Plant Growth-Promoting Bacteria Associated with the Nests of the Seed-Harvester Ant, Trichomyrmex Scabriceps

Colonies of seed harvester ants are commonly found in semiarid and arid areas of the world and have been studied for their seed dispersal behaviour. The present study focused on the bacteria associated with the nests of the harvester ant, Trichomyrmex scabriceps, and reveals that ant colonies link the aboveground resources with the belowground microbial communities as they accumulate organic debris in the close vicinity of their nests via their ecosystem engineering activities. Soil samples were collected from the nest chambers and the external debris piles of T. scabriceps colonies, located in managed ecosystems. The nest soil-associated bacteria were examined for their plant growth-promoting abilities via biochemical assays including phosphate solubilization, Indole acetic acid production, siderophore production and physiological assays including biocontrol potential against the soil pathogen, Sclerotium rolfsii. More than 60% of bacteria isolated from the ant nest-associated soil displayed plant-growth promoting ability. Bacillus sp., Azotobacter sp., Klebsiella sp., Comamonas sp., Tsukamurella sp., and Pseudoxanthomonax sp., demonstrated significantly high levels of gnotobiotic growth of the treated chickpea plants. The activities of phenylalanine ammonia-lyase and peroxidase enzymes were higher in plant growth-promoting bacteria treated and pathogen inoculated plants as compared to the control plants lacking the bacteria. Since T. scabriceps colonies often make their nests in the compact soil of unpaved paths of agroecosystems and gardens, these bacteria can act as highly effective biofertilizers and promote growth of the cultivated plants by increasing soil fertility and disease resistance attributes of the plant.

A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part II

This paper provides a taxonomic revision and reviews natural history for 35 South American species of the seed-harvesting ant genus Pogonomyrmex. Species treated herein mostly comprise the P. rastratus-group; four species are revived from synonomy, three taxa are elevated from subspecies to species, five taxa are synonymized, and 20 new species are described. The following taxa are revived from synonomy: P. intermedia Menozzi, P. semistriata Emery, P. spinolae Emery, and P. weiseri Santschi. The following taxa are raised from subspecies to species: P. leonis Kusnezov, P. pulchellus Santschi, and P. sanmartini Kusnezov. The following new synonymies are proposed, with the senior synonym listed first, and the junior synonym(s) in parentheses: P. carbonarius Mayr (= P. kusnezovi Cuezzo & Claver, = P. weiseri var. neuquensis Santschi, = P. variabilis Santschi); P. vermiculatus Emery (= P. vermiculatus var. chubutensis Forel, = P. vermiculatus var. jorgenseni Forel). The following new species are described: P. apterogenos, P. araucania, P. atacama, P. bolivianus, P. colca, P. cusquena, P. excelsior, P. forelii, P. granulatus, P. lagunabravensis, P. loaensis, P. mapuche, P. maulensis, P. pichachen, P. propinqua, P. santschii, P. strioligaster, P. tafi, P. varicolor, and P. wilsoni. One species treated herein has brachypterous queens (P. atacama), one species has dimorphic queens (winged and brachypterous in P. longibarbis), and two species have ergatoid (permanently wingless) queens and ergatoid males (P. apterogenos, P. laguanbravensis); the latter two are the only known ant species in which both sexual castes are only ergatoid. I also provide keys for workers and queens (in English and Spanish), diagnoses for males, photographs of known castes, distribution maps, and a summary of known biology.

Genomic architecture and evolutionary dynamics of a social niche polymorphism in the California harvester ant,Pogonomyrmex californicus

The societies of social insects are highly variable, including variation in the number of reproductives in a colony. In the California harvester ant,Pogonomyrmex californicus(Buckley 1867), colonies are commonly founded by a single queen (haplometrosis, primary monogyny). However, in some populations in California (USA), two or more queens cooperate in colony founding (pleometrosis) and continue to share a nest over several years (primary polygyny). Here, we use population genomics and linkage mapping to study the evolutionary dynamics and genetic architecture of this social niche polymorphism. Our analyses show that both populations underwent consecutive bottlenecks over the last 100,000 generations, particularly decreasing population size in the P-population and that the two populations diverged until 1,000 generations ago, after which gene flow increased again and we found signs of recent genetic admixture between the two populations. We further uncover an 8 Mb non-recombining region segregating with the observed social niche polymorphism, showing characteristics of a supergene comparable to the ones underlying social niche polymorphism in other ant species. In addition, 57 genes in five genomic regions outside the supergene show signatures of a selective sweep in the P-population, some of which are differentially expressed between haplo- and pleometrotic queens during colony founding. Our findings expose the social niche polymorphism inP. californicusas a polygenic trait involving a supergene.

Genome assembly and annotation of the California harvester ant Pogonomyrmex californicus

The harvester ant genus Pogonomyrmex is endemic to arid and semiarid habitats and deserts of North and South America. The California harvester ant Pogonomyrmex californicus is the most widely distributed Pogonomyrmex species in North America. Pogonomyrmex californicus colonies are usually monogynous, i.e. a colony has one queen. However, in a few populations in California, primary polygyny evolved, i.e. several queens cooperate in colony founding after their mating flights and continue to coexist in mature colonies. Here, we present a genome assembly and annotation of P. californicus. The size of the assembly is 241 Mb, which is in agreement with the previously estimated genome size. We were able to annotate 17,889 genes in total, including 15,688 protein-coding ones with BUSCO (Benchmarking Universal Single-Copy Orthologs) completeness at a 95% level. The presented P. californicus genome assembly will pave the way for investigations of the genomic underpinnings of social polymorphism in the number of queens, regulation of aggression, and the evolution of adaptations to dry habitats.

Pheromone cue triggers switch between vectors in the desert harvest ant, Veromessor pergandei

The desert harvester ant (Veromessor pergandei) employs a mixture of social and individual navigational strategies at separate stages of their foraging trip. Individuals leave the nest along a pheromone-based column, travelling 3-40m before spreading out to forage individually in a fan. Foragers use path integration while in this fan, accumulating a direction and distance estimate (vector) to return to the end of the column (column head), yet foragers’ potential use of path integration in the pheromone-based column is less understood. Here we show foragers rely on path integration both in the foraging fan as well as while in the column to return to the nest, using separate vectors depending on their current foraging stage in the fan or column. Returning foragers displaced while in the fan oriented and travelled to the column head location while those displaced after reaching the column travel in the nest direction, signifying the maintenance of a two-vector system with separate fan and column vectors directing a forager to two separate spatial locations. Interestingly, the trail pheromone and not the surrounding terrestrial cues mediate use of these distinct vectors, as fan foragers briefly exposed to the pheromone cues of the column in isolation altered their paths to a combination of the fan and column vectors. The pheromone cue acts as a contextual cue triggering both the retrieval of the column vector memory and its integration with the forager’s current fan vector.

High-Quality Genome Assembly and Annotation of the California Harvester Ant Pogonomyrmex californicus (Buckley, 1867)

ABSTRACTThe harvester ant genus Pogonomyrmex is endemic to arid and semiarid habitats and deserts of North and South America and California harvester ant Pogonomyrmex californicus is the most widely distributed Pogonomyrmex species in the North America. P. californicus colonies are usually monogynous, i.e. a colony has one queen. However, in a few populations in California, primary polygyny evolved, i.e. several queens cooperate in colony founding after their mating flights and continue to coexist in mature colonies. Here, we present high quality genome assembly and annotation of P. californicus. The size of the assembly is 241 Mb, which is in good agreement with previously estimated genome size and we were able to annotate 17,889 genes in total, including 15,688 protein-coding ones with BUSCO completeness at the 95% level. This high quality genome will pave the way for investigations of the genomic underpinnings of social polymorphism in queen number, regulation of aggression, and the evolution of adaptations to dry habitats in P. californicus.