which even makes use of cues that are probably most often sensed in a different context

Biogeography of mutualistic fungi cultivated by leafcutter ants

Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite-marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade-A and Clade-B). The dominant and widespread Clade-A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade-A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade-B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade-A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade-B fungi occur only in South America. Diversity of Clade-A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov–Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot-specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus-growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars

Ventilation of the giant nests of Atta leaf-cutting ants: does underground circulating air enter the fungus chambers?

Nest ventilation should be particularly relevant for the huge colonies of leaf-cutting ants, genus Atta. Considerable amounts of O-2 are consumed and CO2 produced by both the fungus gardens and the ants inside nest chambers, which are located at deep soil layers characterized by high CO2 and low O-2 concentrations. In this work, passive nest ventilation was investigated in field Atta capiguara and Atta laevigata nests, first, by evaluating air movements through the nest using propane as tracer gas as well as the CO2 and O-2 concentrations of the circulating air, and second, by exposing the internal nest morphology with the use of cement casts and excavations. Results showed that even though outflow of CO2-rich air and inflow of O-2-rich air occurred at high-placed and low-placed openings, respectively, supporting a wind-induced interpretation of air movements through the nest, circulating air was never detected inside fungus chambers. The CO2 and O-2 levels inside the fungus chambers increased and decreased with increasing soil depth, respectively, and were in the range observed in the soil phase. Based on the underground nest architecture, it is concluded that although the external shape of the nest induces underground air circulation, the inflowing air is unable to directly reach the fungus chambers. It is argued that colony respiration completely depends on diffusive flows between the chamber air and the adjacent nest and soil atmospheres. Circulating air, although not directly renewing the air inside the nest chambers, may contribute to colony respiration by increasing the capacity of the nest and soil airs to act as an O-2-source and a CO2-sink, because of the decrease in the CO2 and the increase in the O-2 levels in the underground air phase. Possible adaptations of both ants and fungus to the high CO2 and low O-2 concentrations usually found in soils are discussed.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

First record of the eucalypt gall-wasp Leptocybe invasa (Hymenoptera: Eulophidae) from Uruguay = Primer reporte de la avispa agalladora del eucalipto Leptocybe invasa (Hymenoptera: Eulophidae) para Uruguay.

Leptocybe invasa es una plaga forestal de reciente introducción, responsable de importantes pérdidas económicas en plantaciones de Eucalyptus spp. a nivel mundial. El objetivo de este trabajo fue reportar su presencia para Uruguay, aportar datos de distribución y biología. Se observó la presencia de agallas de 2013 a 2015, confirmada en 15 de 35 puntos muestreados y en cuatro de 157 trampas.Eucalyptus benthamii se registra como nuevo hospedero. Fueron observados tres períodos de emergencia de adultos. El ciclo de vida fue completado solamente en E. tereticornis, E. camaldulensis y E. grandis

Acromyrmex charruanus: a new inquiline social parasite species of leaf-cutting ants

Social parasites exploit the colony resources of social species to secure their own survival and reproduction. Social parasites are frequently studied as models for conflict and cooperation as well as for speciation. The eusocial Hymenoptera harbor a diverse array of socially parasitic species with idiosyncratic life history strategies, but it is probably in the ants where social parasites are most speciose and have evolved the highest degrees of morphological and behavioral specialization. In the fungus-growing ants, a total of five obligate social parasites are known: four species are parasites of leaf-cutting ants and one species parasitizes a primitive fungus-growing ant species in the genus Mycocepurus. Here we describe a new species of socially parasitic leaf-cutting ant, Acromyrmex charruanus sp. nov., from Uruguay, and we report initial observations on the parasite's life history as well as on the morphological and behavioral adaptations related to the inquiline syndrome. Our observations suggest that Acromyrmex charruanus is an obligate inquiline social parasite of the thatch-mound-building, leaf-cutting ant Acromyrmex heyeri. Acromyrmex charruanus appears to be tolerant of the host, producing sexual offspring in the presence of the A. heyeri host queen. Queens of A. charruanus appear to reproduce semelparously and sexual offspring are produced during the austral fall (February), which differs significantly from the mating biology of the host species, which reproduces during the southern-hemisphere spring (October-December). We suggest that the diametrically opposed mating seasons of parasite and host might be adaptive, allowing the parasite to avoid competition for resources with the host sexual brood. The morphological and behavioral adaptations of A. charruanus accord with characters observed to arise early during the evolution of other ant inquiline parasite species, and so far we have no evidence for the existence of a worker caste in A. charruanus. Further field studies and behavioral experiments need to confirm our first observations and explore A. charruanus's behavioral ecology, evolution, and life history in more detail.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq